Starting Problem When Hot

[Richard R.]

My 72 (base engine) automatic intermittenly will start up and run for 15 seconds then die. Their is no fuel shooting from the jets when the throtel is pumped. If the choke plate is held closed it will eventual start. I replaced the fuel pump, filter, and hoses from fuel line to pump and line to the carb. Fuel poured out of the line when disconnected from pump, blew air into return line and heard it in tank. Lines are not leaking, orginal carb was rebuilt and float is not stuck in the up postion.
If you pour gas in the carb it will eventually start up. any suggestions onwhat else i might look for?

[Edward J.]

Re: Starting Problem When Hot

Rich, sounds like you have about all bases covered, the only thing that comes to mind is the fuel pump push rod is it moving up and down when you crank engine over, you'll need to remove pump and plate to see if the push rod throw in enough to move the pump lever. if okay,also check the pump rod to see if its worn, I do not have the spec.s on the length, but maybe someone does.

Also make sure no kinked fuel lines, or hoses.

[Patrick H.]

Re: Starting Problem When Hot

Richard,

Read this thread:

https://www.forums.ncrs.org/showthre...F-470&uid=2298

I think that after almost 40 years of use/wear/etc, gas eventually leaks backward and the carb has just enough in it to start but not enough to keep going. It can't hurt to try one of the filters with the check valve as described in the thread - I need one in my 72 and in my Cutlass, and it's time I go out and buy them since this thread is over a year old.

Patrick

[Richard R.]

Re: Starting Problem When Hot

Thanks for the ideas but I have also replaced the push rod and the filter with a check valve in it. The hoses have no kinks in them. The car runs fine once you get over this problem and may not happen again for a couple of days. any more ideas because I am stumped.

[Patrick H.]

Re: Starting Problem When Hot

any more ideas because I am stumped.

Thoughts...

It's an old car, and with a few of them around here I can tell you that sometimes they just don't work like my 2008 especially when it comes to starting. My Cutlass does the same thing and even with carb rebuild and many other attempts it still happens; Dad's 72 Corvette is about the same. My 72 Corvette hates to start when the engine is cold but after that starts no matter what; my 71 Corvette starts any time and every time.

The only thing I note is that you say that if the choke is held closed it will eventually start. Does the choke need to be adjusted? Does the choke coil need to be replaced? Does it happen more on hot days than cooler ones? More if it sits for 1 day or if it sits for a week? Something binding in the linkage?

If I had an easy answer I'd have changed it on mine too by now.

Patrick

[Edward J.]

Re: Starting Problem When Hot

Patrick, I read the thread on the check valve, the only reason GM used the check was in case of a roll over, this keep the gas in the tank from feeding a fire in the engine compartment when a car rolled over in a accident, I have not seen any other use for the check valve, since the carb.s needle and seat shuts the fuel flow off. The check valve sometimes will limit the flow of fuel into float bowl on the big block cars or trucks that get thisty when really stepping on the gas, pre emisson cars did not have the check valve in filter, but those with emisson controls the float levels where set low from the factory and sometimes they would tend to run out fuel in the float bowl when on a long hard acceleration.

[Edward J.]

Re: Starting Problem When Hot

Thanks for the ideas but I have also replaced the push rod and the filter with a check valve in it. The hoses have no kinks in them. The car runs fine once you get over this problem and may not happen again for a couple of days. any more ideas because I am stumped.

Rich, maybe some sort of vapor lock problem, Do you notice the problem when hot? or can it be on a cold start-up also?

[Richard R.]

Re: Starting Problem When Hot

Ed, it only happens when its hot. Their is no fuel coming into the carb with the engine turning over. Pour some gas in and it starts up but runs rough for a few seconds until gas starts flowing again then runs fine. Seems like it looses its prime. I have put 2 rebuilt fuel pumps on n the last few months so I doubt that is the problem.

[Edward J.]

Re: Starting Problem When Hot

Rich, how about the sock on the end of the fuel sender in tank, maybe its plugged?

Its a pretty cut and dry operation, fuel supplyed from tank to pump and pumped to the carb.,its either before the pump or after the pump, if there is a chance that it before the pump it would be sucking air and not fuel. hose clamp? are you using the original style clamps that maynot have enough spring tension to seal around the hose.

There was some recent disscussion on the rebuilt fuel pumps, and they were not saying anything good about them. if you happen to have a fuel pump tester hook it up and see what the PSI is. (3-5PSI ).

One other thing do you have the S shaped hose at the fuel pump? I have seen hose that are cut to length that just don,t make the bends and results in a kink slowing fuel flow down into the pump.

[Richard R.]

Re: Starting Problem When Hot

Ed, I have the S hose and the orginal style clamps, I will try new style clamps and see if thats it. the tank was replaced a number of years ago, their is no rust in the bottom and the sock looks ok but guess it could be plugged. Can that be changed without removing the tank?