Johnson 120hp Looper Idle problems

[JasonB]

Last year, bought nice boat that has a 1994 Johnson 120TLERC. This boat sat unused for at least 6 years. I cleaned the fuel out, replaced filters, etc and jot it running for a couple trips to the lake last fall and ordered a set of carb kits. This year, it was stumbling at idle, so I cleaned and rebuilt the carbs. No help with the idle, so I suspect I need to clean the calibration pockets in the throttle body. I'm away from the boat at the moment, so I can't look at it. Can these be adequately cleaned without pulling the core plugs (trying to locate some). Anyone know what size welding tip cleaner it usually takes? The plugs seem to run about $6 each and looks like I need 4 if I have to pull them? Can't find them here at iBoats.

 

[Roj115]

I can't really answer your questions but I can tell you that those loopers never idled that well. I have a friend with a '98 120 looper and it has always idled rough. I may be talking out of place here but I don't think anyone has gotten one of those engines to idle very smoothly. The cross-flows idle much better, or at least mine did. Maybe you've done all you can do and it can't be improved upon due to the natural tendency of those motors to idle poorly.

 

[racerone]

What trouble shooting has been done ??------Compression test ?----Looked into issues with crankcase compression ?

 

[JasonB]

I have not tested compression yet as the engine runs great once you pass ~1000 rpm. Will run all day at 1100 without a hiccup. Also tends to idle a bit better when warm, but is still very difficult to manage around the dock as it dies often.. When on a hose, at idle, it stumbles every 10-15 seconds and puffs a small cloud of smoke.

 

[racerone]

Start with trouble shooting this motor !-----Motors of this type are a 2 stage " air processing machine " and at idle there is more time for air to leak internally from place to place.----Most motors will run ok at full throttle because there is less time for leakage to occur.----Compression values are ?

 

[JasonB]

I'll try to get compression numbers this afternoon. Any help on how to clean the calibration pockets and if the core plugs have to be pulled? If I need to order parts, I would like to get them on the way.

 

[JasonB]

My Hrbor Freight compression gauge shows all 4 cylinders between 100 and 105 cold. To answer my own question partially, I was able to pull the carbs back off and use a fresh can of carb spray with a straw to blast into the calibration pocket. After a few seconds of strong spray, I judged the idle holes to be open. I then took the carb, and shot cleaner through the 2 brass idle and intermediate jets on the front of the carb, both with my finger over the air bleed at the needle valve and without. On one carb, I found I had spray coming out the side plate, so I pulled the plate off, checked the rubber gasket, and reassembled. Found another I didn't like the look of, so I redid it as well. No more leaks visible. Turned on the water, pumped the primer build and it lit off. No choke needed. Let it idle and after a bit it smoothed out to what I would more expect. It never completely idled down where it would in the water, but that's not unusual. I still get a puff of smoke every 10-15 seconds, but it's less pronounced. I won't say it's 100% fixed, but it does seem better. It is also quite a bit easier to start and it only died once maybe 30 seconds after the initial startup.

What would be the next steps in tuning and making sure it is up to speed outside of an in-the-water test?