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Annoying warm engine flooding condition

6K views 60 replies 26 participants last post by  Radar Pete 
#1 · (Edited)
Update below: http://www.ffcars.com/forums/17-fac...rm-engine-flooding-condition.html#post5663458

My car is near perfect, I love the way it runs and idles, except after the engine is all nice a hot (normal temps) and I shut the engine off and leave it 15-40 minutes.

I'm running a Quick Fuel 650 mechanical secondary carb with 6.5 psi fuel pressure. I have a heat spacer (layered aluminum/gasket material), an aluminum heat shield, and the fuel lines have heat sleeves. So I think I've ruled out a heat issue.

The fuel pressure drops almost immediately, so don't think that's the problem.

The carb has glass bowl site windows. When it's running the fuel level is close to half way up. When the engine is shut off, the fuel levels in both bowls drop out of site.

It restarts after about 5-6 seconds of cranking with the throttle open almost all the way and sputters, idles poorly, and under hard acceleration pops and stumbles until the excess fuel is burned up. It's like the raw fuel is just sitting in the intake and braking or accelerating is sloshing that still-liquid gas and being sucked into the cylinders.
 
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#2 ·
After shutdown, open the hood, remove the aircleaner and look down the carb. Fuel leaking in? Open the throttle and check again. Could be bad powervalve...
 
#4 ·
I've used a Q-F 650 and 750 in my builds. Both running a mechanical fuel pump with 6.5 PSI and no issues. So I don't think too much pressure is the problem. That's exactly what they're supposed to have. Mine haven't had the draining problem you're describing. In fact, even sitting over the winter the fuel is still visible in the sight windows.

The fuel is draining somewhere. Power valve could cause that problem, but that should only affect the primary bowl. The secondary side typically doesn't have a power valve, unless yours is different. The fuel pump has check valves to keep it from draining back to the tank, but in theory that shouldn't affect the carb if there were a failure since the fuel comes into the bowls from the top.

The fuel is going somewhere. Agree with the recommendation to take the air cleaner off right after shutdown and see if you can tell where it's going. Even with the precautions you're taking, still could be heat related and evaporating. I was quite surprised when I was tuning my 750 and doing frequent jet changes how warm the fuel was in the bowls when draining from a warm engine (very carefully!).
 
#5 ·
Update: At the advice of Quick Fuel technicians I replaced my heat spacer and aluminum heat shield with Cool Carb spacer and shield, and I lowered the float level to where the fuel level is a 1/3 of the way up the sight windows.

Like EdwardB said, my 6.5psi fuel pressure is exactly what Quick Fuel recommends. Both bowls are doing the same thing and only the primary side has a power valve, so that's not the problem.

My laser thermometer says the float bowls are reaching 140-150 degrees. I'm guessing the boiling point of gasoline is higher than that, I don't know.

Any other suggestions?
 
#6 ·
My laser thermometer says the float bowls are reaching 140-150 degrees. I'm guessing the boiling point of gasoline is higher than that, I don't know.
Gasoline contains many different chemicals which vaporize out at different temperatures.

The first thing to go is probably the butane, followed by any toulene content.


Consider them to be approximately like ether - they only exist as "vapor" at 100F (+ atmospheric pressure).

I think todays' gasoline blends are probably more volatile than 30 years ago, due to the (now "normal") widespread use of pressurized fuel tanks and EFI.


If you have an electric fuel pump, you can wire it up separately, shut off the pump and idle the float bowls empty before engine shutdown (several of us do).


Good luck,

Mike
 
#8 ·
Are you running the "COBRA" oval air cleaner?

Mine, with the thin filter they come with, was actually sitting on the carb vent tubes. I guess just enough to close them off when hot. I could see little circles lightly scratched into the lid, after I knew to look for it.

The car ran great, until it got hot, then I had a wicked flooding issue. I switched to a taller S&B filter. Problem solved. The hair on my left arm grew back too. Nice header fire.
 
#10 ·
Yes I am using an oval Cobra air cleaner, but also using taller K&N filter. Clearance is good.

