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 my numbers are.
Posted via Mobile Device

[burnin oil]

you might try replacing the power valve or adjusting it so that its richer to compensate. 144 isn't that bad temp wise. Headers usually dump alot of heat under the hood where the stock manifolds retain it. They make a sheet metal plate that sits under the carb that helps reflect the heat back down also but I have never tried it. Double check that there isn't a vac leak under the carb.

[geezer#99]

Several things come to mind.
Float level too high. Could be flooding a bit.
Vacuum leak. You got gaskets on both sides of the spacer?
Your hei. Do you have a full 12v to it?
Timing. What’s your initial timing?
Fuel pressure. Too high.

[PGSigns]

You have done a lot of what normally helps. Next thing I can think of is the float levels. Have you checked them? Also you can put a clear filter in it and see if the fuel is boiling. When you have the top off check the accelerator pump. Also set the fuel pressure at 4 to 4 1/2 psi. You need a pressure gauge in the line just after the regulator to ensure what you have.
Jimmy

[68 P.O.S.]

The usual suspects for Edelbrock carbs:

Float levels. Floats are normally off right out of the box due to shipping and handling. This causes flooding. Set float levels to Edelbrock specs of 7/16” float rise and 15/16” to 1” of float drop.

Fuel pressure. Excessive fuel pressure will also cause flooding. Edelbrock recommends fuel pressure be restricted to 5.5 psi.

Setting transition slots. Set transition slots in the main throttle bores to form a square. This ensures you’re idling only on the idle circuit and will help when transitioning from idle to acceleration. You can see the transition slots in the main throttle bores and will look like a rectangle when overexposed. You want to use your idle adjustment screw to get those little buggers back to square.

Accelerator pump. Set the accelerator pump to the middle adjustment hole. This is where Edelbrock normally suggests to set it at for mild builds, or where to start at when tuning. Also, ensure only 13/32” of the pump rod is exposed above the top of the carb plate.

Fuel percolation. This is notorious with Edelbrock carbs. With your setup, you shouldn’t need 2 spacers. You should only need the Edelbrock 9266 heat insulating gasket. It seals on its own and you don’t need any other gaskets with it.

Carb tuning. You’ll also want to buy the tuning kit for that carb to set it up correctly. How old is the carb? It may possibly need a rebuild too.

Timing. Increased timing helps the engine run more efficiently, and in turn, it will make the engine run cooler. What is your timing set at?

Connecting your vacuum advance to manifold vacuum will also help the engine run cooler at idle. You’ll have to set up the distributor for that as well.

For your HEI, are you using the original power wire? If so, you need to replace it with one meant for HEI in order to get the proper voltage to it. Do the dizzy and weights move freely? Also, what are your spark plugs gapped at? Standard gap for HEI is 0.045, unless otherwise specified by the HEI manufacturer.

[Ltpowers]

Originally Posted by geezer#99

Several things come to mind.
Float level too high. Could be flooding a bit.
Vacuum leak. You got gaskets on both sides of the spacer?
Your hei. Do you have a full 12v to it?
Timing. What’s your initial timing?
Fuel pressure. Too high.

I’ve never had to adjust the float level carb is a few months old and I do have a gasket on both sides. My timing is off now since I’ve been messing with it

[Ltpowers]

Originally Posted by PGSigns

You have done a lot of what normally helps. Next thing I can think of is the float levels. Have you checked them? Also you can put a clear filter in it and see if the fuel is boiling. When you have the top off check the accelerator pump. Also set the fuel pressure at 4 to 4 1/2 psi. You need a pressure gauge in the line just after the regulator to ensure what you have.
Jimmy

I have not checked the float levels but will

[geezer#99]

When you check float level, lower them about 1/8 inch. I’ve found eddy carbs run better with a slightly lowered level.

What’s your normal initial timing setting?

[Ltpowers]

I’m not exactly sure. I’m not very good with my timing light. And for some reason even though I changed my plugs and wires and it is a new distributor my timing light is kind of jumpy

[toolboxchev]

Originally Posted by 68 P.O.S.

The usual suspects for Edelbrock carbs:

Float levels. Floats are normally off right out of the box due to shipping and handling. This causes flooding. Set float levels to Edelbrock specs of 7/16” float rise and 15/16” to 1” of float drop.

