5S276 Fuel distribution problem?

[2112]

I would not argue with any of that. I believe that is exactly what you experienced.

OP mentioned an "ultra" lean condition on #4 & #8, lean enough to burn ceramic coating (even if crappy) off the headers. That sounds pretty lean to me.

I wish I paid attention to my lean #5 & #6 (common on BBF SVO spider manifolds) cylinders, but it was running so good................

[shelbydoug]

Here's my view.

This depends on which carb you are running. IF you are running the Shelby 715 Holley, that thing is so rich at WOT there is no way that you are going to run lean.

It is one of the reasons that it was selected to begin with by the Shelby people.


IF you are running a stock 1848 Holley, it will run lean at WOT BUT you won't have enough capacity to run much over 5,000 rpm. In effect, it is a rpm limiter.


If you are running  an 1850 Holley, it tends to idle a little rich but will have the same effect on the top end, but with about  500 to 600 rpm more rpm.


Webers will not run lean. Period.


If you are running two 1850 Holleys stock, you are right on the T/A designed mixture.

Dual AFB's...don't know.



There is talk of the headers showing lean. The only place that reading can be coming from is the silver ceramic coating loosing it's shine near the flanges. That's not lean, that's the correct exhaust temps and how the ceramic coating reacts to that temp when the engine is working right.


With the last Holley "Motorcraft" carbs on whatever year that was, 84, 85, 86 Mustang GT, the carbs were set to idle at stoichemic ratio of 14.6:1 AT IDLE. That setting is within the DESIGNED running capabilities of the original Ford valve train and the only thing that it does is turn the TUBE "headers" all sorts of interesting colors on the primary tubes.


You CAN'T blow up an engine by suddenly running lean UNLESS you instantaneously lost fuel delivery (fuel pump failure) at WOT OR it would have to be a massive vacuum lean at maximum load.

When this happens you will backfire through the exhaust and you will blow the mufflers out or up. That I personally can attest to. I did that twice and now always run with an electric pump in the system to reduce the possibility of this happening again. So far, so good.


The intake manifold design HAD NOTHING TO DO WITH ANY OF THIS. Ignorance on my part did.

Just the mufflers blew up. The engine was fine both times.

It will backfire like the "rice rocket bikes" do that have had the mufflers removed when the rider suddenly closes the the throttle from WOT in gear, i.e., a BIG firecracker.


Incidentally the Webers will do this EXHAUST BURBLING to a lesser extent when you decelerate with the car in gear. There it tends to be the overlap timing in the cam scavenging a reverse flow of cold air through the exhaust.


...anyway, I tend to agree with Zray here, all "normal" operation and is expected to cause reading of plugs and exhausts just like this. Drive the car. You worry too much. 

[kram350]

Just an observation; In trying to correct lean cylinders for years in a road racing environment, many different intakes tried, about 15 years ago I built a set of equal length (EL) headers. Boy did that ever make the plugs color even and yielded pipe temps all within 25 degrees. Water temps came down and even with huge overlap in the cam, idled better. To say the least I was astonished at the results. The variance in cylinder temps varied little whether a dual plane, single spider or the ram box I currently run. Staggered jetting and 4 corner mixture screws helped,  but did not come close to EL headers. I had the lean issue with hooker super comps and the stock try-wye's, all with the same intake manifolds. I spoke with Ed of Headers by Ed quite a bit and he convinced me of the advantage of equal length and really equal flow that will produce the best power. It was a lot of work to build the things, but it would seem the end result was justified. My next car will get EL's, worth the effort to me. For the street, don't know if it is worth the cost and work involved. I would think just converting to 4 corner idle would help on a stock dual plane on the street .