If I restart right away it fires immediately. If I let it sit for more than 15-20 minutes I have to run the starter for 3-5 seconds with the throttle mostly open, it then idles poorly and sputters a bit under acceleration. It's more aggravating and embarrassing than anything else.
 
#11 ·
Sounds to me that you need to check the needle and seat for trash. Have built Holley's for track cars and boats for many years. The only time I have had fuel pressure overwhelm the needle and seat flow is when the pressure is too high, over 9 psi or trash allows fuel to flow after the pump is off. Try a different gage, might be wrong. Off should be off.
 
#12 ·
There is no way a properly operating carb would loose level in the bowls in 30 seconds unless there was an abnormal internal leak path. You need to remove the carb and check for the source of the leak. Sit the carb on a coffee can, put fuel in the bowls and find out where it is leaking. Fix the internal leak.
 
#13 ·
I have same setup QF 650 mech 2nds except low pressure elect pump. Last drove it on Sunday, I just went out and looked and my bowls all show fuel. I have mine set at 1/2 way up when car running. My fuel pres gauge shows 0 pressure. Right now the fuel is about 1/4 way up the window.

Once my car is warmed up and/or still warm after being shut down, all I need to do is get in turn the key and it fires right up at idle 700 -800 rpm. The only time I touch the pedal is a cold start in the morning to activate choke. Something isn't mechanically right.

What do you need to do to start it cold? I get in and steadily press the pedal all the way to floor once and release it then a little 1/4 press to squirt in some more fuel, turn the key fires right up and the carb does the rest. The next time I touch the pedal is to open choke and lower the rpms with a slight tap on the pedal after a few minutes. My choke will increase revs slowly to 2000 rpm then it just stays at 2000 rpm till I tap the pedal.
 
#14 ·
You didn't exactly answer the question so I'll just take a guess. If this is what you do already then I give up. On a restart after it has been sitting for 15 + minutes, give the throttle about a half pump of the primaries only and release the pedal. Then with the throttle barely cracked engage the starter. Should light right off.
Frank
 
#15 ·
There is no way a properly operating carb would loose level in the bowls in 30 seconds unless there was an abnormal internal leak path.
Seems you misread my symptoms, I said that the fuel pressure drops to 0 in less than 30 seconds. It takes 10-15 minutes for the fuel level to drop.

If the needle value was faulty or dirty, the fuel level would rise and/or overfill, not the case.

Actually, I did try another gauge, 6.5psi too.

My cold start depends on if the fuel drained out of the bowls that last time I shut it down or not. If the engine is not fully hot when it's shut off, the fuel level stays put. Then the car starts easily and choke works fine.

Today, the Quick Fuel tech said that it's probably the low boiling point of gasoline mixed with ethanol. Suggested filled the car with non-ethanol gas to see if that changes the issue, but I can't find any in my area. I might try to add yet another heat spacer to the combination to get the temps down.
 
#16 ·
Frank, I was typing my response when you were typing yours. I appreciate the advice, but my issue is a pool of raw fuel sitting in the intake because the bowls have drained (but not completely). I need to solve this issue.
 
#17 ·
Bill as a reference point I just checked my carb. Car was last driven at 4PM Saturday. Normal float level is 1/2 way up the glass. Now it is at the bottom of the glass. I have same carb as you, a QF SS650AN mech secondary w/ a 1/2 inch insulator under it. It's that brown composite material. Gas is 7-11 premium so nothing special. Oh, intake manifold is Edel Performer RPM. Not an airgap model.
 
#18 ·
Thanks Craig, it sounds like we have identical setups, I also have a Performer RPM intake. The Quick Fuel guy said that the ethanol part of the mixture would evaporate before the gas part.
 
#19 ·
Not much help but try a marina for ethanol free gas. Can't remember if any marinas close around Manassas.
JR
 
#20 ·
It doesn't sound right that because of an additive in the gas that it would cause the fuel to evaporate in 30 seconds. If you have fuel pooling in the intake, then it is not evaporating at all. Remove the carb and take it apart, clean, reset to spec. Replace the power valve and re-install. Something is causing the leak.
 
