Story of the demon posessed Quadrajet

[mountainexplorer]

When I got Dillon's '84 K5, he said the carb was bad, despite it being rebuilt twice. I picked it up and towed it to the lake I stayed at (Mason Lake) and checked it all out, fixed a wiring issue, put a battery in it and it fired up.

At this point, I was wondering, what's wrong with the carb? It idled fine, didn't smoke; ran so good I decided to take it to a day Seattle trip rather than lug around the 25ft motorhome. It started loading up once on the trip, blew out some black smoke, but cleared out. Did that again once before I hooked it up to tow it home.

I get home, and it seems to load up and sputter and backfire when it's cold, but clears out when it warms up and smooths out. So I get used to that. I drive it to Ione flawlessly. Does the same thing every time I start it up cold, but it would clear out and smooth out when it decided to, and I used it up there to do a few things.

Then I put 3/4 ton axles under it and a 6" lift and 35's, and tow my trailer with it back to Spokane. Runs fine, but starts getting a bit warm on the temp gauge as I'm entering Spokane city limits.

As soon as it gets hotter, it starts backfiring. When I say backfiring, I mean louder than gunshots. Kind of like a huge cannon being fired. I tried getting it all the way home with it loading up and backfiring along the way. I had people staring at me, slowing down, looking around, and I ran one guy off the road- when it backfired once so loud the car next to me swerved across opposing traffic lanes and went up onto the sidewalk and got out of his car and looked around cautiousely, only to see a red/white K5 and trailer lug up a hill sputtering.

Because of it's irratic nature and such loud backfires that sounded like an electrical/spark issue, I theorized that the carb itself may not be the culprit. 305 Motor came out, 454 went in it... bypassing the '84 spark control computer and using a different distributor. The 305 and carb sat since then.

Last week, I took the carb and put it on my '77 K5 with a 350. Fired right up. Ran smooth, didn't smoke or backfire. I drove it around a little (just the neighborhood). Moved it the other day, and it ran fine. Then, I go to start it and move it again, and it starts loading up. I rev it up to clear it out, and it starts acting like it's about to let off another cannonball again. So I parked it and shut it down.

Appearently, the demons haven't left this carb yet.

 

[steve_kibbe]

I ran one guy off the road- when it backfired once so loud the car next to me swerved across opposing traffic lanes and went up onto the sidewalk

Thats really wierd, timing and all is fine? It seems like the advance isn't working

 

[mountainexplorer]

Well, it would go from running perfect to backfiring and loading up and blowing black smoke and vice versa without me changing a thing.

And now the same carb starts doing weird things to a perfectly running motor that never had an issue before. I had really thought of timing, electrical, or a distributor problem on the 305 in the '84, but now it just does seem to be the carb itself thats posessed.

 

[1-ton]

Carburetors don't really cause backfires...exhaust leaks, vacuum leaks, and incorrect timing do. That is what I would look for. The description of backfiring when it is cold, but not after it is warm sounds like some type of leak that seals up after it is warm, but then the leak comes back when it is really hot.

 

[mountainexplorer]

Yeah, I had eliminated the carb in my mind as the problem. But now it's doing the same thing on a 350 in a '77 K5... completely different motor, different rig. I had a different Q-jet on it off a 4spd truck (no kickdown bracket) and it ran just fine with that. After a few days of the other Q-jet on it, it starts doing the same thing.

 

[kgblazerfive]

They don't call them qudra-junk for nothing Just use it for target practice and be done with it

 

[koldsimer]

They don't call them qudra-junk for nothing

Funny how it's always FI'd guys saying this. My Q-Jet starts my blazer on it's side... good enough for me. As for your carb mounatinexplorer, something is sticking. Have fun.

 

[diesel4me]

too lean somehow..

A super lean mixture will cause backfiring,like when you try driving without a choke in cold weather right after starting..your needle and seat or float might be sticking closed just enough so it still gets barely enough gas to keep it running at times.I had a Q-jet on my GTO that ran like dogdoo(stalling at idle,rich smell,loading up) until it reached 195 degrees on the temp gauge,then like someone flipped a switch,it would smooth right out and idle fine..but it never backfired once..

Have the wells been epoxied in the base of the carb,where those plugs always leak??..could have a crack there that opens and shuts according to teparature..

Are you sure the OEM paper fuel filter is in right(if it still has one!)..
I put one in backwards one dark night,with the wrong end facing the fuel line!--and had a herky-jerky ride for 65 miles on the highway,but it ran great on the side roads..I guess going 65 took enough gas for the bowl to run dry,and the fuel filter's spring would then let fuel bypass it enough to fill the bowl again,and just before I'd come to a complete halt,the motor would spring back to life,and roar up to 65 mph again,run for about a mile,and do it again!..it did backfire a few times just before shutting down too...

If none of the above are wrong,I guess I'd say shoot it too!..or better yet,put it in a roaring wood stove and melt it back into an ingot!... --there was about 500 Q-jets at the swap meet last week..like mushrooms sprouting all over the field!..too many good ones out there to be messing with that haunted one..I should have bought a few and sold them to you guys, I didn't know they are getting scarce out west..not many in junkyards here lately,but everyone at the swap meet had at least one or two...

 

[tunedportk5]

I still have the one I took off my 84 when I swapped in the TPI?