[Murp]

I have a Mariner 25hp Year ? Serial # 6611310, on a 14ft Alum Boat, Run’s Great at mid and top end Speed is 30mph on GPS, I can take it out run it at 20-30 mph for 10-20 miles a day and it runs great.But will not Idle at low speed,will Shake and Stall out,I put new Spark Plug, new gas,new Gas Tank, compression test 110lb in Both Cylinders,I Would Appreciate any HELP Please

[ifixf18s]

I have operations manual for 20 -25 HP mercury outboards, there is a section for hand tiller models, not sure if thats what you have. There might be a knob on the front of the motor "Primer/Idle Speed Knob". Pulling the knob out supplies a small amount of fuel to the engine for cold statring. Rotate knob to adjust idle speed after engine warms up. (verbatum from the manual). Also it says clockwise increases idle engine speed. Hope this helps.

[Murp]

Ifixf18s,yes it is a hand tiller models and has the Idle screw in the center of the Choke just like your saying,but when I turn counter clockwise to lower Idle,below about 12-1500rpm,it shake and stall out,

[will941s]

Not sure what year model your motor is but I have two 25hp 2-strokes. One is a 98' and ones a 89' The newer one is remote and the other is tiller. You can rebuild the carb yourself pretty cheap and that may work....spray out all the holes, tubes, parts with carb cleaner and compressed air. The other thing you could try is....on the right side of the motor (looking from the back) is a little arm going from the carb to the shift / stator connection. This arm sometimes adjust its self with the vibration of the motor. You can pop on end of the arm off from the ball joint and adjust it a LITTLE bit. Put it back on and see if that helps the idle. Basically adjusting the butterfly in the carb open a fraction if a inch. This is something I would try first before I go too in depth. Make small adjustments with it though. If you go too much you could knock it out of sync. Worth a shot though.