70 Vette-- Hard Starting When Hot

[GARYP1]

HAve 70 vette 350/350 with holly spread bore 650 cpm. starts instantly when
cold, but when she gets hot in the summer, leave her sit a short while, no problem cranking, but I have to turn her over several time before she fires.
what is going on here

 

[Robin7TFour]

sounds,to me, that your holley is causing the problem. probably fuel leaking into the motor after shut-down. thus, you have to turn the engine over alot to clear the cylinders.
maybe a needle & seat issue, allow the fuel to seep.

my 02

ROBIN

 

[GARYP1]

holly is fairly new, 1 year old new. Try this on for size, the problem started when a local mechanic change the fuel pump, is it possible that the pump is the problem.

 

[Robin7TFour]

GARY, it is not likely. unless you have drivability issues . i.e. running too rich,fouling plugs,stalling. sounds like it's all after you stop. so, think about what could go wrong after shut-down.

hope this helps

robin

 

[GARYP1]

so, if you are right, the only way to fix it is to remove the front fuel bowl and change the needle and seat. unfortunatly this version of the holly does not allow me adjust the height of the float as well externally. is their any way to double check that its a needle and seat problem before I start messing with the carb.

 

[Robin7TFour]

GARY, take the air cleaner off while it's idling. then after shut doen watch for whisps of smoke coming from the carb opening. if so that will be fuel leaking into the hot manifold. if it continues more than a few seconds,then i would suspect a leaking seat.
another thought,while the fuel pump was being changed a bit of debris got into the line and maybe causing the n&s to leak.
hang in there you'll get this one solved.


robin

 

[72Mako]

holly is fairly new, 1 year old new. Try this on for size, the problem started when a local mechanic change the fuel pump, is it possible that the pump is the problem.

Gary, if nothing was changed for the exception of the fuel pump, that may be your problem. Did your mechanic replace it with a correct fuel pump. Believe on the L48-300 hp and 350/350 hp engines that the fuel pump should have 3 ports. Fuel in, fuel out and a 3rd smaller line that returns excess fuel to the gas tank. If he put on a 2 port fuel pump ( used on LT-1) and blocked off the return line, it may be over pressuring the carb as the fuel perculates during hotsoaks. Just something to check. Charles

 

[Robin7TFour]

CHARLES, good idea. i didn't think about the by-pass line. guess i need to study more .

robin

 

[72Mako]

Robin, not at all, from your posts, sounds like you got a good handle on things. LOL.
I found out about this when I dropped in my new motor with a new Carter hipo fuel pump. No return line port. Ended up having to use the base engine 3 port pump and it does seem to support this new motor ok. But if you know of anybody who makes a hipo aftermarket 3 port, I'd be interested. Anyway, it was just a shot in the dark. Charles

 

[GARYP1]

Sorry for the delay in responding to your timely reply. I checked the pump and it has three fittings as you describe. Its not an ac pump, should'nt matter ???, I wonder if it would pay to get a new pump from ekers, I've checked the carb after shuting down the motor it seems dry inside the throat and does'nt seem to be leaking into the intake manifold.

 

[mike weyman]

sounds like there is air getting in the fuel line , make sure the lines are tight. it may not leak fuel out, but may be sucking air in and breaking the vaccum,thus making you crank the motor to pump up more fuel???

 

[wishuwerehere82]

It might be a bad check valve in your new fuel pump.

It can cause the fuel to drain back from the carb to the point in your fuel line that is level with the amount of gas in your tank.
Do check the fittings for leaks, but you would probably see gas leaking when the motor is running.