quadrajet problem

[gpane]

hi, i have a 1985 galaxy 21' with an OMC GM 305 5.0l and 800 stringer drive. I have an original quadrajet, rebuilt it put it back on but now seem to have a vacuum leak at carb. Engine runs fine at 1200 rpm but when bring it down close to idle it stalls but at around 800 rpm it runs but have erratic rpm( surge up and down)and I also don't get any response at all from idle mixture screws whether i turn them all the way in or out they have no effect. sprayed carb cleaner around carb and found rpm increase around hold down bolts mainly rear ones and around accelerator plunger. Took carb off again and replaced plunger, examined inside again; hanger rods are not bent, float ajusted to right level; replaced again and still have same problem. Checked manifold for leaks with carb cleaner but none and engine dies if I cover the choke opening. Choke also operating because it opens when engine is warm. Please help with any ideas. Thanks! This is a carb I bought to replace another so can't explain if had problem before, but carb is very clean and i did rebuild and adjust to specs.....

 

[denniz]

Re: quadrajet problem

Hey Gerry P, take the carb off flip it over and tighten the two phillips screws on the throttle plate. If you rebuilt the carb they shouldnt be loose but if you neglect to tighten that bottom gasket it will suck air. Letting your air idle adj. be all out of wack.See it all the time.D

 

[gpane]

Re: quadrajet problem

when i took the carb back off definitely did check those two screws, they were tight and still same problem

 

[magster65]

Re: quadrajet problem

When it's running poorly, look down the carb to see if it's flooding. If it is, reset your float height. If it's not you may have missed a little dirt that's stuck in the idle circuit. Also, if it's cold and humid where you are, your carb may be icing a little.

 

[Bondo]

Re: quadrajet problem

Ya, + the Rottenchester is Known to Wear around the Throttle shafts,+ Leak air there...

 

[wheels4]

Re: quadrajet problem

Ditto the throttle shafts.Call summit racing 1-800-230-3030 they have marine app. parts as well as auto. parts with great prices.Or get a remanufactured unit some rebuilders sleeve the throttle shaft.( if thats the problem)Start your engine and spray carb cleaner around the throttle shaft.If your rpm picks up you have a leak if not thats not the problem.Good Luck,Jonny

 

[proline2]

Re: quadrajet problem

gerryp; I had similar problems on my 3.8 OMC with Quadrajet and 800 outdrive when I rebuilt the whole engine a while back. I had erratic rpms, no effect from idle screws, acted like vacuum leak. I tried everything, but couldn't pinpoint the problem. I had rebuilt the carb and rechecked everything for adjustment and tightness.I took the carb to the local engine rebuilder who told me he would show me where it was leaking air. He found nothing. I had another engine rebuilder work on the carb and guaranteed me it was a vacuum problem, but couldn't find it. Eventually I started testing and changing parts other than the carb until it started running smooth as silk. The problem was a bad condenser, the last part I would have suspected. You might also check your coil to make sure it's putting out correctly. A couple years ago my coil developed a pinhole leak and lost it's fluid. It ran well enough to get me on the ocean but wouldn't get me back. It took a while to track that down too, but when I took the coil off and noticed how light it was I changed it and end of problem.

 

[gpane]

Re: quadrajet problem

I tried putting new thicker base gasket and started engine. sounded fine and sprayed around carb didn't get any leaks, tried to lower idle and again once around 800 rpm started to surge and got rpm increace near hold down nuts and top of accelerator pump. Have new coil from aaa marine and installed, same problem. Also I replaced points with petronix kit couple years ago. Anyway I disassembled carb again and inspecting closely noticed sligh opening in rear of carb body( on top side of that indentation on back of carb) about size of med. tip flat screwdriver....is that supposed to be there? and also on front throttle side there is an open hole which when i sprayed with compressed air came of a small hole on bottom of carb body is there supposed to be a plug there?