Merc 25 idle

[Gerald K4NHN]

My sons 1990 Merc 25 didn't want to run at idle after a good run up the river. I would have to give it help with fuel to get it to start and then it didn't want to keep running at a slow speed.

I put a carb kit in it and that helped... It's the carb with the fuel pump on the side, and used the kit #1395-9761. I have the Clymer book and find that the pictures for the carb that I have, they say is for the smaller motors. The carb pictures that they say are for his 25 hp motor isn't his.. I hope that they just have the pictures marked wrong.

The only thing that I saw wrong was the the fuel pump diaphragm was stiff and stuck to the wall of the houseing where the spring contacted it... I don't think it was pumping at low RPM.. If it would run at low RPM's it was real rough..

I noticed that the manual said how set the level of the float. The pictures didn't fit the carb and where the dimensons were given weren't correct in the pictures... They said it was to be set at 1 " to the top of the float, but showed that the 1 " was to top on the frame. The float on this one isn't close to either.

The motor idles much better now, but I noticed that the mixture adjustment is a little hard to adjust. The longer that the motor idles I have to readjust it.. I noticed that after the motor idles a while I can pump the bulb and the motor will go rich and then will soon go back to where it was...

I'm leaning that maybe the float level may not be correct.. I would like to get it back to a nice reliable, smooth idle again..

New plugs, a good hot spark, it'll jump a good 1" out of the boots to the top of the spark plugs, but I haven't check the compression.

S/N OC287406

Anyones thoughts about this..

Gerald K4NHN
Cayce, SC

 

[Laddies]

Re: Merc 25 idle

Some 25s can be alittle temperment at idle, it is very important the the syn on the carb is right, this is some what differant model to model on 25s as they have used 2 or 3 differant carbs over the years. You need to buy the correct manual from Mercury, It's a lession on aftermarket manuals for all of us I guess

 

[Gerald K4NHN]

Re: Merc 25 idle

Can anyone tell me what the correct height adjustment is for the float and where it's measurement is taken, from where to where. I think it a Walbro carb.

I'm trying to locate a true Mercury manual for this year model. At present I have the Clymer manual.

Gerald K4NHN
Cayce

 

[Laddies]

Re: Merc 25 idle

With the carb upside down the top of the float should be down 1" from the center casting, that the float bowl attaches too