1987 Merc 115 hp tower of power midrange problem

[johntho]

I have a 1987 merc 115 hp tower of power inline six. having problems with midrange power. Found one problem in that the starter gear was not disengaging and putting big drag on the motor got that fixed with wd40 and a hamer and had a few good runs, boat ripped. next time out does not want to rev up. Pulled the carbs and they look pristine clean but ordered rebuild kits and new floats since i had them apart anyway. The engine is electronic ignition and electric choke with fuel enrichment soenoid and separate fuel line for it to the block. The solenoid shows signs of leaking and I'm wondering if I could be getting bleed thru causing engine to flood out. don't really think carbs are the issue as they look like they have been gone through recently and the floats are in good shape with no leaks. The new solenoid valve is about $150 does anyone know how this solenoid functions i.e. is it just an open or closed valve that works when choke is activated? If so could I just jury rig a solenoid fuel valve in place of the stock unit since I can get one of those for about $15. Thanks for your input.
John Thomas

 

[jimmbo]

Midrange power problem... What does "does not want to rev up" mean? Stays at idle? up to 2500 rpm? up to 4500rpm? Do you have spark on all cylinders?
Your motor does not have a choke. It has, as you know an enrichment system that uses gravity to dump fuel from the top carb into the transfer ports of lower cylinders. The valve is normally closed and is opened by the solenoid. A jury rigged system might not meet USCG standards.

 

[johntho]

Jimmbo,
thanks for the response. good point on USCG standards. The rev problem is that from idle the engine will start to rev up to maybe 2000 to 2500 rpm just a guess in that there is no tach then it will bog down to idle again then it will start to rev up again and then bogs down to idle again. So power in midrange is just not there. Dropped the 15 hp kicker motor and got the boat going pretty good with that and the main motor took over and pulled good again - so midrange is just not there. top end pulls great. any ideas. Spark is good although could be cutting out under acceleration but that doesn't make sense when it goes so good at full throtle.
Thanks for your input.

 

[jimmbo]

Low floats. Carb to spark advance out of sync. Idle mixture screws set too lean. Off idle fuel passages in carb dirty/plugged

 

[johntho]

Floats look good no fuel in them and seem to float just fine - new ones on order just in case. Carb to spark advance - how do you check that? Idle mixture screws - which ones are those? Carb rebuild kits on order I'll be going through them once parts are in. Any pictures of carbs with labels on screws?
Thanks,
​John