Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
'78 Suburban 'chugging' on long grades
RyanAK:
Thanks, Keith. Appreciate the response. Two quick things...
Truck ran strong and without incident all winter and spring. Seems to have become an issue with the onset of hot, humid weather. Is this something to consider, or just a red herring?
And...
When it does this, it
Cliff Ruggles:
Couple of things I would do.
First order one of my SR rebuild kits and go completely through the carb.
My kit will have the larger solid (not windowed) .135" fuel inlet set in it. I'll bet at some point the carb was kitted with over the counter parts and it has the tiny N/S assembly. Even with the little 350 stock crate engine I've seen them suck the bowl low or dry with the smaller fuel inlet seats.
During the rebuild install my filter/spring w/o the check valve in it. The check valve is not needed when you use the solid fuel inlet seat and it is very restrictive.
Check the power piston and polish it up with some 600 grit auto body sandpaper and brush the PP bore with the appropriate rifle brush.
I'll supply a new correct PP spring with the kit.
Set the float to factory specs and check the power piston hanger arms to make sure they are level and exactly even.
Once the carb has the correct parts in it and correct settings it will take it out of the equation when troubleshooting.
If your fuel delivery condition still exists make sure all the rubber hoses on the supply side of the pump get replaced and clamps are tight.
If all this fails to correct the issue I'd drop the tank and take a look at the pick-up inside the tank to see if it's cracked and sucking air or the "sock" is plugged up with debris.
It wouldn't hurt to move up a jet size with that carb number but if it was working fine then things went South it's going to be something else......Cliff
von:
This sounds exactly like what my '73 Monte Carlo did in the mid 70's. The culprit was a clogged fuel filter "sock" (nylon mesh) on the fuel pickup in the tank. Going up hills or on level with heavy throttle it would bog then die if I pushed it. I could pull off the road, turn it off (if not already off), and wait a few minutes. Then it would start and run fine for a while. Rust and/or sediment would evidently get sucked onto the sock and clog it, then after sitting turned off for a while the crud would evidently fall off the sock and it would run fine til the cycle would start over. The fix was removing the sock from from the pickup (tank must be removed to get to it), cleaning out the tank, and installing an in-line fuel filter between the tank and fuel pump. No problems after that even when I was towing a Corvette on a trailer at times.
RyanAK:
Great stuff. Thank you.
Ya know... When this first happened and I dove into it, I changed the filter to one without a check valve because that's the only one the parts place could get. The issue seemed to (seemed to) have gone away. Later I sourced one with a check valve and the issue returned. Could it be as simple as that?
Cliff - I'll call you to place an order for book, kit, jets, etc.
Dropping the tank will be my last move. It's a 40 gal tank and I'd need to cut the big tube steel hitch off the frame to remove the tank. Next time I'm low on gas I do intend to stick a borescope down the filler neck to try to get a look at the pick up and filter sock.
Much appreciated fellas. Now to find my spare no-check-valve filter...
R
Cliff Ruggles:
If a slight restriction at the filter is causing fuel delivery issues I'm betting you have bigger issues elsewhere. In any case I'd still do two things. Get rid of the check valve in the filter and rebuild the carb with the larger N/S. I'm betting your troubles will be gone just doing those two things.......
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version