[Bobalong]

Drove goat about 40 minutes to a restaurant yesterday.

Started cold with no issues. Had to crank it a little since it's been weeks since I drove it. Full tank of non ethanol.
After about an hour in the place it did the same ole same. Crank and it burns whatever is left in the bowl then dies.Then comes the embarrassing crank and crank and crank till it finally fires off.

40 minutes back to town and now the outside temp has dropped to the low 70's outside. Parked it for over an hour, got in, fired right off, was waiting for the dreaded start and die routine . . . . never happened.

I have Mr Gasket 86B heat dissipator gasket on the way, it's a 2+2 gasket, metal
sandwich. Hopefully this will help.
I was really hoping the non ethanol would be the answer but it didn't help.

But it is really pricey anyway so the new gasket set will be way cheaper in the long run.
As long as I've had this car I don't remember this hot start issue in the past, BUT, then I realized I never drove it on hot days (not for lack of AC), It's always been a fair weather car. As I've said before, I'm over that, I driving it.

Now if I just could get the Rostra cruise control installed there might be some long trips in the future.

[Schurkey]

If it cranks, runs, burns what's left in the float bowl, and then dies until it cranks and cranks and cranks while the fuel pump is sucking vapor instead of liquid...




...a carb heat shield is not going to help. The carb still has fuel, or it wouldn't run at all before dying and needing to crank forever. You've got vapor at the pump, not an overheated carb.

[77 TRASHCAN]

What carb base gasket do you have now???
Fuel pump type?
Fuel line size?

[STEELCITYFIREBIRD]

Logical...Totally agree,!
180 stat to start easypeasy. it's you under hood ambient temp... with a heat soak.
Leave the hood open on your heat soak on a hot day.

. Hose off the pump and line nearby @ shutdown and/or startup for a second added pinpoint.
Check condition and tighten clamps on any rubber fuel line. The suction line soft line tends to harden @ the pump area also and get loose over time. You may be pulling some air with a heat soak, possibly at a connection or thru a deteriorated hose.

[dataway]

Curious ... what keeps fuel from siphoning back to the tank on shut down? Check valve in pump? Engine sitting there shut down, fuel level in bowl drops from evap, float valve opens allowing air in the system ... gravity pulls the fuel back down to pump level or father? Specially if parked nose up on a hill.

Does a closed float valve usually prevent this, or is there some other part of the system that prevents it? Diaphragm type pump would have to have a check valve right?

[Schurkey]

There's at least two check valves in an engine-mounted fuel pump. Some HP pumps advertise six valves.

If they leak, the pump becomes inefficient AND the fuel can drain down from above the pump, to the level of fuel in the tank.

So, yes, that's a possibility in this situation. But since heat seems to be a factor in when the car won't continue running, I'm really leaning toward vapor-lock at the pump and in the plumbing near the biggest heat-source--the engine.

'Course, it could be vapor lock AND a failing fuel pump AND air leaks into the fuel plumbing from rotted hose(s)...

[mgarblik]

Your problem is a tough one to deal with because multiple factors can be involved. Based on your description of the problem, the carburetor base gasket will not solve it. The number 1 factor is the fuel itself. Modern fuel is not designed for engines with carburetors. That alone is an issue. The vapor pressure is so high, vapor lock is always an issue on hot days. Probably the simplest fix that would really help is a new mechanical fuel pump with a return line to the gas tank. Many AC equipped cars from the 60's came with one. Another fix that is more of an aggravation, especially if on a long trip is adding just a little race gas to a full tank of pump gas. Just 1 gallon to a full tank will make a world of difference as far as vapor lock. Another fix is a low pressure electric pump in the supply line between the tank and mechanical fuel pump. Having low pressure, just 2-3 lbs vs vacuum in the line naturally raises the boiling point of the fuel. Good luck with the fix.

[STEELCITYFIREBIRD]

CV products very hi output pump disassembled for new check valves and diaphragm install.
5 valve.

