454 Problems =(=(=(

[kmyers]

Great site. Learned a lot in the last couple of hours.
But sadly I didnt find a answer to my problem.

Heres what is going on. I have a 85 C30 1ton with a 454.

The motor is bogging down under a load, back firing out the carb, and pipes.

I have replaced, The Rotor, Disp. PLug Wires,(didnt change plugs they where Tanish Smokey Grey if that makes sense) I have changed the timing the like was about a inch past the gauge(towards the pass. side of block/even side)

I moved it down to around 2degs as the gauge is unreadable.

This is all happening under a load. I can run the motor up to 3500+ rpms sitting still but as soon as I let out on the clutch thats it, back firing, no power,

I have ran some Sea Foam thru the Fuel System that didnt help.

I did get the pipes redone right before all this started(but it also had this problem before just was just happening when flooring the truck at highway speed)

I will be doing a vac test on it in the next day or so to see if that has anything to do with it.

PLease any help or ideas on this would be great, Ive been at this for weeks now trying to fix it, and Im ready to pull out a 30-06AP round and shoot it with a M1 =D lol

I dont know if this has anything to do with it. But my read lights on the bed/fenders are really really dim and I installed a tach to help work on this, the light comes on and the tach reads 0 till light goes back out(but I think thats cause I have it grounded into my trailer brake box) it was blowing fuses when the running lights where turned on.. Im thinking maybe it has a grounding problem?

Thanks a head of time.

[595sparky]

Maby vacume advance,

[rwhit57]

It could be electrical. I have no idea what you described in that last part, but if you have power going to ground it could be the problem. Without hearing about some wiring problem , I would say it sounds like it's jumped time.

[74 stepside]

Some of those BBCs had plastic teeth on the timing gears. Might cause it to jump out of time if the teeth are bad or chain is stretched. Had a SBC act the same as yours because it had a couple bad lifters too. Just keep checking. Vacuum test might help.

[BMERDOC]

Just wanted to say I saw this and I'm thinkin. I'll try to come back woth a good answer.

[72longhornTX]

The truck I just got has a 454 in it and doing the same thing. I was planning on doing a vacuum test on it Saturday. Maybe see if that is it, or try a different carb I have sitting in the garage. It has all new wires, plugs, cap, and rotor and still runs rough under load. No weird wiring here. The truck has a painless harness that is installed great.

[Rifter_Chevy]

had similar issue with a 350, it was the carb. Float was messed up, it would randomly not fill properly and run lean but then float all the way to the top and flood with too much fuel. Backfired like crazy.

[406 Q-ship]

Put a vacuum gauge on it and note if the needle is steady or not. I am betting that the needle will jump up and down, because you have a flat cam or burned valves.

[88bagedntaged]

I have had the same problem before. I'm assuming that it's HEI ?? If so pull the cap off the distributor and look at the counter weights that expand out. There are little platic bushings in them, pull the weight off because they may look ok to the eye but they wear out on the bottom side not showing its wear. Make sure they are in good working order, mine looked fine then I removed the weight and it was gone on the bottom side. Not allowing the weight to go where it needs to under a load. Let us know !!

Under where the screw driver is pointing.

Bump on that flat cam lobe.... That can be a elusive little creature !!

[SeanPaintsFlames]

I had the same problem on my Cougar a couple months ago- it came down to two flat lobes on the cam and the springs on the distributor's advance weights were broken.

I hope it's something simple for you!

[pig rig]

being a big block some times the like to eat cams and what your discribing sound like a flat cam

[Your41Plague12]

I really hope it's the advance weights being frozen up, but it could also be a flat lobe or two on the cam. Check the distributor and pray for the best, I guess.

['76 Big Block]

I got to thinking about this also, and remembered that many moons ago, I had an Oldsmobile that would run like a top, until you tried to accelerate---that problem turned out to be a wire from the pick up coil below the advanve (in the distributor). The wire would stay connected until the advance tried to work, then connection would break or get erratic----let off the gas, and things would be fine.
It's an odd problem, but things happen. To fix that, the distributor had to be pulled to replace the part.
Good Luck!

[motornut]

advance weights have done that to me