Re: inline six woes
I agree with Quest's comments- what does your timing mark say when #1 cylinder is at TDC? If it lines up at "zero", then good. If not, the timing gear chain may have jumped a tooth. Timing is everything...
- you should also be able to spark all of your plugs one at a time, if one is not firing, then this could explain the unburned gas you describe. BUT, running on 5 cylinders would be very noticeable.
- have you taken off the valve cover to see the valves in action at idle? You should see that they all are lifting about the same. A flat cam lobe will make your engine run like doo-doo, as you describe, but it will be "running" on all cylinders.
- have you done a compression check on the cylinders? This could reveal something. Do it "dry" first, then "wet" with a squirt of oil. If your valves and valve train are working properly, then a compression test "wet" will get you a higher number, if not, then the problem may be in the valve/valve train.
- the power brake booster; remove the vacuum hose from your carb manifold vacuum and plug it such that it does not leak, and take it for a spin. Maybe the booster is leaking internally allowing unwanted air into the engine? Not a common problem, but you may find something here.
- the carb; what is the history? If you bought the truck and it has always had the problems you are describing, this is worth investigating. I don't know anything about single-barrel Rochester carbs, but if there is something in your carb that does not belong, like a jet/metering rod that does not belong there. You might want to consider taking the carb off and paying somebody old-school who does this for a living go through it and rebuild it to factory specs. Probably will set you back about a bill-and-a-half. Carburetors can be a bit tricky, even single barrel ones.
I was battling a carb problem with the accelerator pump after it was rebuilt and came to find out that the leather cup (umbrella) was no longer being made, the replacement style was an O-ring on a detent acc pump shaft that was simply rolling itself off and dislodging itself, but this only caused me problems in starting it- once I got it running it ran fine, but getting it fired up was a real chore.
Hope this gives you some help along the way and gets you and your truck happily back on the road.
Cheers,
Jim
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Jim Jantzen
Tempe AZ
63 GMC K1000 Sub restored original
63 GMC C1000 Sub original
65 GMC C1000 Sub OEM modified
72 GMC 1500 Super Custom SWB original
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