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The Cars => 1965 GT350/R-Model => Topic started by: Helmantel on August 26, 2020, 06:13:56 AM

Title: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on August 26, 2020, 06:13:56 AM
Hi,
I have a question about some adjustments of the 715 cfm Holley carburator. My car is just a regular Mustang but I hope you allow me to ask this question here anyway. My main concern is the float level height.

Quick background:
Engine: 289 with ported 351W heads, Shelby Hiriser intake, 10:1 CR, short duration high lift hydraulic roller cam, headers
I used a 600 cfm Holley 1850 previously, which ran OK but developed a lean stumble that I probably could have fixed if I had spent some time on it but I decided to try my Holley 3259 (reissue) instead. It started right up but didn’t run right. After some reading I set the float levels and it ran decent, but very rich (sooty exhaust pipes, fuel smell), still had some stumble and required the idle screws to be closed much more than the typical 1.5 turns out. Fuel consumption was high.

I decided to recheck the float levels and check if the power valve doesn’t leak. When trying to find the correct float setting, I found the following:
1.   1/2” front, 3/8” rear
2.   3/8” front, ½” rear (to the top of the bowl), confirmed by the same person who confirmed setting #1 was correct in another forum post  :)
3.   13/32”
4.   Float arms parallel to the bowl
5.   Set floats 1/8” lower than stock to compensate for modern fuels

Needless to say, I was a bit confused. I decided to go for #2, since it was recommended twice by people who seemed to have clue and because somebody with a Cobra 289 said that the correct levels were sensitive to the angle of the engine in the car. Since the engine leans backwards in a Mustang, I figured the front float had to sit a little higher to compensate.

The float levels turned out to be much too low. I probably measured from the bottom instead of the top, last time I set them. Half an hour of tinkering later, I considered them close enough to 3/8” and ½” and put the carb back on the car. It started right up, idled OK and ran good with considerably less stumble (a little remains) and the fuel smell seemed to be less. Back home and the engine warm, I adjusted the idle screws and had to turn them in more (not sure how much). Vacuum ended up at 18” but the RPM is too high at 950. I guess I need to close the secondaries a little, because the primary blades are right where they need to be, relative to the transfer slots.

Before I go on and fine tune this carburetor further, can anybody confirm that these float levels are correct? I’d like to avoid to tune and adjust it based on the wrong float level. Also, do you think that the float type makes a difference? Mine are the Nitrophyle type and I figured their setting may differ from a brass type? I don’t know what was original though and if the 3/8” and ½” float settings apply to brass or nitrophyle floats.
 
It would sure be easier to have some side plugs (and an internal adjuster!) to check the level.... The bowls have flat areas where a side plug would normally be mounted . I’m considering to drill and tap them for side plugs.

Well, a long story but I figured that visiting this forum means you like reading about Mustangs, so you probably wouldn’t mind  :)
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on August 26, 2020, 09:00:02 AM
I don't think that you are having an issue with the fuel levels.

The carb that you are working with was originally sourced by Shelby from the 427 Ford. It was selected for racing Homoligation reasons and really is too big for a 289 street engine. Period.

It was just carried over on the following model years as it had become a selling feature of the GT350. It was the era of bigger is better.


Normally the plugs are going to read rich with it. You need to use a cam with timing of at least that of a 289hp cam.

It likes lots os static compression. Around 10.5 to 11 to 1. Lots of ignition timing and as a result high octane fuel.

Today's ethanol fuels are causing lots of issues never seen before in the '60s simply because they didn't exist even in concept form.


Even 10% ethanol requires you to adjust fuel levels down and can cause isolated hot restart issues. Carry a can of starting fluid with you.


Even the 289hp cam, by today's standards, is a pathetic display of overselling by just calling it a high performance cam. Back then, relatively speaking to other factory offerings, it was.

To really make that carb work, you need more cubic inches, real 4 into 1 headers and a camshaft with lots of lift and duration that will compliment a scavenging effect to both the intake and the exhaust.

The Holley CFM v. CI chart shows something like 450 to 500 cfm for a 289. Not a 715.


I ran that carb on a 351 Cleveland with little positive to say about it. When it comes down to it, it's just a nostalgia thing as are the 289hp engines in general.

