Rebuilt qjet - leaks fuel

[czarcaustic]

I rebuilt my ol' qjet and everything was going along just fine, I went to the bank and home and a few other quick errands around the neighborhood. I got under the hood to look around and make sure everything seemed to be dialed in correctly on the carb. Everything looked good and I didn't have any stutter or hesitations on my bank trip so I was pretty happy and then went the grocery to pick up a few things. When I got back out to the truck I tried to start her up and she just didn't want to turn over - then I could smell gas really strongly.

I popped the hood and there was gas leaking from the side of the carb (somewhere on the passenger side) and evaporating on the hot manifold. I let the fuel evap. sat for a bit and fired her up (She hesitated some but eventually came around) to see if I could see/reproduce the leak. When I visually inspected the carb @ idle I saw no leaking, when I manually advanced the throttle everything seemed fine for a bit then there was some fuel bubbling up from the accelerator pump - Then I shut the engine off and the fuel really started seeping and hissing on the manifold.

I got a buddy to tow me home - ripped the carb off and pulled it apart again. I reseated the brass needle valve seat and made sure it was shmutz free. I made sure the float was adjusted correctly and not binding and then blew compressed air through every passage I could see.

I put everything back together and remounted it on the manifold. I fired the truck right up and everything sounded great. I let it run for a few minutes and shut the truck off - nothing. No fuel seeping anywhere. I fired the truck up again and went for a 15 minute drive. When I pulled up to my garage the trucks started bogging down a bit at idle and smelled real rich (like it was flooding out). When I shut the engine off I could hear the fuel hitting the manifold SHHHHHHHHHHH.

What is the deal? It only seems to be seeping when the engine is warm? Any suggestions?

[unclewatts]

This is just a guess. Could it be the float hanging up and flooding out the engine?

[czarcaustic]

Originally Posted by unclewatts

This is just a guess. Could it be the float hanging up and flooding out the engine?

The float seems to be working correctly to me when I have the carb off the truck - doesn't bind and is set correctly according to the spec sheet. The only thing I can think of is that the brass needle valve seat is stripped out and fuel is bypassing the valve.

So frustrating.

[68gmsee]

From my experience with this problem it's always been float/needle valve/debris related. In other words, something has kept the needle valve from shutting off the fuel when the bowl was full. Some might say that the fuel pump may be producing too much pressure, but I've never experienced that.

I would take the top back off and install another kit in it. Something aint right and setting the engine and truck on fire is costly. I had a friend destroy his truck because of a leaky carb.

[texanidiot25]

Originally Posted by 68gmsee

From my experience with this problem it's always been float/needle valve/debris related. In other words, something has kept the needle valve from shutting off the fuel when the bowl was full. Some might say that the fuel pump may be producing too much pressure, but I've never experienced that.

I would take the top back off and install another kit in it. Something aint right and setting the engine and truck on fire is costly. I had a friend destroy his truck because of a leaky carb.

+1, happened to me when some gunk got in the carb.

[Wrenchbender Ret]

You are getting dirt in the needle & seat. Put an inline filter between the tank & pump. That should catch anything that goes to the system. Also have a filter in the neck of the carb. Keep an eye on it. If it gets plugged up pretty quick you will need to pull the tank & clean it. There is a quick fix for the carb when it does that. Clamp a vise grip to the flex line. Start the engine & run it till it uses all the gas in the carb & dies. Remove the vise grip & restart it. The sudden rush of gas into the carb will usually flush the foriegn material through. Beats tearing it down but you are getting good at it by know.

[Sport/Truck]

I had the same problem with my SMI q-jet. Sean said it was common for fuel pumps to be putting out too much pressure, sure enough mine was like 10-10.5. Installed a magna-fuel regulator and problem solved.
s/t

[Pont406]

Make sure that a check ball under needle valve is seated. Use an old check ball, punch and give it a couple smacks with a hammer.

[czarcaustic]

What pressures should I be getting at the carb from my fuel pump?

[silverstreak]

I have a Rochester carb manual here that states the preffered fuel pressure for a Quadrajet is 4-6 psi.

[Jim_PA]

Did you put the needle clip on the right side of the float clip?

[czarcaustic]

Originally Posted by Jim_PA

Did you put the needle clip on the right side of the float clip?

The float arm didn't have a needle clip on it when I took the carb apart the first time - I just assumed that it didn't require one (and had heard of others simply running w/out one). Because of this I didn't install a needle clip at all on the float arm - it just sits in the brass seat with the float arm above it.

Could this be the problem?

[geezer#99]

Sounds like what Jim Pa said is right. You need the clip on the top of the needle to hook onto the float arm or the needle will hang up and flooding will occur. The clip hooks onto the arm. I've found some with the hook through the arm.

[Wrenchbender Ret]

Not haveing the clip will not cause that problem. Haveing it on wrong might. Ive run many of them without it & have opened many withoutb it & never had a problem.

[czarcaustic]

FIXED!

It is almost embarrassing to admit as to what the problem was. Especially after tearing the carb apart 4 times.

The spring that holds the filter flush against the fuel line housing in the front of the carb was weak. That is all. I put a new spring in that housing and a new filter in place - No more problems.

It seems that the filter slows flow, and the fuel was just bypassing the filter because it wasn't tight.

I feel like such a moron! Thanks for all the tips and suggestions guys.

Not all is lost - I feel like I could rebuild a Rochester Q-Jet blindfolded now!