Bought this truck with a running 351M but issues. I've turned the 600cfm edelbrock back to 1.5 turns out on both air screws, that helped. Turned the timing back from 20 something degrees advance to about 6 (far as I know its stock, no modified cam) It idles nice and smooth now, and revs in neutral/park nicely. As soon as its under load it pops and coughs like mad. While setting timing I was watching it with the advance hooked up and its all over the place, even at idle. Its hooked on via the port on the carb. Line looks nice, no visible cracks or holes in it. Plugs are all carmel colored, not fouled, though the truck smells like its running rich, and the exhaust is putting a nice black soot on my paint by where it exits. I've tried all i can think of, and I'm not a motor guy. Starting to question if it would be worthwhile to swap out advance units hoping the diaphram in mine took a ****. Suggestions?
Easy enough to tell. put a piece of rubber hose on the unit and apply some vacuum (****) if it holds vacuum it's probably OK. The only other problem could be with the advance plate not rotating (sticking) or there could be a wire under the plate that is shorting out when the plate moves.
This is the acid test for a bad vacuum advance. If it doesn't hold vacuum, change it. In addition to the sticky plate, look for a broken weight spring. Bob
I had a work distributor in a Buick that allowed the shaft to ride up on the distributor gear under load....Caused really erradic timing and poor engine performance.
Check your engine vacuum with a gauge to make sure it is steady.Could be a mechanical problem if its not steady IE cam,valves,valve adjustment
**** test p***es. Tomorrow night I'm goin to yank the distributor and see if I can't find something in it hanging up. If that fails I guess I'll be checking rockers.
Ok. I've got a magnetic pickup distributor. Still have weights to be an issue there or is it a whole new can of worms?
If this is a stock point distributor check for worn breaker plate. Mine just broke on way back from having exhaust hooked up. Remove your cap and wiggle the points. Should not move. Common problem on these distributors. Breaker place still sold by Standard for less than 30 dollars.
OK, first off you need to check you timing with the hose off. Second, drive it with the hose off. You dont need vacuum advance but it helps gas mileage.With the vacuum off rev the engine and timing should advance smoothly. I would think at 20 degrees of timeing it would have cranked hard at hot start up. What color is the plastic on the ignition module where the wires go in? Have you checked for excessive play in timing chain?
Could be ignition breakdown, wires, cracked cap, bad rotor. If the caramel color on the plugs has a shiny look to it they could be breaking down, if it is just a normal dusty brown they might be alright. Also check the firing order. Could also be a lean condition in the carb when you put a load on it.
Found last night there are 2 fuel filters inline on the truck. Going to check them both out and get a fuel pressure regulator/guage and see if maybe its just not getting enough fuel when under load. simple and somewhat makes sense. Hopefully it works
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