I have an 87 B2200 that I just rebuilt the engine in. IT runs fine and idles well until after about 5 to 10 minutes of driving the idles starts to drop and in short order it will stumble and stall. At this point I can keep the engine running but if I let it get near idle it will miss and stumble and then stall. As soon as the truck sits for 15 minutes or so it will idle fine again.

I installed the Weber 32/36 and removed all of the emission control devices. The EGR is removed and a block plate installed. I can't find any vacuum leaks. The only vacuum lines connected are one coming from the base of the carb to the distributor and the large one going to the vapor canister. I have a mechanical fuel pump and it seems to be pumping fine.

As far as I can tell my timing is set correctly but I am confused about whether the vacuum line should be connected to the distributor when setting it. The label on my hood seems to indicate that the vacuum line should be attached when setting the timing (6 degrees BTDC @ idle) but the Haynes manual suggests that it should be disconnected?????

Any help please??

Update: now the poor and erratic idle is constant regardless of temp... It doesn't want to idle if the choke is not at least half way on and the exhaust smells very rich when I can get it to idle...I have hunted but I can still find no vacuum leaks..

 

Well it was a plugged up idle jet which I didn't suspect since the carb is new. I don't know how the temp or run time effected it. In the process I realized that I had a stuck open thermostat, a leaking fuel pump, and plugs with too much gap so it wasn't completely a waste of time. Purrs like a kitten now.

 

WOW, I wouldnt expect a plugged jet either on a new carb but at least that was something simple. Glad you found the other problems too!! Did you get it timed as well?

 

I still don't understand why the decal under my hood seems to suggest that the timing is set with the vacuum hose attached to the distributor. The decal says:

"AT IDLE WITH DIST. VACUUM LINE CONNECTED"

I set the timing with the vacuum line disconnected. When I connect the vacuum line the timing, even at idle, seems to advance around 10 degrees so that would mean that if I set it with the vacuum hose connected that I would be retarding it around 10 degrees and I can't imagine that that would be correct given how well it runs right now so I'm going to operate under the assumption that the timing should be set with the vacuum line disconnected.

 

You are supposed to adjust it with the vac line connected so it IS retarded at idle for emissions and start-ability. You may find with your timing now you will not pass a smog check and may have starting issues when cold or hot.

 

Thanks for the advice on the timing. I wonder why the Haynes says that you are supposed to set it with the vacuum line disconnected? I will try setting it with the line connected. Fortunately for us down here in the south I have no emissions checks and it rarely drops below freezing......but it does get hot.

 

I set the timing with the vacuum hose attached to the distributor and I was surprised that it didn't make that much difference, the idle of course dropped and I had to adjust the carburetor but that was to be expected. It runs just as good as it did before. When I was having problems with the idle it was hard for me to imagine retarding the timing that much but now with the carburetor issues solved it didn't make much any difference to how well the truck runs. Thanks for the advice..

 

No problem, glad its all running good now