1986 25hp Yamaha - Model # 25SJ

[scout-j-m]

I went with a friend and helped him buy a 1986 Yamaha 25hp, manual start, short shaft, model # 25SJ. The motor had a broken recoil starter and was not in running condition so we checked spark, compression, and shifting operation along with general overall condition. We got 120 psi on each cylinder with 3-4 good yanks using a rope around the flywheel, so it may actually be even higher if we choose to spin it over more but that was a good number and they were even so we checked that off. Spark jumped a 3/8" gap on my tester. Everything else seemed good aside from normal grime.

Since this is his motor, Im just helping how I can. He doesn't want to spend any money on it until he is confident we can get it going. Personally I would at least install a new impeller, but he wants to hold off so that's the path for now. We flushed the existing fuel lines and filter and gave the carb a very mediocre cleaning just spraying it with cleaner and making sure the jets were clear. It started pretty easy in a barrel and ran ok for a minute or so and then developed a very hard cough accompanied by a knocking sound which occurred every few seconds.

Before messing with it too much more I want to verify the link and sync and timing is good. What I have found via online searches is an idle timing of 1 degree ATDC to 1 degree BTDC and WOT timing of 24-26 degrees BTDC. Also, what is the idle mixture screw initial setting? It was on 2 1/2 turns but I reset it at 1 1/2 before testing running it. Could anyone help me verify these numbers?

 

[scout-j-m]

Spent a little time yesterday afternoon looking at this motor. I found that the plugs' gaps wouldn't even fit in the smallest 0.020" part of my sparkplug feeler gauge. I reset them to 0.039". I also got it to run a little smoother after that but it eventually flooded out or something and died and became difficult to restart. So much so that I gave up as rope pulling it is just a pain. I orginally thought the bottom cylinder was running rich by looking at the plugs like maybe the fuel pump diaphragm was leaking into the crankcase but after the period it ran pretty good after regapping the plugs that didn't seem to be the case. I have yet to check timing but I'm pretty confident a more thorough carb rebuild will be the ticket here.