Missing @ 2000 rpm ???
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Freshman User
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Missing @ 2000 rpm ???
1968 F600 with a FT Big Block 331, 361 ?? with a original ? 2 BBl Carb. New plugs, new wires, new cap and rotor, recently rebuilt carb. Motor has 12,000 miles. For some reason my engine is missing under load as it hits around 2000rpm. I have noticed the after market tach is bouncing around alot when it misses. Do I have an ignition prob ? It starts and idles fine. It will pop through the carb around 2K like the accel pump is not working If I floor it when shifting and get beyond 2K on the tach it does not miss or pop. I have set timing and carb settings to no avail. I am thinking that the tach bouncing around is an indication that there is some arcing going on in the ignition system. Just installed new poiunts and it is no better. Can this be carb related ? Ignition ??? Any help is surely appreciated.
Fleet Mechanic
Joined: May 2001
Posts: 1,396
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From: Cupertino
Taf, the tach counts the number of pulses in the low voltage primary. The bouncing in the tach means that there is a problem somewhere in the 12v primary path- wiring, ignition switch, distributor, points or condensor. Did you replace the condensor? Did you scuff up the plate under the points and clean all oil off to get a good ground? You might consider a rebuilt distributor with a Pertronix unit if you budget permits it.
Semper Fi
Semper Fi
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No I have not replaced the condensor. I did wipe any oil off the plate. I will remove and scuff as you have mentioned. Also noticed the grounding wire inside the dist that goes to the points looks original, and could stand to be replaced. I'll try the a new condensor and and these other items and see how it runs. Thanks for your help, it s appreciated. TAF
Senior User
Joined: Sep 2009
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From: Burbank, CA
I agree with CougarJohn that it could be the condenser. They don't fail often, but when they do, that's the type of behavior you'll get. At some combination of voltage and rpm, they'll start shorting to ground, causing false triggers of the ignition. I'd just automatically replace the condenser the next time you have the cap off. They're cheap. Or at least they used to be.....The one I bought recently for my F100 was about $7.
What about the coil? Have you replaced it? That's another major candidate for this type of symptoms. Coils go bad by themselves over time, with a gradual breakdown of the internal insulation in the windings. You get the same result, false triggers and sparks at the wrong time, generally coming in at higher rpm and load, while being okay at idle. And, when it false triggers, I believe that the tach will also read those extra pulses.
What about the coil? Have you replaced it? That's another major candidate for this type of symptoms. Coils go bad by themselves over time, with a gradual breakdown of the internal insulation in the windings. You get the same result, false triggers and sparks at the wrong time, generally coming in at higher rpm and load, while being okay at idle. And, when it false triggers, I believe that the tach will also read those extra pulses.
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I beleive that I have found the problem. I went ahead and scuffed up the plate below the points and replaced the ground wire that looked to be original. It starts better and does not miss anymore. I bought a new condensor, but am not installing unless I notice a prob.
THANKS TO ALL FOR THE INFO.
THANKS TO ALL FOR THE INFO.
