Street Rod fuel question

[SStockDart]

Our 55 F100 will not idle correctly now. Here is the deal...it is a pretty basic street rod motor.....sounds fast but it isn't. 302 SBF, C4, Headers, high rise, EbelBrock 500, HEI distributor, and Crane cam..lifters. Somewhere around 224 degrees (at 50) and around 480 lift...so not crazy but sounds good when right. Electric fuel pump.
Recently, I have been using the manual choke to idle it so I can drive it. If not choked, it will idle (but just doesn't sound right..too smooth and sounds "sour") and eventually die. At wfo it runs good, no issues. I have a replacement carburetor I can try.

Does this sound like it might be sucking some air in the fuel line??? I have checked all fuel lines that I can reach....but have not dropped the tank out.

[Eman]

Sounds more like a vacum leak somewhere. If you had a fuel supply issue it wouldn't run good at wide open throttle. Do the spray choke cleaner around to see if you find a vacum leak. A smoke machine or a homemade one will let you see a vacum leak.
Is it responsive to idle mixture adjustments?

[Ed Wright]

Guessing it prefers the idle fuel adjustment screws backed out further than the normal 1 1/2 turns or so? Carter AFB style carb? With a larger cam, with those carburetors it is not uncommon to need to drill the idle fuel restrictions out to .035" will usually get it.

[Kegracing]

Few more questions:
You said "recently" you have had to use choke to idle it. So that means that this carb and setup did work fine until recently?
In park or out of gear, does the idle speed/rpm go up without the choke on? What does the rpm do when you pull the choke on?
What about timing? Does it use vacuum advance or locked?

Ken

Stock 412

[Dave Gantz]

If it ran okay at some point in the past, you might want to check for a vacuum leak, as previously mentioned, by either slowly closing the choke flap or covering the air horn with a rag and see if it smooths out. If it does, you can use propane (Unlit!) to try to determine where it's leaking. Don't forget to check the brake booster, if any.

If no leak, pour some Seafoam (I've had success with this product on small engines.) or other gas additive, in a heavy dose in the tank. Drive it a while. A vehicle that doesn't get driven much may have some build-up of crud in the carb.
A carb rebuild may be necessary if it is crud and Seafood doesn't get it clean.

[SStockDart]

Thanks for the ideas guys. It is vacuum advance HEI distributor.....that reminded me, I just replaced the distributor a while back. When ya only drive it once a week or two...the memory gets bad. Now I am thinking that the advance in the distributor might be "walking" around....the idle adjustments make very little difference. Now and before at 1and 1/2 turns. Think I will watch college football today, then tackle the problem tomorrow.

Thanks again,,,
GOT IT....I took the vacuum line off the distributor and now it idles and rumbles like it should. So a distributor or timing issue. Not fuel. Awesome.

Thanks, I would have tank out, changed carburetor and stuff laying all over the place....thanks

[FireSale]

I had a similar problem in the 302 in my street rod Mustang. I took a look in the MSD distributor and the advance cam had unscrewed itself and was bouncing around the bottom of the distributor.

Dale

[SStockDart]

I couldn't stand it....I had to go take cap and rotor out. Found nothing wrong. Springs are fine and the mechanical advance works fine. It runs perfect now....rev it up then let off....comes right back to 800 RPM each time. Think I'll go for a ride, lol. Thanks again.

[GTX JOHN]

Since you mentioned the distributor change..........It sounds like that might be
the issue. A lot of Hot rods when you put into gear it lowers the RPM enough
that the plate moves and takes out timing. Play with the weights in MSD or for
testing only lock out the curve complete and see if that cures it. Then you know it is a spring problem.

There are bushings in the plate that can easily
be changed to give more initial advance and less advance in plate. My street cars like more initial
and less in plate = 9 Degree bushings (18 engine).

Of Course I am a Mopar guy......Your experiences may vary!

[Kegracing]

Glad that fixed it Gary!

I had an HEI do that and drove me crazy years ago... was that ghost that made me start locking out all my distributors or doing mechanical advance only.

Ken

Stock 412