Problem with 44IDF Carbs Flooding after Engine Shutdown...

[John M.]

I've been dealing with this for awhile. I'll try to explain everything I've done.

New 1914cc engine / New Dual 44IDFs
Fuel Pressure 3.5psi
Floats Set to spec.
All Seals/Tin are in place.
Does not run hot via CHT / OT.
Timing set to 32BTDC / Bosch 010.


Symptom - Gas leaks onto the #3/#4 Butterflies about 25 minutes after the engine is shutdown. Then it seeps out around the base gaskets and leaks down. Sounds like the gas is boiling in the bowls and overflowing. I can hear gurgling / bubbling. It seems to be doing it a little bit on the 1/2 side too, but not nearly as bad as the 3/4 side.

It will do this even on short drives (<5 miles.) The intakes are nice and cool right after the drive. Once the engine is turned off, the intake manifolds really heat up, almost too hot to touch. I assume the intake manifolds are transferring heat to the carb and boiling the gas in the bowls. I am using the fiber intake gaskets.

What can I do to fix this? Driving me nuts, since the engine runs so good!

It doesn't start leaking until 20-30mins after engine shutdown!

[clearsurf2001]

John ... that's one I've yet to encounter. PM John C. over at ac.net and see if he's seen this one before.
_________________
Get ready for the injection

[clearsurf2001]

Just read some V8 forum posts on this. Their solution ... phenolic spacers, aftermarket needle and seat, and (don't laugh) rigging a return fuel line from the float bowls back to the tank. One theory sounded interesting ... cheap ass fuel reg allowing fuel past in combination with a poorly vented tank ... not too probable on our application though. Heat transfer into the manifolds and subsequently the carbs is evidently not that rare with the V8 crowd.
_________________
Get ready for the injection

[mharney]

Didn't we talk about this?

Another experiment: Right after you turn off the engine, disconnect the fuel line where it leaves the pump and goes to the carbs. Get a little spill cup or something to catch what comes out of the line. Then let it sit and see if it still does it. That'll tell you if the fuel pump is heating up what's in there and forcing it into the carb.

What happened with the test I left you with to try?

[nsracing]

Either the needle valve is leaky...or the float is cracked.

Take the top cover off...turn it upside down with the weight of the float on the needle. Try to blow into the inlet hose going to the needle. You should not be able to blow through. If you blow and actually end up with a hernia, then you know the needle is good.

After the needle checks out, then disconnect the float. Have a small can of for fuel and lay the float on there. You will see if it is cracked...the sucker will sink.

I will just use water for this test though to save the fuel.

Pressure like that... 3.5 psi ought not to get passed the needle if the float is pushing on it.

Good luck.

[John M.]

[John M.]

It's fixed. When I first put the engine in, I had replaced the small metal line that runs through the firewall with a rubber line. Well that rubber line was laying on the HOT intake manifold. So I put the hard line back in, and like magic I have no more leaks.

[mharney]

Yay! Good job. Keeping those lines as far as you can from anything is the best solution. Glad you found it.

[John M.]

Just when I think it's fixed...It's still leaking, on all barrells. So I did your test and removed the output fuel line to the carbs and that stopped the leaking. Obviously the fuel pump was pressurizing the lines after shutdown. Forcing fuel into the carburetors.

So, this afternoon I'm putting in a Rotary Electric pump....provided my local NAPA can get one today.

[nsracing]

[John M.]

[nsracing]

The fuel boiling point is 100 - 400 deg F. And with increase in pressure, you also increase its boiling point. So as long as you have pressure, it is not going to boil over. WE are talking MORE pressure now. That kills the boiling theory all to hell right there.

And I know, you are NOT that high up in the mountains. Boiling point is DECREASED with altitude.

Needles and floats. The needles are probably corroded or just old. The needles and seats will wear out too you know.

Have you thought of changing them out?

[John M.]

I guess anything is a possibilty. But these are brand new carbs, I have even swapped in a totally different new 44IDF and it still does it. I can't imagine the needles would be corroded and the seats having wear after only fifty miles.

OK, say your right. Why do none of the barrels flood when the output line is disconnected from the fuel pump?

[JEECOMAN]

Try leaving the gas cap off after you park. Maybe you are building up pressure in the tank.

[RockNbus]

In your original post you said that the floats are set to spec. What exactly did you set the floats to? When I got my new 44IDF's the floats were way out of adjustment.

[Loopole]

i see the same symptoms with my old drla 36s and my brand new weber 44s, ambient temps have to be hot like around 90 and engine has to be hot also, if it sits for 15-20 min it is hard to start and flooded, a good simple test to see if it is the fuel quality, put a few gallons of avgas in on an empty tank and run it, it wont boil like the autogas, it also will not hurt your engine at all, in fact it will give your valves a nice shot of lead.

[Loopole]

i see the same symptoms with my old drla 36s and my brand new weber 44s, ambient temps have to be hot like around 90 and engine has to be hot also, if it sits for 15-20 min it is hard to start and flooded, a good simple test to see if it is the fuel quality, put a few gallons of avgas in on an empty tank and run it, it wont boil like the autogas, it also will not hurt your engine at all, in fact it will give your valves a nice shot of lead.

[John M.]

Update: I first tried another mechanical fuel pump. Still leaked gas after shutdown.

I called NAPA and they sourced a Carter rotary electric pump. I installed it underneath the gas tank this afternoon. No more leaks after shutdown.

[mharney]

You go boy.

I knew you'd find it.