Vapor lock/percolation?

[Ltpowers]

I’ll start out saying I have a 1971 gmc c15.

Eps edlebrock intake with avs2 edlebrock carb. Under than I have a heat insulated gasket and then a phenolic spacer. They have help with what I think is vapor lock alittle but not solved it b

The the truck is warm and it’s hot out. I’ll rev the engine from the throttle and it doesn’t get gas till about 1/8 of the way back. Shoots what I assume are vapor fumes until then. I was told to get the spacers I listed about. Helped alittle but not a lot. So I got a fuel filter with the little return oriffice and that also helped alittle but not enough.

I’ve wrap hoses with cooling sleeves no help. It mostly studder and stumbles from stop to go or under light throttle while drive. I can rev it in park and it does miss a beat.

I installed headers this weekend cause my ram
Horns just didn’t get enough airflow. But even with the headers the problem still persist.

Street fire distributor I installed back in January or February. So hei and not points. While doing the headers I did an oil change and plugs and wires. Currently running muffles of the headers till I can get this heat soak problem solved.

Brand new mechanical fuel pump. No return line on it which is why I got the fuel filter. I do have a regulator at 5.5 max psi

I’ve been dealing with this for acouple months now and just can’t figure out how to fix it. I’m relatively new to working on these but have never had this heat problem with any older vehicle I’ve had. In desperate need of help. The truck will start to overheat if I’m sitting and idling for like ten minutes but never overheats or gets that hot it seems

Later today I will buy a temp gun to show what exactly my numbers are.
Well I guess I can’t put pictures up here for some reason but my fuel pump was running around 130-140
Posted via Mobile Device

[hairball]

The amount of alcohol in todays fuel is part of the problem. The fuel will usually vaporize at the pump. In our town we have a few stations that carry non ethanol fuel but it can be hard to find otherwise. You may have to resort to adding an electric fuel pump. It can be installed in addition to the manual pump. It has to be a push/pull type pump. Of coarse there are aways safety concerns when wiring the pump. Might want to install an off/on switch for the pump. Hope this helps.

Hairball

[special-K]

Doesn't necessarily sound like vapor lock to me. What engine? How long have you had the truck? Has it been a running driving truck all along, just got it running, problem started with new carb, or other?

as far as the heating up problem, is there a fan shroud? Fan clutch, straight-mount, or flex fan? back to what engine and what radiator? what transmission? Is it an automatic? Just give us all the info on your truck, what it has and what it's doing, and you'll get great insight from members who know.

EDIT: I just noticed this post is in General Discussion. What year truck do you have? We can move this to that specific forum. Or start all over in that forum with a new thread and we can delete this one.

[72c20customcamper]

Under light throttle sounds like a lean miss . Check all your vac lines and headers will contrary to popular belief make it hotter under the hood.

If it stumbles and you quickly punch it does it smooth out?

[Ltpowers]

Originally Posted by special-K

Doesn't necessarily sound like vapor lock to me. What engine? How long have you had the truck? Has it been a running driving truck all along, just got it running, problem started with new carb, or other?

as far as the heating up problem, is there a fan shroud? Fan clutch, straight-mount, or flex fan? back to what engine and what radiator? what transmission? Is it an automatic? Just give us all the info on your truck, what it has and what it's doing, and you'll get great insight from members who know.

EDIT: I just noticed this post is in General Discussion. What year truck do you have? We can move this to that specific forum. Or start all over in that forum with a new thread and we can delete this one.

1971 gmc c15 350 engine and tranny. I’ve had the truck about a year now. All last summer I didn’t deal with any problems but an alternator.

It’s been running and driving the entire time I’ve had it. When I first bought it I had to replace a fuel tank. I came out to work about two months ago and a 5 Hour Dr. later one of my exhaust manifold is cracked and was blowing on my spark plugs making them hot. Since then the truck has not ran anywhere near what it has before.

It’s been running and driving the entire time I’ve had it. When I first bought it I had to replace a fuel tank. I came out to work about two months ago and a 5 Hour Dr. later one of my exhaust manifold is cracked and was blowing on my spark plugs making them hot. Since then the truck has not ran anywhere near what it has before.I got the carb back about 2 1/2 months ago. And it was so smooth. Original radiator. I think maybe 2 row brass? Not sure what they came with stock. I replaced the water pump the fan clutch not the fan the fan shroud is on there. I’m not sure if it’s a flex fan or not. And it is an automatic.

Once the truck is warmed up and it’s hot out I can go to the front of the carb and push the throttle in here almost a haze of fumes before the gas starts to come out. The float level should be good since I’ve never had to adjust it or didn’t adjust it out of the box. I did just find that my rotor cap had dirty connections on the inside so I’m going to get a new cap and I know that was probably part of my problem

[Dead Parrot]

I have a 75 C10 with a similar setup. Stock 350 crate motor/TH350. Performer manifold(spread bore), earlier 1405 eddy carb, no return mechanical fuel pump. 1" aluminum 4 hole spacer advertised to improve low end performance. Ceramic coated headers. Never had a vapor lock or similar issue. It will evaporate off some of the carb bowl gas if it is hot which will give a few seconds of cranking before start.

I still have some exhaust crossover flow but no riser valve to get stuck.
7 blade fan, 3 row radiator, OEM shroud, and standard duty fan clutch 195* Thermostat.
Only emissions are PCV and THERMAC.
About 12* initial advance, vacuum advance connected to manifold vacuum. As much initial as it will let me do before hot hard to start happens.

What is your initial timing? Most stock 350's like lots. More idle timing means less idle fuel needed = cooler engine and engine compartment.
How many blades on your Fan?
Thermostat temp?

[BigBird05]

If you think you have vapor lock, install a fuel pressure gauge. I would add a return fuel line. Run a temporary line way from the engine I have seen chevy engines pick up heat because the fuel line runs close to the block behind everything and doesn't get any air flow.