The Stovebolt Site Forums The Shop Area Engine Shop Carbureator leaks with electric fuel pump conversi

I replaced my mechanical fuel pump with an electric pump, and the 4 barrel carb leaks in the inside at the 4 jets so when I shut the engine off it floods the engine. I put a fuel bypass regulator in and I still have the same problem even with the fuel pressure at 4psi. so what can i do to remedy this? I also have the float bowls adjusted to factory settings (2 1/4''). I have the return line pumping back at the bottom of the gas tank is that to much back pressure for fuel to return?

Thanks for any advice
-Mitch

It could be too much pressure. My first thought is too much pump pressure, but if you are sure you have only 4 psi and you didn't do anything else you're not saying, then on to the back pressure thought. First thing to always do when you have a theory, is test it in a fool proof way. All I can think of right now is take the return hose off, plug it so gas doesn't leak from tank, put another hose on pump and run into a gas can and see if relieving the back pressure stops the carb leak. If it did'nt leak before with a mechanical pump you know it's the electric pump. Why the hell do you want an electric? they are for fuel injection and blowers and huge carbs. What carb do you have? If it's a Quadrajet or equivalent, it wants 5 1/2 to 6 lbs. Put the mechanical back on. You need to tell us the engine, the vehicle and the carb. When you ask for help, always tell what you have. Since you are new, you're forgiven. I don't know what "float bowl adjustment to 2 1/4" means. Never heard of 2 1/4 inches, the whole bowl section isn't that deep? Are you talking idle screw turns? BTW I am not very up on electric pumps so........Good luck Atkins. Bartamos.

Knowing what carb you have would help. You might have picked up some foriegn material in the needle valve. Try this. Turn off the pump & run the engine till it uses all the gas in the carb & dies. Restart the engine. If it is dirt in the needle & seat this will usually wash it on through.

I usually do put the info up but my question is a blasphemous one, my post pertains to a car not truck question here, a 1956 Oldsmobile Super88 Rocket 324 V-8 4 barrel GM (Rochester) Quadrajet. After going through 4 classic trucks I felt like trying out owning a classic car and making my friends use their trucks for my projects to compensate. I've found that the classic car forum people have no idea what they're talking about, so I like to stick to classic truck forums where people fix the problems themselves. I always use these classics for my daily driver. I always stick to keeping a mechanical pump but being a college student I go the cheap route, turns out a mechanical pump for the Olds Rocket V-8 is 300 dollars while a electric pump is 85 dollars. I rebuilt the carb and cleaned it very thoroughly. With the air horn off, (top part of the carb) and holding it up the floats are supposed to drop down to 2 1/4''. This is my first carb that has more than one barrel so I'm learning as I go. I'm going to go test this back pressure theory and report back, but thank you both your advice.

Being young once upon a time....................and knowing Qjets like I do.... you are reading the instructions wrong, like I said it ain't no 2 1/4", you are looking at the wrong column. And you probably have other mis-assembly problems also. Sorry, but redo it and re read it. Too much gas means the float is set too high. From the top of the bowl to inward of the tip of the float about 3/16 is about 1/4-3/8. This is the adjustment to the float you care about, while holding the valve end down into the seat with gentle force and being sure the hinge pin does not raise up, measure from the bowl rim as I said above. You don't care about how much it goes toward the bottom when released, that is a given when the other is adjusted correctly. Also you could have gaskets on backwards or flipped and causing vacuum leaks. On early rochesters the plugs leak and need jb weld and some carbs leak around the throttle shafts. No cars.... next time we will put the stovebolt curse on your super 88 and it will morph into a Yugo.
Eliminate the back pressure theory first then chop, cut and rebuild your Qjet, carefully!!!!! on the bench, with good light and NO Pabst!!!!!!!!!!!!!!! Yes we always read the Bio. NOBODY can do a qjet right their first time, everything has to be right, no forcing of rods etc. or it's wrong!!! It's hard to "close up" after assembly, you need four hands. There are 30 things you could have done wrong. The always upbeat and positive, Bartamos.

A stock 56 Olds would not have a Rochester Q jet carb, it would have a Rochester 4 jet carb. They are completly different. Unless you changed the manifold or use an adaptor the Q jet will not even fit on the stock manifold.
Fred

56Trk is correct. It is a 4 barrel but not a Q-jet. You are measuring float drop. It does not effect driveability. You need to measure the float level if you already havn't. Take the top off & make sure there is no gas in any of the float pontoons. These are the brass floats & are nortorious for leaking gas into the float. Hold it upside down & maesure the float level acording to the direction sheet.

Yes the Qjet is a spread bore and the 4GC is a square bore. That's a good point that it was a square bore in 56. The same advice as per above still applies. Assume that you got the correct kit? These would not be easy to find except at the carb doctor.

