1981 yamaha maxim misfiring? problem.

[maxim81]

I bought this bike a couple weeks ago. I was told the carbs were recently cleaned and synched. The bike sounds like it backfires/or misses though when it heats up some, 2-3min of running. The person I bought it from had the spark plugs changed also, and said that was when the missing started, the wires were not changed and he was told that, or the coils were more than likely the problem.

Is there a way for me to test and see what the problem may be? I tried to see if I could see any sparks or anything in the dark but saw nothing, and the wires look to be hardwired into the coil. Thanks

[maxim81]

After trying some different things, I decided to leave the choke on while riding, runs much better with the cluth on all the way, does that help pinpoint anything?

[studly256]

I bought this bike a couple weeks ago. I was told the carbs were recently cleaned and synched. The bike sounds like it backfires/or misses though when it heats up some, 2-3min of running. The person I bought it from had the spark plugs changed also, and said that was when the missing started, the wires were not changed and he was told that, or the coils were more than likely the problem.

Is there a way for me to test and see what the problem may be? I tried to see if I could see any sparks or anything in the dark but saw nothing, and the wires look to be hardwired into the coil. Thanks

To test Change the plugs!

Sounds like you got a hold of a or some bad Plugs. Try changing the plugs. Make sure the plugs go to that bike too!

Also,could be a sticky Valve.Pure some brake Fluid in the Gas tank with Gas and let it run for bout 2-3 Min (Its gonna smoke white Heavy)then shut it down . Drain the Tank then put new gas 93 in the tank. Then Clean the Carb Bowls

And niddle Valves.Make sure all Floats are set the same.Also, wouldn't hurt to add another -or a New Gas Filter.

(Sounds like Shit in the Tank getting to the niddle Valves-Or Sticky Valve-or Bad Plugs-bad coil.or wireing Problem).

Brake Fluid Loosens up sticky valves.Take the coils in and get them tested.I have 2 coils laying around somewhere if you need. Just pay for shipping.

Lets kill too birds with one stone.

Can you tell me where the Vacme Line from the Carb boot goes?

Also, what kind-size-type of battery that bike takes?

Because,I have a 1980 yamaha 650 Maxima ......

Thanks ! Good luck.....

[maxim81]

Thanks for the info, today I pulled all 4 plugs, 1 at a time, they smell like gas and are very black, kinda oily looking. I wiped them off but they are covered in carbon. Haynes manual says fuel mixture problem. I haven't really done anything with the carbs other than pull the diaphram tops off and look in to see what it looked like in there. I already ordered some used coils, but thanks for the offr, I got them pretty cheap, hopefully they are good.

Also I checked the air filter, it was fine. Is there a way to adjust the fuel mixture? Haynes manual mentions it then kinda never comes back around to it.

Also I took the bike out on the road 2 days ago, I put 10 miles or so on it, it ran decent till the last mile, it pretty much died, kinda did a bunch of skipping sounds from the carb area, then it cut off, no matter how much throttle I was giving it would keep it running, just died. It wouldn't crank, I sat with it 5 min or so, still no crank, as a last ditch effort I turned the choke all the way on and it fired up and got me home. Thanks for any more info.