People are building 331's and 347's (me) out of the original basic concept, using better heads (AFR, Edelbrock) and real headers like the JBA 6610's.


There if you are going to turn the engine into the 8,000rpm range, that is where that carb comes into it's own. In around street driving it really is just disappointing and makes a mess.

It does look impressive though. ;)

Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: 67350#1242 on August 26, 2020, 09:43:23 AM
The rear fuel level is set lower than the front to prevent spillover into secondaries when braking hard so the 1/2" measure top of float to top of bowl was the original spec. and  3/8" for the front.
I suggest adding at least 1/16" to these measurements to lower fuel levels a little more for today's fuels.
Set the primary transition slot to "square".  This should be pretty close to 1 full turn of the primary idle screw after it contacts the tang on the throttle rod.   Set the secondary butterflies to completely closed and just bump the secondary idle screw so the plates won't bind in the bores - you want secondary closed as possible.  This way the primary is in control of the idle.

When setting idle speed try not to move the primary idle screw more than about 1/8 turn.  If idle too low try bumping the timing to increase it. Goal is to keep the transition slot very close to square.
These are the steps I have taken to dial in my 3259.  Shelbydoug is right the carb is too big but these steps should help to make it easier to live with.
Kurt.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on August 27, 2020, 07:00:59 AM
The rear fuel level is set lower than the front to prevent spillover into secondaries when braking hard so the 1/2" measure top of float to top of bowl was the original spec. and  3/8" for the front.
I suggest adding at least 1/16" to these measurements to lower fuel levels a little more for today's fuels.
Set the primary transition slot to "square".  This should be pretty close to 1 full turn of the primary idle screw after it contacts the tang on the throttle rod.   Set the secondary butterflies to completely closed and just bump the secondary idle screw so the plates won't bind in the bores - you want secondary closed as possible.  This way the primary is in control of the idle.

When setting idle speed try not to move the primary idle screw more than about 1/8 turn.  If idle too low try bumping the timing to increase it. Goal is to keep the transition slot very close to square.
These are the steps I have taken to dial in my 3259.  Shelbydoug is right the carb is too big but these steps should help to make it easier to live with.
Kurt.

+1  ;)
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on August 27, 2020, 07:48:49 AM
Thanks for your answers. I agree that 715 cfm is more than necessary for a street driven 289 and if I were to buy a generic Holley for it, I would have picked a 600. But I had this one and figured that since Shelby used it for several years it can’t be all bad and that I at least could try and make it work as good as on a 65-67 Shelby.

I have now driven it a little more with the readjusted float settings. ~50 miles to and from work including city, freeway and stop-and-go driving plus some spirited driving on country roads. It starts easy, idles smoothly, smells much less, has much less hesitation and when I took out a spark plug, the tip and porcelain were light tan/beige (while the metal was still covered with thick black soot, from earlier I guess). Don’t know about the fuel consumption yet.
I may try lowering the float settings a little later on, but I think I first will hook up my wide band AFR sensor and see how things look.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on August 27, 2020, 10:38:53 AM
Lot of Really bad info here.

There is zero reason you cannot do some basic tuning and have a 1 5/16, 1 3/8 venturi, 1 11/16 bore carb work perfectly on a 289.

Ford had many sizes available both larger and smaller. There is a valid reason to use this size.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on October 29, 2020, 06:46:25 PM
I finally got a wide band AFR sensor hooked up which showed that it's still running (much) too rich: ~10-11 at idle and ~12,5 at cruising speed. My first thought was a leaking Power valve but vacuum testing it showed that it was OK. I then noticed that front float was bottoming out against the bowl. I had set it at 3/8" (see first picture) but that is apparently is right where the float hits the bowl. It is hitting at the edge just below the upper bolt holes (see second picture)

The probably means that the float valve wasn't closing properly and the actual fuel level in the bowl could have been anything. The engine actually ran surprisingly well despite this (although rich at idle).

I guess that means that I have to set the float a little lower (as was already recommended for modern fuels).

Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on October 29, 2020, 07:01:02 PM
Go to Air Fuel Spark on Facebook and ask Drew. He's done a zillion of these carbs and will help you get it right.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on October 30, 2020, 06:55:55 AM
The same Drew as above? I don't have Facebook so I hope he'll answer here :)
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on October 30, 2020, 06:58:43 AM
The same Drew as above? I don't have Facebook so I hope he'll answer here :)
Yes.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on October 30, 2020, 07:05:35 AM
Yup the float can hit the bowl. Just set it lower.
When manually working the float you can feel if it hits the bowl or the needle and seat
(One feels spongy, one clunks)
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on October 30, 2020, 09:52:33 AM
Yes, I noticed the difference (spongy vs clunk). Any tips on how much lower?

Odd that the official setting is 3/8" then, or is that specification for a different/older float design?

Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on October 30, 2020, 10:15:56 AM
I dunno. I just eyeball them and adjust as needed.

Appears new vs old floats are same size and construction despite being a different color.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: gt350hr on October 30, 2020, 11:24:57 AM
  Let me add to this a bit.
     "ALL" engines will ONLY flow a specific amount of air through a carburetor REGARDLESS of CFM capability of the carburetor. Now it would be stupid to take my statement and put a ONE barrel , 6 cylinder carb on a 427 or vice versa. Those who subscribe to the 289=600cfm rule as an absolute are WRONG. Last time I checked there are about 60 DIFFERENT 600cfm Holleys and only about 5 or 6 that really work well on a 289. WHY? Because they are "generic" in design. In late '64 , Holley engineers spent allot of time calibrating an existing Holley four barrel to work on a 289 High performance engine with a "high rise" intake and tubular steel headers. The result is the 3259 , "GT350" carburetor. It was revised ( better front metering block) and given the 3259-1 list number and the S2MS9510-A ID number added . The adjustments made allowed this former 427 FE carburetor to work on the smaller 289. While the maximum air flow potential is 715CFM , (again) the 289 will only flow a lesser number as produced. The extra air capacity does NOT  "flood" the engine!!!!!!! THAT is a physical impossibility! Pure and simple. Carburetors are not designed to POUR fuel into an engine , they are designed to add fuel to air SUCKED in by the engine underneath it. The vacuum "signal" that the "boosters" "see" , pulls fuel out of the float bowls. YES a smaller CFM carburetor "can" be easier to calibrate because the smaller venturi helps the "pull" on the fuel. The amount of air flowing through the carburetor is UNCHANGED from the 715. Now change the camshaft , port the heads etc . and the AIRFLOW the engine creates will change and a larger carburetor "might" be needed. Random picking of a carburetor by size alone "may" not provide perfect calibration and require adjustments ( much like Holley engineers did on the 3259). There are at least 30 different 750 cfm carbs and "most" of them would require adjustments to fine tune them to a specific engine.
     This is what keeps carburetor specialists like Drew busy. Drew has the experience needed to match a carburetor to an application OR tell us it won't work. Most of us can change jets , power valves , gaskets .FEW of us can "optimally" tune a carburetor with air bleeds, power valve restrictions etc. like an expert does.
    Randy
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: S7MS427 on October 30, 2020, 12:26:41 PM
+1, Randy.  Good explanation in terms most everyone can understand.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: mygt350 on October 30, 2020, 02:59:52 PM
My 3259 was pushing out so much fuel enriched exhaust, my neighbors prius was crying. Car was bucking like a pissed bull. Sent it off to Drew with engine specifics and my driving style and when he sent it back, only adjustment was curb idle. Now its running like a 60's muscle car.
+1 for Drew
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: maxjets on October 31, 2020, 03:40:10 PM
  Let me add to this a bit.
     "ALL" engines will ONLY flow a specific amount of air through a carburetor REGARDLESS of CFM capability of the carburetor. Now it would be stupid to take my statement and put a ONE barrel , 6 cylinder carb on a 427 or vice versa. Those who subscribe to the 289=600cfm rule as an absolute are WRONG. Last time I checked there are about 60 DIFFERENT 600cfm Holleys and only about 5 or 6 that really work well on a 289. WHY? Because they are "generic" in design. In late '64 , Holley engineers spent allot of time calibrating an existing Holley four barrel to work on a 289 High performance engine with a "high rise" intake and tubular steel headers. The result is the 3259 , "GT350" carburetor. It was revised ( better front metering block) and given the 3259-1 list number and the S2MS9510-A ID number added . The adjustments made allowed this former 427 FE carburetor to work on the smaller 289. While the maximum air flow potential is 715CFM , (again) the 289 will only flow a lesser number as produced. The extra air capacity does NOT  "flood" the engine!!!!!!! THAT is a physical impossibility! Pure and simple. Carburetors are not designed to POUR fuel into an engine , they are designed to add fuel to air SUCKED in by the engine underneath it. The vacuum "signal" that the "boosters" "see" , pulls fuel out of the float bowls. YES a smaller CFM carburetor "can" be easier to calibrate because the smaller venturi helps the "pull" on the fuel. The amount of air flowing through the carburetor is UNCHANGED from the 715. Now change the camshaft , port the heads etc . and the AIRFLOW the engine creates will change and a larger carburetor "might" be needed. Random picking of a carburetor by size alone "may" not provide perfect calibration and require adjustments ( much like Holley engineers did on the 3259). There are at least 30 different 750 cfm carbs and "most" of them would require adjustments to fine tune them to a specific engine.
     This is what keeps carburetor specialists like Drew busy. Drew has the experience needed to match a carburetor to an application OR tell us it won't work. Most of us can change jets , power valves , gaskets .FEW of us can "optimally" tune a carburetor with air bleeds, power valve restrictions etc. like an expert does.
    Randy