Okay here's the shop manual for this carb it's pretty straight forward on how to adjust it. Unfortunately unexpected guests with unneeded Pabst showed up last night, and postponed my work so I'll go and fiddle around and see what can be done right now. The picture I scanned turned out small but shows you that you bend the float tang and measure the drop 2 1/4. I'll try and reduce the float level and disconnect the return line and pray to the Oldsmobile Engineer gods that it works. And just to clarify when I say jets I mean the 4 Venturi things, and I'm pretty sure their gaskets are not leaking. I'll post a link of a video to show whats going on just to clarify as much as I can.

Heres the link to the photocopy---->

[IMG]http://i945.photobucket.com/albums/ad291/victrolarepairman/rochestercarb.jpg[/IMG]

Alright here's the video of the issue, if you look close you can see a Mosquito made his way in there. But It leaks like that and is obviously terrible on engine performance and wear. But vacuum read at 20psi.

Link ----->

I guess we are not getting the point through. There are 2 adjustments for the floats. The float level is described in #1 of the instruction sheet. It is critical that it is correct. The float drop is the one you circled. Although it should be adjusted correctly, it is not critical to the running of the engine. While you have it apart remove the needle valves & make sure there is no dirt or foreign material in the seat.

Saw the video, like Wrenchbender said, forget that measurement it's the one in the picture above that (float level). My post also tells you that you don't care about that adjustment. Is the noise we hear the pump? O'reilly's/Checker shows a mechanical pump for your car pn: 40050 for $40. Also Napa. You can not figure this out with a rebuilt carb (by you) and a new fuel pump idea (by you). Get rid of the electric until you get the carb right. Dripping is float adjustment, needle valve not seating, leaky float (test in the sink with water) bad timing, vacuum leaks, rebuild goof up. It sure seems like it would not idle with that leak? Does it idle OK? or do you have it set real high so it will run? 4th WARNING!!!: FORGET THE FLOAT DROP MEASUREMENT. Do a careful float level measurement. Think outside the bottle.

I add my encouragement to Mitch to set the float level, and not worry a lot about float drop.

Are you sure about the part #, bartamos?
I don't get any results when I try to look up the 56 super 88
on O'reilly, Autozone, Napa or the Airtex catalog.

regards,
Leon

Set the vehicle search to 1956 olds 88, then fuel pump. I still get a "universal" one for $34. Don't know if it fits or not. I see why he used a electric, the pump is too much money. That's why I stick with Chevys. The old pump can be rebuilt. I saw parts for them when I was searching the web for a pump. Make a diaphragm if you have to, that's what we all do in here. NOTHING stops us but money. Anyway, I'm done.

Yeah the websites say they have the parts but the arm that goes in the block is way to short, that's one thing you can trust me on I checked. Bartmos, Wrenchbender thankyou for getting that involved in my problem. I have it idle at 2000 RPM for moving it around.And yes thats the noisy pump running, I'm planning on hooking it up to a oil pressure sensor so it's not on when just the key is on and the engine isnt running. I'll reset the float level and see if it's the remedy. The way I interpreted that diagram was for leveling the float bowls. But I'll do as the elders command. On single barrels the float tang has the needle rest on top of the tang so when you adjust that everything is adjusted. Just to explain my confusion.

Okay got it to stop leaking by setting the float level, thankyou guys for the help.

Mitch

Glad you got the leak stopped. Now is the time to set the float drop.

Understanding why an adjustment is made makes doing the adjustment easier.

The float drop adjustment is too prevent the float from hitting the bottom of the bowl (center section) if all of the fuel evaporates from the bowl.

So, measure the distance from the top of the bowl to the bottom of the bowl at the point where the lower part of the float would hit if allowed to do so. Subtract 1/16 of an inch. Turn the airhorn (top section) such that it is in its normal upright position with the floats hanging down. Bend the float arm tang such that when down the lowest point of the float is at your adjusted measurement. Now recheck the float level adjustment; easy to get the float level out of adjustment when making the drop adjustment.

Jon.

What happens if the float hits the bottom, electrical short? No, really.

The world comes to an end!

More seriously, when modern fuel evaporates, it leaves a gummy substance which makes a great glue. Allowing the float to hit the bottom of the bowl allows the "glue" to affix the float to the bottom of the bowl, and when the owner attempts to start the vehicle, the float will not shut off, and fuel goes all over the engine.

Jon.

Float level and drop are extremely critical on 4GC carbs. The float chambers are so small that if the level adjustment is even a little bit low, the bowl gets sucked dry on full-throttle acceleration, and the engine bogs. Slightly too high, and it floods. The gummy residue at the bottom will definitely glue a float down if it rests on the bottom of the bowl!
Jerry