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Author Topic: Missfire at 5,000 RPM  (Read 2133 times)

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jay1981650

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Missfire at 5,000 RPM
« on: May 24, 2006, 06:59:07 AM »
hello all thanks for stopping in to help me... i have a 1981 Honda CB650.
the problem i m having is  I'm getting a missfire at 5,000 rpm and the bike wont let me wind it out?!
in the beginning i thought it was the fuel so i cleaned it out,then coils (checked OK)
so then i was looking in my book and found it may be the  spark advance(pulse generator)

any help would be greatly  appreciated!

thanks allot for all the input
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jay1981650

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Re: Missfire at 5,000 RPM
« Reply #1 on: May 24, 2006, 07:27:17 AM »
also i forgot to mention   it purrs like a kitten when idle its only a problem at 5,000 and above
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Offline TwoTired

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Re: Missfire at 5,000 RPM
« Reply #2 on: May 24, 2006, 08:56:58 AM »
Air filter?
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

jay1981650

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Re: Missfire at 5,000 RPM
« Reply #3 on: May 25, 2006, 10:28:28 PM »
airfilter is new
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jay1981650

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Re: Missfire at 5,000 RPM
« Reply #4 on: June 03, 2006, 05:36:29 AM »
i took the air filter out and it  works  50% better...   any ideas?
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Offline Bob Wessner

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Re: Missfire at 5,000 RPM
« Reply #5 on: June 03, 2006, 05:46:25 AM »
Have you done a plug chop? If there is an improvement with the air filter out, maybe running rich on the main needles/jets since removing the filter improves air flow.
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Offline KB02

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Re: Missfire at 5,000 RPM
« Reply #6 on: June 03, 2006, 06:51:58 AM »
Spark advancer was my first though, too... but running better without the air filter confuses me...

When was the last time your carbs were cleaned? Blocked Main jet, per chance?
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Offline TwoTired

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Re: Missfire at 5,000 RPM
« Reply #7 on: June 03, 2006, 10:59:48 AM »
Without some definative data beyond one symptom, we can only guess.  Here's a punch list of things that can help indentify the culprit.

1- tune up history.
2- compression test (yes, I'm dreaming)
3- spark plug deposit color description/ correct gaps, correct number selection.
4- Spark plug cap condition/electrical value.
5- Ignition lead condition.
6- fuel tank condition (rust scale?)
7- Fuel tank vent clear?
8- fuel filter condition
9- fuel line condition kinks/cracks/ internal deterioration
10- Fuel contaminants in the carbs bowls?

We can help, but we need details and you're the closest one to the bike.

Another guess is that there is fuel restriction limiting fuel to carbs.  As the bike uses more at higher RPM, the carb bowls empty and the engine starves for fuel.

Cheers,

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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline DaveInTexas

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Re: Missfire at 5,000 RPM
« Reply #8 on: June 03, 2006, 01:17:32 PM »
I am a complete newbie and don't know #$%* but I would add this to your list:
Years, like 25 years ago I had a small twin engine honda with the same problem that no one could figure out.  It resolved when I switched the coil out with a VW beetle coil I had laying around.  Seems like the coil was breaking down under high demand.
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