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Rough running up to 2000rpm

Posted: Wed Apr 07, 2021 4:46 pm
by zalle
Hi guys, my 1979 Z is running a bit rough in low revs.

I thought it was carbs, but my mechanic tuned them.

What happens is: below 2000rpm, it feels like the engine is running on 4 or 5 cyls, a bit like when the petrol is running out and you have to turn the petcock to reserve. After 2000rpm it runs great.

I have aftermarket exhausts (similar to original but a bit louder).

Not really sure if this is electric or carb related, but maybe you guys can give an idea of what might be happening? Maybe one of the coils? Maybe the spark plug cables? Maybe none of the above???

Any help would be greatly appreciated.

Thanks

CBX Rui Barbosa.jpg

Re: Rough running up to 2000rpm

Posted: Thu Apr 08, 2021 6:24 am
by steve murdoch icoa #5322
Despite your mechanic tuning your carbs it sounds your idle jets still need attention.
Did the carb tune/cleaning include pulling the idle jets?

Btw, nice looking bike.

Re: Rough running up to 2000rpm

Posted: Thu Apr 08, 2021 7:18 am
by tevan
steve murdoch icoa #5322 wrote:
Thu Apr 08, 2021 6:24 am
Despite your mechanic tuning your carbs it sounds your idle jets still need attention.
Did the carb tune/cleaning include pulling the idle jets?

Btw, nice looking bike.
I agree I would bet on idle jets plugged.

Re: Rough running up to 2000rpm

Posted: Thu Apr 08, 2021 7:34 am
by daves79x
Guaranteed, it's the carbs. They need to come off and be completely rebuilt.

Dave

Re: Rough running up to 2000rpm

Posted: Thu Apr 08, 2021 4:59 pm
by zalle
Ok... They did not come off, they were just tuned.
No easy way of doing this, right? They need to come off?

"Btw, nice looking bike." Thanks Steve.

Re: Rough running up to 2000rpm

Posted: Fri Apr 09, 2021 7:07 am
by daves79x
Correct, but most importantly, find someone that actually rebuilds CBX carbs to do it, not just a 'mechanic'. Ask around.

Dave

Re: Rough running up to 2000rpm

Posted: Sat Apr 10, 2021 3:06 am
by zalle
Thanks