1998 Johnson 50hp 2-stroke dies while in gear at idle speeds

[skoboten2day]

I have checked the other posts and not seen a similar issue. Apologies if it's on an old page or been answered. Inherited a Seaark 16' jon boat from my old man. He bought it new in 1998 and probably put less than 100 hours on it total. It sat on a farm for 6 years before I got a hold of it this spring. I took it to a recommended boat mechanic. Paid him to clean & rebuild carbs, tune up, replaced spark plugs, replaced impeller, and disable VRO so it runs on 50:1 premix. Used new gas with no ethanol and high quality oil. New cranking battery and battery tender too. He says he ran it on the lake and it ran great. Took it on a fishing trip and it ran well at first, but coming into the dock or lining it up on the trailer after running for over an hour, it died while in gear at idle speeds. Took it back to the mechanic. He took the carbs apart again, new spark plugs, new gas and oil, same problem again the last time I took it out. Oddly enough, it starts and runs so smooth on the trailer with the ear muffs. Thought about back pressure carbon deposit problems, or old hose problems, but most people tell me the idle screws/jets still need adjusting. I'm not sure if I want to take it back to the same mechanic again. Thoughts? Thanks!

 

[Joe Reeves]

If you or someone else pumps the fuel primer bulb constantly, acting as a manual fuel pump... does that cure the problem? If so, suspect the fuel pump.

 

[skoboten2day]

Haven't tried that. You think that's more likely than adjusting the idle clockwise to a more rich burn? One source told me Johnsons tend to run a bit lean and that they need to be adjusted after a carb rebuild. Thanks!

 

[Joe Reeves]

If a carburetor has a slow speed adjustable needle valve..........................

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[oldboat1]

"In" (clockwise) is lean.

 

[jakedaawg]

...

 

[Joe Reeves]

...

Nah, I don't buy that for a minute Jake!

 

[TNBoatGirl]

I am having this exact issir with a 1972 Johnson. Mechanic replaced water pump, carbs, cables etc. 1st time out we lost all throttle. They said cable had snapped. Had it out last night and same issue. Motor purrs at half throttle and dies if we go up or back on throttle. An old mehanic friend that my Dad used years ago said to try adding 2+1 addiditve to the fuel. Fuel was allegedly non ethanol when I picked boat up last weekend. Could this be the adjustment described above or bad coil? Mechanic wants me to bring boat back so he can test it on water.

 

[jakedaawg]

Nah, I don't buy that for a minute Jake!

I was going to mention that sometimes it's a metered air bleed and screwing in would in effect enrichen but decided against confusing the situation as those are few and temporary in actuality (they become fuel after butterfly passes over).

Sure is nice to have you back around Mr Joe Reeves, your patience and dedication to correct info has been a bit of an online role model for me anyways...

 

[skoboten2day]

So I've taken the front part off from the carburetors. Not sure if this was even necessary? Hope I can re-seat everything together again when I'm done, ha! Are the idle adjustment screws the flat head screws top left of each opening to the carb that I'm pointing to? Is this what I'm turning clockwise all the way in then starting to back out counter clockwise? Do you do one at a time or in tandem? Pictures attached. Thanks.

 

[Vintin]

Just like Joe R. says. Here are two photos from the service manual. I have this same motor in a short shaft version.