Any suggestions? 351 Cubes with 4 barrel. engine was rebuilt 33,000 miles ago. The following emmisions items have been replaced and checked for proper functioning in the last 33,000 miles; pollution pump, check valve, egr valve, replaced catalytic converter, points, dist cap, wires, rebuilt carb.

THE PROBLEM; with the idle mixture screws set at two turns out from bottomed, the truck idles rough( like the mixture is off, splashy miss). If I turn the screws out to about 3-1/2 turns out total it smooths right out. That said, I have for the passed two years failed the emissions test with too high of an HC output at idle. I f the screws are turned almost to the bottom -out position it will pass. This has been the case with two different rebuilt carbs.

THE OTHER PROBLEM: during the last 33,000 miles I have had a problem that comes and goes that seems to come more than it goes! I can be driving the vehicle at highway speeds and it runs great. When I come to a stop after that high speed and sit at a light for a minute or two or if I am just driving through your typical stretch of shopping centers and traffic light congestion and have to sit at the light for several minutes I get this really bad smell out of the tailpipe. It used to smell like rotten eggs but lately it is not quite as rotten as it was but is still bad. The problem seems to appear faster and more often the hotter it is outside. This winter it seems to be showing up more regardless of the temperature. I tried changing gas stations, have checked for vacuum leaks, emiss. hoses hooked up wrong, the timing, etc. I read something about a hot idle compensator but I don't know if I have one. I don't think I do and I don't know if that could be a problem. Thr truck does not have a dashpot, only a soleniod similar to a dashpot that only functions for idle up with the A\C on. I have had the smell both with the idle screws turned way down and with them out at smooth idle. Has anybody got any suggestions as to what is causing the idle and stink problems????
I am wondering if the two are connected.
Thanks for any advice you can give me!
P

 

First of all, that rotten egg smell usually means a plugged cat. converter. You said that was replaced, so maybe your exhaust is too hot, pointing to a "too lean" situation.Your idle problem sounds like a possible vaccume leak, causing a "too lean" situation. I would check for vaccume leaks, you may just solve both problems. Check all vaccume hoses for deterioration. If no problems are found,check for carb gasket, and intake manifold gasket leaks. While engine is warm and idling, spray WD-40, or carb cleaner around gasket areas. If there is any change in engine RPM, either up or down, you have a leak. Hopefully this helps.

Nathan

 

Nathan:

thanks for the advice. I replaced the intake gaskets a while back and was hoping they weren't the problem. I'll check them and carb gaskets for leaks. Thanks. You know, it's funny, I had the converter go out on a trip to south texas and had it replaced . The rotten egg smell started as soon as I picked it up from the muffler shop. They said it had to be something in the fuel delivery, "couldn't possibly be related to new converter". I know that is probably the case but it sure makes you wonder. Other than the emissions failure at the inspection station and the splashy idle that adjusts out with idle mixture screws it runs pretty darn good. I should have gotten bronc with EFI! Thanks again,
pensar

 

Bear with me here, but did you look at your new converter? You wouldnt be the first person to get stiffed by a mechanic. Is is possible that they installed another used cat after seeing out of state plates, figuring you would never come back and call them on it? Its just kinda funny that you didnt have a plugged cat smell untill it was replaced. Keep us informed on the outcome. Good luck

NATHAN