break up at high rpm
08-18-2018, 02:58 PM
#1
Drifting
Thread Starter
break up at high rpm
would an overly lean carb cause break up in the upper rpm? or is that an ignition issue only?
its not point float, not valve float - i know what those feel/sound like.
its either a bad condenser (my guess) although its brand new - or the carb is too lean on the top end - or perhaps pulling air in from somewhere.
Any advice?
Thansk
its not point float, not valve float - i know what those feel/sound like.
its either a bad condenser (my guess) although its brand new - or the carb is too lean on the top end - or perhaps pulling air in from somewhere.
Any advice?
Thansk
08-18-2018, 03:18 PM
#2
Le Mans Master
Member Since: Jul 2018
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2024 Corvette of the Year Finalist - Modified
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Is it breaking up or surging? Breaking up sounds like misfiring, but surging feels like what it is a lean fuel/air mixture. They sound and feel very different. Also, a lean mixture usually also causes significant popping in the exhaust when you decelerate.
08-18-2018, 03:28 PM
#3
Drifting
Thread Starter
my guess is the "new old stock" Delco condenser that probably can't keep up.
08-18-2018, 03:34 PM
#4
Le Mans Master
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2018 C1 of Year Finalist
If you think it is the condenser, that is an easy swap. Make it and see if it changes anything. However, I suspect this might be something more than a bad condenser.
08-18-2018, 03:43 PM
#5
Team Owner
Old or faulty plug wires will do it along with carbon tracking in the distributor cap. Plugs themselves are sometimes the culprit. A quick check is to rev the engine in a dark but well ventilated garage and look for any arcing at the wires.
08-18-2018, 03:53 PM
#6
Drifting
Thread Starter
time to install the TI lol
08-18-2018, 04:56 PM
#7
Le Mans Master
What rpm are you calling "high" RPM? The ONLY points which will reliably fire your engine at 7000rpm are Borg Warner A112.
YES, all the other things pointed out above can also cause misfires.
YES, all the other things pointed out above can also cause misfires.
08-18-2018, 05:03 PM
#8
Race Director
My C5 was once had issues around 5,000 rpms that acted as if it were bouncing off the limiter. Pulled all the wires and plugs and one of the spark plugs had a hairline crack that was arcing under load. A new spark plug made the issue go away.
08-18-2018, 05:58 PM
#9
Race Director
Is your point dwell stable across the rpm range? Worn distributor bushings can cause fluctuations in dwell which often results in higher rpm missing.
08-18-2018, 06:06 PM
#10
Race Director
Member Since: Apr 2015
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Try disconnecting and plugging the vacuum advance and go for a run.
08-19-2018, 12:41 AM
#12
Burning Brakes
Well I'll add one more. Rebuilt my 327 way back when up to a 365 horse with a holley. Good in 1st and 2nd but 3rd would start surging above 6000 rpm. Replaced the old mechanical fuel pump with a holley electric and she would turn all the way to 6500-7000 rpm.
08-19-2018, 06:33 AM
#13
Drifting
Thread Starter
Its a broken plug boot
was listening yesterday, and heard what i thought was the beginning of an exhaust leak - Looked closer and could see the plug boot arcing on the heat shield
thanks all!
was listening yesterday, and heard what i thought was the beginning of an exhaust leak - Looked closer and could see the plug boot arcing on the heat shield
thanks all!
The following 2 users liked this post by aaronz28:
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08-19-2018, 07:42 AM
#14
Team Owner
Thanks for letting us know the solution - many don't get back here with the fix.