Question on 115hp 1991 yamaha

[MAKO72]

My motor is a 1991 115 yamaha. Recently the motor is rough at idle it will backfire and sputter then it recovers for a second or will cut out. It seems to run fine at higher rpms or at least I cant notice if it is missing. I changed the plugs, pulled off the carbs and cleaned them out(I am a novice at this but it seemed pretty basic I took them apart let them soak in carb cleaner blew them out with my scuba tank and put them back together). No luck it is still missing. I checked the compression and they were all at 125 lbs. except for one that was 122 or 123lbs. I also noticed since the motor has been missing I'm getting burnt oil behind the prop which I know is not a big deal but wondering if it could be related. Any ideas? Could the cylinder with slightly lower compression be getting water in it? Did I not do the carbs properly? Please help very frustrating.

 

[Ray Neudecker]

Re: Question on 115hp 1991 yamaha

Need to be sure the carbs are synced and air adjustments done properly. Best of my memory the air adjustment on those should be 1 1/4 turns from a soft stop plus or minus a 1/4 turn.

 

[MAKO72]

Re: Question on 115hp 1991 yamaha

I did not touch the air adjustment when I took the carbs apart should I adjust them anyway?

 

[rodbolt]

Re: Question on 115hp 1991 yamaha

hello if you did not remove the screws and blow all passages out I would suggest a dissasembly and another thorough cleaning. pay special attention to the idle fuel jets in the bowls. the yamaha kit does not come with new washers to seal the access screws so dont lose the old ones. carefully blow out the idle fuel transfer tube in the body. its the tiny ones with 4 holes in it beside the emulsion tubes. carefully blow out the idle air jets in the top front of the carb throats. dont worry much about removing the large brass screws at the carb top just blow cleaner through the passage.<br /> good luck and keep posting

 

[MAKO72]

Re: Question on 115hp 1991 yamaha

Thanks for the replies I guess I will be pulling them off again. Is there anywhere I can get a schematic for the carbs as I am not aware of the names of all the parts (such as the emulsion tubes)?