Hello,
I’m dealing with an issue with my bike 1990 cbr600 where it starts and within 30sec or so, starts reving the engine as high as 6000/7000 RPMs, and it stays there.
The bike was running fine before i put it together (took it apart to restore it)
Carbs were clean before taking the bike apart and couple of times after I put it together (thinking the carbs are the issue)
I’ve checked for vacuum leaks by spraying carb cleaner and can’t seem to find anything.
after testing most components, I’m struggling to find the culprit.
the last thing I would like to test is the CDI, but there isn’t much info how to test it and what reading should i see between the connections.

does anyone experience this reving issue and also, has knowledge of how to test the CDI?

thanks in advance for the assistance

Alex

 

Sudden rev is not going to be the CDI. The CDI has a preprogramed spark curve. If you suddenly advanced your spark at idle it's not going to rev very high before stalling, maybe 2200 or so. The rubber boots between the carbs and the head are known to get cracks in them, which would allow the engine to draw more air in and slowly rise to that rpm, before choking due to the throttle plates being shut. The screws in the head for the synchronizer ports also are known to vibrate open, or fall out completely.
I've chased this breadcrumb previously and if you can see light in every port on the carb, and feel like everything is perfect there, check the rubber boots and the sync port.

 

thanks for the feedback. i ended up taking the carbs apaeRt again and doing everything as the service manual suggest. the bike is running now; if i have to guess, i would say it was the balancing of the carbs. the bike feels like still running rich as it seems like it wants to hesitate at cruising speeds. thx again

 

Carb balance won’t cause the symptoms you describe unless completely out of whack...if even then. As Drakito suggested it was likely a vacuum leak. Most often carbs not properly seated in the carb boots after removing and re-installing.

 

thanks for the feedback