68 327 Corvette - I have had my 68 for just over a year. Really like the car but I have been having issues with fuel supply. It runs great until it gets nice and warm. If i stop shut the engine off for 15 or 20 minutes I can't get it to start again until it cools off. Sounds like some sort of an airlock, and I just have very basic mechanical skills but really enjoy working on the car and keeping it running well.

Suggestions, Gord

 

Heat soak. Is the factory shielding on the starter?

 

What do you mean start? Cranks good but doesn't fire, or barely cranks cuz starter too hot?

 

Sounds like a "vapor lock". That is- the gas in the carb bowl and the fuel lines vaporize and the pump cannot force liquid fuel to the carb. Lots of solutions. Just search the forum.

 

I don't think it's a starting problem as the starting turns over fine, I think it's a vapor lock in the carburetor as suggested by the member below. Thanks for your input.

 

Thanks for your input, I think you are right. Do you have any suggestions onsearching the forum, I just joined the website today and have already gotten lot's of great info.

 

Contact Lars at v8fastcars@msn.com, explain that you are having vapor lock issues and request his fuel line papers. He will send instructions on the cure.

 

Gordon...Easy Mike touched on this....but I'll expound a bit.

There are two things that contribute to VAPORLOCK.
1 Excessive heat creeping into the fuel lines on shutdown...which causes the gas to vaporize in the line....you cannot 'pump' air/ vapor and at 7-9 psi that your normal fuel pump makes...just can't re-compress it.
2. Weakening fuel pump.

So wrap your lines with a high tech TWO heat-soak repeller...such as Reflective Mylar (radiant heat). Fiberglass insulator (conductive heat).

Check the fuel pump output and possibly upgrade to a hi output pump.

Good Luck

Unkahal
who lives in planet Crematoria!

 

Could it just be flooded?
Have you tried to press down and hold the gas pedal to the floor while cranking?

 

Seems like a heat soak issue compounded by manifold heating. My 68 SB responds similarly- it will start warm, but runs like **** for several minutes. The problem may be the heat riser circuit. It heats the manifold, which in turn heats the carb and boils the fuel out. In my case driving the car easy after starting warm apparently cools the mani enough to let the float bowl fill normally. I suggest you defeat the heat riser circuit with a doughnut and a blocked gasket set. I am certainly going this route once I figure out what kind of manifold I want, since I live in a warm climate.

 

Are you in an ethanol state?
Here in CA we are having lots of problems with the ethanol fuel on carburated cars. Most complaints sound exactly like yours.
Download the app "puregas" and check your area for ethanol free fuel.
Greg

 

I had the same problem in my 68. I had an Edelbrock carb that was very susceptible to fuel boiling. I added a 1/2" phenolic spacer and that helped alot. I finally settled on a 1" spacer to make sure. I have an L88 hood so space wasnt an issue. You may need a drop base air cleaner if you have to add the wood spacer. I went back to a quadrajet and kept the spacers

If you have a quadrajet, GM produced a 1/4" gasket that was a heat shield of sorts to keep this from happening

Also make sure your fuel line isnt sitting on the engine at all, The heat will transfer to the fuel line. Thats more heat and problems

If you have a heat crossover in your manifold, next time its off the motor make sure you use a manifold gasket that blocks it off.

Make sure your timing is optimized for your setup. It should be around advanced 12 to 14 degrees at idle and 36 or so at 2500/3000 rpm. The motor will run better and a tiny bit cooler.

I also keep a can of starter fluid for really hot days. If I'm at a car show with the hood up and its in the direct sun, the fuel will boil off just because its ethanol


you can barley see the brown spacer in this pic. Its the only one I have of the spacer up close

 

x2 on our lousy gas. Sure in the 70s, middle of summer you could get vapor lock but not like today.
I used a phenolic spacer, its not enough .Gonna try a heat shield, hope for the best. Once its turned off all bets are off.
Even running, notice around 200 idle quality isnt quiiite the way it is under say 190. Not rich/lean either.

Dont think a cool can would help much either unless it was running. The dist and coil can get awful warm, too.

 

Speaking of cool cans I'm giving this a shot to see how it works. It should cool the incoming fuel charge since it runs next to the side pipe, and since it will be cooler I'm hoping it doesnt evaporate as quickly.


Summit Racing Heat sink fluid cooler. THey say it rated for transmission cooling and good for fuel