Matt69-ZO6

Two cars - '68 and '69 with L36 427's. The 68 is older and the 69 is a recent rebuild. Can't seem to get a handle on the vapor lock. Both cars run nice and cool temp wise.

The 68 has had an electric fuel pump installed and it seems to cure it until the weather get up into the 80's.

The 69 doesn't do it as bad, but sometimes is tough to restart after a long drive and might give you a little fit after a good highway run.

Anyway, what have you guys/gals done that has worked?

PRNDL

What exactly happens and under what conditions? (more details pls) Are the fuel return lines intact and working? ie, are you using the original style GF432 fuel filter with the fuel return line? I was having a problem that I felt was a fuel starvation issue, not vapor lock. My car would fall on its face under hard acceleration, usually at the top of 2nd gear at around 5000 rpm. I bent a new fuel pump to carb fuel line with a big modern inline fuel filter and no more problems. The new fuel line I think flows better than the old and is far enough from the engine so I think it stays cooler. My fuel return line is not connected, but I have heard the return line keeps the fuel cool. MJ


[Modified by MNJack, 2:14 AM 4/19/2004]

mrvette

I usually used a Carter electric pump back at the tank area, pushing forward, and that cured every car I ever had of vapor lock problems.....mechanical pumps are prone to the problem....

you have a hot pump trying to suck gasoline through a long straw, and that situation encourages the gas to perk right in the lines, sucking on vapors then, and just foam gets to the carb.....not enough gas....

need pressureize the entire line....I ran about 4-5 lbs on it....

GENE

Matt69-ZO6

Not too many details to provide! The condition is not consistent, though happens more often as the air temps rise. It sure acts like vapor lock. Heck, sometimes on a restart there is not a drop of fuel left in the bowls! It just boils it dry. All the fuel lines are intact, tanks, screens are clean. Both filters have been replaced.

The '69 does have a newer fuel pump (maybe why it is not as bad as the 68 was before the electric pump was put in). The electric fuel pump was placed in the engine compartment (yes, I know wrong location for a few reasons). It was placed there as a test. I think the electic pump is just getting cooked. Moving it to its correct location would probably go far in solving the problem, I just wanted to see what everyone else has done before going any further.

Thanks for your input... :seeya :steering:

70vert

I would like to hear more details, but do you have your heat shield on? Are you running a stock fuel line, is it rubbing against anything hot? Check your float level, fuel filter?
I added a 1" phenolic block between the intake and carb to solve my perculation problem.
Also check your fuel cap, vented is better.

gkull

The only cure that i have ever found is:

You have to use a small return line system. IF your using and electric pump with a regulator. Install the regulator after the fuel log regulating the fuel pressure by how much it returns to the gas tank.

If your using a mech pump get the GM return style type.


[Modified by gkull, 9:06 AM 4/19/2004]

Matt Gruber

i once plumbed a return line THRU the back of a holley :cool: carb was constantly fed fresh cool gas

norvalwilhelm

The 69 doesn't do it as bad, but sometimes is tough to restart after a long drive and might give you a little fit after a good highway run.

I have never experienced vapor lock on my big block in the 14 years I have been running it.
I did experience hard starting after a run, say you pull in for gas, shut the engine off for a few minutes then go to restart. Very embarrassing.
Turned out to be a fuel leak in the carb, flooding the motor. When the car does refire do you have to give it a few revs to clean it out??
Vapor lock is boiled fuel in the fuel line causing fuel starvation but for initial fireing the motor after a run the carb would still have fuel in it so why won't it refire even if it was vapor locked?????

Matt Gruber

he has percolation,
but,
you can't expect newbies to have the correct medical terms :lol:

norvalwilhelm

That said how about fuel perculating in the carb itself. You have a hot motor, a hot carb and you stop. The fuel in the fuel bowl starts to cook causing fuel vapors to rise and start pushing fuel out the jets causing a massive flood.
Anything you have done to the fuel supply will not help this situation. You would need a carb insulator to prevent boiling fuel.

