WWYD What would you do? 1981 johnson 25 hp short shaft

[danboatman44]

Hello all,
looking for some insight to an issue i am having with a 25hp 1981 Johnson J25RCIM , Please look at issue from this view point with the fuel system working up to manifold intake, The carb , fuel pump , tank, bulb are all working fine up to the manifold is best i can tell so far.
The motor will start and run as long as i am giving some gas from tiller , if i try to let it idle it will die, also i can be running it at mid rpm 1500-1800 and it just die's out at times. The water pump is Peeing just fine. (all this is when in neutral) . The carb, and fuel pump are rebuilt and working. as stated above all fuel issues ruled out up to manifold just after carb. I have not removed heads and i believe they have never been off. this is a low hour low use motor that was stored in a shed in northeast US for the last 5 years before that it was garaged. There is very little signs of wear anywhere on engine. When engine is running it sounds very nice. There is excellent spark on both cylinders. Plugs and wires are new. Any suggestion as to what should be done next would be greatly appreciated.
Thank you much.
Dan

 

[quackaddict1]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

Have you tried the simple things first? The air/fuel mixture screw on the carb?

 

[Okee Jimmy]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

Hi, sounds like the low speed mixture is off. The low speed mixture screw is at the top of the carburetor at the throat. if you turn the screw counter clockwise it richens he mixture, clockwise will lean it. My guess is, it is lean. open the screw (ccw) until the motor will idle cleanly. If adjusting the mixture screw doesn't make a difference, the carburetor may need more work. Pay close attention to the little tube in the big tube going into the carburetor body, make sure it is open, but do not enlarge it with torch tip cleaners ect. Also the nozzle gasket (around the big tube) must seal properly. Hope this helps, Jimmy.

 

[tashasdaddy]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

carb adjustments > http://forums.iboats.com/showthread.php?t=299680 also look at carb cleaning, and make sure the venturi (little holes) in the top of the carb barrel are clear.

 

[5150abf]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

Ya, the carb may be rebuilt but it doesn't sound like it is working so I wouldn't pull the heads till you try what the guys have suggested.

Mine had a similar problem, cleaned the carbs, new fuel pump, still there, changed CDI, still there, changed coil still there geuss what it was, my clean wasn't, I spent $300 bucks and had 3 bad fishing trips cause I cleaned the carb and that can't be the problem.

Always do the free stuff first, even if you have to do it again.

 

[danboatman44]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

i got the carb apart now and everything looks good.. i ran little wire thru every opening, i am wondering if it isnt the new gasket i put in around the nozzle,,, Jimmy mentioned the "nozzle gasket (around the big tube) must seal properly" ....is this the odd shapped round gasket that goes over the stem (brass looking pipe) and sits down the bottom? how do i know if it is seated properly it just lays there? thanks to all i will be working on more tonight and tomorrow... oh so close!!!

 

[danboatman44]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

would having fast screw to tight on carb prevent from starting?

 

[jbjennings]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

Your carb doesn't have a high speed adjustment. The high speed nozzle is a fixed jet. Part #36 in the link below is the low speed idle adjustment, and if it is tight, that is most definitely why your motor won't idle. Maybe this link will help. I believe about 3/4 to 1 turn counterclockwise on part #36 will get you close on your adjustment. If it idles then, turn the screw clockwise very slowly until the motor starts sneezing and back it back off about 1/8 of a turn. That should be just right.
Hope this helps,
JBJ

http://www.crowleymarine.com/brp_parts/diagrams/23064.cfm

 

[danboatman44]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

okie dokie... thanks for the advice...


i have adjusted the slow idle as directed and cannot get the motor to run on its own,,,, almost but not for more than about a 30 to 40 second idle and cant get to start unless add fuel mixture spray to cylinders than she starts and idles for a few seconds and dies... if i give gas from tiller than it revs but eventually dies out... about 30-40 second max... idle or rev.. after this last try.. i noticed there was gas in bowl of carb , i loosened the drain screw and fuel dripped out. all hose are new no leaks that i can detect, the primer bulb i think should be staying harder than what it is... but i am no expert.. thats why i seek your guys knowledge...i really wanna get her on the back of the boat and get her out there.. i am replacing a tansome. so i have a fw weeks. i will post some pics. any and all help is appreciated. !there seems to be some play but not enough to cause this issue.

 

[danboatman44]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

continued.. there seems top be some play in the tiller linkage yet not enugh to cause this prob... reminder the spark is perfect... checked and recked...

 

[Ironguts]

Re: WWYD What would you do? 1981 johnson 25 hp short shaft

Did you use a carb rebuild kit for this model? It's only about $30 bucks but well worth the investment. FYI, there's more to carb cleaning/inpecting/repair than meets the eye. I have the OMC service manual for this model. You'll need to carefully inspect(with a magnifying glass) the inlet float valve/seat and needle valve for even the slightest groves, nicks or scratches. You need to inspect the float and arm for any wear or damage. Also check the hinge pin. The only way to properly check the float level is with a float gauge (part 0324891). Also, float drop must be within 1-1/8 to 1-5/8" from top of float chamber to bottom of float. To clean the low speed orifice holes you'll need to remove the core plug. This can be difficult however. E-mail me and I can send you the carb maintenance procedures.