| fordtruck41 | -- 05-30-2017 @ 9:07 AM |
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I have a 41 Ford truck stock 6 cyl flathead engine with 1 barrel stock carb The engine misses when aggressively pushing the gas but is fine when accelerating slowly. Same problem occurs when no load on engine "Out of Gear" Condition. Idles fine otherwise and runs smooth after engine RPM increases. Any suggestions? Thanks...Robert
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| ken ct. | -- 05-30-2017 @ 4:19 PM |
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Could be carb,fuel pump or electrical in nature,you would have to pin it down more its a big choice to be of much help ?? ken ct.
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| len47merc | -- 05-30-2017 @ 4:48 PM |
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Had a similar issue - ran fine except when pressed such as when going up a long hill at speed. Acted like it was starved for fuel - let off and the fuel would 'catch-up' and it would run fine again. Found the glass fuel pump bowl gasket was leaking air but not fuel. Disassembled, cleaned, reassembled and tightened firmly - problem solved. No experience with trucks and not sure whether you have a glass bowl on you fp or not, but check to ensure your fuel delivery up to and through the pump is clear, buttoned-up tight/not leaking air (yes it can leak air in but not fuel out), flex line is not collapsing, all connections are tight, etc. Eliminate any chance you have an issue causing a fuel starvation problem. If you exhaust all this and still have the issue, next I'd look at the pump in the carb - look down into the carb and manually actuate the throttle and ensure you see a clean, robust stream of fuel pumped into the carb. Let us know what you find - those air leaks in your fuel line from the tank through the fuel pump can really create havoc like this. Hopefully it is something simple in the fuel line that you can find quickly and be back on the road. Fwiw - just my $0.02 suggestion for starters. Steve
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| TomO | -- 05-31-2017 @ 6:51 AM |
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Here is a way to check your fuel delivery Insufficient fuel delivery: This condition shows up when driving at highway speeds as a miss or the engine dies. Vapor lock occurs when the fuel pump output pressure is very low and the engine is hot. It is much rarer than commonly thought. Most cases of suspected vapor lock can be attributed to another problem such as a weak coil or condenser, but can be caused by a weak fuel pump. To determine if you really have vapor lock, remove the air cleaner and look in the bowl of the carburetor, while operating the accelerator linkage. You should see two streams of gas in the carburetor if you don’t, you have a fuel pump problem. Fuel pump pressure is controlled by the return spring under the diaphragm, too little pressure means the spring is weak, too much pressure means the wrong spring was used. Pressure should be between 1.5 - 3.0 lbs at all engine RPMs. Too much pressure will not allow the float to control the amount of fuel in the carburetor bowl, low pressure will affect fuel delivery. To check fuel delivery, you need a graduated 16 ounce or larger container to determine the amount of fuel delivered in a measured time. Disconnect the fuel pump line from the carburetor and direct it into a graduated container. Crank the engine long enough to get 2 ounces of gas in the container and then continue cranking for 15 more strokes of the pump. The pump should have delivered 6 more ounces of gas. Insufficient fuel delivery can be caused by a vacuum leak, plugged flex line, worn pivot in the pump arm, stretched diaphragm, plugged fuel line or tank pickup, plugged tank vent or wrong gas cap or a worn push rod. If your fuel system is in good shape, check the spark when the engine is at operating temperature. At idle it should be 1/2" long and blue in color. Weak spark can be caused by a bad condenser, bad coil, incorrect voltage to the coil, incorrect point dwell and worn parts in the distributor. Tom
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| fordtruck41 | -- 06-02-2017 @ 3:11 PM |
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Hi Tom and Steve Thanks for all the suggestions. I did check the fuel flow and all looks ok. Also checked the carb accelerator pump and there is a good stream of gas when the throttle is depressed. Running the engine with the air filter off and upon depressing the accelerator quickly from idle there is a pop back through the carb. This only happens for a half second or so. After engine rpm increases everything is ok. Any more suggestions are welcome Thanks...Robert
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| TomO | -- 06-03-2017 @ 7:11 AM |
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Look for a vacuum leak, most likely place is where the main body of the carburetor meets the throttle body, or a cracked hose leading to the wiper motor. You could also have e vacuum leak where the manifold meets the block. Tom
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