Yamaha 25 hp - Cutting out on top end

[Jimmy Stewart]

I have a 25 hp electric start Yamaha that is cutting out on top end. It runs fine for about 10 minutes including on top end. Once its warm it spits and sputters at about 80%-100% throttle. Anything below that it runs like a top. I have changed the plugs and gaped them per the motors specifications. I have also ran sea foam through the engine. Any and all help would be greatly appreciated.

Thanks!

[99yam40]

need to find out if it is spark or fuel related.
Spark is easy to see by hooking up an inductive timing light to the different plug wires to see if light cuts out while problem is occurring. and watch the timing
If it is then will need to test inputs and out puts of CDI with peak reading voltmeter made for these ignitions or DVA adapter and volt meter to find what part is failing
But most issues end up being fuel related.
check fuel pump to see if it is leaking and pressure/vacuum.
then you have the carbs

[Jimmy Stewart]

need to find out if it is spark or fuel related.
Spark is easy to see by hooking up an inductive timing light to the different plug wires to see if light cuts out while problem is occurring. and watch the timing
If it is then will need to test inputs and out puts of CDI with peak reading voltmeter made for these ignitions or DVA adapter and volt meter to find what part is failing
But most issues end up being fuel related.
check fuel pump to see if it is leaking and pressure/vacuum.
then you have the carbs

Everyone I have talked to seems to think it might be the coil. I was going to just change them out but realized they are like 125 bucks a piece. Not that its not worth the money but just to change them and they not be the problem would stink. Thanks for the input maybe I just need to take it to a mechanic. A different mechanic since the first guy couldn't find anything wrong.

[rodbolt17]

if you change both coils you wil have replaced more yamaha coils than I have in the past 10 years,other than F225, long story.
electrical system failures are incredibly rare on the 25.
what is the model number 25 you are dealing with as they made a 3 cyl 3 carb,a two cyl single carb and a 2 cyl 2 carb.

[Jimmy Stewart]

yamaha 25 eshp

I have the 2 carb version. 25eshp. Took it out today and I tell you for the first mile and half or so at full throttle it runs like a brand new one. After it gets good and warm it starts to sputter at 80-100 percent of full throttle. Any advice I do appreciate it very much.

Thanks much guys

[boats.net]

Probably need to have timing checked to make sure it is set to 25 degrees at full throttle and while have timing light you can check to see if it is misfiring on one of the cylinders.