Yamaha 25 hp 4 stroke, runs great with out battery, like crap with battery

[Donmcc]

I have a 2000 Yamaha 25 hp 4 stroke that has a miss at half to wide open most of the time. By accident I found with the battery dissconnected it runs perfect. I read in the Yamaha manual that it took a certain cranking amp battery to make it run properly, I tried that, didnt help. Any help would greatly be appreciated. The Yamaha dealer that we have should be selling paddle boats instead of motors. They have been no help at all after $200 to tell me they was nothing wrong.

 

[SleekCraft85]

Re: Yamaha 25 hp 4 stroke, runs great with out battery, like crap with battery

test the battery with a volt meter. on my boat i had 2 batteries, i slow charged them with my charger. i had one that was fine (would fully charge to 12.7v) and one that was bad (would top out at 6v). boat started a few times then would cut out after 30 secs. after a few times cranking it over it burnt out the starter. i rebuilt the starter and replaced the bad battery and now turns over like new.

 

[Donmcc]

Re: Yamaha 25 hp 4 stroke, runs great with out battery, like crap with battery

test the battery with a volt meter. on my boat i had 2 batteries, i slow charged them with my charger. i had one that was fine (would fully charge to 12.7v) and one that was bad (would top out at 6v). boat started a few times then would cut out after 30 secs. after a few times cranking it over it burnt out the starter. i rebuilt the starter and replaced the bad battery and now turns over like new.

Thanks for the info, The battery stays fully charged, it starts up and idles perfect. But mid to high range it misses and sometimes missfires causing it to backfire thru the carb. After starting I can dissconnect the battery and it runs perfect. I was thinking that it had something to do with the charging system back feeding to many volts or amps to the electrical system. Thanks