That is GOLD! Great explanation.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on October 31, 2020, 06:31:41 PM
I lowered the primary floats a little to prevent them from bottoming out, but the engine runs just as rich as before: 12,5 at idle (tuned for best idle setting, ~3/4 turns out, 18" vacuum), ~10 at light cruise, ~11-12 at highway cruise and ~12,5 under acceleration. It idles smoothly and doesn't run bad otherwise but smells fuel and fuel consumption is high.

It seems that something is leaking fuel but I can't figure out what. A leaking power valve could be a possibility but it worked fine when I tested it with a vacuum tester (pulling vacuum on the membrane side) and all gaskets seem fine (the blue non-sticking type on the metering blocks). I didn't have any new ones handy but I guess I'll buy some and see if that helps.

Unless the specific calibration of this carb works ONLY on a GT350 engine and not at all on my 289 (short duration but .533 lift roller cam, Shelby Hirise manifolds, 351W heads with mild porting, headers, 10:1 compression), but that seems unlikely.


Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: 67350#1242 on October 31, 2020, 09:52:15 PM
It is possible that the float bracket is tweaked such that the float will contact the front of the bowl before fully seating on the needle.  This can be fixed by bending the bracket such that the float is moved away or outward from the bowl.  This adjustment is not done with the tang that contacts the seat, but where the bracket makes a 90 degree bend.  Readjust the tang afterwards to set the float level to spec.
Kurt.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on November 01, 2020, 06:05:59 AM
Thanks for the suggestion but that doesn’t seem to be the case. Although Now that I look it it, it does seem possible to bend the tab and the float bracket in such a way that a 3/8” setting can be achieved without the float hitting the bowl.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on November 01, 2020, 09:59:21 AM
It has the symptoms of the fuel level being set too high.

You need to verify that you have the correct needle and seat part in the carb.

I would use only a Holley replacement needle and seat. Some of the aftermarket ones are too short.

It's better to have the levels a little too low then too high.


You need to use a "power valve" tester to verify the power valve is good. I've had a number of them bad out of the box most likely due to age. Make sure the power valve gasket is the right one. There are other gaskets in the kit that are similar but not quite right.

If you have a fuel level that is "dripping" into the intake it will make the idle too rich as well.


With all due respect to Drew, setting the float levels just right is no longer a simple task like it should be. Ethanol in the fuel has something to do with it and they will also stick closed after being run and sitting for a week or so.

I have also found the Holley dry float settings too high. Not everyone can just eyeball them and get them right the first time.

