Runs great when cold. As soon as the needle hits the 1/2 way point up the thermostat guage it starts running rough at idle and sputters when I start on the throttle, almost as if it's going to stall. Once it gets into higher RPM's or cools down it runs better.
Friends have suggested vapor lock.
I noticed the radiator fan turn on the other day for the first time since I bought it after pressing the wiring harness to make sure it had a good connection, but even with the fan, it still ran a little rough even just above the half way point to hot.
Haven't had much time to keep it hot and run it for any lengthy period of time this season, it being New England the weather not yet cooperating.
Bike was purchased from dealer used, they cleaned/synched the carbs, flushed the coolant, oil change, etc... (supposedly).
Any ideas?
Thanks so much!
Hi mmagliozzi
I bought a cbr 600 fy new back in 2000. After about 3 years I've always had the same problem in summer when sitting in traffic, ie. anything that put the temperature up to about half way causing the fan to cut in. I thought it was a carb problem. also thought it could be the spark plug caps(coils built in breaking down only when warm).
Anyway, mine had become so bad recently that it had become almost unrideable as it kept cutting out and spluttering, only at tickover and low revs. Anything over 3000rpm it was fine. I thought it might be an electrical problem so put a meter across the battery. It was only showing 11.5v when running at tickover. Rev it up to 2000rpm it was showing about 12.5v. It should at this rpm show more. If you have the same problem you can rule out the alternator by taking the plug of the rectifier/regulator( under the seat cowling, you can access it by removing the seat) and putting the the leads of the meter across the yellow wires. test all 3 wires. ie if you were to number them 1, 2, 3 then test form 1 to 2, 2 to 3 then 1 to 3. You should get somewhere in the region of 20v at tickover and 50v at 5000rpm. If this figure varies by a large amount between each wire ( alternator winding) then the alternator is the likely problem. But i reckon it will be your regulator/rectifier. They are not cheap at £141 from honda. You can get them from ebay but the guy at honda (mechanic)reckons they are inferior and he has had to repair bikes with boiled batteries and burnt wiring looms. This maybe nonsense but I took the safe route. Whatever one you do decide to get(if it is the rectifier/regulator at fault) then make sure it is the cast ally heat sink type not the original one which has the gubbins incased in rubber.I reckon its a design fault with the originals hence the updated replacement which disippates the heat better.
Going back to diagnosing the problem. I found mine by running the bike stationary until the fan cut in, make sure your lights are on then operate the front or rear brake light. by doing this you are loading the electrical curcuit. When I did this my bike cut out straight away or very nearly did so. Yours might not if your battery is very good. If you notice it running worse then I would bet that you have the same problem.
Hope this helps.
Dan
Hi
Me again. I forgot to mention that after replacing the rectifier/regulator my bike runs like a dream with no misfiring or cutting out when at tickover or low revs in the warmer weather. Nice feeling to have after living with the problem for 6 years!
dan.
Hi Again mmagliozzi
Have you fixed the new rectifier/regulator to a flat aluminium surface? I'm not 100 percent certain but I reckon it is important to mount it to a surface similar to where it is originally located as the aluminium surface will dissipate the heat better than air alone.
If you could get some seating/mounting compound, i think that is what it is called will provide a better heat conducting bridge between the back of the R/R and the surface of the frame. Its a white paste that usually comes in a tube.
dan
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Could be not getting enough fuel and running lean, try Berrymans B12 fuel system cleaner additive, put double dose in tank, get it warm then let it stand overnight and see how it goes. it cured my vxs 650 bad running problem, well my bike wouldn't run, just start and thats it. damn new england weather i know that. cape cod sucks this week. try here for a free pdf service manual too http://www.carlsalter.com/motorcycle-manuals.asp
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i have the same problem on the same bike and i feel like its worse when my fan kicks on. like its too much of an electrical load. but i dont know why the bike is getting that hot in the first place.
Dan,
Thanks for your insight on the rectifier. Apparently this is a common problem on this bike and others.
I've ordered the part from my favorite website, www.oldbikebarn.com, and in the meantime relocated the recitifer from under the seat cowl to an open area between frame rails near the the battery. Should get a lot more fresh air in that location, but it still runs a little sputtery when really hot. Could be going bad from all the "overheating," and with no real means to dissapate the heat, well....
Anyway, the new rectifier has some heavy duty aluminum fins for a heatsink, which should keep it really cool on it's own. Mounted in the new location with the heatsink sticking out in the fresh air should keep it near ice cold, haha.
I'll keep you posted, but thanks again, I think we're definitely on the right track - noted the bike cooling off a lot quicker on the first ride alone.
To combat the problem, I had an idea that seems to be working great so far! (as I wait for my new rectifier in the mail)
I took a small heatsink/computer-fan setup and strapped that puppy onto the back of the rectifier. Wired it up to an accessory line and it the bike runs phenominally!
Whereas, I couldn't even touch the rectifier for more than a split second without a severe burning sensation, now it's hot, but not so hot that I can't leave my finger on it for a few seconds comfortably.
When the new one arrives, I'll likely put it back under the seat cowl and see how it runs, but for now things are looking good!
Thanks so much for your post, Dan, saved me from buying a new bike!
-Matt
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