25HP Johnson running rough at high speed

[Jon Boat Jim]

I'm working on a 1990 TJ25ESLESE 25HP Johnson that has been stored for several years. It started fine and had balanced compression at ~ 105 psig. After doing a decarb the compression is up to ~115 each. I changed to new plugs and ran it with water muffs. It seems to idle well enough but it misses or cuts-out at high speed. What is my next step to get it running right?

 

[Cofe]

Re: 25HP Johnson running rough at high speed

Sounds like your high speed jet is gummed up. If you remove the hose connection at the front of the carb. The high speed jet is just behind it. Use a small piece of wire to make sure it is cleaned out. You may have to disassemble clean and rekit the carb.

Never put a motor in gear and rev it up on muffs. The motor can run away with auto ignition and disintegrate your motor.

 

[Jon Boat Jim]

Re: 25HP Johnson running rough at high speed

Sounds like your high speed jet is gummed up. If you remove the hose connection at the front of the carb. The high speed jet is just behind it. Use a small piece of wire to make sure it is cleaned out. You may have to disassemble clean and rekit the carb.

Never put a motor in gear and rev it up on muffs. The motor can run away with auto ignition and disintegrate your motor.

Do you mean the gas line connection to carb?

 

[Cofe]

Re: 25HP Johnson running rough at high speed

Yes

 

[bonz_d]

Re: 25HP Johnson running rough at high speed

I would suggest taking the carb off and rebuild it. The kit can be bought at most napa stores and they are not exspensive. All that is needed are a few basic tools a couple cans of spray carb cleaner and a couple cans of canned air like that used to blow out computers.

These carbs are very basic. A float and needle valve and one removable jet. You want to spray cleaner into all passages and the pickup tube that exyends down the center until there is a good flow of cleaner. Then blow it out with the canned air and repeat the process. Sometimes for a very dirty carb it becomes nessasary to give it a soak to desolce all the varnish.

Could also be helpful to take pictures along the way as a referrence to help take it off and then get everything back where it belongs. Also while it is apart I would suggest replacing all the fuel lines inside the engine, ethonal plays havoc on old rubber.

 

[Jon Boat Jim]

Re: 25HP Johnson running rough at high speed

Thank you for the great advice!

 

[Jon Boat Jim]

Re: 25HP Johnson running rough at high speed

Cofe,

Would you suggest that
1) I take the high speed orifice out to clean it (I have the correct tool needed)
2) leave the orifice in-place, and spray Gum-out through it
3) poke small wire through it, as you suggested
4) some combination of 1, 2, and 3