1988 Johnson 25HP Spits hard on idle and shuts down

[Big_Kahuna]

88 Johnson 25HP
J25TECCA Tiller Steer

What I have done: Taken carb off (numerous times) clean rebuild. Replace fuel lines from tank all the way to fuel pump (new filter, and bulb) Rebuilt fuel pump last month. Redone carb today. Have taken intake off to check reed valves they look good. New used cylinder head put on today (spark plug hole bad). Have done what I could with checking ignition going by the service manual. Coils show good. I replaced power pack just to spend $$$ (cause it didn't solve problem). I replaced the small fuel lines coming off the manual primer. I have checked kill switch. I have adjusted low speed needle both ways using small adjustments still has hard spit then shuts down. It will start back up and run as long as I keep throttle to it.

Got this boat in April 2016 it's always had hesitation at slow speed getting to WOT. WOT no problem or there wasn't any. Don't know now since it's been over a month waiting on cylinder head to get fixed. Now it's to the point I can't get it to idle in the yard. Check out the video you can see it doing in the video but recently it does it way more than what is on the video.


https://www.youtube.com/watch?v=h8-bSpJU0wA

 

[racerone]

Post a picture of the adjustable stop on the thin metal rod that goes to the back of the motor.----Take the picture with contol at the slowest idle position with motor not running.

 

[oldboat1]

I think Racerone may be talking about the idle stop (throttle). Maybe not.

Your motor sounds to me like it's got a chance. I would try tweaking the idle mix up at the carb top. Initial setting sounds pretty close (runs). Try a bit leaner (1/8 turn clockwise) and see if rpms increase -- would throttle it down a bit (throttle idle stop?), and continue adjusting. If the motor stalls, back the needle out some. By the way, there should be a little plastic or rubber friction retainer up at the face of the carb, holding the needle in place -- need that to hold the adjustment.

Need to play with it a little. If you are already getting a lean sneeze (and if it gets more pronounced adjusting clockwise), adjustment would be counterclockwise -- richer. Stumbling indicates too rich. Either way, about 1/8 turn and let the engine catch up.

The fuel mix should be 50:1.

 

[Big_Kahuna]

Post a picture of the adjustable stop on the thin metal rod that goes to the back of the motor.----Take the picture with contol at the slowest idle position with motor not running.

You talking about the throttle linkage at the back of motor. I'll post some this evening

 

[Big_Kahuna]

I think Racerone may be talking about the idle stop (throttle). Maybe not.

Your motor sounds to me like it's got a chance. I would try tweaking the idle mix up at the carb top. Initial setting sounds pretty close (runs). Try a bit leaner (1/8 turn clockwise) and see if rpms increase -- would throttle it down a bit (throttle idle stop?), and continue adjusting. If the motor stalls, back the needle out some. By the way, there should be a little plastic or rubber friction retainer up at the face of the carb, holding the needle in place -- need that to hold the adjustment.

Need to play with it a little. If you are already getting a lean sneeze (and if it gets more pronounced adjusting clockwise), adjustment would be counterclockwise -- richer. Stumbling indicates too rich. Either way, about 1/8 turn and let the engine catch up.

The fuel mix should be 50:1.

All this is good thanks

 

[racerone]

That thin metal rod has an adjustable " stop " on it.-------That is often adjusted because when it is correct it looks wrong to those who are guessing !

 

[Big_Kahuna]

No Title

Here are some photos to help out that your ask for. I got a timing light put #1 cylinder on TDC I'm getting 32 degrees on my spark advance. So manual call for 30 and I should set at 26 4 degrees below correect. :grumpy:

 

[Big_Kahuna]

Post a picture of the adjustable stop on the thin metal rod that goes to the back of the motor.----Take the picture with contol at the slowest idle position with motor not running.

I have some pics posted.

 

[Big_Kahuna]

Check these out and let me know if this is good??? Thanks

 

[James R]

Do you have the lower in a barrel or running on muffs. You probably wont be able to set idle without the lower in water. Needs back pressure on the exhaust. Try squeezing the primer bulb while idling and see if that clears the stalling problem. I dont rebuild fuel pumps they are always suspect. .

 

[Big_Kahuna]

Do you have the lower in a barrel or running on muffs. You probably wont be able to set idle without the lower in water. Needs back pressure on the exhaust. Try squeezing the primer bulb while idling and see if that clears the stalling problem. I dont rebuild fuel pumps they are always suspect. .

