400 Timing Issue
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400 Timing Issue
79 F-150, w/ 400, C6 trans. Engine is apparently an 82, swapped into the 79 P/U. The engine was nice & quiet to about 45 mph then it started to sound like a diesel. Suspected timing advance so pulled the vacuum line to the advance module, problem confirmed. Noise goes away. Obviously the vacuum advance is causing the valves to open too early and I am hearing the detonation of the fuel mixture in the cylinders.
Have retarded the timing (originally at about 10 degrees) and the clatter doesn't start up till about 60 mph. Pulled the vacuum line and it's stays quiet all the way up past 80. (Don't mean to imply that the noise starts up again after 80, just didn't push it any faster than 80ish).
Should I retard the timing a little more? Is there some other problem that I should be looking at?
Have retarded the timing (originally at about 10 degrees) and the clatter doesn't start up till about 60 mph. Pulled the vacuum line and it's stays quiet all the way up past 80. (Don't mean to imply that the noise starts up again after 80, just didn't push it any faster than 80ish).
Should I retard the timing a little more? Is there some other problem that I should be looking at?
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From: chicago burbs
BTW, the vacuum advance doesn't control the valves. it controls the moment in relation to the crankshaft/piston that the spark occurs. the camshaft controls the opening and closing of the valves.
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Yeah I got that, but it's still causing the timing to advance so the valves are open during the fuel burn. At least I think that is what I'm hearing. Have tried turning the allen screw about 1/2 turn this afternoon, but ran out of gas (grrrrrr, stupid guage). The bad news is after I got it filled up, the problem was worse. I'm beginning to suspect the vacuum advance unit. With the vacuum disconnected it sounds great.
Will crank it out some more and see what happens. Thanks.
Will crank it out some more and see what happens. Thanks.
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From: chicago burbs
if the intake valve was open during the fuel burn, you would have flames shooting up out of the carb and very loud violent noise with it. is it possible that the vac hose to the advance unit is not coming from the right place? what is the vacuum source?
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From: in a house
you shouldn't see much change with only 1/2 a turn. there is about 13 total turns of adjustment.
start w/ about 2 turn increments before you fine tune it.
and if you feel a springy little pop while backing it out, well thats the end of its adjustment.
start w/ about 2 turn increments before you fine tune it.
and if you feel a springy little pop while backing it out, well thats the end of its adjustment.
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