| [GMCnet] 1978 GMC 403 backfire through the carb [message #127545] |
Thu, 26 May 2011 13:17  |
rallymaster
Messages: 662
Registered: February 2004
Location: North Plains, ORYGUN
Karma:
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Jim Hupy or anybody with suggestions.
Just went out to move the coach to a level spot, so I could light the
fridge, preparatory to a long weekend trip. It started as usual, but I
could hear a faint pop, pop, pop.
I moved the coach and turned on the furnace and fridge, then took off the
engine cover.
Yup, pop, pop, etc. I revved up the engine, and it got louder. Sounded
like it came from the carb, so I killed the engine and lifted the air
cleaner cover. Restarted the engine, and there it was again. I could
also see a flash in the left side of the carb. Shut it off, put the air
cleaner and hatch covers back on.
Checked my GMC notes and found this:
Backfire
The old basics still hold true.Backfire through the carb = fuel problem.
Backfire through the tailpipe = ignition problems.
I realize it's not always this simple but this is a reliable point of
departure for beginning troubleshooters.
A couple of things.Assuming it idles and runs alright without missing
other than the backfire through the carb.
1. Are the vacuum lines all connected correctly?
2. distributer advance working freely?
3. Timing correct when you set it?
Make sure the ground at the distributer coil has a good ground.
tom
checked internet for oldsmobile backfire through carb and found opposite
comment:
backfire through carb was ignition problem, backfire through exhaust was
fuel.
this sounds more logical, but I'm not an engine person.
Help
RonC
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Ron & Linda Clark
North Plains, ORYGUN
78 Eleganza II
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