Honda CBR 250R Idle speed jumping

Old 06-27-2010, 07:54 PM
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Join Date: Jun 2010
Location: Auckland, New Zealand
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Default Honda CBR 250R Idle speed jumping

Hi all,
I own a Honda CBR 250r 1989 and Its idling strange.

In the mornings im having trouble starting it (resulting in me push starting it most mornings) and if it starts and when cold it often idles at around 300rpm then dies and eventually gets above 1000 after a few starts.

Once running and warm the idle jumps up and down from 2000rpm to 2500/3000rpm to 1600rpm.

Ive been told it sounds like it runs of 3 1/2 cylinders when idling low then jumps to 4 again yet at another mechanic store ive been told it sounds like a Air leak.

Any ideas what this could possibly be? Air leak? Carb problem if so what?
I cant afford to send it in to have a complete Carb overhaul.

Thanks in advance!
Old 07-07-2010, 01:54 AM
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Join Date: Apr 2006
Posts: 456

Sounds like it could be a vacuum leak. (air leak). On top of each carbuerator is a vacuum chamber. There is rubber gaskets/diaphragms which hold the lids on these and give a seal for the slide. If one is torn or wrecked it could cause a problem like this. It is one of the main reasons for a hunting idle on a carbeurated bike. The carbs could also have clogged pilot jets too which could only make the situation worse. I would send the carbs into a shop for servicing if you don't know to much about them.

Otherwise I would go to It is a GREAT resource for CBR250 owners.
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