[Chevelle-list] OT - GMC TRUCK HELP

[Larry Shouse]

I'm hoping some of you my be able to help with a couple of questions I have concerning my 1970 GMC truck. It has a straight 6 250 CID engine with a 3 speed manual tranny and a 1 barrel MonoJet carb.

First question is on timing. My service manual says to refer to the sticker under the hood for timimg, but my sticker is long gone. I did find one of my old tune-up guides from the 70's that says on L6 Chevelles, it should be 0 degrees on automatics and 4 degrees BTDC on manual tranny vehicles... Should I go with 4 degrees BTDC? Also, each mark on the timing guide by the flywheel on these things is 2 degrees right?

Second question is on my carb. While accelerating normally, it starts to spit and sputter at around 2000 rpms, then clears up at around 2500 rpms or so. While it's doing this, I see black smoke coming out of the exhaust. Before and after this rpm range, my truck doesnt smoke. Well, it does at red line but that's gray smoke and I thing an entirely different issue with this tired old engine. Do you think in the 2000 to 2500 rpm range, it's getting too much fuel? If so, how do I fix it?

Thanks for your help guys.

Larry Shouse
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