So which is it?? Fuel perculating when stopped for short times causing flooding or fuel vapor lock causing problems in leaning out while running????

Matt Gruber

this should stop percolation as the carb is cool to the touch. note the word should :lol:

Matt69-ZO6

Let me be a bit clearer. There is a perculation issue, but given the 427 sitting below the carb about all that can be done is to minimize its effect. Very embarassing when you have to turn her over and over to get it going. In the '69 it takes a good long run to cause it (everything under the hood is hot!). Plus, the '69 is a side pipe car and the side pipes put a lot of heat into the frame rails. That is not a factor in the '68.

I agree that a 1" plate (and will install one) would help, but the heat sink under the hood is just excessive - thus the changes made in the 454's to cool the block better...

The vapor lock is the issue I am looking for your solutions. It seems the electric fuel pump idea is the ticket. The caps are vented, lines are clear, returns are correct, etc.

I have had plenty of big block cars, this is a Corvette issue due to the minimal amount of air flow moving through the engine compartment. The darn stock fuel lines run so close the manifolds, it just cooks. My thought was that the pressure from an electrical fuel pump would 'overcome' the vapor lock and keep the lines/bowl full and the electric fuel pump will fill the bowls prior to start up.

Has anyone used a non-stock intact manifold with increased air flow around the intake runs?

Thanks for all the help.... :cheers:

gkull

My bud, owns a BBC 67 Camero. Going down the road or even stopped at a light after the motor comes up to temp. The hotter the part of the day they worse it gets.

He installed a thermal 1 inch carb spacer and a large fuel log to a "CARB SHOP" worked over 930 cfm chokeless race carb. He still had problems.

I told him that my Vette has a return line!

He then went out and did a really clean electrical pump and stainless steel line job. He still had problems so he did the header thermal wrap and fuel line insulator wrap. He still had problems.

So I showed him in the Barry Grant book how they had set up the return line from the fuel log and it's not had a problem since.

Matt Gruber

have an electric pump on my 61 and it fills the bowls without cranking. But, all that fuel washing the rings would cause rapid wear, so i have #2 el. pump the carb dry when i park it.

verskel

Just my 0.02 cents :

IF you're running points - make sure they're adjusted properly.....makes for very difficult starts if they're off.

Also, check the timing because too much advance makes for difficult restarts when very, very hot. ;)

Other than that.......for vaporlock I've always wrapped the steel line with a reflective thermo-tape. :D
A potato works too in a -pinch- :jester

LemansBlue68

Make sure you have the correct 3 layer gasket sandwich with the heat shield in the middle. These gasket sets are EXTREMELY hard to find at your regular auto parts stores and even the better Corvette supply places don't all have them. It may be that Bubba has replaced yours with a generic, "one-size-fits-all" gasket. Lars has them and he sells them for a much better price than you're likely to find anywhere. You might also consider a phenolic carb spacer if the gaskets and heat shield combo isn't enough. You could also try blocking off the exhaust cross over passage in the intake. The car might be a little tempermental when cold but you may even pick up some power (because of the cooler air charge temps) after it warms up.

Make sure your fuel line is well insulated from exhaust heat, too.

norvalwilhelm

have an electric pump on my 61 and it fills the bowls without cranking. But, all that fuel washing the rings would cause rapid wear, so i have #2 el. pump the carb dry when i park it.

Matt isn't this getting a little excessive. I run dual holley pumps but run on only one most of the time. I just shut the pump off about 1/4 mile from home to run the float bowls down before parking it just in case I develope a problem but normally the carb should be able to sit full without a flooding problem.

Matt Gruber

norval
it's part of the hobby.
would i do it again? No! on my 72 i use an entirely different idea; works great many years.
61 was an earlier idea, got 2 pumps $5 ea.why not? the poster wanted to know what we did. i don't expect anyone to copy my work. just food for thought. :cheers: