66 GT 350 Paxton questions

[Fair67]

I have in my shop, a 66GT 350 with a first owner installed Paxton supercharger. I have no experience with a supercharger on a non-fuel infected engine. This setup has functioned correctly for years(I am told). When warm, the engine idles at 1,800 RPM. That is with he idle screw backed all the way out. There is no choke on the carburetor. It is a 650 Holley DP.

My first thought is a vacuum leak or idle mixture is too lean. It runs and pulls strong throughout all RPM ranges and in all four gears. Unless I am mistaken, it shouldn't matter if air is being pushed or pulled through the carburetor. But I doubt there is much if any boost at idle.

Anyone had any experience with these setups?
Am I totally flawed in my thinking?
Any suggestions?

[Sixx7shelby]

I have same set up on my 67 350. my 650 DP is one modified by Craig Conley and once had a problem where car acted up while idling and was the float level. Readjusted floats and ran fine after. I would check float levels first.

Dave

[Fair67]

Thanks for the Intel!
Also, the owner has an original boost gauge-fuel pressure gauge set, that he wants me to install. Where is the correct position to mount it?

I may ask many trivial questions, but I want be as correct as I can....and this car deserves! Although I've always been a Ford guy and Shelby admirer, I'm new to wrenching on genuine Shelby.

[JWH]

Here is a link to an article concerning a 1966 Shelby that came from the factory with the supercharger. If you scroll to the bottom and look at the photo gallery, there is a good picture of the gauges mounted in an an underdash chrome bezel. Craig Connelly is the go-to guy for Paxton supercharger stuff (Google "Paradise Wheels" to find his contact information) and he may be able to supply this bezel. A set of original Paxton gauges with the "birds" on them are extremely rare and pricey, so a large bonus the owner has those!

http://www.mustangandfords.com/featured-vehicles/mump-1008-1966-ford-mustang-shelby-gt350-paxton-supercharged

My '68 has had a Paxton since the early '70s. I do not have the problem of the high idle speed you mention so I am confident it is not the supercharger causing that. Check the floats as mentioned and also check that the fast idle cam is not getting hung up. Check that the linkage from the accelerator pedal-to-the-box-to the carb is not getting hung up. On the outside of my air box where the accelerator pedal linkage connects to the box, there is a stop-screw that can be adjusted (yours may be different??). If that is screwed in too far, it will keep the accelerator linkage in a higher RPM position. Take a look at that too. Good luck, it sounds like a great car.
Jeff
PS - a friendly reminder to put fresh fluid in the supercharger

[gt350hr]

   It is important to remember that carb enclosures were not designed for double pumper carbs. "I" would look to see that no portion of the linkage is touching anywhere. The supercharger alone is not a reason for high idle. There is a mechanical cause "somewhere". I ran one for 20 years back in '68-88.
   Randy

[Fair67]

Thanks for the replies! I have no doubt the supercharger is a non factor. I am going to peel the lid off the air box tonight and ensure no linkage binding, etc. Assuming all is free, I will check/adjust floats, as suggested,and ensure no vacuum leaks.

[Fair67]

I just spoke with the owner of the car and he gave me another carburetor built by Craig out at Paradise. If I can't line this one out, I will install this one.

[Don Johnston]

I am running a 650dp in my 66 blower box.  Another caution is the routing of the fuel hoses in the box to each bowl.  You need to check that they are not interfering with any mechanical parts. 

[Fair67]

I will indeed. I have yet to pop the top and have a look. Thanks for all the help!

[Fastback66]

I had an original style Paxton on my 66, the car idled high as well...the issue ended up being something very simple. The carb linkage was getting caught up and not completely returning to idle position...check that the linkage is clear...you might get lucky.

[Fair67]

I will always check the external easy things first....as for getting lucky....I would rather be lucky than good!!!

[TLea]

   It is important to remember that carb enclosures were not designed for double pumper carbs. "I" would look to see that no portion of the linkage is touching anywhere. The supercharger alone is not a reason for high idle. There is a mechanical cause "somewhere". I ran one for 20 years back in '68-88.
   Randy

+1 The idle adjustment linkage in the enclosure box is very finicky. I would disconnect it and see if the car does the same idle without the Paxton enclosure linkage hooked  up

[Don Johnston]

+1

I had to take the carb. out a few times and run it without the box to set the floats, put in proper jets, etc. In the box, I use short pieces of s.s. tubing where it will fit with limited rubber tubing.  I had had Classic Tubes make a s.s. line into the box as well.  the 650dp is takes up way more room in the box than the 480 but when tuned correctly, really makes the Paxton push lots of power.  It is very easy for the hoses to bind up the linkage on the fuel line input side. 

[Fair67]

The problem turned out to be the cam, that the idle screw rests on, is loose on the throttle shaft. When running, the throttle plates would crack ever so slightly. Thanks for all the replies. I will be installing the carburetor the owner supplied.

[Don Johnston]

Glad you solved the problem.