the_supernerd

I just rebuilt the carburetor on an '86 pickup. I have adjusted the carb idle mixture using the lean drop method specified in the factory manual. The truck runs well and the exhaust does not smell rich. Is this method good enough for a California smog check (assuming everything else works fine) or do I need to find someone with an exhaust gas analyzer to fine-tune it first?

the_supernerd

I messed with it for a while today, fixed a vacuum leak at the EGR tube, and replaced the vacuum advance as the sub-diaphram was bad. It seems now I cannot quite set the mixture properly.

If I lean it out some it hesitates when I start from a stop. If I make it richer it bucks while decelerating at low RPM (like idling through a parking lot, but not with the clutch in or my foot on the accelerator). I cannot seem to adjust it between those points. Other than that it runs very well.

I am thinking I might have another problem other than the idle mixture. Does anyone have some ideas? Any suggestions or guesses are welcome. You might save me a few $$$ at the smog shop!

grumpin

I would trace all my vacuum lines, make sure they are correct. On edit, not sure how many the carb. engines have.

the_supernerd

I think the vacuum lines are correct, but double checking them is a good idea. There are quite a few of them, and the truck is originally from Arizona so I have already had to replace a lot of the rubber pieces. I am thinking there could be a vacuum leak in a hard to find area, or maybe the EGR is not shutting all the way due to a clog or something.

Kiroshu

X2 definatly sounds like incorrect vacuum hose routing. Verify that with a good diagram. Take your time and put all the hoses where they should be.

Hesitation/stumble on acceleration and deceleration could be a fault with the fuel cut solenoid and or the vacuum decel switch.

the_supernerd

I will definitely re-check the vacuum lines as I have only given them a quick check. The diagram on the hood is still in good condition and I have the FSM, so I will compare and make sure they all match. Someone messed with this truck before I got it and it appears they did not know what they were doing, so there is a good chance the hoses are in the wrong place.

The fuel cut solenoid did cross my mind as the problem seems to occur when the fuel cut solenoid kicks back on at about 2000 RPM while decelerating. The vacuum switch kicks on at about 15mmHG of vacuum and the truck stalls when I unplug solenoid. Can you think of anything else I should check regarding the fuel cut system?

the_supernerd

I have been messing with this truck quite a bit now, and the vacuum lines appear to be in the correct place, the smog controls are working properly, and I cannot find any more vacuum leaks. It seems like I have to set the idle mixture too rich for it to idle smooth, but then I get the jerking on deceleration problem. If I set it lean enough to get rid of that it idles rough and surges.

I had to combine parts from a couple of carburetors when rebuilding it since the original had some un-fixable problems. I am thinking maybe the secondaries might not be sealing completely when closed (which would basically cause a vacuum leak), or if that would even cause the problem I am having. Anyone have any more suggestions before I take it in for smog and hope for the best?

the_supernerd

I figured I would post an update in case anyone else is having similar problems. I replaced the EGR with a spare that I had in my garage, and I noticed the large vacuum hose going to the mixture control valve was slightly loose. The EGR seemed like it took very little vacuum to open compared to my spare, so I am thinking the spring wore out, which was causing the off-idle hesitation. I am also thinking the loose MC valve vacuum line could possibly have caused the deceleration jerk.

After fixing those problems, I was able to enrich the idle mixture to where the truck runs decent and it passed California smog.

grumpin

Good news. Sometimes its amazing these things run with all the vacuum lines.