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stumbling and backfiring[120-130/67] posted by bill nesbitt on
Tuesday, 11 April 2000, at 9:50 p.m.
My 123gt(b18b, twin SUs, manual trans. with OD) is bogging down a bit when taking off in first, and stumbles at the top of the rpms before each shift. It really stumbles when I try to push it past 60 mph, and very occaisionally backfires at highway speed. This has come on quite suddenly, it was running very well a week ago. I assume it's either the ignition or fuel system, but any clues about where to start looking would be appreciated. It's cold and snowing up here again, and the less time spent in the driveway figuring things out the better.
--Bill Nesbitt 67 123GT & 68 122s wagon
Re: stumbling and backfiring[120-130/67] posted by JohnH on
Wednesday, 12 April 2000, at 12:14 a.m.
A good start would be see if the points adjustment is correct. If they are a bit loose you could get the symptoms you have.
Re: stumbling and backfiring[120-130/67] posted by George Downs on
Wednesday, 12 April 2000, at 6:23 p.m.
Spark plugs going bad could cause it to miss at high speed but
NOT backfire. Check the inside of your distributor cap and make
sure it doesn't have any tracks between the individual contacts
(which could cause a spark plug to fire on overlap and backfire
either through the carb or exhaust)
Another possibility, especially if you are using original
lifters, is that you have wiped out a lobe on your cam.
This happened to me on a 67 122 and also on two different
B30 engines. Quick way to check is to pull off the
valve cover and using a ruler from the top head surface
to the retainer, have someone turn the engine over slowly
(use a wrench on the front crankshaft bolt) check the lift
of each valve. All should open 3/8" or more. If you find
one that doesn't open, there's your answer. I've been using
IPD lifter and pushrod kits and have eliminated such problems.
(of course if the cam is bad you gotta replace it.)
Under no circumstances reinstall a worn OEM lifter - one
that is not perfectly flat and shiny on the wearing surface.
You will only eat up the next cam.
George Downs, provisionally in Augusta, GA