Let me preface this by saying that I am an IT guy, not a car guy. I can do basic maintenance on my car and am usually fairly good at figuring out what is causing issues, but this problem has me stumped.

My 87 truck backfires, surges forward, and then will sputter almost to the brink of stall. Occasionally it will stall out when decellerating up to stops signs and the idle appears to be a little rough.

This ONLY happens when the truck has warmed up.

So far I have done an Sea Foamed the carb, changed the fuel filter, and changed the spark plugs. The spark plugs were black, as in so black I'm surprised that the thing even started up. If I adjust the warm idle screw on the carb to raise the RPMs it appears to run a little smoother, but this is only when it is almost as high as the cold idle.

I will also state that I have lost my muffler and cat a couple years ago, but I'm not sure that has anything to do with the issue at hand.

Does anyone have any thoughts?

 

Sounds like maybe a bad fuel pump. With engine rpm higher it pumps faster since it's mechanically controlled. Could also be the carb is flooding out for what ever reason. Maybe a bad internal fuel pressure regulator. (there is no external one on the carb trucks) If you can verify the fuel bowl level in the sight glass on the front of the carb.

Also check your ignition timing. It should be 0 degrees.

Here is another reference you might check out as well. AAP diaphragm being one of them. Sometimes the diaphragm goes bad and it sucks additional fuel into the carb flooding it out. http://www.bluebassdesign.com/boonin/carb_faq/#aap

 

Just a quick update. I checked the AAP diaphragm and that doesn't appear to be the problem. I haven't had a chance to run out and get a new fuel pump yet. I did notice that I can let it run for an hour sitting idle without any problems. In order to recreate the problems I MUST drive it. Within 6 trips around the block the issues start. Hopefully that helps give someone an idea of what it could be.

 

Ok, sorry for the long delayed response, I just got back from vacation. I replaced the fuel pump with no luck. I can see fuel in the sight glass, not sure what it should be at. Does anyone have any other ideas?

 

Have you tried spraying carb-cleaner around the carb/hoses when it is idling? That trick can show you if there is a vacuum leak.

 

I sprayed carb cleaner, but didn't hear a difference in the way the motor ran. I did my best to inspect all of the hoses, and didn't see any holes or damage.

 

I had the same problem with an 87 truck. I removed the smog/egr equipment and the problem went away. Start looking there. replace all the hoses even if they look ok.

 

Did you ever figure out yr problem? I am running into the same thing....Thanks