1989 Yamaha 90 hp Performance Issue

[smartens9]

I am looking for some advice on getting my yamaha 90 hp two stroke engine running. Any help would be appreciated.

Background

At this time it fires up and idles perfectly. If I try to increase the throttle it sounds like it is missing clyinders and violently studders till I decrease the throttle and then it idles perfectly at lowest RPM.

I have had the motor for 15 years and had the carbs redone 10 years ago. The motor has always ran great. Has not got a lot of use lately but ran fine 9 months ago.

I have done the following:
1.) added fuel stabilizer to the fuel tank - SeaFoam
2.) fogged the carbs with SeaFoam Spray
3.) Removed the oil tank drained and added fresh oil
4.) Put in new spark plugs.
5.) Ran each cylinder independently and they all start up.

It seems like it should be a carb issue but could it be something else?

 

[dpfundst]

Re: 1989 Yamaha 90 hp Performance Issue

I have a 2001 90hp 2 stroke that had a similar problem.............had to reproduce the problem with a mechanic on board....he held a meter on various eletrical components on the engine as I drove (with the mis-firing happening)
had to replace the coil..

 

[99yam40]

Re: 1989 Yamaha 90 hp Performance Issue

yes testing is the best way to find your problem,
not someone guessing on a computer