Just got a 98 cbr 600 this past summer and only have rode it a few times cuz when i first got my friend was on it and got hit by a car and yes i know the cardnial rule is, never let your friends ride your bike......but now its seriously broke, when i go to fire it up theres a werid clunking noise and it will die, when i finally get it to start and give it some throttle while its idling theres a werid clunking noise as well......i have yet to do a compression test but i took it for a ride the first time it did this and it died on me in 1st gear so im guessing my compression is poor.....i know its not a blown head gasket cuz i still have coolant in my resiviour. Could it be a blown valve or dropped piston, or broken piston rings? Im stummped....please help

 

Well, it is hard to say what the problem may be. I know that a blown head gasket or even a cracked head will not make that type of noise. A blown valve would make more of a loud rattle... the bike usually wouldn't die either. A broken piston ring probably wouldnt make a clunking sound. Low compression would just make it idle rough.

My guess it a bent or broken connecting rod on one of the pistions.

Is there any smoke out the pipe? Does the clunking get faster when you twist the throttle?

I could be wrong on some of the above things but I figure I am close.

 

No the clunking noise does not get faster.....and the only smoke i saw coming from the exhaust was white smoke but not a lot, plus the engine was cold, and its common for a cold engine to blow white smoke.

What about a busted plug or something like that.....?

 

That is interesting?!?! I don't see how it could be a busted plug...best bet is to check them. How often does it make the sound?

Clayton

 

With the bike off will it shift through all the gears? You'll want need to roll it a little between shifts with the clutch out to make sure it gets into all the gears.

 

Check the clutch. A spring might of broke. Does it still make the noise when the clutch is pulled in? Try that first.

 

I dont think its the clutch...what about the carbs being out of sink.......cuz it did rain the night before and the bike wasnt covered up

Oh and it doesnt really clunk anymore I dunno its hard to explain!

 

You find anything out yet?

 

No but I will be working on it today....if I find anything out Ill let you know

 

OK scratch the whole clunking noise thing....it just wont start at all now

Im think either my ignition coil is bad or my plugs are bad.......