Very frustrating carb problem

[Tyler]

Hey everyone...

I'm having a really tough problem with my '83 Silverado 305 4bbl:

I've owned the truck about 5 months, and I've had a rough idle the entire time. I rebuilt the original carb, rebuild another carb and finally bought a new one, all with no improvement.

The truck has always smelled rich, or at least a really heavy exhaust smell. It will run better with the choke on than it does with it off, and now has gotten to the point that it won't really idle. If it dies, you have to pump the gas a couple times to make it catch again.

I have adjusted and adjusted the idle mixture, and the richer you go with it, the more stable the idle, although it still wavers up and down.

Anything off idle, it runs very well, doesn't pop or backfire or anything of the sort, just a horrible idle.

I've adjusted the timing up and down, made no real difference. I checked the egr valve and it was fine.I re-did all the vacuum lines and even started plugging the carb ports to try to make it change, it didnt.

At this point I'm starting to consider mechanical issues although the engine seems to be sound..it only has a little over 100,000 miles on it.

Timing really out of whack? Blown head gasket or intake gasket? Can a fuel pump screw up and start pumping with way too much pressure?

It acts to me like it has a massive vacuum leak, but where?? ive searched and searched.

I appreciate any advice...

[ric]

Check the mechanical advance weights and springs under the rotor, the weights tend to rust in place and cause the type of you describe.

Also make sure the vacuum advance is really working.

Good luck

[Slonaker]

Mine had a huge vacuum leak when I got it. It turned out to be leaking at the spacer between egr bvalve and the intake. It was so rusty it wouldn't seal. I got a spacer from a junkyard, cleaned everything up, and put it all back together with new gaskets, and that fixed the problem.

Maybe use a little carb cleaner and spray it around the intake area with the engine running and see if you can find any vacuum leaks. The engine will speed up a little if you spray carb cleaner on the source of a leak.

Is your power brake booster okay? I had one with a leaky diaphragm once, and it made my engine idle really bad. You can clamp off the vacuum line to it to see if it helps.

You might also check the gasket between the carb and the intake. I have had them leak there before, too.

Slonaker

[Russell]

Believe it or not, sometimes a really LEAN condition can smell just like a rich condition, and cause exactly what you are describing

Look for vaccum leaks as suggested above, esspecially in the brake booster, the line to the tranny (is so equipped) etc, and try enriching the idle mixture.

[crawdad]

Having the exact same problem on one of my trucks. I'll be following your post closely. Maybe it'll help me cure the problem I'm having.