Right turn stumble

[drolston]

Getting a very brief engine stumble occasionally when turning a right corner. Does not happen on a left turn. A whiff of gas fumes as well. Maybe carb float (Stromberg 97 x3) set a bit too high? Otherwise, engine runs like a champ. Any other suggestions?

[Flathead Fever]

It sounds like a float level problem. The carbs will flood only going around a corner in one direction depending on which side of the carb the float hangs off of. The fuel sloshes sideways and bounces the float which opens the needle and seat. I have a '66 Shelby GT-350. When they started racing them in 1965 the carbs were flooding out in the corners. Shelby had Holley build special carbs with the needle and seat and float in the front of the bowl so sideways sloshing did not have any effect on it. Hard braking and acceleration would have? That cured there problem.

Maybe you can just pull the tops off and see if you can spot the one that is too high? You could try pulling off the air cleaners and rocking the car from side to side and see if you can spot any flooding in one of the carbs.

Always work outside of your garage when fiddling with fuel systems. My neighbor just about burned his 5000 sf garage to the ground working on a '40 Ford convertible's fuel tank. Pulled a fuel line, broke an old-fashioned drop light (throw those things in the trash) and it went bah-woosh! The fuel kept draining out of the tank. Sent him to the hospital and the '40 Ford off for a new top and quarter panel repaint. I spent the rest of the night over there mopping up and drying out boxes and boxes and brand new parts. Enough Bob Drake parts to do three '40 Fords.

I use to rebuild a lot of carburetors at work, especially Holley 4V carbs. We sprayed all the gaskets with silicone spray so they would not stick to the carb parts. Some of the gaskets have a sealer on them that glues the gasket to the carb. You can spend more time scraping gaskets and damaging your anodized finish then it takes to rebuild the entire carb. Usually the carb just needs one little part and not a complete rebuild kit. It was easier to pull just a bowl off on the vehicle and repair the problem. Most of the time we were able to reuse the gasket if the carb had already been rebuilt by one us. It saved time and money. We sprayed the gaskets with white lithium grease too instead of silicone spray, depended on which can was closest. The base gaskets we coated with a little lithium brake grease so they did not get baked on. A former Ford Dealer Tuneup guy from the 1960s taught me that trick,

[supereal]

Check the float. If it is brass, shake it to listen for any fuel inside, and observe any leaks while the float is out of the carb. If you have a plastic float, either replace it with a brass type, or a new (not used) plastic float. In either case, carefully check and set the float level. We check the top of the carb by rubbing it on a sheet of emery paper to see if the casting is warped. Over tightening the cover screws is the usual culprit in deforming the die cast. Replace the gasket, and carefully cinch the screws just enough to get a good seal. Over tightening was probably due to trying to tighten the top when a leak was a problem.

[SofaKing]

See if it does stumbles when someone else drives it, maybe it’s your technique. Then check carb linkage and dist advance/ brake.

[drolston]

Float level checked good at .5" on all three carbs. so that was not the stumble issue. When I put it back together it ran very rough at higher rpm much popping. Must have messed up something. Pulled the body from front and center carbs to recheck float sealing and blow the passages out with carb cleaner. Floats were sealing fine, and no obvious problems except the accelerator pump plunger seal crimped over on the center carb. Not sure how that would cause running rough. If the plunger is binding, can it stay stuck on the bottom and hold the power valve open?? Anyway, when I got it back together, it is running good again. Charlie, what's the trick to get those accelerator pump plunger seals in the tube without messing up?

Lesson: sometimes leave well enough alone.

[supereal]

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Rough running and stumbling usually falls in too classes: not enough fuel, or too much. If you are running full acceleration pump stroke on all three carbs, it may be swamping the intake. Three carb setups have always been challenging. We see the same problems when there is a mismatch when carb volume doesn't match the application.

[drolston]

Originally Posted by supereal

Rough running and stumbling usually falls in too classes: not enough fuel, or too much. If you are running full acceleration pump stroke on all three carbs, it may be swamping the intake. Three carb setups have always been challenging. We see the same problems when there is a mismatch when carb volume doesn't match the application.

The engine has 284 cubic inches, and ran great from idle to full throttle until I messed with the carbs to check float levels. The accelerator pumps have been on short stroke. I pulled the front two carb bodies off last night and found one crimped accelerator pump seal. Fixint that helped but it is still running rough. I will pull the rear carb body tonight to check that one. Wish I knew the trick to get those things to go into the pump chamber without getting folded over.