The Lemans bowls are more difficult because you have no sight plugs to check the level with.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on November 02, 2020, 05:21:26 AM
I had set the float levels set to the (somewhat confusing, see first post) recommendation of 3/8" front and 1/2" rear. Now the fronts are a little lower due to the float interference with the bowl. Since the engine ran much better I thought I was on to something, but it's still running rich. I guess I can give it a try and set the floats lower. All this fiddling with the floats sure makes me long for externally adjustable floats and side plugs :) I'm still considering drilling and tapping my bowls for side plugs: there's a patch on the bowls already.

I wonder if the ethanol fuels require a lower fluid level in the bowl or if  the fluid level should be the same but that the density of the fuel requires a lower float dry setting? Or maybe a combination of both.

The needles in seats are in like new condition and the power valve tested as OK, but will replace it anyway and see what that brings. I will also check for any signs of fuel dripping at idle.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on November 02, 2020, 07:04:00 AM
The only other thing that you haven't mentioned that you looked at is the metering block.

The block has emulsion tubes in it for both the idle circuit and the main circuit. I don't think they were ever intended to be serviced after manufacture.

Drew has a video on his Facebook page that shows you how to service them.
since you are having issues with the idle circuit, you need to consider servicing them.

There are also air bleeds in the main body and need to be cleared out with a numbered drill bit. They are small and clog easily.


It wouldn't be a bad idea to ask Drew to go through that carb for you, set it up and test run it for you? The issue is he's a very busy guy and it might take a while for him to get to it?
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: 67350#1242 on November 02, 2020, 02:52:10 PM
Quote
I wonder if the ethanol fuels require a lower fluid level in the bowl or if  the fluid level should be the same but that the density of the fuel requires a lower float dry setting? Or maybe a combination of both.

I think you are correct about that.  Less dense fuel will make the float ride lower in the fuel - causing a higher actual fuel level before being cut off at the needle.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on November 02, 2020, 03:00:09 PM
You’ll find the difference is negligible....
Specific gravity of .748 vs .756 etc. the range from E0 to E10 is well within the range of gasoline variability.

Fuel pressure variation and needle/seat diameters have a much greater impact.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on November 03, 2020, 02:50:31 AM
The only other thing that you haven't mentioned that you looked at is the metering block.

The block has emulsion tubes in it for both the idle circuit and the main circuit. I don't think they were ever intended to be serviced after manufacture.

Drew has a video on his Facebook page that shows you how to service them.
since you are having issues with the idle circuit, you need to consider servicing them.

There are also air bleeds in the main body and need to be cleared out with a numbered drill bit. They are small and clog easily.

It wouldn't be a bad idea to ask Drew to go through that carb for you, set it up and test run it for you? The issue is he's a very busy guy and it might take a while for him to get to it?

For what it's worth, this carburetor is hardly used and everything inside looks brand new and clean, including the air bleeds. I don't know about the emulsion tubes though.

I'm sure Drew could get it right. I do live in Sweden though, so shipping it back and forth would be a bit of a hassle. Also, I had this carb intended for a new engine build I have planned (if I ever get to it....) so if I can't get it right, I might have Drew look at it for that application instead.


You’ll find the difference is negligible....
Specific gravity of .748 vs .756 etc. the range from E0 to E10 is well within the range of gasoline variability.

Fuel pressure variation and needle/seat diameters have a much greater impact.

Yeah, you're right. Density is probably not much affected by the ethanol.

I wondered about the (strong) influence of fuel level on the mixture. Initially I thought that the pressure of an inch (or thereabout) of fuel would be negligible, but when looking into the vacuum created in a booster venturi, I found that the vacuum at cruising speed for a 289 is probably only 1-2" of water or so (~40CFM per venturi at 2000 RPM/half load). Compare that to an inch of fuel (~3/4" of water) and it becomes obvious that the influence of the fuel level will be significant at low airflow levels.

When running on the idle and transfer circuit, the holes are directly exposed to the manfold vacuum (or whatever the vacuum will be right at the tip of the throttle blade) so it is much higher than in the venturi booster. Could there be an effect of the exposure of the different emulsion tube holes, with the holes being under or over the fuel level under different operating conditions? Thereby affecting the amount of air that enters the emulsion?

Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on November 03, 2020, 03:45:58 PM
Drew is the only one that I know of who as "played with" the Holley emulsion tubes.

