flooding engine

[mikefam]

tmodel66 - \

Do you remember the diameter of the hole plug? I don't have the carb off the car right now and would like to buy the plugs.

Mike.

[tmodel66]

No I don't. I just had these laying around in the toolbox.

[Petes L48]

I'm trying to use steel core plugs so I don't have to tap the holes and get metal down the intake.  Dorman 1/2 was too large, 3/8 too small.  They also have a 7/16 and one slightly smaller size I'll try next.  Car is in storage a couple states away so I'm still shooting in the dark on this.  Good thing they're only about $4 a box. 

[JohnZ]

I've used 7/16" plugs with success on small-block Corvette cast iron Holley intakes.

[mikefam]

I'm thinking a little permatex non-hardening sealer in there to seal it up and as long as it fits in the hole and is too big to go down into the intake it'll be fine. I'll go get some 7/16" plugs and give it a shot.
Mike.

[mikefam]

Having a problem after engine,(sb350) is good and hot, will not start after sets 5 min or so without crankkkkking foot to floor.
Have rebuilt the 4bl qjet. Covered all that I thought would be related to carb itself.
Thinking that it might be related to the heat from the exhaust crossover??



I thought I had seen some discussion in the forum relating to this a short time back but can't find anything now.

Any help out there on this?

I've had the carb off about five times and still the engine floods when I shut it off. I proved that the fuel is passing through the carb into the engine by clamping off a rubber section of fuel line between the fuel pump and carb, waiting a half hour and then disconnecting the hose at each end of the clamp. The pump side still had pressure in it and the carb side did not.

So far I have

1 - Cleaned and rebuilt the carb with kit
2 - Installed 1/4" paper gasket under carb
3 - Installed metal plugs in heat ports in manifold
4 - Installed new float needle and seat and gasket with Cliff's improved seat (no fuel inlet windows)
5 - adjusted new brass float leaner that specs (I forget the exact measure offhand)
6 - installed new fuel pump

I even checked the plugs carefully in the bottom of the float bowl by spraying soapy water on the plugs and blowing compressed air into the jet openings inside the bowl. It's a 1974 carb with the improved plugs and they look good.

All this work and still the carb floods the engine and loses float bowl pressure. The engine starts great shortly after stopping and runs great but floods when left to stand a while.  Does anyone know what I missed? I'm stumped.

Mike.




 

[Stingr69]

Having a problem after engine,(sb350) is good and hot, will not start after sets 5 min or so without crankkkkking foot to floor.
Have rebuilt the 4bl qjet. Covered all that I thought would be related to carb itself.
Thinking that it might be related to the heat from the exhaust crossover??



I thought I had seen some discussion in the forum relating to this a short time back but can't find anything now.

Any help out there on this?

I've had the carb off about five times and still the engine floods when I shut it off. I proved that the fuel is passing through the carb into the engine by clamping off a rubber section of fuel line between the fuel pump and carb, waiting a half hour and then disconnecting the hose at each end of the clamp. The pump side still had pressure in it and the carb side did not.

So far I have

1 - Cleaned and rebuilt the carb with kit
2 - Installed 1/4" paper gasket under carb
3 - Installed metal plugs in heat ports in manifold
4 - Installed new float needle and seat and gasket with Cliff's improved seat (no fuel inlet windows)
5 - adjusted new brass float leaner that specs (I forget the exact measure offhand)
6 - installed new fuel pump

I even checked the plugs carefully in the bottom of the float bowl by spraying soapy water on the plugs and blowing compressed air into the jet openings inside the bowl. It's a 1974 carb with the improved plugs and they look good.

All this work and still the carb floods the engine and loses float bowl pressure. The engine starts great shortly after stopping and runs great but floods when left to stand a while.  Does anyone know what I missed? I'm stumped.

Mike.

Mike,
I have suggested clamping off the rubber line in the past to verify if the fuel bowl was leaking at the well plugs on Q-Jets.  They get blamed for hard restarts more than they should IMO. They can leak but it is not as common as other issues. Are you working on a q-Jet?

Heat can boil out the gas in the carb and cause the hard re-start. You might try observing the inside of the carb after a hot run. Pinch off the fuel line and look down into the throat and see if gas starts to boil and puddle on the top of the butterflies when you shut the engine off. If you do see gas boiling out, you might want to try wrapping the carb with an ice water soaked towell and see if it changes the gas boiling situation. If the towell helps, heat is a problem.

