1955 WOT stumble

zeroroadkill

zeroroadkill

BlackBird Fly
Gold Member
Last seen
Joined
Mar 2, 2020
Thunderbird Year
1955
I noticed this stumble/stall before I installed an electric fuel pump which I thought fixed the problem. From a start @ WOT she’ll accelerate and suddenly stall. If I back off the throttle she’ll start to come back to life, bucking for a few seconds then all is fine. Not electrical. Sounds like fuel starving or could it be the float level is too high causing spillage on hard acceleration off the line? It was warm today 85°, but she was running at about 75%-80% on the gauge. I did smell fuel prior and maybe thought vapor lock, but I have vented the gas cap, no vacuum from tank. There are no fuel leaks around the Holley 4000 Tee-Pot (like the secondary fuel tubes). Fuel filter is new & clean. Gas tank is new and all fuel lines are clean & excellent condition. This hasn’t happened in a long time since I installed the electric fuel pump. Is it fuel starvation or fuel spillage? WOT while driving is ok and she runs strong and smooth. No stumble on hard turns or braking.

Thanks
 

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You have conflicting symptoms. If you smelled fuel it's not from vapor lock. If you couldn't find a leak, follow your nose. Vapor lock is actually very rare. Too high of a float level would not cause hesitation just a rich fuel mixture and black exhaust and/or leaks.
Did you run it on the new electric fuel pump before replacing the filter? Ever had home incoming plumbing done and all of a sudden your faucet screens are full of crud? My guess is that the needle valve on the secondary float is contaminated or stuck and you are dealing with fuel starvation on hard acceleration. Pull the carb bowls and I'll bet you find debris in there and in the needle valve. Or even more simple, Most carbs have a screen on the fuel inlet into the carb and it could be clogged restricting flow.
 
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zeroroadkill said:
I noticed this stumble/stall before I installed an electric fuel pump which I thought fixed the problem. From a start @ WOT she’ll accelerate and suddenly stall. If I back off the throttle she’ll start to come back to life, bucking for a few seconds then all is fine. Not electrical. Sounds like fuel starving or could it be the float level is too high causing spillage on hard acceleration off the line? It was warm today 85°, but she was running at about 75%-80% on the gauge. I did smell fuel prior and maybe thought vapor lock, but I have vented the gas cap, no vacuum from tank. There are no fuel leaks around the Holley 4000 Tee-Pot (like the secondary fuel tubes). Fuel filter is new & clean. Gas tank is new and all fuel lines are clean & excellent condition. This hasn’t happened in a long time since I installed the electric fuel pump. Is it fuel starvation or fuel spillage? WOT while driving is ok and she runs strong and smooth. No stumble on hard turns or braking.

Thanks
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I had a sort of similar problem where my 57 would start and run fine for a few minutes down a residential street at about 20 - 30 MPH, but would stumble/stutter when approaching highway speed. Backing off the gas it ran normal. After a few seconds it ran great. Did this for a few trips. Checked out the usual suspects. For some reason I checked/ adjusted/ played with the choke ( Edelbrock carb) thinking it might be sticking. Anyway. haven't had an issue since - not sure if that fixed anything but, like I said, the issue has not returned to date.
 
All fuel delivery new and clean. New tank, flushed lines, new filter, carb bowls inspected with no debris & cleaned anyway. Ran first with new manual pump then install electric pump and flushed out line before connecting to new filter and carb. Filter bowl clean. will check screen on carb inlet. Last check looked clean, no debris.
 
zeroroadkill said:
All fuel delivery new and clean. New tank, flushed lines, new filter, carb bowls inspected with no debris & cleaned anyway. Ran first with new manual pump then install electric pump and flushed out line before connecting to new filter and carb. Filter bowl clean. will check screen on carb inlet. Last check looked clean, no debris.
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Still sounds like a fuel delivery issue. Or even your dist. advance is sticking or not working correctly. All speculation of course not being there.
 
