Yamaha 90 missing badly!

[Popeye 17]

The motor is a 1996 Yamaha 90. It is missing badly up to about 2500 rpm then clears up and will pull 5200 no problem. Idle back down and starts missing again. Has 120 lbs in all cylinders. The carbs were pulled apart and cleaned. New fuel tank, hoses,bulb,fittings. New fuel pump. Inline spark checker shows spark at all three plugs, but #1 is not igniting fuel. Plug is cold at idle. Spraying fuel in carbs, the motor does nothing on # 1, and stumbles on # 2 and # 3. Putting hand on carbs results in no change on #1. Mechanic wants to check the cdi unit. He's thinking the computer may have the timing firing at the wrong time on # 1. Does this sound right? Thanks, Mark

 

[bonitoman]

Re: Yamaha 90 missing badly!

Swap the coils for the one that is not firing with the other coil. See if it is not a coil breaking down before you change the cdi. It definitely sounds electrical.

 

[DB.Beachum]

Re: Yamaha 90 missing badly!

I would check ,plug wire ,and the lead going to the coil,the coil it's self ,put a new plug in that hole or change it from another cylinder that you know it is firing,I do not think that it is a spark control issue,but I here and your there ,it's kinda hard to work on them over the phone or computer

 

[Capt Ken]

Re: Yamaha 90 missing badly!

Timing would be easy to check with a simple timing light. Doubt if its the CDI. I'm wondering if maybe there's a problem with the reeds on #1. I'd remove the carb and check the reeds out with a flashlight.

 

[rickdb1boat]

Re: Yamaha 90 missing badly!

Is the #1 Plug wet or dry after you run it at idle?

 

[Popeye 17]

Re: Yamaha 90 missing badly!

Thanks for the replies. I put a new plug in # 1 and it made no difference. Switching plug and coil wire is doable, even though the inline spark checker shows spark, stranger things have happened. I got my hands on a timing light and will attempt to check that.And yes the plug is wet at idle!<br /> The reeds sound like a possibility. Engine only has about 400 hrs on it, but that doesn't mean anything really. So here is my plan. Recheck spark, swap coil and plug wire. Check timing. Pull carbs and check reeds. I have never looked at reeds before, but would assume broken,damaged,missing, bent is what IM looking for. I will be going out of town for the weekend and will check this out on Monday. Thanks for the ideas.Mark