[goa484]

Does this car have a fuel return line in working order? Ive driven my gto in humid Pensacola summer heat and had zero issues with heat soak(even if only sitting for a few min), even with a stock pump and ethanol gas, but I did have a return line.

[coonhunter70]

I would stick with the ethanol free gas

[Formulajones]

Originally Posted by Schurkey

If it cranks, runs, burns what's left in the float bowl, and then dies until it cranks and cranks and cranks while the fuel pump is sucking vapor instead of liquid...




...a carb heat shield is not going to help. The carb still has fuel, or it wouldn't run at all before dying and needing to crank forever. You've got vapor at the pump, not an overheated carb.

Originally Posted by mgarblik

Your problem is a tough one to deal with because multiple factors can be involved. Based on your description of the problem, the carburetor base gasket will not solve it. Probably the simplest fix that would really help is a new mechanical fuel pump with a return line to the gas tank. .

^^^^ This.....I've mentioned this on several occasions now. There are steps you'll have to go through to completely cure the issue.

I agree if it runs with the fuel in the bowl and then dies, the heat around the carb likely isn't the entire issue. Sounds like you have a fuel line that is getting hot somewhere along the path. A return line is an extremely helpful addition, if you don't have one, like I said before, it's beneficial you add it.

I don't believe it's the fuel pump itself getting hot, because I have plenty of mechanical fuel pump cars here we drive daily in the desert heat and the fuel pumps themselves have never been an issue. But you have to make sure the lines are away from heat. Now if it's an old pump, say 10+ years, it could be a weak pump which is going to have more trouble dealing with the heat and vapor fuel because your fuel pressure could be lower than optimal, so that's something to consider.

[Formulajones]

Here are pics of the 2 cars we daily drive. I'll break this down in 2 posts

The Z has no return line, which is correct for a solid lifter 4 barrel engine. Factory lines everywhere with plenty of clearance, and a stock replacement GM mechanical pump. Stock brass fuel filters in the holley carb.

You didn't mention what octane you're running but that makes a big difference, ethanol or not. The only non ethanol we have here is 87 octane. No way am I going to run that in an 11:1 iron headed engine.

Best we have is 91 ethanol fuel here so that's what it gets. It runs absolutely flawless in the heat, I've been to phoenix when it's 110+ and this summer up here at 5,000 ft it's been 100-105 the last few weeks, the car never complains. Even has a completely open heat cross over and a working divorce choke.

[Formulajones]

My firebird was impossible to get a fuel pump picture because the fuel pumps on these cars are absolutely just buried under the PS pump and Alternator.

This car has a factory return line which helps tremendously. I bent my own line to the carb because I didn't like how the factory line ran nearly on top of the thermostat housing. I gave it a good 2" clearance. The rest of the lines on the car are factory issue.

This engine is 10:1 with iron heads, and gets nothing but 91 ethanol pump gas. I just recently installed a RAIV intake and separate heat cross over with functioning divorce choke in an effort to keep the carb cooler as an experiment of sorts. Happy to say this works flawless in the same heat conditions I drive the Z. And this car is still running a 20 year old AC mechanical pump that is still working perfectly.

[Bobalong]

The fuel pump is a few years old, have to look at my receipts.

I have a steel factory repop fuel pump to carb fuel line.

Rubber hoses have all been replaced over time, except maybe if there's some buried in the frame; (70 GTO)

I have a return line to the tank, maybe thru a vapor canister first, have to go look.

My non ethanol is 89 octane.

The carb gasket right now is probably what came with my Cliff rebuild kit, not sure, but it's just a gasket.

400 engine, factory air cleaner. RA III exhaust manifolds. Factory Intake.

[STEELCITYFIREBIRD]

Well me thinks you need to definitively diagnose what is lacking at the no start time.
Schurkey about covered all the likely fuel system problems. A fuel pressure gauge T Ed in would be a helpful tool. Will tell you how strong the heart is, and if your holding pressure after shutdown.
You have verified the carb goes dry ( no pump shot)when you have the no start condition?

