Vapor lock w/ electric fuel pump?

[dhouser]

I have dual weber 34 icts with 1600. All proper tin and fuel line. I have a carter fuel pump set at 2.5psi with a holley regulator. I have a Carter fuel filter before the pump, and the standard plastic filter just after the exit from the tunnel.

I notice that when I drive for a while on the highway, then i park it for a few minutes, the car has trouble starting. The fuel pump is hooked to a relay that is activated by the ignition and the alternator, so I am pretty sure the pump is powered. It eventually starts, but it seems to have trouble. I do not have any issues while driving, just starting after a 20 minute or more drive.

These sound like symptoms of vapor lock, but I figured I was not in danger of that because of my electric fuel pump. What could it be?

I was recently almost stuck because it had such a hard time starting that it almost killed my pos battery. Luckily I got a good deal on a nice trojan battery. The temperatures around here are pretty mild, mid 70's to low 80's. The engine is not overheating, I have the gb227 dipstick.

I do have an overide switch to power the pump manually, maybe that will help?

What do u guys think?

[Max Welton]

My understanding of vapor-lock is when the fuel in the pump turns from a liquid into a gas (vapor). Ordinarily the diaphragm can move the fuel to the carb(s) by simply pushing on it. Liquid gas doesn't really compress.

But as a vapor, it compresses just fine. So when the diaphragm pushes on it, the gas just sits there and smiles.

Pouring water on the pump drops the temperature and re-liquefies the fuel.

I can't see any way vapor-lock can happen with the pump located where it can't get hot enough to boil the fuel.

Max
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[don-m]

I don't understand the "powered by both the ign. and alternator" I would check to see that the pump has power with just the IGN. The alternator would provide power only when it has reached speed.
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[dhouser]

The pump is hooked up to a relay. The relay gets it's signal voltage from both the alternator and the ignition. You can't just use the alternator, as you say, because the relay wouldn't get a signal until the alternator is up to speed. So you would use ignition to send power to the relay while you are cranking. The bowls have enough fuel for the time between ignition and full speed alternator. The ignition wire has a diode so as to not get current from the alternator when it is running.

I don't think the problem is the pump. I think it's the carbs.

[carcass]

About 20 years ago I had a '71 Cal Bug with dual 34ICT's,and it did the same thing.
What happens is when you shut the car off,the carbs,which stay reasonably cool while the engine's running,heat up when you shut it off and it sits for awhile-(due to the stubby manifolds) the gas in them expands when it gets hot,and (you can watch them do this) the excess fuel escapes through the overflow tube and into the heads,so the reason it won't start isn't lack of fuel,but just the opposite-it's flooded (if it sits overnight,it starts just fine in the morning,right?)
Adjusting the float level as low as you can get it in the ICT's will help,but it'll still do it occasionally.
Someone else may chime in with another fix,but lowering the float levels is the only thing I found that made any difference at all..

[dhouser]

thanks for the input.

i did check the floats when i got the carbs, but they were adjusted per their spec. however your explanation sounds perfectly reasonable.

i do notice - and i am not sure that this is related, that the engine tends to want to keep running when i shut the car off. only for about a few seconds though

[low_67]

Soooooo what's the prognosis? Mine does the same thing. Don't know if I need to get an electric pump or adjust/clean the carbs or some other fix. I see a lot of people have this issue but no one really has an answer!

[Max Welton]

The original poster last visited this forum on February 19, 2013 so we probably won't hear from him on how things turned out.

An electric fuel pump WILL push through what would be a vapor-lock condition. As long as the pump is not located where it gets too hot.

Just like the stock pump.

Max
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[Aussiebug]

Following on from Carcass's post above, if his description of "heat" flooding is correct (sounds very possible) then as a test, try starting the car (after it's been sitting for a while after a run) by SLOWLY pressing the throttle to the floor (slowly so the accel pumps don't squirt extra fuel down the throat), and whilst holding the throttle wide open, crank the engine - DON'T pump the throttle. This will allow the most air for the least fuel (not a lot of vacuum at cranking speeds to pull fuel into the open throat), so the car SHOULD start after a little cranking blows the excess fuel through the cylinders.

If that happens, then carcass has found the cause. An additional confirmation of that would be if you go for a run, then the car sits overnight before you use it again and it then starts fine - that would indicate that extra fuel in the cylinders has had time to vent or settle back into a liquid rather than the overabundance of vapour which causes a rich mixture (liquid fuel does not burn - only vapourised fuel mixed with oxygen will burn, and then only when the mixture is close to the correct strength - stoichiometry).

If carcass is right, maybe using an extra paper gasket or two between the heads and the manifolds might reduce the heat soak the carbs get after you switch off.

Lowering the height of the fuel in the blow might help a little too, but of course that will also weaken the mixture right through the rev range, so use that technique with caution.

You might also check the strength of your spark - they should be fat/blue coloured, rather than thin/yellow. Obviously a strong spark will light an incorrect mixture better than a weak spark. Also check your plug gap - make sure it's stock or fractionally less, rather than wider than stock (easier sparking for wet plugs). What plugs are you using - standard heat range (Bosch W8AC or NGK B5HS)? or something colder? A "cold" plug will tend to carbon up a little more and might result in less starting capacity. And don't bother with fancy platinum plugs etc - the normal copper core steel plugs work best. The fancy plugs are really designed for modern lean burning engine and high intensity ignition systems.

Do you have a vented engine lid - they will allow heat to escape from the engine bay faster than a non-vented lid, maybe fast enough to prevent the carbs heat-soaking to the point of boiling off the fuel in the bowls.
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