Running in barrel
Primer bulb stays hard plus I have tried this.
Fuel Pump was rebuilt last month.

 

[James R]

Ok. At this point I would be thinking bad crank shaft seal. The fuel mix may not be pressurized enough to overcome a leaking seal at idle and the motor leans out. No real way to test for this except spraying fuel mix into the carb throat which may keep it running at idle. Will only partially prove faulty seals.

 

[Big_Kahuna]

Ok. At this point I would be thinking bad crank shaft seal. The fuel mix may not be pressurized enough to overcome a leaking seal at idle and the motor leans out. No real way to test for this except spraying fuel mix into the carb throat which may keep it running at idle. Will only partially prove faulty seals.

Does the whole powerhead have to be removed???

 

[oldboat1]

To check for crankcase or shaft seal leak, lightly spray some WD-40 or carb cleaner around the base of the engine while running, and see if rpms change. Shield the carb intake -- try to hit the carb-to-manifold mounting gasket, and manifold mounting joints. For a lower crank seal, can also remove lower unit and look for oil/gas up around the shaft splines at the powerhead. (Repair would involve removal of the powerhead, per your question.)

If you did not resurface the replacement cylinder head before mounting, it would be a good idea to do that -- not difficult to do. And when you rebuilt the carb, did you open up and clean the idle passages? Unresponsive needle adjustments often point to some sort of blockage -- even the tip of another needle broken off in the passage opening (unlikely, as you would have noticed the obstruction when you cleaned out passages under the domed expansion cap.)

 

[Big_Kahuna]

To check for crankcase or shaft seal leak, lightly spray some WD-40 or carb cleaner around the base of the engine while running, and see if rpms change. Shield the carb intake -- try to hit the carb-to-manifold mounting gasket, and manifold mounting joints. For a lower crank seal, can also remove lower unit and look for oil/gas up around the shaft splines at the powerhead. (Repair would involve removal of the powerhead, per your question.)

If you did not resurface the replacement cylinder head before mounting, it would be a good idea to do that -- not difficult to do. And when you rebuilt the carb, did you open up and clean the idle passages? Unresponsive needle adjustments often point to some sort of blockage -- even the tip of another needle broken off in the passage opening (unlikely, as you would have noticed the obstruction when you cleaned out passages under the domed expansion cap.)

Thanks for the info. I remove all Welch plus soaked in engine tuner for a day rinse with water then air per mechanic at local Jon boat dealer. Used small wire to check passages. Head was resurfaced bolts were torqued to specs and by pattern the manual calls for. I'll have to wait for gaskets to come in for me to do your test.

 

[oldboat1]

Carb cleaning technique sounds right. Not sure what gaskets you reference -- would not need to remove anything to check the crank seal from above. If you get no change in rpms, assume the seal is likely OK.

 

[Big_Kahuna]

Carb cleaning technique sounds right. Not sure what gaskets you reference -- would not need to remove anything to check the crank seal from above. If you get no change in rpms, assume the seal is likely OK.

Gaskets for outer exhaust cover. I removed to check it out. I removed the flywheel to check top crank seal looks good. Used the gas/oil mixture put it around shaft and turned it didn't see any bubbles. Is this a good way to check this one??? I'll post some pics.

 

[Big_Kahuna]

Here are some photos under the flywheel looks good to me. I check seal via fuel/oil turning crank no bubbles. Let me know if this is correct.

 

[oldboat1]

Seal check sounds ok. Your sensor doesn't look quite right to me somehow -- think I might just replace it, given issues (not a real expensive item: 0583387): http://www.iboats.com/Ignition/dm/cart_id.123809806--session_id.176204501--view_id.1537646 . Fit/placement on the plate might not be quite right. Maybe a hair too close to the flywheel, just not quite sure.

 

[Big_Kahuna]

Seal check sounds ok. Your sensor doesn't look quite right to me somehow -- think I might just replace it, given issues (not a real expensive item: 0583387): http://www.iboats.com/Ignition/dm/*******.123809806--**********.176204501--view_id.1537646 . Fit/placement on the plate might not be quite right. Maybe a hair too close to the flywheel, just not quite sure.

Yeah that's what I was thinking since the flywheel is off.