warm engine hard to start

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klburnham

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I have a 56 f-100 with a 312 y-block, 4 bbl carb. It starts right up when cold but when it warms up it is hard to start or won't start at all. I replaced the fuel filter. Could it be a vapor lock in the carb? Thanks for any help
 
Had the same problem with my 56 f100 292 2 bbl when using ethanol based gas. What was happening after I turned the engine off fuel was boiling over in the float bowl, due to heat in the engine compartment, and dripping down the throat of the carb flooding the engine. I would have to crank the engine longer then normal to get it fired up, drove me nuts. Solved the issue by finding a gas station with ethnol free gas.
 
Next time it happens open up the air cleaner and move the throttle linkage to see if it squirts fuel inside the carb. The heat from driving builds up when it's parked for a bit and can boil the fuel out of the carb bowl or create air bubbles in the line from the fuel pump to the carb. If you've got a fiber heat spacer between the manifold and carb it can help. A see-thru fuel filter near the carb should show full too.
 

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im with the others, engine gets hot and over heats the intake manifold, boils the fuel out of carb into the intake and flooding engine, next time when it happens don't pump carb, instead just hold gas pedal all the way to the floor and hold it there till engine starts
 
I had the same problem with my 223 six holley single barrel carb. Lowering the float resolved the issue.
 
Same as all who indicate fuel in line boiling is the issue. Dmsfrr has a good idea with the fiber spacer but I believe they're only 1/2 " or maybe as thick as an inch that will give thermal separation to the carb but not so much the heat to the fuel line from compartment heat. You want to get the fuel line away from the engine, further the better. If your not that concerned about being totally stock a better idea is a tunnel ram spacer up to 4 " high. Speedway has several height variety's 1", 2", & 4". I believe you have enough height under the hood on your '56. The higher the spacer the better for your issue. You will see an increase in torque as well.

Having said all that does you '56 run good when engine is running / driving. Do you have a bogging issue when accelerating? If so it could be a coil as well. A coil going bad will give this as a indication and when the engine is hot it will be hard to start as well. After cooling it will start relatively normal.
 
Carburetor spacers are a big part of the answer here. A two inch four hole spacer has served me well for years. A plastic one may be better than aluminum. Use thick gaskets top and bottom. If you put on a spacer with one big hole, your bottom rpm range with be unsatisfactory. A spacer with four holes will keep the air velocity in the manifold up, giving more bottom end, better mixture control, and bottom end throttle response. Most carbuerators have a tolerance for float level. Spend some time and adjust it on the low side.
 
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