Yet another carb issue

I have an 82 Mercury Cougar station wagon with the 200 six and the proper Motorcraft (holley 1946) carb.

The car runs great at idle and all speeds. Passed the California emissions test last March after months of problems with carbs and also had the head inspected, cleaned, valve seats ground and one new valve installed.

Here's the problem: After running at full operating temperature and parked for 20 minutes or so it's flooded but not severely but enough to have to crank for 10 seconds or so and when it starts a nice amount of black smoke from the exhaust. I cannot catch any boilover from the bowl. No dribbling....nothing. After a couple of hours there's no problem starting. The car has sat for up to two weeks and it starts instantly after setting the choke.

I have set the float 1/8" lower than spec (spec is even with the top of the bowl) because of the boilover problem here in the summer. Our daytime temps run up to 115* and usually average above 100* June through August. The problem occurs even now that the outside air temps are in the 30's overnight and highs in the 70's daytime. The car is factory stock. It does not have a water cooled base plate nor does it have any sort of heat shield nor did it come with those things.

If the bottom plugs were leaking I would expect the bowl to empty over a couple of weeks.
The accelerator pump wouldn't siphon, I think, especially since it works great. And I think I'd see that dribble from the port in the throat.
How about the power valve? Could that siphon fuel out below the throttle plate? I think the only port below the plate is the idle port, and it's such a simple vacuum operated device I'm wondering if it could be a problem at all.

So, how can fuel dribble in to the intake without me seeing it? I know fuels have changed over the years and result in wierd problems and I would expect that the car did not do these things when new even here in the desert.

Thanks in advance for any ideas.

Silly question, but are you sure its the carb and not the timing? If I had the problem you described, I would be looking at timing first.

SteveS":igpdz7jy said:

...it's flooded but not severely but enough to have to crank for 10 seconds or so and when it starts a nice amount of black smoke from the exhaust. ...

Click to expand...

I wouldn't think ignition, I'd be thinking boiling fuel and flooding as well. It doesn't have to have liquid fuel going in to flood, too much vapor will do the same thing....hmm...

Miht try this: Get it good and warm, and remove the air cleaner right before you turn it off. Leave the top of the carb open (make sure the choke stays full open) so any vapors can be carried off. Then try to start it after 20 minutes, and see what happens.

My suspicion is that you're going to need a heat shield and/or insulating gasket to stop boiling the fuel in the carb bowl. I'm convinced that most OEM engineers (living in colder climates) just don't comprehend how hot it gets in other parts of the world - and the issues that arise from it.

8) i agree with jamyers, remember that gasoline vapor is heavier than air so it will fall into the carb as if it were a liquid causing flooding.

I never thought of vapor flooding. Certainly it would re-condense in the manifold after it cools a bit. I try that taking the cover off and letting it vent.

Thanks jaymers and rbohm I'll give it a shot.

The ignition timing so spot on 10*.

Come to think of it back in the olden days the air cleaners were open to the atmosphere. On mine it's completely closed and only open to the fender intake when hot but the vapors would normally run downhill and can't get there from the carb throat and can't possibly vent. Along with the fact that the fuel tank vent goes to the evap canister and those vapors are sucked up in to the car during startup too.

I think you all are on to something. I'll let you know what I find after lunch today.

8) one big issue you have that is likely causing you problem is the catalytic converter being right below the carb. you might pull that apart and check it for damage inside the converter. had a similar problem with my 80 fairmont wagon with the 200.

One of my cars does the exact same thing, im sure its fuel boilover as it only happens when hot. Its an 81 pontiac catalina with a rochester 2b on it. I have to hold mine to the floor to crank it when hot though.

A good test to see if you have gas leaking down into your cylinders is to smell the oil in your crankcase. Pull the dip stick and take a good whiff. If you smell gas in the oil, you got gas leaking down into your cylinders..What makes me think that is the black smoke you see when you start up the warm engine. That smoke is a sign of a very rich mix in the cylinders. Once the engine is cold, all the gas is leaked out of the cylinders down into the pan, and you won't see anymore black smoke. Another clue is how bad is your average gas mileage?

All,

The test today was that instead of taking the aircleaner off to vent the fumes after i got home for lunch I took the top off and drove it home that way. No change but also no liquid fuel boiling over from the bowl. Dry as a bone.

The car only rich starts after sitting 20-60 minutes or so. No gassy smell in the oil. I can only assume that the fuel is leaking from below the throttle plate. It's not leaking enough to wet the cylinders until the start up. It would take a whole lot of fuel to overflow the intake manifold.

After an hour it starts normally with no smoke. I did however find a seep at the inlet port that needs to get fixed.

I guess it's coming off this weekend. By the way the car is running at about 190* I've never seen it above 210* in the summer.

The catalytic converter is below the passenger front seat. There is not one at the exhast manifold.

Thanks all more investigation tomorrow. This is exactly why I love EFI of any type. The only way Ca. will allow dinking with the fuel system is to change the whole engine for a EFI equipped engine.

Steve

Over the last week I tried several things. First I made a heat shield. No help with that. Then I changed the timing to 9* BTDC. No help.

I've lowered the float. It's 1/4" lower than spec. This so far has seemed to help.

If it's running fine otherwise (with no lean surging), sounds like you're on the right track. Stock fuel pump? Might double-check the sparkplugs after awhile to ensure it's not too lean.