what the F*%K

never in my life have i seen this happen before. the 305 in my off topic truck has been giving me problems for the past month. tried differt carbs replaced the cap, wires, and such. even took the cat off and cleaned out the beads (as its one of those big oval style that the late70-80's truck have). on my way to work it just felt real sluggish and i pull over, popped the hood and noticed the exhaust manifolds glowing red hot. what the heck is causing this?

 

It may be running real lean (too much air not enough fuel) , with the motor running spray it with starting fluid or parts washer around the intake and varied parts of the engine if the motor reves up thats the sourse of you vacuum leak.

 

Ignition timing retarded, or something fell apart in your latest carb and it was drowning in fuel.

 

Exhaust manifolds run cherry red with extreme, heavy, constant load on the motor... Big loads, not just a half cord of wood.

Dragging brakes? trans seizing up? who knows..

I doubt a plugged tailpipe can do that, but maybe? Was some of the cat guts melted and gone?


Too much fuel will make it run cooler..not hotter.

 

timing checked?
if the cat was failing,there's a godd possibility the debris mate it to the muffler and plugged it.
a better description of your symptoms would help.
the mechanical advance should be checked as well.
rough idle,poor accelleration,wont rev over a certain rpm?
things like this will get us on the right path.

 

I was going to say retarded timing as well, I would check that and if nothing else unbolt the cats and try it, maybe some guts from the cat(s) came out before you cleaned them out and block up the muffler(s).

 

plugged or inner exhaust pipe collapsed

 

be very cautious with this method,i lit up an engine compartment doing this.shoulda let it burn,but it was in my garage.
i use water in a spray bottle to check for vacum leaks.just as effective without the pucker factor.

 

Sounds like plugged exhaust to me. I would drill a hole near the manifolds and put a pressure guage in. Check the back-pressure while revving the engine.

 

Piston return spring ?

 

That didn't take long...

 

Back in the 70's gm had a problem with there double wall pipe (leading to the cat)
collapsing you may try unboling it at the manifolds and take it for a run.As stated above the mffler could be packed try seperating behind the cat and taking it for a run as well.
when I was typing the other collapsed pipe wasn't there but 2x that

 

exhaust is flowing fine, new carb base gasket, timing set and no vacuum leaks.

 

Have you checked that the harmonic balancer ring hasn't shifted on the hub? That will throw your reference mark off and play hell with the timing...

 

Does it coast Ok down hills, or do you have to keep on the gas pedal?

 

This may be a long shot.... but is your pvc valve clogged. a clogged pvc valve would may the engine run harder thus increasing exhaust temp

 

In the early 80's (81-87) GM had a MASSIVE problem with soft camshafts in their 305 motors. Many motors were replaced at little to no cost of the original owner if they took it to their GM dealer and complained well-mannered, but loudly. I had one such car (84 Z-28). Had the same problem you are describing. Manifolds would turn cherry red. Sluggish acceleration. Run like ca-ca poo-poo. Took off the exhaust in front of the cat..... still had the problem. Replaced with a new cam kit and re-did the heads (cooked), problem went away forever ....., well at least until I sold the car. Just another idea in the basket from someone who has experienced it.

Bruce

 

Fly weights on distributor are hung up or the tuiming is retarded. Lack of timing is causing late ignition in the cycle and the combustion is occuring in the exhaust manifold instead of the cylinder.

 

How old is the timing chain? It could have jumped a tooth. Doesn't happen very often, but it does happen.
Larry T

 

Not disagreeing (you've been there), but what would go wrong with the cam itself to cause those symptoms...with no obvious rattles clanks or squeals? Maybe too much scotch, but I'm not wrapping my head around this.

 

it idles fine, no kind of noises beside the exhaust cuz i dont a clamp here at the monent. it is a 1976 305. i do know about the later 78-84 305's having cam problems, but it could that and not letting the valve open right or possible valve guides shot and not letting the valve close properly.
at this point i think its just time to off it as a parts truck.

 

sounds correct to me LOL

 

check for side play in distributor shaft, have seen this problem before, top bushing goes out and timing is all over the place, wont run right so a carb adjustment makes it a little better, pretty soon everything is out of whack. good luck

 

sounds like a timing issue

 

I think also that you have a timing problem. Maybe lean, so check the vacuum line and the distributor for advance. Lean engines start hard. retarded engines start easy. Blah blah. Good luck and let us know.

 

Just another idea - an intake leak (lean condition) can also be on the inside -gasket leaking to the engine valley- tougher to find- usually smokes out the tailpipe.

 

I agree with F&J........ Something is dragging, most likely brakes.

 

I think if it were plugged, a very large oil consumption or expulsion issue would be evident before glowing manifolds...

 

Motors bad. Buy a new crate engine.
If that doesn't do it. Get a performance exhast system.
If not that. New induction system.
If that doesn't do it. Replace all of the brakes.
If they aren't dragging. Rebuild the transmission.
All else fails, check the Piston Return Spring.....

 

I had a 81 Chevy pickup with a 305 as well with much the same problem. We tried everything, it turned out to be a harmonic balancer problem .