Need Help With 350 Engine

rphowell · October 12, 2007

Here's the background. My friend and I flew out to CA (from Tennessee) to drive back a motorhome his in-laws gave him. It's a 1983 Fourwinds and it had a new engine installed something like 5 years ago. I'm not sure of the engine year, but I don't think it was updated much from the original motor.

The RV drove like a new machine all the way back to Tennessee. About 70 miles from home it suddenly had a hard time running at idle. This problem has persisted to date. It also seems to take longer to start than it did on the long trip. And now it bellows black smoke while turning over and then initially when it starts. After that it seems to clear up. It's become harder and harder to keep idling.

We fixed a bunch of minor vacuum leaks, cleaned the smutty black plugs, and tried to adjust the timing a little (but can't seem to make much difference). It now is backfiring and has NO power.

We don't really know where to start. Any advice will be appreciated. We're trying to get this going on a low budget, so we want to solve this ourselves. Thanks.

Zembonez · October 12, 2007

We fixed a bunch of minor vacuum leaks, cleaned the smutty black plugs, and tried to adjust the timing a little (but can't seem to make much difference). It now is backfiring and has NO power.
We don't really know where to start. Any advice will be appreciated. We're trying to get this going on a low budget, so we want to solve this ourselves. Thanks.

Black smoke is a "running rich" problem... Sounds like an old carburetor kicking the bucket. The OEM carbs weren't much good new. Sitting for long periods was the kiss of death for them. Rubber accelerator pumps and paper gaskets dried out and cracked. Once you start using them again air and fuel leaks were common... usually resulting in a poor running engine. They probably just reused the original when they installed the new engine.

Its a good place to start. If you don't know anything about carbs, you can do more harm than good tinkering with it. I'd look for "that guy" in town that is a carb specialist. He can check and possibly rebuild it if he determines that is the issue.

Good luck.

Tucson_02Silverado · October 12, 2007

As mentioned, the culprit is the most likely the QJet. There was probably a lot of "varnish" coating the interior of the carb. Driving for a period, cleaned it up leaving some brittle parts exposed eventually failing. The quickest, although around $275, is to go to Checkers or Autozone and get a rebuilt QJet. It should start right up out of the box (well when it gets fully primed), the rebuilders put the settings 90-95% close to a good tune. Also check the fuel pump pressure, the varnish thing can mess up the diaphram in the mechanical pump as well. Mounted at bottom, right side (passenger) towards the front.

The only other thing that will eventually happen is the valve cover gaskets start leaking. The best fix is to get the more expensive Felpro ones with a fixed silcone gasket as oppose to the basic cheapy cork ones. If you do replace them, it's only like 5-10lbs of torque to tighten (finger tight then 1/4 to 1/2 turn). And add long style bolt spreaders to the cover bolts.

rphowell · October 12, 2007

Thanks for the advice from both of you. It makes sense, but I just wanted to clarify, Tucson, you are just referencing another common issue with the motor, right? The valve cover gasket has nothing to do with my current issue. Just making sure.

I've been searching on the forum and have come up with a list of things that potentially could be an issue. Does this look like a good list to you guys?

carburetor

coolant temp sensor

throttle body gasket

o2 sensor

Mass Airflow Sensor

I'm thinking that's a good order to follow also.

Tucson_02Silverado · October 13, 2007

cover gasket are another issue on the list of common known problems with the Gen I SBC v1

But like ricer stickers, the expensive chrome valve covers will make any vehicle go 2000 billion trillion miles per hour faster

Zembonez · October 13, 2007

Thanks for the advice from both of you. It makes sense, but I just wanted to clarify, Tucson, you are just referencing another common issue with the motor, right? The valve cover gasket has nothing to do with my current issue. Just making sure.

I've been searching on the forum and have come up with a list of things that potentially could be an issue. Does this look like a good list to you guys?

carburetor

coolant temp sensor

throttle body gasket

o2 sensor

Mass Airflow Sensor

I'm thinking that's a good order to follow also.

On a vehicle that old you are looking at a carb. No mass airflow sensor, throtle body, etc. Just a good old carb on a GM intake. Pretty basic technology. The black smoke you mention is the biggest clue... too much fuel. Possible a flooding carb, stuck choke, etc.

Good luck!