merc 90 2 stroke stalls except when, any plug pulled

[geo whifl]

Hi Forum,
I have a 2005 Merc 90 hp 2 stroke which will stall around 2800-3000 rpm when run up in a tank,
and if I pull off any plug's 1 or 2 or 3 wire the engine will run up to 5000 rpm. Engine will start up easy
and idle well, run up to 2000-2500 OK, above that stumbles and dies. Had Bad gas and pulled carbs and
Cleaned them, new plugs, seems to be electronic, where to start???
Thanks for any help,
George

 

[Faztbullet]

Re: merc 90 2 stroke stalls except when, any plug pulled

I hope you mean a test tank and that its in gear at 2800-3000 rpm....

 

[geo whifl]

Re: merc 90 2 stroke stalls except when, any plug pulled

ReaFaztbullet,
Thanks for the response, and yes the motor is in a tank large enough to trim the motor fully down and full of water and a running hose.
I had the prop engaged and throttled up slowly, fearing pushing all of the water out, didn't happen , tank worked OK.
The motor idled normally and when below 2500 rpm ran smooth.
Only when approaching 3000 rpm did it stumble and stall.
Could restart and repeat several times.
One time I had 1 spark plug wire off and the motor started OK and ran above 3000 rpm up to 5000ish without any
problems.
Shut down replaced that plug and unplugged the next plug wire, and motor ran normally up to 5000.
Did it with the last plug and same good effect.
It runs well with 1 wire off, any wire, and stumbles when all plugs connected.
I have the Secor book and could use some suggestions as where to start.
Again thanks for any help.
George