[Jackel]

I'm having a little problem with my 70 Nova SS starting. It appears that fuel is being sucked back into the tank after the motor is turned off. If the car sits around too long then I really have to crank / pump it a long time to start. No leaks visible. SMI stage II Q-Jet. It has the stock style return line and all the tank vents hooked up to the carb and charcoal canister OEM style. I was thinking a fuel line check valve would help. Anyone know of a reasonably priced valve for 3/8" rubber fuel line? Looking at a check valve for a diesel engine. They are around $10.00. Thanks, Jack

 

[sbc1320]

Qjets leak under the carb body where the welch type plugs were put in from the factory. When rebuilding them it is common practice to epoxy(JB Weld) over those plugs so they don't leak gas into the engine.

You can see the plugs on the bottom when you flip the carb over.

 

[Jackel]

Qjets leak under the carb body where the welch type plugs were put in from the factory. When rebuilding them it is common practice to epoxy(JB Weld) over those plugs so they don't leak gas into the engine.
You can see the plugs on the bottom when you flip the carb over.

Thanks for the reply. I have a NEW SMI Stage II Q-Jet with less than 100 miles driving time on the new engine. I don't think that is where the issue is but you never know. I had the engine on a test stand running for about five hours before the install into the car and pulled the carb to check if I was getting any gas out the bottom and it was dry. Jack

 

[sbc1320]

Maybe a faulty fuel pump allowing fuel to drain back into the tank?

Is tank vented well so as not to create a vacuum perhaps and suck the fuel back when shut down.

I assume there is some sort of check valve built into a mechanical fuel pump.

 

[the FLYER]

i'm not a carb guy but unless it's leaking somewhere, shouldn't there be fuel in the bowls Jack?

 

[the FLYER]

after running it a while pull the gas cap, is it under suction? i'd think if the system is working right it vents through the return canister? check for hose kinks, plugs etc... make sure the lines are open...

maybe?

 

[sbc1320]

i'm not a carb guy but unless it's leaking somewhere, shouldn't there be fuel in the bowls Jack?

True that's why I was telling him in my first post about the plugs that get epoxied. I have built a few and epoxied them. Don't think the fuel can actually siphon back to the top of the carb once it gets below the fuel inlet which is near the top.

 

[sbc1320]

If the car is hard to start after just a couple of hours, it could be flooding out from the fuel dripping from the bottom of those plugs.

You would think though since it is a reputable carb company that standard procedure would be for them to epoxy those plugs.

 

[the FLYER]

when it's hot... if started there may be still fuel residue in the system assisting initial fire. when cold it's evaporated...

hot immediate starts? cold you have to pump it once or twice?

 

[Jackel]

Thanks JR and 1320. JR, every time I look at that "Phillip" up-side-down ID with the JR "MODIFICATIONS" it cracks me up. Funny, funny, funny.

If the car sits overnight then it is had to start. WAY more than a few pedal pumps to get it to fire up. Once it starts, it is fine. I can turn it off and it starts again without hesitation. Sometimes it will burp up gas after I shut it off.

I had this issue when it was on the test stand but it never burped up gas. Just hard to start if it sat overnight. I would always just fill the chamber with gas using the vent tube and it would fire but I thought it was the way the test stand was set up gas tank wise.

The car is currently at the dyno shop so I can't get at it for any checks and the shop GURU said it will be about 2 weeks to get it done because he has just had a shoulder rotator replacement done and can't work very long at one time getting it all set up. He may find the problem. Thanks Jack

 

[oiler]

My Rochester has a huge vent area with a screen and a vent to the carbon canister. With the carb on the bench, the gas in the bowl would mostly evaporate in 24-30 hours. [lots of alcohol in the gas].

There are two kinds of filters- one with a check valve . The check valve is a black rubber disk in the inlet to the filter.
http://www.digitalcorvettes.com/forums/showthread.php?t=153051

 

[sbc1320]

There are two kinds of filters- one with a check valve . The check valve is a black rubber disk in the inlet to the filter.
http://www.digitalcorvettes.com/forums/showthread.php?t=153051

I forgot about the filter with the check valve in it, it's been a few years. Good catch.:yes:

 

[Jackel]

My Rochester has a huge vent area with a screen and a vent to the carbon canister. With the carb on the bench, the gas in the bowl would mostly evaporate in 24-30 hours. [lots of alcohol in the gas].

There are two kinds of filters- one with a check valve . The check valve is a black rubber disk in the inlet to the filter.
http://www.digitalcorvettes.com/forums/showthread.php?t=153051

Thanks Oiler, I have never seen the filter with the check valve built in. I dug out my original Service and Maintenance Manuals to check and see which one came as OEM on my 70 and it is the one without the check valve. Could be the pre-70's with 3/8inch gas line HP model carbs used the ones with no check valve filter for better flow??? When the car was new I don't remember having to crank it much but it was my daily driver and driven almost every day. If it is going out the vent tube then there is really nothing I can do to stop it. Thanks, Jack

 

[Baddbob]

My cars sit for weeks and never evaporate the fuel out of the carb. The carb is leaking.

 

[Jackel]

My cars sit for weeks and never evaporate the fuel out of the carb. The carb is leaking.

DANG, brand new custom Q-Jet, sent back twice already. Always comes back to me as "the carb is OK, your problem". Engine currently at the dyno shop, I'll have him check it over. You are badddddddddddddddd Bob...lol. Thanks for the reply. Jack

 

[Burke]

Should be easy enough to check. With the carb off the vehicleand spaced above the work bench fill the bowl and watch for leaks. The bowl can be gravity fed through the fuel inlet from a container placed well above the carb.

 

[Jackel]

Should be easy enough to check. With the carb off the vehicleand spaced above the work bench fill the bowl and watch for leaks. The bowl can be gravity fed through the fuel inlet from a container placed well above the carb.

Thanks Burke, I checked it when the motor was first running but it has gotten much, much worse so I will have the dyno guy check it while he is tuning my engine....Jack