260 -Quadrajet rebuild

[Icefire55]

Re: 260 -Quadrajet rebuild

Mine (a 350/260hp) with the same carb would run pretty nice but If I would try to go over 2500-3000 rpm, the engine would die.

Found out that the secondairy butterfly (the lower) were stuck against something and never opened.

so was only working on the primairy.

 

[joenapier]

Re: 260 -Quadrajet rebuild

I think you guys should arm wrestle.

Actually, thanks to everyone for the help so far. If anyone of you all is like me, I get involved in a project, it takes longer than I think it should, and all I think about during the project is how the **** works. I'm going to bed at night thinking about these secondaries opening up.

I'm going to reset the spring tension on the secondary choke plates and see if that helps. I also will check to see if the throttle plates below are opening like they should be. I should be able to do this later this afternoon. Checking vacuum of the engine is another step...I just hope I don't have to chase down a vacuum leak. It's hot outside here in SC!

I have another question. Of course the rebuild kit comes with several gaskets to satisfy most any qjet setup - most of them I did not need. The old gasket between the airhorn and the bowl had a small cut through between the primaries and their respective secondary. (see picture). No gasket like this came with my kit. Should I cut some gaps in the new gasket? Apparently these cuts allow some bleed over of air between the primaries and secondaries...but why?

 

[hydraulic lock]

Re: 260 -Quadrajet rebuild

As to the issue about slots in the base gasket, i believe they are to equalize between the bores, similar to balance tubes on dual exhaust on cars. Dont think it matters much, just use closest one in kit that matches yours.

KUJAWAT-mentioned to adjust the secondaries in 1/8 steps. Thats probably true, but i would go 1/4-1/2, only to make a big change first, see how it responds then fine tune in even 1/16-1/8 if needed. He has a pretty big bog, and dont forget those sec. springs can be 20-40 years old, they do weaken.

JOE- didnt say if this carb. came with the engine. Q-jets can be 700-850cfm, they have to cover alot of cubes, up to 455 or so. Dont be looking for those sec. valves to fly open on a smaller motor.

 

[hydraulic lock]

Re: 260 -Quadrajet rebuild

On second thought about those slots, change that to helping transition from primaries to secondaries.

 

[joenapier]

Re: 260 -Quadrajet rebuild

Thanks you all for the help.

I noticed online somewhere that the spring tension is 60 grams. Not sure where to take this reading (center of the choke plate, edge of the choke plate...whatever. It really won't matter as I found the plates were much stiffer than that at the edge and I will use your recommendations about how to fine tune it on the water. If I can adjust out the bog, I know it's right.

I'm not there yet, but I'm getting closer. Thanks again!

 

[full stringer]

Re: 260 -Quadrajet rebuild

recheck your float setting in the secondary bowl i bet it is closing off the needle valve before enough fuel gets to the bowl and when running at full throttle you simply run out of gas

 

[joenapier]

Re: 260 -Quadrajet rebuild

No secondary bowl on a Quadrajet.

 

[joenapier]

Re: 260 -Quadrajet rebuild

After many adjustments to the float, secondary air valves, and the ckhock pull-off - I?m convinced my problem is not in the carb. I can adjust and adjust in very small increments, but I get no appreciable ?dialed in? feedback. Always the same issue - I run at WOT for 30 seconds and then I sputter. It has to be a matter of the fuel flow into the carb (or within the internal passage to the bowl) not being able to replenish the carb bowl as fast as the motor demands fuel at WOT.

I think it must be a fuel flow problem.

I've now gone full circle - I worked a fule flow problem before I even touched the carb, but I don;t know if I fixed it because then I went right into the carb rebuild. Before rebuilding the carb, I changed the fuel pump and replaced the fuel / water separator filter.

There is the main fuel line from the tank running to the fuel pump, then lines running from there to the filter, then to the carb. One of these has to be blocked. (when I rebuilt the carb, I found several places that had a waxy greenish black gunk - probably from running that corn gas).

The rated flow rate through the fuel / water separator is 80 gal / hour ? which is MUCH more than any engine can swallow. There is a little particulate filter at the intake of the carb, and I?ll check that again.

When I get to the bottom of this, I will post the solution for posterity's sake.

 

[joenapier]

Re: 260 -Quadrajet rebuild

An additional thought -

The problem seemed to get worse and worse as I ran the boat around. I'm guessing this would NOT be a symptom of a carb issue - right?

If it got worse and worse, does that lead anyone to think it is a clogging issue? What if the next time I run it, the problem is as bad as ever - that's a clogging line, right?

Marine engines run cooler than car engines. Mine runs around 130F and then rises to 160F or so after shutoff, which I agree would be typical behavior. The fuel line is metal and pretty much runs along the engine block -could vapor lock be an issue in the fuel line?

It took aver an hour for the stubbling problem to get worse and worse and the engine reaches running temp afoer 10 minutes or so, so I'm not too inclined to think heat is an issue. Any thoughts?

 

[Bondo]

Re: 260 -Quadrajet rebuild

There is the main fuel line from the tank running to the fuel pump, then lines running from there to the filter, then to the carb. One of these has to be blocked. (when I rebuilt the carb, I found several places that had a waxy greenish black gunk - probably from running that corn gas).

Ayuh,... The Filter should be Before the fuelpump, not after...
Did you check the Tank,+ it's fittings..??

 

[Bt Doctur]

Re: 260 -Quadrajet rebuild

http://www.florida4x4.com/tech/quadrajet/index.php
best link I have

 

[joenapier]

Re: 260 -Quadrajet rebuild

You are correct, Bond-O - the fuel filter is first.