Fuel pressure. Excessive fuel pressure will also cause flooding. Edelbrock recommends fuel pressure be restricted to 5.5 psi.

Setting transition slots. Set transition slots in the main throttle bores to form a square. This ensures you’re idling only on the idle circuit and will help when transitioning from idle to acceleration. You can see the transition slots in the main throttle bores and will look like a rectangle when overexposed. You want to use your idle adjustment screw to get those little buggers back to square.

Accelerator pump. Set the accelerator pump to the middle adjustment hole. This is where Edelbrock normally suggests to set it at for mild builds, or where to start at when tuning. Also, ensure only 13/32” of the pump rod is exposed above the top of the carb plate.

Fuel percolation. This is notorious with Edelbrock carbs. With your setup, you shouldn’t need 2 spacers. You should only need the Edelbrock 9266 heat insulating gasket. It seals on its own and you don’t need any other gaskets with it.

Carb tuning. You’ll also want to buy the tuning kit for that carb to set it up correctly. How old is the carb? It may possibly need a rebuild too.

Timing. Increased timing helps the engine run more efficiently, and in turn, it will make the engine run cooler. What is your timing set at?

Connecting your vacuum advance to manifold vacuum will also help the engine run cooler at idle. You’ll have to set up the distributor for that as well.

For your HEI, are you using the original power wire? If so, you need to replace it with one meant for HEI in order to get the proper voltage to it. Do the dizzy and weights move freely? Also, what are your spark plugs gapped at? Standard gap for HEI is 0.045, unless otherwise specified by the HEI manufacturer.

Hey, that was really good. Even though I have no percolation problem, I will be going over my carb.

[Greasey Harley]

Originally Posted by geezer#99

When you check float level, lower them about 1/8 inch. I’ve found eddy carbs run better with a slightly lowered level.

What’s your normal initial timing setting?

Originally Posted by Ltpowers

I’m not exactly sure. not very good with my timing light. And for some reason even though I changed my plugs and wires and it is a new distributor my timing light is kind of jumpy

Can't tune around bad timing.
Get your timing SET. Tighten it down, then leave it alone.
Did you disconnect the Vacuum advance before you checked the timing? (You need to)

Firing order good? Are you sure? (I've been fooled before)
Any vacuum leaks? Are you sure?
How do your plugs look?
What kind of plugs did you use?
What did you gap them at?
How do they look now?
Point is, make sure all the basics are taken care of, BEFORE you go rippin' into the carburetor.
If the ignition isn't set up properly, you can NEVER get the carburetor to work properly.

"90% of carburetor problems are ignition problems." -Larz Grimsrud (If you haven't heard of him, look him up)

Anyway, that's just my $.02 worth, but it might not even be worth that much.
I hope you get it dialed in.
-Russ

[Ltpowers]

Not sure what’s going on with it. All spark plugs were just put in this weekend. Gapped at .045. All wires are brand new as well. A/c delco plugs and 7.5 msd wires. Everything is going to where it should be but I’m still getting a misfire and can’t figure out why. None of my plugs could have oil fouled already.

I did find that under my rotor whatever the piece is called is alittle loose like it broke or something. Maybe that’s where I’m getting a miss. I took a video with the timing gun on the engine but can’t send videos or can’t figure out how over this

[Ltpowers]

Float levels have never been adjusted and haven’t seemed to have problems but I will check them when I get a chance.

I do have a regulator that is maxed out at 5.5 psi so all should be good. Also brand new fuel pump

I’ll have to look for the transition slots. Looked yesterday quick but didn’t see anything right away.

I switched to the middle hole for the accelerator pump last night. It had been on the top hole. But when the engine is warm it always sprays alittle fumes out before gas no matter which hole I have it in on the pump.

So are you thinking I should take the wood fiber spacer of and just run the heat insulated gasket?

The carb is an edlebrock avs2. About three months old. Took it apart and cleaned everything acouple weeks ago. Had a weak accelerator pump gasket probably from the heat before I had the wood fiber spacer and insulated gasket. Original jets and everything on the carb haven’t changed and needles or jet sizes.

I have to figure out where my timing is at. I know it’s alittle retarted right now. Just don’t know where the timing light is jumping all around.

