Yesterday I filled tank, started right up but idle speed normally 500 dropped to around 300 and ran a little bumpy for a few minutes then smoothed out and ran fine. Carburetor temperature when I got home 135 degrees. Any thoughts?


1955 312 T-Bird Warwick, NY

Different station you’ve never used, filters and what kind, octane, what carb, was the base 135*, do you have a heat crossover? Just asking. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Same Sunoco station I always use, 91 octane, filter perforated stone type element used on C1 vets, clean. Carb is Summit 600 cfm, 2 years old. .032” Edelbrock heat insulator gasket to manifold. Carb body 135 degrees F. Happened the instant I started it for just a few minutes never happened before. I doubt gas was boiling and pulling bubbles into cylinders and if methanol was high it would have taken at least a few seconds to get into the carb. Anyway it it cleared up and ten fine, just puzzling.

1955 312 T-Bird Warwick, NY

Sounds to me like you stirred up some dirt in your gas tank that got by the filter.  I chased this problem for a long time when I first bought my car.  Pulled the tank and the bottom was coated with fine rust.  I opened the carb and the bowls were covered in the stuff. Installed a new tank, No more problems.

Hi Phil, I had that happen also driving from Memphis, Tennessee back to NY several years ago. I had to crank up the idle to bypass the circuit, made that trip on the original tank, big mistake, carburetor float chambers were loaded with fine rust. I replaced the tank. I have an electric choke; I’m thinking it might have engaged part way making the mixture too rich until it opened. The duration of the event was in line with the choke release time.

1955 312 T-Bird Warwick, NY

Weirdest thing that happened to me was last year coming home from a cruise night.  On the way home my car wouldn't idle at all. I kept it running long enough to get it back to the garage by working the throttle.  I have a Holley 1848-1 465 cfm carburetor on my Tbird engine. This is a copy of the original 1957 312 TBird carb. The carb has a hole in the top of the front fuel bowl that is partially covered by linkage. When I removed the front fuel bowl to see what had happened, I discovered a tiny bug have crawled into the hole and was restricting the idle circuit.  The Tbird has an open hood scoop and the hole is outside the breather. I was happy to see it wasn't my gas tank.  If you own one of these old cars, do yourself a favor and check the tank.

I believe I figured it out. When I set the mixture screws I remember backing them out quite far to obtain highest vacuum. I believe I made it too rich feeding too much fuel at warm idle causing the stumble.

1955 312 T-Bird Warwick, NY