[Bobalong]

Originally Posted by Schurkey

If it cranks, runs, burns what's left in the float bowl, and then dies until it cranks and cranks and cranks while the fuel pump is sucking vapor instead of liquid...




...a carb heat shield is not going to help. The carb still has fuel, or it wouldn't run at all before dying and needing to crank forever. You've got vapor at the pump, not an overheated carb.

Vapor a the pump ? Factory pump, only a few years old. Factory steel line from pump to carb. Non ethanol gas. Factory intake, RAIII exhaust manifolds.
They didn't do this back in the day.
I'm open to suggestions.

[Bobalong]

Originally Posted by Schurkey

If it cranks, runs, burns what's left in the float bowl, and then dies until it cranks and cranks and cranks while the fuel pump is sucking vapor instead of liquid...




...a carb heat shield is not going to help. The carb still has fuel, or it wouldn't run at all before dying and needing to crank forever. You've got vapor at the pump, not an overheated carb.

Originally Posted by 77 TRASHCAN

What carb base gasket do you have now???
Fuel pump type?
Fuel line size?

Just a out of the box gasket, factory fuel line, have to look at receipts but the pump I think came from AMES.

[Bobalong]

Originally Posted by STEELCITYFIREBIRD

Well me thinks you need to definitively diagnose what is lacking at the no start time.
Schurkey about covered all the likely fuel system problems. A fuel pressure gauge T Ed in would be a helpful tool. Will tell you how strong the heart is, and if your holding pressure after shutdown.
You have verified the carb goes dry ( no pump shot)when you have the no start condition?

Can't T in a pressure gauge (don't want to cut a factory repop steel fuel line)

Haven't verified no pump shot, but that's a good way to know for sure the fuel bowl is empty. Seems like we're always in a restaurant parking lot on a 90+ degree day when it happens. I need to drive it and park it at home to replicate the hard start.

[Formulajones]

I've never had any issues with the mechanical pumps getting hot as I mentioned. I had pics up of 2 daily drivers we use set up with factory parts, no issues. One with a factory return line, and the other does not.

The only piece I changed on my 70 Firebird was that factory pump-to-carb line. I didn't like how the original ran so close to the thermostat housing. Practically right on top of it. I bent a new line with more clearance in that area. As long as you can get a thumb between your metal line and any hot parts on the engine, it should be fine. It still may heat soak a bit on a really hot day, but with a return line and within a minute of a hot start and the fuel circulating, it shouldn't be a problem. By no means should it take tons of cranking to get the engine to start, and no starting and die symptoms either.

I never run just a paper gasket under the carb either so I feel your changing that is a good step. I always run a 1/4" thick gasket minimum, or a 1/4" piece of wood that I blend with the intake and carb with paper gaskets on either side works even better.

For the record, I ran the factory iron intake on my RAIII for decades, with a 1/4" carb gasket, and the heat cross over open and working divorce choke. I never had any hard restart issues or vapor locking with that setup either. During all this time I've been back and forth with headers and factory RA manifolds on the car with no affect as far as drivability.

["QUICK-SILVER"]

Originally Posted by Bobalong

Crank and it burns whatever is left in the bowl then dies.

How much time are you talking about here? One second? One minute?

Fuel lines from pump to tank stay cooled off from air flow when you're driving.

A fuel line that's close to any exhaust part (from front to rear) will heat up enough to vaporize or boil gas when you park the car. Hotter it is outside the worse that gets. If it happens towards the front of the car, the pressure can push all the fuel in the line back to the tank. It can take quite a bit of cranking to get the lines back full and going up to the carburetor.

I've seen a few comments, in the past here at PY, about leaving the wire hook off the needle that hooks to the float. That lets the needle stay shut, when the float drops, and relies on fuel pressure to push the needle off the seat. Not sure that's a good idea when you need the needle and seat open to let air purge out of the system. If fuel pressure is even slightly weak that could be a problem when you're pumping air instead of gas.

It takes a lot more pumping to compress air than it does to compress liquid fuel. IDK just how much pumping that would take to push a needle off the seat if the wire hook isn't in place.

Clay