390 troubles
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390 troubles
Hi guys,I had a problem here that I was hoping that you could help with.I just recently replaced the points in my 390,gapped them and everything,all appears to be right inside the distrubutor.When I assemble everything,the engine turns over very slowly,like it is hanging up or something.But when I take the rotor off,it turns over very quickly.Does this sound like something is wrong with my cap and rotor?I have never seen anything like this before.
Also,side question,what does a typical Vin number for these trucks look like?
thanks
Also,side question,what does a typical Vin number for these trucks look like?
thanks
Post Fiend
Joined: Feb 2000
Posts: 5,130
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From: Brea CA
Sound like your timing is way advanced causing the motor to buck when started.
Recheck you point gap to make sure it's set correctly while on the exact peak of the cam lobe. 0.017" should be the gap unless you have a dual advance vacuum canister.
Then check your timing with a timing light. Start at 6* BTDC.
Recheck you point gap to make sure it's set correctly while on the exact peak of the cam lobe. 0.017" should be the gap unless you have a dual advance vacuum canister.
Then check your timing with a timing light. Start at 6* BTDC.
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Yeah,I gapped it at .017 at the peak of the cam lobe,triple checked that over and over.I agree that it sounds like a timing issue,but the one thing that I can't get over is the fact that before I replaced the points,it ran fine(till the points went bad)What happened to the original points is the plastic block that opens the points(the one that touches the lobe),was wore out,it had been there so long.But right up until that point,it seemed to run fine.
Post Fiend
Joined: Feb 2000
Posts: 5,130
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From: Brea CA
As the points wear your timing retards. Maybe the timing was set with worn points and now with the bigger gap the timing is advanced? I used to know the number of degrees for each .001" change in gap but that was yesterday....
Or, maybe when you tightened the screws for the points, the vacuum advance plate shifted and now it's cocked in an advance position?
Or, maybe when you tightened the screws for the points, the vacuum advance plate shifted and now it's cocked in an advance position?
Post Fiend
Joined: Feb 2000
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From: Brea CA
Thinking out loud here...
Maybe something happened to the mechanical advance and the breaker cam is running advanced now? Try rotating it with the rotor on to use as a handle. It should smoothly rotate without any binding in one direction against spring pressure and return to it's resting position without any or slop or play at the end.
Maybe something happened to the mechanical advance and the breaker cam is running advanced now? Try rotating it with the rotor on to use as a handle. It should smoothly rotate without any binding in one direction against spring pressure and return to it's resting position without any or slop or play at the end.
Post Fiend
Joined: Feb 2000
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From: Brea CA
or maybe somehow the whole distributor moved during the process and it's now advanced, seems unlikely but?
If the condensor wire broke or it opened up internally, that would severely retard the timing like around 14 degrees or more. If it shorted you wouldn't get any spark at all. (interestingly, you can run without a condensor if you advance the timing back up to normal but the points will burn up quick with all the arcing.)
just drawing at straws now.
If the condensor wire broke or it opened up internally, that would severely retard the timing like around 14 degrees or more. If it shorted you wouldn't get any spark at all. (interestingly, you can run without a condensor if you advance the timing back up to normal but the points will burn up quick with all the arcing.)
just drawing at straws now.
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I honestly don't know.I just decided to recheck the firing order,and voila,engine running.Runs good too,took it around the block to make sure everything is running right,did advance the timing a little bit,as it seemed a lil retarded.Thanks for all your input BB,I preciate it.Will prolly be asking more questions,as I continue bringing this truck back from the dead.
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