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Re: Backfire through carb

To: "M. Edwin Vaughan" <>, <>
Subject: Re: Backfire through carb
From: <>
Date: Sat, 23 Feb 2002 14:19:26 -0000
> I am having a problem with backfiring through my carb.  when the engine is
> cold, under load, or I am really getting into the throttle it sputters,
> backfires through the carb, and robs the engine of power. Since it is
> backfiring through the carb, then I must have an intake valve that is not
> fully shutting before the mixture is ignited and burned, right?

Unlikely.  If an intake valve is not seating there would be a regular
backfiring or whatever in the intake, it wouldn't come and go.  I suppose it
could be a bent pushrod bending more under greater revs, unlikely to vary
with temp though.  Do gulp valves cause carb backfiring?  Or exhaust

> I did
> have a problem setting my valve clearances about a year and a half ago
> (it seems that valve #6 wouldn't fully open so I couldn't set #3, but I
> can't remember for sure).

Please explain.  Even if valve 6 *didn't* open fully, how did that stop you
adjusting valve 3  (apart from the fact that it indicated a far more serious
problem, making adjusting the valve clearances a bit pointless)?

> What could be causing this? A bad cam, lifters,
> or some other valve problem? What kind of repair might be needed? Is it
> something that my friend and I (moderate and modest mechanical repair
> experience, respectively) can tackle?

In what way wasn't it opening fully?  Do you mean there wasn't as much lift
on that as any of the others?  Did you set the clearance of that valve?  Was
it still the same?  If so it sounds like a badly worn cam lobe.  If you
really have cam/pushrod problems there is little point following up the
backfiring until you get those fixed.

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