1981 Yamaha 650 Maxim is sputtering

[dejaentendu247]

Hi there. Before this past winter I stored my bike with a full tank of gas/stabilizer. I tried to start it after, but it ran really rough, so I took the carbs off and cleaned them really good with a toothbrush and cleaner. The bike ran much better then, but would "sputter" after a few minutes of use. (And I replaced the solenoid because the oil light kept coming on when trying to start the bike and that fixed that problem) I then tried to figure out the sputtering problem. I checked the fuel filter, that was good. I checked the petcock for good gas flow, that was good. I checked the spark plug wires for any cracks or arcing and that was good. I sprayed the boots with WD-40 while revving the engine and there were no leaks. I changed the air filter also. Finally I checked the coils with a multimeter and they seemed to be fine. So I am absolutely stumped. I did buy some SeaFoam and the bike runs great with it in the gas, but as soon as it runs out it sputters again. I ran the bike today, and the first few minutes were great, then it sputtered again after the bike warmed up. Last year it had all its power, and now I hit 65-70 and it tops out...I'll give it throttle and literally nothing happens, complete loss of power. But when riding it, sometimes I'll get a quick surge like how the bike should be running, almost as if it got the right spark or fuel, or a cylinder kicked in. I am really stumped on this one. If anyone has had a similar problem or has an idea please let me know, it would be greatly appreciated. I still think it could be one of the coils because it runs worse after warming up...

[Johnj]

Hello Kramer and welcome to the forum. Yes I think you've got it, now you need to check the coils when they're warm, and I think you've found the problem.

[dejaentendu247]

So do you think I should run the bike for a bit then check the coil? I wish there was a way to check it while it was running, cause if there is I don't have the equipment..

[Johnj]

yes