25s hp efi runs half speed

Got a Tohatsu MFS 25B new in Nov 2012. It came on a small pontoon bought from dealer. He winterized the fuel system by draining and showed me the brass screw at the bottom of the fuel body(?)--left side just forward of the float bowl.
Fired it up a year ago and ran all year with no problems--except maybe for a surgey low idle. No other problems.
I serviced it last fall-oil, filter, lower unit, etc and drained the gas.
Pulled it out last weekend, hooked up water muffs and, with a 1/4 warm lever fired right up. Let it run 4-5 mins at various revs--but it wouldn't idle even after much warm up. Pushing the warm up lever closed rpms must have been about 300 and then died.
Rechecked all the connections and retried next day--same thing. Soooo...
I turned out the throttle link about 3 turns---and it started, idled, and revved fine with the warm up lever. Engaged gear and reved it a bit, seemed OK.
Lauched it with the wife piloting. Started and she took off for home. I drove truck and trailer home expecting her to be at the dock as the launch is only 1/2 by water. Could see her half way and was moving, wondered why she wasn't blasting along----she had it wide open but only going 1/3 to 1/2 speed.
Wife not happy, thus I'm not.
Any ideas for something stupid before we try to get back to the landing and head for a dealer??
Thanks
Mike

When you say throttle link, are you referring to the RC box throttle cable, or a link rod on the motor. If the latter, you may have just disturbed link and sync. These motors seldom need any warm-up lever.
You are under warranty; If you have purged all old gas from the vapor separator, and have good plugs, see your dealer.

Thanks. Yes, it was the latter.
Why did it not start/idle without the lever?
In retrospect it didn't need it last yr.

Opening the throttle a little can mask a host of issues. The MFS25/30B should not need it.

I would reset that link, drain the fuel system of the motor (even the fuel rail); make sure you have fresh gas, and re-test.

Will give it one more shot. Suspect a fuel delivery problem but at a loss for why. Line Bulb didn't seem to get hard--but didn't push it.
Had put new gas in tank--non-ehtynol as always.
Just disappointed and wondering what I did to create problem.
Thanks
Mike

OK, update.
Did not seem to be running on middle cylinder since it was fouled. Took it to dealer yesterday. He said the plug was oil fouled. Pulled the dip stick and oil was at top of hole and misted all over engine. Since I have the second partial quart bottle with 1/3 left, it's gas in the oil.
We'll see what he finds.

Possible blown diaphragm in the low pressure fuel pump. That can happen if you don't disconnect the fuel line at the end of each day. The solar heating/cooling can cause the primer bulb to over-pressurize the fuel system. If the bulb didn't get really firm, that may be because fuel was leaking from the low pressure fuel pump (not the high pressure FFP) into the crankcase. Regardless, it should be covered under warranty.