The Stovebolt Site Forums The Shop Area Engine Shop Engine related troubles

Recently my 350 decided to go completely out of whack and I had to retime the engine, and things were well again.

Well lately when i'm driving i'll sit at a stop light and notice a slight stumble in the engines idle, and when i try to accelerate i get what you might call, hesitation...but really a stumble. Making me think i'm not firing on all cylinders. I recently put in new spark plugs and new spark plug wires, but i haven't played with the distributer.

Here's a little info for you:
79 Chevrolet big10 silverado
350 w/ vortec heads, GM High-rise intake, Rochester Quadra-jet 4bbl carb(yeah i don't like it...but its working for now). I found out recently that whoever put this engine back together put on a counter-clockwise water pump, which makes the engine run a little warm(i need to replace it with a clockwise pump).

Hopefully i'm making sense to anyone who reads this, and hopefully you can give some suggestions as to what the problem might be...and how i might go about fixing it.

I finally have a day off work so i'm going out to check for any fouled plugs and or faulty wires. I'll update soon.

Check for vacuum leaks at the manifold to head area. A lot of people really crank the manifold bolts down like they were the old style manifolds. I can't remember the actual torque spec, but it's very low, like around 20 ft.lbs.
Scott

How old is the carb? Check for play between the throttle shaft and the base plate. Notorious vaccuum leak area!!! Spray some carb cleaner or some starting fluid around the base of the carb, and the intake flanges like Scott said. New intake? If it's used I would be about 90% sure it needs to be re-surfaced. Once torqued and used, aluminum intakes warp. Also, I don't use the rubber end seals on my intake manifolds. Especially aluminum, they tend to hold the manifold up and it's harder to get sealed to the heads. Just silicone on the ends.

Got any Stovebolts?

Its the original carb, from 79...verified by the serial number.

I'll look into a vacuum leak, thank you.

Didja have the stumble before you retimed it?

If not, then one would think timing.

Otherwise, accelerator pump workin? Have a helper step on gas and watch to see if fuel is squirted into the carb.

I'm gonna say that you might need a rebuild on that carb. But there are a few things that are cheaper to check first. If you want to check for a vacuum leak, get a propane torch bottle and with the engine running, crack it open unlit, and move the nozzle around any possible joints where a vacuum leak could have formed, like around the base of the carb, between the manifold and the heads, etc. If there is a vacuum leak, rpms will pick up when the propane gets sucked into the engine.

Another thing you can check for is a worn cap and rotor. Just pull the cap off and check for erosion. You'll usually see it on the blade of the rotor. Those are cheap to replace.

If everything checks out, then I think you might be getting close to carb rebuild time.

I wonder if your timing chain is getting sloppy. Put a 5/8 socket on a breakover bar & put it on the crank bolt. Pull back & forth & feel haw much play is in it. About 2-4 degrees is normal.

Hy Will79big10, why did you have to retime it in the first place, was the distributor hold down loose? If it wasn't loose one of the few ways the timing can change is the timing chain moving on the camshaft gear as Wrenchbender said check how much slack there is in the chain, with the distributor cap off move the crankshaft and make sure the rotor responds immediately, if not it's chain and gears time. Hope this helps.

Apparently the first time the engine retarded itself...wasn't that the distributor moved, the holddown bolt was very tight. But the first time it went off by a good 10 degrees at least.

I'll look into the timing chain senario just as soon as i get my truck back from the transmission shop, it finally decided to give out yesterday.

*UPDATE*

Ok truck is back from transmission shop, theres no stumble at idle, but when you hit the gas theres hesitation and stumble...and the occasional backfire when you let off. Backfire is rare though.

You guys still thinking its the carb? I'm wanting to get a new one, but i think my brother can get me a Road Demon for $150 from his mechanic.

Hy I don't care about any thing but how and why the timing changed, thought of one more scenario, a broken rotor tip, I've only seen it once, but I have seen it.