#22 ·
It doesn't sound right that because of an additive in the gas that it would cause the fuel to evaporate in 30 seconds
Guys, you're not reading the thread. The fuel is NOT evaporating in 30 seconds. The problem isn't evaporation at all. The problem is the fuel bowls (both) are draining into the intake 15-20 minutes after a hot engine shutdown. The only time 30 seconds was mentioned by me is to describe the fuel pressure drops to zero in less than 30 seconds. It is true that there will always be some small amount of evaporation over time, but this is not the issue.
 
#25 ·
When Talking to the tech department ,Why in the world would he bring up a type of fuel when you clearly have issues with a carb leak. Is he reading from a set of trouble shooting guides. When you just look at the root of the problem and disregard everything else ,the carb get hot ,then the pressure drops in 30 seconds ,than a puddle in the intake in 15 to 20 min . Either the heat is causing the leak or debris /puncture. Is it a newer carb ? or did it work for a time and than started acting up. When you mention your symptoms to the tech guy ,ask him how fuel type relates to fuel drainage in intake.Low boiling point isn't sending fuel into intake. If carb is new, than send it back ,If not ,rebuild it. I think the evaporation questions came about from the comments about fuel type and low boiling points and caused confusion. Hope you figure it out
 
#23 ·
None of us believe the fuel could possibly evaporate in 30 seconds. We firmly believe you have an internal leak path allowing the fuel to trickle into the manifold. As the fuel level drops, the fuel bowl needle allows more fuel to enter the bowl until the pressure falls to 0 (in 30 seconds.)
Where is the internal leak?
 
#24 ·
Bill,
Have you re-checked your timing recently? I recently helped a buddy with a big FE and Demon that was experiencing the same warm restart issues as you. The carb was crap but ultimately his timing was retarded. Also, I believe that the clear fuel bowl sight plugs cause us to run a higher fuel level than is optimum. Historically, the fuel level was set such that fuel just dribbled out the hole. You may want to try that, you won't run out of fuel.
Frank
 
#26 ·
Sounds like fuel percolation in the float bowls. Caused by heat.

As soon as you shut it down, open the hood, remove the air cleaner and watch what happens. The fuel is probably boiling and then escaping out the vent tubes emptying the float bowl and depositing fresh fuel into the intake. Ethanol has a much lower boiling point than gasoline. Winter gas is notorious for causing this problem. Even though you have a spacer, try a plastic one instead of aluminum.
 
#27 ·
Prior to this recent attempt to solve this nagging issue (since installation), I have had a holley aluminum heat shield (large flat shield), and a heat spacer made by sandwiching layers of aluminum and gasket material. As stated earlier, I bought and installed a Cool Carb spacer and heat shield, each one about 1/8" thick. Today I added back the other heat spacer.

BTW, I spoke with a local speed shop owner and described the issue to him and he also recommended the Cool Carb spacer. However he said to get the ones with 4 butterfly holes, not the one big opening (which I was sold). If you get the one with 4 holes, the bottom of the carb doesn't get directly heated, just the butterflies.

Well, I went for a couple rides today and parked in the garage and sat there and waited for the levels to drop and took temperature readings on the bowls. The bowls were about 10 degrees cooler and the levels didn't drop. FWIW, it was also about 10 degrees cooler outside today too.

I'm going with this setup for a while and see happens. I like the idea of a plastic spacer. I'll do some research.

Thanks guys for the advice and suggestions. It's hard to believe this doesn't happen more frequently.
 
#28 ·
Quote: "BTW, I spoke with a local speed shop owner and described the issue to him and he also recommended the Cool Carb spacer. However he said to get the ones with 4 butterfly holes, not the one big opening (which I was sold). If you get the one with 4 holes, the bottom of the carb doesn't get directly heated, just the butterflies."
That is very interesting info. I know there are tuning effects that the two types of spacers can have and I don't really remember which type mine is. But that really gives an added vote to the 4 hole style doesn't it.
 
#29 ·
Bill-I had very similar symptoms with my quickfuel 750 cfm 347 stroker engine initially. I added a phenolic (plastic) 1/2" spacer 1000 miles ago and instantly all my issues went away. No more flooding, fuel boil, or garage that smelled like gasoline 24/7.

I say if what your trying now doesn't work. Give a $35 plastic spacer a shot.
 
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