I have an 87 3.9l carbureted and I noticed black smoke coming out of my exhaust. So having just replaced the carburetor I thought it must have been running too rich. I hooked up my exhaust gas analyzer and turned the mixture screws until it improved to about 4 or 5% carbon monoxide emissions (from the tailpipe). After that I put the truck in gear and set the idle speed to the spec listed under the hood (700 rpm). However now when I put the truck in park or neutral it races and then when I put it back in gear it jumps. What could be going on? Any ideas on how to fix this?

oh ps. the truck has a bad valve (not sure if that would have an affect).

 

i would check your vacuum lines to
a) check to see if they are all in there correct location and
b) to see if there are any cracks or splits in them

 

I think I know just the vacuum line that might need to be done (I did sort of an improvised fix on it which is probably not doing the job). Although simply replacing all of them, though a lot of work would probably help a lot (since they are 22 years old).

 

I think I know just the vacuum line that might need to be done (I did sort of an improvised fix on it which is probably not doing the job). Although simply replacing all of them, though a lot of work would probably help a lot (since they are 22 years old).