There is also a concern related to Q-jets and the return line that comes off the original fuel filter canister. The factory Q-jet cars have this line but factory Holley carb cars do not need it. I just wish I could remember the exact reason you need the return line on a Q-jet car. Something about overpowering the needle and seat? HELP ME HERE GUYS! There IS a reason Q-jets used it from the factory but my memory is not as good as it used to be. LOTS of people have eliminated this return line function over the years and I am certain that is a bad idea to get rid of it.

-Mark.

[Kelley W King]

My car has the return on the carb but not the return line. I plugged the return and it did not run right. I was told that it is a vent also. I run mine open with no line and have never seen anything come out of it.

[mikefam]

Mark:

Yes I should have said that this is a Q-jet carb. It came to me on an engine taken from a 74 Nova. It had a fuel pump that vented back to the fuel tank and I used the pump with the vent plugged for years. Recently I replaced the pump with a 1967 style pump with no vent.
 
I have looked inside the carb and while I don't see the gas entering the engine I believe that it is because the throttle plates appear to be wet. There are no fumes to be seen and no dripping to be seen but when I removed the carb, the right front port had gas in the intake manifold. It's not enough gas that the engine starts with any black smoke so maybe the gas is evaporating before getting into the cylinders. I just have to hold the throttle to the floor and spin it for a dozen spins or so to get it to start. Another clue may be that I'm only getting about 14 mpg.

I worked as a mechanic in the 1970's and tuned and repaired tons of Q-jet engines and never had this kind of problem. I've seen the gas drilpping into the engine when a float valve sticks and I don't see that here. I'm beginning to think that it is the new gas causing a problem somehow. I just don't see it boiling into the engine. Can it maybe ust be evaporating?

I wish that I had a known good spread bore carb to try on there and see if it corrects the problem.

Mike.

[Stingr69]

Mike,
I am guessing the problem is 1 or 2 things. You might benefit from adding a fuel filter with the vapor/bypass hookup and hooking that extra line up to the fuel return hard line. The Q-jet is sensitive to excessive fuel pressure. If you are above about 6 PSI operating pressure then you can push the gas level in the bowl too high. Checking that would be best but not allways as easy to do as it is to say. You could try adding a filter with the extra vapor return tap rather than go buy a pressure guage. The stock type inline vapor return filter that goes between the pump and the carb has a return line that would allow excess pressure to bleed back to the tank. This could help releave fuel line pressure when the engine is shut down as well as help with too much fuel pressure at cruise. Too much pressure at cruise would cause bowl fuel levels to rise above set point and that causes rich cruise mix. Bad fuel economy and hard restarts would be a symptom of too much fuel pressure. This is cheap and easy to try so give it a shot.

You could add a home made fuel bypass after the pump but it is a lot more work. Doug Roe describes it in his Q-jet book.

You also could have fuel flash from heat soak especially with todays gas formulation. The hot carb will cause the fuel to vaporize at shut down. When you crank it back up. the bowl fills with gas that also boils quickly and the fresh fuel can vaporize causing additional hard cranking. The combination of heat and todays gas does not work well with carbs.

Hope this helps,

-Mark.

[mikefam]

Mark:

Thanks for the detailed reply.

I have a section of hose in the fuel line between the pump and carb so I think that I'll install a pressure gauge inline and see what I have there. There is no return line to the fuel tank so installing a return line won't be a small matter but maybe an inline pressure regulator would help.

The heat soak problem seems more like to me but I don't know what to do about that. I have a 1/4" thick gasket on the carb now. Maybe I can find a heat shield to add to it.

I'm getting ready to just get used to having to crank the engine a little.
 
Mike.

[bc69]

Mark,
I still am interested by one of your earlier thoughts on the purpose for the return line on the Qjets to start with. I think somebody out there should have the answer.
Makes sense to me that it would be a relief, and allow a better fuel flow helping to keep the fuel temp in the line down. No...maybe...?
I have changed the carb since, dont seem to have the same problem, but it has not been a hot as it was. I think that the above question is addressing my problem. It seems as if the fuel line is getting hot enough to overpressure the line or vaporize the fuel. We all can remember the days when "vapor lock" was a common word.
Brad