Original wire that came with the hei is on it and from there I added new wires. I took the dizzy cap off and unplugged the vaccine advance and either blew into or sucked on it and the weights did move. Spark plugs gapped at 0.45

[geezer#99]

Don’t trust the regulator. Especially that cheap style. Adjust it down to 3 psi. See if that helps.
You can’t see the transition slots unless you pull the carb off. They’re under the throttle plate.
Leave the spacer in place. Check for vacuum leaks. I use wd40.
Some timing lights don’t work well with an hei.
You can adjust timing by ear or use a vacuum gauge. Listen as you advance it slowly. You’ll hear it smooth out. Or set timing to highest vacuum. Then check with your timing light.
A new carb or new filter doesn’t gaurentee you have a float set wrong or trash in the carb.

Did you have fun putting the metering rods back in when you had the carb apart?

[toolboxchev]

Yea check that trash in carb. I had 2 fuel filters on mine since the install of an Eddy, ran it 10 years, found about an 1/8 of an inch of crap in the bottom of the float bowls last year.

That got thru the filters? What? Huh?

[toolboxchev]

Originally Posted by 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 my numbers are.
Posted via Mobile Device

Temp shows 144 coming out of radiator into engine I assume?

Yea, like everyone else says, go completely thru timing and get it dead on. You can even buy an adjustable vac advance can from Pertronix. I am at roughly 14-16 intial, 22 vac, and way up around 50 all in. 76 cc chamber heads, and 87 octane pump gas. Does not knock, I need to get the all in down on timing, it loses a lot of power over 3500.

I am running a pretty stock 350, Hei, Accel super coil, accel module, accel wires and stock intake with adapter and 1/4 gasket under it. Eddy manual choke carb on top.

[Ltpowers]

Update. Got my timing and 12.5 degrees I believe.
Switched to vacuum at idle and have not dealt with whatever was going on

[nxtruck]

Originally Posted by Ltpowers

Update. Got my timing and 12.5 degrees I believe.
Switched to vacuum at idle and have not dealt with whatever was going on

Set your initial timing with the vacuum advance UNPLUGGED and the fitting on the carb capped. Make sure idle speed is around 600-700 so that the mechanical advance is not beginning to advance your timing. Shoot for around 12-14*. Then, reconnect your vacuum advance to manifold vacuum ( the lower of the two ports on the front of your carb ). You will find it idling a few hundred rpms higher like this. Then, adjust your idle speed accordingly ( 800 or so in park, depending on cam profile ). Once this is done, proceed further. As has been said, you need a 10-12 gauge wire with 12v feeding your HEI. Not a resistor wire. 12v with the key in the run position.

[nxtruck]

Originally Posted by toolboxchev

Temp shows 144 coming out of radiator into engine I assume?

Yea, like everyone else says, go completely thru timing and get it dead on. You can even buy an adjustable vac advance can from Pertronix. I am at roughly 14-16 intial, 22 vac, and way up around 50 all in. 76 cc chamber heads, and 87 octane pump gas. Does not knock, I need to get the all in down on timing, it loses a lot of power over 3500.

I am running a pretty stock 350, Hei, Accel super coil, accel module, accel wires and stock intake with adapter and 1/4 gasket under it. Eddy manual choke carb on top.

His pic with the temp gun is showing 144* at the fuel pump. Pretty normal in warmer weather, for sure. Personally, I would fab a heat shield similar to what's available for Holleys for your Edelbrock. Something that sandwiches in-between your existing spacers that extends out on each side and shields the float bowl areas of the carb. This is where the fuel sits and has a tendency to boil in hotter weather. Vapor lock/fuel boiling seems to affect these older carbureted vehicles more so than the newer injected vehicles and can be difficult to eliminate. I would do everything I could to insulate the fuel lines from any heat sources.

[nxtruck]

Originally Posted by nxtruck

His pic with the temp gun is showing 144* at the fuel pump. Pretty normal in warmer weather, for sure. Personally, I would fab a heat shield similar to what's available for Holleys for your Edelbrock. Something that sandwiches in-between your existing spacers that extends out on each side and shields the float bowl areas of the carb. This is where the fuel sits and has a tendency to boil in hotter weather. Vapor lock/fuel boiling seems to affect these older carbureted vehicles more so than the newer injected vehicles and can be difficult to eliminate. I would do everything I could to insulate the fuel lines from any heat sources.

Oops. This response was aimed at the OP. Sorry for any confusion.