not firing on 2 cylinders

[paultg]

I have a 1987 115 hp yamaha. While my son was out boating yesterday, the motor starting going slow and would not go full speed. When I checked it out. I found that it was only firing on the top two cylinders. I changed spark plugs and tried spraying gas directly into the bottom carb with no results. Any suggestions.<br /><br />paultg05@yahoo.com

 

[Knightgang]

Re: not firing on 2 cylinders

I had about the same thing happend with my '85 Suzuki 115. I rebuilt carbs trying to get to the problem, and I am now thinking that I have a couple of coils that have gone bad. If you have a manual, it should have resistance spefications in it to trouble shoot your coils. I would start there.<br />Good luck and keep posting.

 

[snookin]

Re: not firing on 2 cylinders

Theres no dought about it replace your coils, I'v spent so much moneys on things that had nothing to do with the firing. Its also like a light bulb, best bet change all of them at the same time. Hopes this helps,DaveS.

 

[BRIAN03]

Re: not firing on 2 cylinders

Its not the coils. Coil failure on a Yamaha is slim to NONE. You have a better chance of winning the lottery. If the engine went in to RPM reduction. Its heat,bad heat sensor or the oil tank sensor on the engine is low of oil. If pink wire on the engine is put to gound. The engine will be in RPM reduction. On the cylinder heads there is a heat sensor on each Head. Black and pink wire. Remove the connection on the pink wire on the cylinder head or pull the pink wire connector on the oil tank(its behind the tank). Disconnect one pink wire at a time till you find out what put the engine in RPM reduction.

 

[Capt Ken]

Re: not firing on 2 cylinders

If the bottom two cylinders are not firing on that V4, then you more than likely have a bad CDI. Seems the older V4's are the only CDI's that I've ever had problems with. Use a spark checker to be sure of the spark. If no spark, then swap the charge wire from #1 and #3. (thats the small wire coming from the CDI) If the spark moves with the wire, then the coil is good. If #3 still doesn't fire, the coil is bad. If the temp sender was causing the problem, it would only misfire the engine above 2500 rpms.