87 442 carb always seems to drain gas from bowl

[Mat1227]

87 442, standard quadrajet carb, had rebuilt a year ago, (Mountain Man Fuel Systems) it runs great, but if you let the car sit for about 3 days, seems like the carb is empty of fuel, spray eyther and it fires instantly. Mountain Man put epoxy on the lead plugs in the bottom of the bowl, I cleaned it off and re-applied JB Weld to make sure all was sealed, but I still have the same problem. Anyone have any ideas? Car has 128k miles, I removed gas tank and cleaned out and sealed inside with POR15 gas tank sealer, even replaced the fuel pump thinking maybe it just allowing fuel to siphon back to the gas tank. I'm open to suggestions.
Mark

 

[pontiacgp]

sounds like the needle seal is leaking

 

[Clone TIE Pilot]

Are you using a fuel filter with a anti drain back valve? Modern E10 gas evaporates out of the bowl faster than old plain gas. Also make sure your fuel lines from the tank to the carb are not leaking. Couple of days ago I found the rubber fuel hose that connects to the fuel tank had a hairline crack leaking fuel onto the exhaust pipe!

 

[airboatgreg]

1. Q jet main well plug leaking was cured by late 70's. When you redo the main well plugs on a later carb you are usually screwing up a carburetor
2. Is the choke closing? Rule of thumb, choke plate should just close after depressing throttle at 70 degrees and maybe 2 notches richer
3. Is accelerator pump in carb delivering 2 good sprays of fuel? Hold choke open on cold engine while looking in throat of carb and depress accelerator a couple of times.
4. Fuel today is designed for fuel injection, not carbs. so...
5. I have found that due the expanse of the intake manifold that you may have to pump accelerator 3 or 4 times to floor. Take foot off gas and crank engine. Make sure fast idle cam is set to specs. Usually about 1100 RPM on low step
6. You have a relatively low mileage car for the year so there may be a carbon build up in the intake and around the intake valves due to the PCV, EGR systems and multi grade oil such as 10w-40 which was the worst culprit for creating deposits. Use AC Delco X66a and clean intake system as the carbon acts like a sponge and the fuel never reaches the combustion chamber.

 

[pontiacgp]

Are you using a fuel filter with a anti drain back valve? Modern E10 gas evaporates out of the bowl faster than old plain gas. Also make sure your fuel lines from the tank to the carb are not leaking. Couple of days ago I found the rubber fuel hose that connects to the fuel tank had a hairline crack leaking fuel onto the exhaust pipe!

I'm glad you found that before it caused a fire...

 

[Texas82GP]

When I read the post where Clone discovered fuel leaking on the exhaust pipe, this was my first thought....


Seriously, glad you found that.

 

[MrSony]

If the needle and seat is the windowed type, that could be allowing fuel to drain out of the carb when at rest. As others have said make sure you have the filter with the check valve in it INSTALL IT CORRECTLY WITH THE SPRING if you don't. New gas evaporates way faster than actual gasoline so that could be the culprit as well. Next time you drive it, take it on a nice long drive. To see weather it is actually leaking out the carb, unhook the line going into the carb and have it going to a container. If there is gas in it when you come back say an hour later, gas is leaving the carb. If not and the problem persists, it's just evaporating which you can do nothing about.

 

[Quadrajet Power]

I hear this a lot.
Fuel evaporating faster when sitting a few days. Can't help that, but couple of things you might do to possibly help.
Make sure float is set correctly. Keep it about 9/32". This allows maximum fuel in bowl.
Don't use the seat clip on needle/seat that holds it to float. This allows seat to close when fuel isn't coming in to carb.

 

[Mat1227]

Thank you all for the suggestions, plan to take carb off and completely dis-assemble it this weekend. Although I can't rule out the leaking fuel lines, but I did replace all rubber lines at the tank area, doesn't mean there isn't a leak somewhere. There is another Issue we noticed, I Can't seem to get the secondaries to come in at all, My previous 87 442 that I bought new, you had to completely stand on it to get them to open, this one not at all yet. I did replace all vacuum lines on the car, as well as the air pump and converter.

 

[pontiacgp]

if the gas was evaporating that quickly you'd have have an odor of gas in the engine bay