427 C2 Percolation or Vapor Lock Problem

[William F.]

Re: 427 C2 Percolation or Vapor Lock Problem

Yes, check floats for pin holes. I had 2 new Holley carbs with float pin holes causing float to sink to bottom of bowl , opening needle valve and causing flooding

[Frank D.]

Re: 427 C2 Percolation or Vapor Lock Problem

I've rebuilt a ton of carbs and some with leaky floats, but those always caused running problems, not just starting problems...
Fouled plugs, "eight-stroking" and the like...

As stated earlier, listening for boiling fuel, observing the squirters in the carb and shooting the carb bowl with an I/R temp gun will cut out a lot of the extraneous possible causes. Takes all of 5 minutes.

[Joe T.]

Re: 427 C2 Percolation or Vapor Lock Problem

Thanks for all the reply's. I started with removing the rain shields, pumped out current fuel and replaced it with VP110. Got approximately 20 miles while stopping for a half hour twice and it started with no problem. Hopefully this solved my problem. If not, I will continue on with other suggestions.

Joe

[Joe T.]

Re: 427 C2 Percolation or Vapor Lock Problem

Well, the VP110 and removing the rain shields helped. I continue to have a problem of backfiring through the carburetor on a hot start but it does start, unlike before. When starting with a cold motor, after setting a week or so, requires many fast pumps (8 to 10) while running the starter. After started it runs fine and the choke works as it should. After setting a few minutes and hot motor, it will start with no throttle. After a half hour or so with a hot motor it requires a couple mild pumps but it backfires through the carburetor before it starts on a couple tries. After that it runs fine. I am thinking accelerator pump adjustment?? Any suggestions?

[Frank D.]

Re: 427 C2 Percolation or Vapor Lock Problem

Start by walking through the advice in this video:
https://www.holley.com/blog/post/tro...h_carburetor_/

[Danny P.]

Re: 427 C2 Percolation or Vapor Lock Problem

With the hot temperatures (85 - 95) driving the corvette is fine. It does not over heat. It's when I park for a half hour or so, all indications point to a vapor lock or percolation and it will not start. I was going to install an electric fuel pump in line with the mechanical pump.

Any suggestions or thoughts?

check for a bad float or a high float adjustment or a warp metering plate and housing, could be flooding when you shut engine off.

[Joe T.]

Re: 427 C2 Percolation or Vapor Lock Problem

Frank
Thanks for the video. The backfire only occurs when starting with a hot motor along with sitting for a half hour or so. Once started it runs great with no hesitation or problems. I would assume many of the issues in the video would cause a a idling and/or performance problem. It never backfires when starting cold.

[William F.]

Re: 427 C2 Percolation or Vapor Lock Problem

Do you have 12V at coil when key is in start position?

[Timothy B.]

Re: 427 C2 Percolation or Vapor Lock Problem

Well, the VP110 and removing the rain shields helped. I continue to have a problem of backfiring through the carburetor on a hot start but it does start, unlike before. When starting with a cold motor, after setting a week or so, requires many fast pumps (8 to 10) while running the starter. After started it runs fine and the choke works as it should. After setting a few minutes and hot motor, it will start with no throttle. After a half hour or so with a hot motor it requires a couple mild pumps but it backfires through the carburetor before it starts on a couple tries. After that it runs fine. I am thinking accelerator pump adjustment?? Any suggestions?

Joe,

Where is the initial timing set, if the accelerator pump needed adjustment you would notice it driving. Having the primary throttle blades set to where there is approx .020 transfer slot showing below the blade is important.

When the engine fires do it seem flooded or run normal.

[Joe T.]

Re: 427 C2 Percolation or Vapor Lock Problem

Tim,
I have gone through timing, coil, vapor lock, plug wires, float adjustment, choke operation, removing rain shields, wrapping fuel line and using VP110. This all seems to lead me to the carburetor heating after setting for a half hour or so on 80 degree plus days. My next move will be a carb spacer. Now, that seems to be a problem with space. I used putty (play dough) on the high point of the air cleaner. Closing the hood, I have 3/8 inch clearance between the hood and air cleaner. I am reluctant to install a 1/4 inch phenolic spacer with two 1/16 inch gaskets. This would let me with hardly any or no space. I have been unsuccessful finding a spacer not requiring gaskets. Considering everything, this Corvette runs fantastically hot or cold.