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#23024 03/23/2004 11:50 PM | Joined: Jan 2004 Posts: 58 Member | | Member Joined: Jan 2004 Posts: 58 | Truck runs fine for about 3 miles then starts to miss, doesn't accelarate, runs really rough. When I check the plugs they are black with carbon, heads were rebuilt completely, new carb, wires, caps, everything. Some say it's the carburator, others is the valves, others the manifold spring. I have no clue. Any suggestions, since I have no specific mechanic, I would like to know atleast what it could be before I take it in for professional help and get raped. My brother and law started it for me and then got deployed. Thanks | | |
#23025 03/24/2004 12:01 AM | Joined: Oct 2001 Posts: 3,458 Extreme Gabster | | Extreme Gabster Joined: Oct 2001 Posts: 3,458 | Fouled plugs are an indication of overly rich mixture and/or late timing. Check the timing and point gap first. Then check the valve lash warm. Finally, check the carburator. It sounds like you might have a stuck power valve or too rich a jet for your engine.
A Rochester "B" should have a 53 or 54 main jet for a 235 and a 57-58 main jet for a 261. The power piston should move freely and hold the ball off the seat when the engine is not running, but should get sucked up into the airhorn and let the ball seat with about 7 lbs of vacuum. The correct gaskets are required for the power valve to work. The most overlooked one is the spacer on the manifold, it should have notches to line up with the small hole on the base of the carb. The other overlooked ones are between the throttle body and the bowl, and between the air horn and the bowl. Make sure none of the passages are plugged.
A stuck manifold heat valve causes a lean condition when the engine is warm.
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#23026 03/24/2004 8:37 PM | Joined: Aug 2003 Posts: 264 Member | | Member Joined: Aug 2003 Posts: 264 | If the carb is running rich to the point where the plugs are fouling after three miles then there should be a lot of black smoke coming out the tailpipe. If not, your ignition coil may be weak, i.e. not enough spark. | | |
#23027 03/25/2004 3:31 AM | Joined: Jan 2004 Posts: 58 Member | | Member Joined: Jan 2004 Posts: 58 | Yea alot of black smoke, I haven't changed the coil, should I? | | |
#23028 03/25/2004 5:36 AM | Joined: Jun 2003 Posts: 56 Member | | Member Joined: Jun 2003 Posts: 56 | Make sure your choke plate is opening all the way and that the choke linkage is not sloppy enough to allow it to close.
Make sure you have the correct spark plugs, yours may be too cold for your driving, but cold plugs don't normally cause fouling that fast.
To foul in that short a distance has to be caused by an excessively rich mixture.
'31 Chevy 1 1/2 ton,
'42 GMC 2 1/2 ton 6x4,
'52 GMC 2 1/2 ton 6x6,
'53 GMC 5 ton
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