71 LT-1 Holley Problem
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Joined: Mar 2018
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71 LT-1 Holley Problem
Need help with 71 LT-1 carb problem. The car starts just fine and runs fine but after a while it starts stumbling when I take off from a stop (this has just started). I have to pump the accelerator to keep it from stalling. The carb has been gone thru twice. It is the original 780 Holley. Any suggestions?
Cruising
Joined: Aug 2016
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The first thing I would check is the float level when the stumble occurs, but be VERY CAREFUL when you remove the screw on the float bowl, you DONOT want a fire! Second , I would suspect the fuel filter . Third , is the fuel pump losing pressure or volume to the carb, that requires an in line fuel pressure gauge. Fourth if you have a SOCK on the fuel pickup in the tank it might be very well be clogged with debris. Number four is probably the most hassle because you have use compressed air to blow back from the fuel pump inlet into the tank to clear any debris around the Sock Good Luck . Steve.
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Thanks Steve! I have done most of what you have suggested. The car runs just fine for 45 min or so. It seems to start after I run it at about 3500 rpm on a highway and then into city traffic. Like stopping at a light and then starting. The engine runs at normal temp 160 degrees. Once the car starts moving it runs like an LT-1 should. Steve
Cruising
Joined: Aug 2016
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Well plan B. Do you have a heat isolator under the carb? Usually they are phenolic or a composit wood material, I'm leaning towards a fuel percolation problem in the float bowels or a incorrect Power Valve in the primary metering block.
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Yes, there is a heat isolator under the carb. I also think it is some kind of fuel problem. If it was a Power valve wouldn't it stumble or do the same thing all the time (car runs great for about 30 min)? When this happens I remove the air cleaner and can see fuel squirting into the venturi while operating the accelerator. This is why this has me baffled.
Cruising
Joined: Aug 2016
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The accelerator pump draws fuel directly from the float bowl . It,s a totally separate circuit from the power valve, however they both share the same float bowel. I know its a hassle but I suspect you have a flaky power valve or a needle valve and seat that is binding in the float bowel. I think this plan C. Steve
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Burning Brakes
Joined: Sep 2018
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Is your heat riser opening?
Mine was not and was forcing hot air under the carb causing it to boil the fuel out of the bowls percolating not allowing it to run through the jets or pv. IT would run fine for 30 min or so then would die... then would restart after cooling off.
Mine was not and was forcing hot air under the carb causing it to boil the fuel out of the bowls percolating not allowing it to run through the jets or pv. IT would run fine for 30 min or so then would die... then would restart after cooling off.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Is your heat riser opening?
Mine was not and was forcing hot air under the carb causing it to boil the fuel out of the bowls percolating not allowing it to run through the jets or pv. IT would run fine for 30 min or so then would die... then would restart after cooling off.
Mine was not and was forcing hot air under the carb causing it to boil the fuel out of the bowls percolating not allowing it to run through the jets or pv. IT would run fine for 30 min or so then would die... then would restart after cooling off.
Jebby