225 V6 Carb problem - help

I am having an intermitten carb problem on a 65 Buick V6 225 in a 46 Willys cj2a. Motor is internaly stock that I know of, has headers and I installed a HEI, compression ranges from 130 to 150 psi per cylinder. The carb is a motorcraft 2100 series. Yes a Ford carb on a GM engine. I have used this model carb on AMC v8s in jeeps and had good off road performance. Anyway the problem appears to be carb floods the engine and have to crank the starter a bunch with throttle wide open till starts and then the usual black smoke. It happens after engine is warmed up in summer or winter and also happened with the original point distributor and the HEI installed so I am ruling out ignition problem and also the black smoke when it does fires and previous experience all point to carb flooding. The carb was rebuilt by a professional that does good work two years ago and has about 2000 miles on it. Vehicle lives in higher altitude 9500 ft and is a daily driver and has been up to 12,000 ft + a few times and runs good except for the intermitten problem. The carb rebuilder suggested I may need to drop jet size and that the carb might just be too big for the motor altogether when I asked him to rebuild it. I have dropped the jet size from the original 52 to 48s and I think I could even go smaller although plugs look pretty good and high altitude operation is good, however engine does not need a lot of choke on cold mornings ( we have been seeing below zero for about 2 weeks this winter so far) to get running and stay running - has manual choke. One thing I question is the other day when I was changing the jets back to 48s ( I had it back at 52 for a bit because lived at low elevation for a while) is that when I removed the airhorn and began to remove the float to access jets, gas sprayed out from needle and seat under pretty high pressure. It seemed to have quite a bit of pressure and volume of fuel trapped in the fuel line (30 inches long) between needle and seat at float and the original type mechanical fuel pump. I have done a bit of carb work and messed around with this one a bunch with jets and changing float level and never before saw fuel spraying like this before. Does anyone have any ideas? I never have checked fuel pressure. Problem is intermitten and may happen one out of every twenty times starting give or take. The fuel tank does not have a vent but has a locking cap that leaks so I feel tank is vented. I am thinking pressure problem, heat problem, or?

Thanks for any ideas.

 

Check out the high pressure in the fuel line. Don't know why it would be intermittant. Is the pressure building between the pump and the carb? If so, it wouldn't matter if the tank is vented. Could just be a gremlin. How big is the carb you're using in CFM?

 

fuel pump pressure at carb should be between 3-4 lbs at idle
I suspect high float level; I would try lowering the float level first.
Another possiblilty is heat source close to fuel line; after engine shutdown, the fuel is heating up and expanding; with float already as high as it can go, needle and seat are closed; gas is expanding and has to go somewhere; so it may be dribbling by the needle and seat and flooding the engine after shut down; we refer to this as a "hot soak" condition.
One cure if all others have been exhausted would be to install a fuel return line set-up back to the tank. Full size Jeeps used this set-up; whatever fuel was not being used, or fuel expansion after shut down, the fuel had somehwere to go, back to the tank. This also keeps the fuel somewhat cooler and cures vapor lock problems in most instances. This fuel return line would come off of the fuel filter, and the port on the filter is smaller than the regular fuel line, 5/16" vs 1/4". On stock V/6s that had fuel return, I believe it came right off of the fuel pump. Either way, plumbing back to the tank would need to be fabricated.
Another quick try would be to install an in line fuel pressure regulator between the pump and the carb; you could turn it down to say 2 lbs and adjust accordingly.
my o.2 worth

 

another thought
in Jeep applications, the Motocraft carbs used a thick plastic base plate along with a thick composition type insulator; this would insulate the carb base from heat on the intake manifold.
How is your carb mounted on the V/6?
Do you have such insulators?
Carb could be absorbing heat from intake manifold, expanding the fuel, causing the same problem
just a thought

 

Posimoto, pressure is was talking about is between pump and carb. I do not know cfm - would that make any difference?

Jpflat2a, I have messed with float level for climbing issues and it is a bit high - think I'll try lowering also I suppose I should test fuel pressure. I have the fuel line insulated and away from any big heat source. Carb is mounted with a aluminum adapter plate. Good idea on an insulator. Anyone have one? Or application I should try to get one for?

Thanks to both of you.

tiptop

 

sounds like float needs to be lowered.

 

It does sound like the float is too high. You might try asking about it here:

http://www.network54.com/Forum/88781?it=0

 

A hard plastic insulator is pretty easy to find at a big u-pull-it yard. Look for 302 and 351 Fords - usually the insulator will be there even if the carb is gone. You can get the thick paper insulators at Autozone, but I'd rec the plastic one. Where are you located - Colorado?

 

I agree with float level being to high. And checking those fuel lines and getting them away from heat sources where you can, It sounds like fuel is still dumping into the carb after shutdown thus causing the black smoke and the need to start with the pedal too the floor.Check it out and post your results please.We like hearing about fixes as well to try to help the next guy.