Black Smoke At Idle??

[Dave1]

My 1986 GMC 3/4 4WD pick up truck with stock 350 engine and 200K miles is blowing black smoke and spitting some black liquid out the exhaust pipes while at idle and has very rich exhaust fumes. I checked the choke plate and it seems to be free but is not perfectly verticle/straight up & down. It doesn't look like it could be causing a choking condition.

 

I am guessing the problem is in the carb. Any ideas what is wrong with it and/or what the fix will be? If it is the old carb, should I rebuild or replace?

 

Thanks, Dave

[mazingo]

How does it run under a load? at idle? partial throttle?

It sounds like it is flooding or loading up at idle the liquid is probably just moisture, but the black smoke is raw fuel. Could be trash or a falty needle valve not sealing all the way. if it is the carb and you are not to familiar with rebuilding one, you might be better off buying a reman or an aftermarket carb. hope this helps.

 

 

ps try some carb cleaner and or sea foam first

[Dave1]

If my problem is an internal carb situation such as a float or needle valve sticking, how can carb cleaner or Sea Foam sprayed into the throttle plate area help?

 

I have seen brand new replacement carbs in part stores for $200+. Are they good ones? When buying one of those, is it a bolt on and go application or does the carb require "tuning" for proper air/fuel/lean/rich mixture?

 

Dave1