Thread: 1990 Mercury 25hp Carb

That seat may be removable with a screw driver not sure. But do not bore it out. If the needle has a rubber tip on it could be that ethanol gas has caused it to deteriate and some is on the seat causing it to stick when closed. Also check the pin that holds the float. Pin and hole in float could be gummed up causing it to stick. Go to auto parts store and find a spray product called DeepCreep. It is made by SeaFoam. Spray everything good with it. Spray up into seat,pin,float hole, into opening of carb into jet holes in body and let sit overnight then spray again. Put it back together and run it and see if that helps.

Thanks for the reply. I have replaced the needle before and I have cleaned it with similar carb spray with the same sticking needle result

Are you sure the needle is sticking and not the float?

I take the bottom bowl off and the float and the little lever falls down but the needle stays in the seat

I've encountered that in the past and I fixed it by sanding the 3 sides of the needle. Use very fine sandpaper on a piece if glass (to be sure it is flat) and gently sand the 3 edges. Be very careful not to sand the tip. It doesn't take much

What Bill said. Also might try finding a diagram of the carb on the net that gives a parts break down. I worked on a Mariner/Yamaha that had replaceable rubber seats that were a nightmare to change. If that happens to be the case that also might explain it sticking closed. It should also show you if the seat is actually replaceable.

I'll try the sanding thanks for all the help. The seat seems to just be brass and the diagrams I've found don't really show much about the seat but thanks again!

An easy fix to that problem is to take a Q-tip and fine grit lapping compound. Go easy on the lapping compound, dip Q-tip in it and insert into seat. Twist repeatedly with finger tips. Thoroughly rinse and flush the fuel circuit afterwards. It only takes a minute of this to have the bore of the seat shining line new.