I can tell you that with drastic changes of the emulsion tubes in a Weber 48ida you do get significant changes BUT there are three commonly used in 289's that are similar, F5, F7 and F11 that have only subtle changes at certain rpms.

In Webers, the location of the holes in the tubes effects the leaning or enrichening of the fuel mixture at one particular rpm.


Does that vary according to the engines vacuum draw related to engine size? Yes. The draw of a 427 is different then a 289.


Drew pointed out to me that the idle emulsion tube in a Holley metering block is used to keep the main circuit from coming in too early. So from his empirical method of learning Holleys, he has a different definition of an emulsion tube rather then a textbook one. Who am I to argue? I ask him for help and not the other way around?

That design happens to be Holley's application to their specific issue solution but not the traditional use of an emulsion tube.


What he told me to do is probably what you should do also. You need to remove the brass caps on the idle tubes. Those you drill out with a #1 drill bit.

New caps are available and reinstall easily. Now in theory you thread in a 8-32 screw into the top of the tube and pull it out. In theory.

Mine wouldn't come out and you need to go to the next step and use heat on the metering block. How much heat? 'don't know but keep in mind Holley metering blocks do warp just from engine heat and if they do, will leak past the gasket at the pump transfer hole.


Again, on Drew's Facebook page, he shows you what the removed emulsion tubes look like and take it from me, those are what emulsion tubes do look like.

You can see the holes in them, just like the Weber tubes at various heights.

Now don't ask me if they have different part numbers like the Webers do BUT one of the things that Holley did to that carb to make it acceptable to use on a 289 was "re-calibrate" it, which absolutely would include the emulsion tubes so count on the 3259 being just a little bit uniquely calibrated for a 289.


Drews point was that those tube transfer holes OFTEN are clogged and create crazy rich idle characteristics very similar to what you are going through with the carb right now.
Sometimes that shows in the response of the engine to the idle set screws.


I just went through this and still am. I have a little bit of a unique situation in running 2x4's on a C60A T/A intake on a 347. I'm set on 1-1/8 turns out and that's where that sucker wants to run.

What I think is happening with mine, I think, is that at 1-1/8 turns, it is idling partially on the mains. A purist will say, no it shouldn't, that's wrong but this intake has just a little different idling characteristics then a COBRA high rise does. It was never put on a production car and what I am experiencing MIGHT just be the reason? I don't think you could sanely use it with an automatic transmission at all.

It's difficult for the Doctor to tell if you are absolutely nuts or just a genius because he has no one else to compare you too? I suppose it is at least entertaining?



Now the point of taking out those tubes is to clean out the transfer holes and the idle passage at the top of the tube if it is located there. That orafice can be located in one of three spots in the carb. The one at the top of the tube is an .028 (look at your numbered drill set to see how small that is) and can clog if a cow in China farts 10,000 miles away from you?  ;)


My suggestion is to get Facebook just to see his page. He is a very helpful guy and readily shares what he knows but I think being offshore for 4 weeks at a time on a tug the crew and diesel fumes get to him and he starts throwing around wrenches if you piss him off? That would make me temperamental too for sure? Especially with a crew of 9 and cookie making fried Spam three times a day and only having condensed milk for your coffee the whole time? Yikes, I'm getting anxiety already? ;D
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on November 03, 2020, 05:26:16 PM
I think perhaps you misunderstood some of what I said... or perhaps I described it badly.

3259’s  do not have an idle emulsion tube. Never did, nor do any other 4150 performance carbs.
The mainwell has a tube, but best to leave it alone for the layman.

I was showing you the idle feed restriction which is under the cup plug inside the idle well. Important to clean those.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on November 03, 2020, 07:52:35 PM
Yes, idle feed restriction mentioned above. One metering block had it located there under the cap, the other was in an accessible part of the block.

.028 sounds big until you see how small it is.

Thanks for that information. It helped.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on November 03, 2020, 10:26:24 PM
Lol, and .028 to .035 seems like a small change until you do the math and figure the area 😀
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: 67350#1242 on November 03, 2020, 11:04:06 PM
Can the metering block be ultrasonic cleaned without removing the caps?
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on November 04, 2020, 06:33:19 AM
Can the metering block be ultrasonic cleaned without removing the caps?