No gas smell now. Checked for evidence of leaks, none, all dry. Carb professional rebuilt so I assume screen is new?
fiber carburetor/manifold gasket for heat block. Perplexed…
 
zeroroadkill said:
No gas smell now. Checked for evidence of leaks, none, all dry. Carb professional rebuilt so I assume screen is new?
fiber carburetor/manifold gasket for heat block. Perplexed…
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Thinking the gas smell was because of the jackrabbit start splashing fuel up the filler tube to the vented cap? 3/4 tank.
 
zeroroadkill said:
I noticed this stumble/stall before I installed an electric fuel pump which I thought fixed the problem. From a start @ WOT she’ll accelerate and suddenly stall. If I back off the throttle she’ll start to come back to life, bucking for a few seconds then all is fine. Not electrical. Sounds like fuel starving or could it be the float level is too high causing spillage on hard acceleration off the line? It was warm today 85°, but she was running at about 75%-80% on the gauge. I did smell fuel prior and maybe thought vapor lock, but I have vented the gas cap, no vacuum from tank. There are no fuel leaks around the Holley 4000 Tee-Pot (like the secondary fuel tubes). Fuel filter is new & clean. Gas tank is new and all fuel lines are clean & excellent condition. This hasn’t happened in a long time since I installed the electric fuel pump. Is it fuel starvation or fuel spillage? WOT while driving is ok and she runs strong and smooth. No stumble on hard turns or braking.

Thanks
Click to expand...
I'd be inclined to think it's lack of fuel. Either not enough pump output or the hard acceleration is making the carb float bind and not open the needle valve so it uses up the fuel in the bowl and then stalls out.
 
I will pop the top off and check the float movement! Thanks
 
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Agree with all of the above, however, my Ford engine experience starts with the 289 and 260 mills.
But I've had similar symptons when advance centrifugal weights "stick"; if this applies on this motor its simple to check and correct. I've also experrienced the same thing when the small wire to the distributor breaker plate frayed and was nearly broken in two - AND when the points condensor began failing. All worth checking if they apply to your engine.
 
Frankie the Fink said:
Agree with all of the above, however, my Ford engine experience starts with the 289 and 260 mills.
But I've had similar symptons when advance centrifugal weights "stick"; if this applies on this motor its simple to check and correct. I've also experrienced the same thing when the small wire to the distributor breaker plate frayed and was nearly broken in two - AND when the points condensor began failing. All worth checking if they apply to your engine.
Click to expand...
I have pertronics but will pop the top off and check advance movement. Thanks
 
If your car runs fine at WOT at normal driving speeds and bogs down at WOT from the start it is either the distributor advance, spark plugs or spark plug wires or possibly a wrong coil or the engine is still too cold. Y blocks like their timing advanced try 8-10 degrees at idle and verify advance at rpm increase, Mallory with a "hell of a coil" set up is unbeatable. One other thing to check is that the choke plates are staying open as the Holley tea pots are notorious for problems when cold. As for Fuel pumps I always used manual pumps and even with trips or duel quads fuel was never a problem.
 
Brax said:
If your car runs fine at WOT at normal driving speeds and bogs down at WOT from the start it is either the distributor advance, spark plugs or spark plug wires or possibly a wrong coil or the engine is still too cold. Y blocks like their timing advanced try 8-10 degrees at idle and verify advance at rpm increase, Mallory with a "hell of a coil" set up is unbeatable. One other thing to check is that the choke plates are staying open as the Holley tea pots are notorious for problems when cold. As for Fuel pumps I always used manual pumps and even with trips or duel quads fuel was never a problem.
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As stated the car was at 75%-80% on the temp gauge. 80 miles into the trip. 80° outside. All electronics are new. Proper coil, new wires, new plugs, new dist cap, pertronics, Timing 8° BTDC. Advance is working properly.
 
Brax said:
Is the carb a rebuilt or longtime use carb. Do you have another carb?
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Year old professionally rebuild. Idles fine, runs smooth and strong, all new fuel system.
Since it started to accelerate on WOT and then stalled and starting bucking about 15 seconds later then ran normal after that. I assume it's a fuel problem?
 
When you check the float check the power valve and power valve diaphragm if your fuel pressure is good at WOT then I would think the PV or related parts are problematic as this is what adds the needed fuel at WOT.
 
I agree, but
Brax said:
When you check the float check the power valve and power valve diaphragm if your fuel pressure is good at WOT then I would think the PV or related parts are problematic as this is what adds the needed fuel at WOT.
Click to expand...
when I tried to find a PV to replace it I couldn't find the part and it wasn't in any of the older rebuild kits I have! I assumed (not good) that they replaced the PV when it was rebuilt???
 
OK, stupid question number 7,312 ...... What does WOT stand for? Vern :>)
 
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