Hard to start when warm.

My 2004 vfr800 w 20k has recently become hard to start once warmed up. The bike acts like the battery is weak and slowly chugs the motor over a few times before giving up. But wait about 30mins and it fires up great. New battery, 13.67v when running, so im kinda stumped. I pulled the starter off and replaced the brushes (old ones didnt look much shorter) tonight and will see how it does in the morning. If it still does the same thing what else could it be? Is this a rare issue? Any help would be much appreciated.

 

well took it for a spin today and same thing happened. looking back on my battery and charging voltages I am only getting 13 ish at 5000 rpm which is kind of low according to the service manual. so I think my next move will be replacing the battery and upgrading the rectifier. Although I thought those issues were only on the 5th generation. Is this the right train of thought?

 

How old is the battery,they can show voltage but have no cranking power. Do you have a volt meter fitted to the bike, what voltage does it drop to when cranking when hot?

 

No meter on the bike And havent tried it while cranking. Charging battery now to see if it will hold a charge. Battery was replaced in January or at least the guy i bought it from said it was. 3/14 on the sticker new one at the store said 4/14...so im assuming here. This being why i want to replace it so at least ill have that ground covered.

 

ge the battery load tested or put your meter on it while cranking and see what it is doing, it may be ok, then again if it is a wet acid battery it could be junk. Do not replace with wet acid battery, get an AGM type