With the Holley metering block, I'm still learning. I don't think so because what pics that I seen from Drew on the emulsion tubes, they look more like they are aluminum and have oxide corrosion on them?

Those have minimal effects on the idle circuit and even so, the main circuit is leaner then the idle circuit is.

I'd actually be leaning towards replacing them with new ones if possible.


Having said that though, rich idle issues seem to be the predominant problem. If the idle restrictions and air bleeds are clear then the most likely is the fuel level is too high or the power valve is leaking?

There is no other source of fuel to the engine.

Is it possible that the seats on the idle screws are worn out and damaged?



Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: csxsfm on November 04, 2020, 09:59:42 AM
Are there any replacement options for the 3259 metering blocks other than eBay junk?
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on November 04, 2020, 11:54:17 AM
Yes they can be cleaned ultrasonically, but it’s impossible to see or visually inspect.

I wouldn’t consider even a rebuild without cleaning the idle feed by removing the cup plug.
I buy them by the 1,000@$.016 each so not worth leaving them.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on November 15, 2020, 10:16:22 AM
Yes they can be cleaned ultrasonically, but it’s impossible to see or visually inspect.

I wouldn’t consider even a rebuild without cleaning the idle feed by removing the cup plug.
I buy them by the 1,000@$.016 each so not worth leaving them.

I can report positive vibes on that one. It makes you feel like you accomplished something important and very sophisticated and advanced.

Do it. It's easy but don't try to remove the idle emulsion tube like I did, because there isn't one.  ::)
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on November 15, 2020, 10:59:16 AM
If removing and replacing a cup plug is sophisticated or advanced, we might need to hide your drill bits from you 😂
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: shelbydoug on November 15, 2020, 05:21:41 PM
If removing and replacing a cup plug is sophisticated or advanced, we might need to hide your drill bits from you 😂

I use a pin vise for brain surgery. A frontal lobe lobotomy procedure. Leaves an almost invisible scar. It's very sophisticated.

It's similar to removing the metering block plug except you need to get the patient very drunk so they don't notice.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on June 15, 2021, 05:45:40 PM
Well, after a long break I finally got back at tuning the Holley. Last year I already installed some bowl sight plugs and had adjusted the float levels a bit below the bottom of the hole (which is the normal rule of thumb setting). But that didn't make any difference.

This time, I took Drew's advice and popped out the idle well plugs. Everything was nice and clean in there, but these carbs have the idle feed restrictors hidden in this well. Measuring their size with a 1 mm drill showed that they were probably ~0.041". I had no idea if that was big or small, but some googling showed that a normal size for a ~750 cfm Holley is in the low .030 range. In combination with my mild roller cam (and thus extra high vacuum), this was probably the reason for the rich transition circuit.

I stuck in some small wires and made some new caps out of aluminum (I didn't have any brass ones). That leaned out the transition circuit somewhat from 10 to 11.5 and thus not nearly enough. At cruising speeds, the AFR creep up somewhat but dropped back to 12 right away due to the power valve. Looking at the vacuum gauge during driving, I concluded that the 8,5" power valve kicked in way too soon. I then installed a 6,5" PV which allowed the AFR creep up to 14, but the power valve still kicked in too soon, especially in fifth gear.

I took it apart again, inserted a thicker wire in the idle feed restriction (0.024", reducing the flow area by 1/3th) and at the same time, I also installed #66 jets (instead of the stock #68), a 3.5" power valve and the stiffest (black) spring in the secondary canister (it had the next to lightest yellow one, which I assume is what it came with). Not very scientific perhaps to make so many changes at the same time, but I had grown tired of taking the carb apart all the time.

Anyway, idle AFR remained at ~13, light cruise (on the transfer circuit) increased the AFR to ~13, cruise (on the main jets) to 14.5-15 and WOT to ~13. It smelled much less and drove smoothly without much hesitation. There's still some under some conditions, so a little more tuning of the acceleration circuit required I guess, but overall it drives well. At 6000 RPM, manifold vacuum crept up to maybe 1" Hg (hard to see exactly when trying to look at the tach, the vacuum gauge and of course the road at the same time...), so I guess the stiff secondary spring didn't make the carb very restrictive. The light cruise AFR didn't increase as much as the flow area reduction suggested but I guess that's due to the unchanged secondary idle circuit. Maybe I'll give it one more go and fix that too.


Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on June 15, 2021, 08:12:05 PM
The original 3259 had a .031 ifr, I consider this a touch too small. Early 3259-1 had a .033 ifr which is perfect.
Later 3259-1 and reproduction ones (as well as 4118) have a .040 which is massive. Reduce to .033

I do this regularly and am lauded as some carb genius...  (I am not, it’s physics).
.033 ifr and .070 idle air bleed is appropriate for 90% of all cars with a 1 5/16, 1 3/8 venturi, 1 11/16 throttle bore carb.
Very rarely does an engine require being outside of this range.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: mygt350 on June 15, 2021, 09:47:47 PM
Misplaced my notes or they are in my filing system, somewhere.
Can anyone please tell me, again, what metering block numbers are correct for a 3259-1 Holley from a 66 GT350?
Thanks
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on June 16, 2021, 01:00:29 AM
Mine are now at the equivalent of .0323 but still a little rich, at least for my engine. On an actual GT350 it may be different.

I wonder why they made those idle feed restrictors so large? I understand that they already did that during the 60's?
Do you know if they increased the secondary idle feed as well?
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on June 16, 2021, 07:20:36 AM
No, secondary ifr was .031 on all of them.

.033 shouldn’t be overly rich, or it should be within range to correct with mixture screws.
The only reason I can see running larger would be due to a radical camshaft. As the camshaft duration or intake plenum becomes larger, more fuel is required.

Example:
If I take a cobrajet carb with it’s typical .076 idle air bleed, and .029 ifr and put it on my truck engine (20in vac at idle, stockish cam, small edelbrock intake), it will run flawlessly as is with mixture screws out 1 turn.
If I take the same carb and put it on my Galaxie (250@.050 cam and massive Tunnelwedge intake), it will barely run with the mixture screws 2.5 turns out.  I would have to alter the idle feed.  I could drill ifr to .035, or could reduce idle air bleed and increase ifr to something like .067/.033

Fairly drastic changes.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: TA Coupe on June 16, 2021, 03:13:46 PM
I may have missed it but was fuel pressure ever checked? Or does it make much of a difference on these carburetors. I have only messed around with 4160 carburetors and it does make a big difference.

       Roy
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on June 16, 2021, 04:28:04 PM
I didn't check it, but it's a regular 289 fuel pump. I did rev it up to max with the sight plugs off to see if fuel level rose abnormally but it stayed were it was so I called it good.

I had a look at Holley's chart for secondary springs which listed the start of opening and fully open engine speeds for a 350 and a 402 with a 3310 (750 cfm) carburetor. The different values scaled almost perfectly with the difference in displacement between the two, so I recalculated them for a 289, also taking into account that secondaries are a little larger and thus flow a little more. The results are in the chart. For the black spring it actually said that it didn't fully open so I had to make a guess here for the "fully open RPM".

As I wrote yesterday, manifold vacuum was just about to creep up (an inch Hg or so) at 6000 RPM with the black spring installed. The theoretical air consumption of a 289 at 6000 RPM is ~500 cfm, which matches the chart almost perfectly. Maybe dumb luck, because I made several assumptions, but still fun to see.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Drew Pojedinec on June 17, 2021, 09:18:00 AM
My way of tuning secondary spring is to use a quick change pot.
Find the bog, and scale to heavier until desired results occur.
Once found reinstall original housing with appropriate spring.

The charts are ok ish. Like many such charts it would be hard to take all factors in account....
Especially that there is a bleed hole from the primary signal hole to the secondary.
This is not the same size on all carbs. On old holley spec sheets the bleed hole was noted.
Title: Re: Holley 715 CFM #3259 float level adjustment
Post by: Helmantel on June 18, 2021, 01:40:48 AM
I have a quick change pot on another carb so I'll probably install that some time and test to find out the best spring. Installing the heavy one was more a matter of let's see what it does.

I agree that the chart is just an approximation with many variables. Or rather, the Holley table is probably accurate for that particular carb on that particular engine and serves as an approximation for other applications.