1994 Johnson 120 V4 stutters between 1000 - 2000 RPM

[loweL1930]

I have a fresh rebuilt 1994 Johnson 120 V4. It runs great at top end and idles beautifully, can even troll with it and it just hums. But when I travel at slow speeds between 1000 and 2000 RPM it stutters quite a bit but doesn't stall out....what could this be? Thanks in advance for any input.

 

[The Marine Doctor]

Re: 1994 Johnson 120 V4 stutters between 1000 - 2000 RPM

Sounds like you are not getting enough fuel in that rpm range.<br /><br />Might try oversizing the lowspeed jets to get more fuel.<br /><br />TMD

 

[loweL1930]

Re: 1994 Johnson 120 V4 stutters between 1000 - 2000 RPM

I thought that I may not be getting enough fuel at that RPM so I tried pushing in the choke and then it just stalled out. I thought by pushing in the choke it would give me more fuel. I do remeber the mechanic changing the jet screws around. It was 33 on top 31 on bottom and now it's reversed. Johnson says that if it's starving for fuel pushing the choke in would help, if it doesn't it's electrical. I thought maybe it could be a weak coil, I have a spare coil and I could switch one by one to see if that makes a difference. Also the mechanic put in different plugs than what Johnson calls for, I was running QL7 plugs and he put in LL7. Guess I can keep playing with all of the above and hope that something helps. Until then if anyone has any input to save me some work with the info that I given it would be much appreciated.

 

[loweL1930]

Re: 1994 Johnson 120 V4 stutters between 1000 - 2000 RPM

Just spoke with the mechanic that overhauled the engine. He did put the jets back to where they came from so they are now in the right place. Could it be a weak coil that only acts up at that RPM?

 

[SCO]

Re: 1994 Johnson 120 V4 stutters between 1000 - 2000 RPM

This is just an fyi. I had a power pack that went bad and exhibited similar symptoms, rough from zero to about 1500 rpm then it smoothed out like flipping a switch at 1500 rpm +. The rough to smooth rpm crept upward in time till it became impossible to get the boat on a plane. Just something else to try. Good luck

 

[93bronco]

Re: 1994 Johnson 120 V4 stutters between 1000 - 2000 RPM

according to the 1994 parts manual-<br />carb # 436277 120-125SX<br />idle air bleed #37 (bottom)<br />intermediate #30 (top)<br />high speed #63D (fuel bowel)<br />----<br />carb # 436552 120-125SX<br />idle air bleed #35<br />intermediate #31<br />high speed #76D<br />just trying to help

 

[loweL1930]

Re: 1994 Johnson 120 V4 stutters between 1000 - 2000 RPM

Thank you all very much for the info, a few more things to check out. "Life would be a lot easier without my toys.....but then it wouldn't be much of a life".

 

[fubarman]

Re: 1994 Johnson 120 V4 stutters between 1000 - 2000 RPM

May I am barking up the wrong tree with this but do the carbies on these boats have hi and low mixture settings?<br /><br />With the experience that I've had with 2 stroke engines, the engine might run well when idling and also up high but in the transition between low to high mixture, settings can be critical for smooth acceleration. Its the low speed mixture that is the culprit in this case.<br /><br />The engine is best tuned under normal load.