1989 Jonson 40 One Cylinder at Idle

[gsutton]

1989 Jonson 40 runs on one cylinder at idle and great just above idle through full throttle. I have replaced the spark plugs, spark plug wires and coil. When I remove the top spark plug wire at idle it runs the same and when the bottom is removed at idle it stalls. Any suggestions?

 

[AlanR]

Re: 1989 Jonson 40 One Cylinder at Idle

check your wiring diagram and check your powerpack with a manual

 

[gsutton]

Re: 1989 Jonson 40 One Cylinder at Idle

It seems it would have to be the power pack, since everything else is new. Is there a way to test it?

 

[F_R]

Re: 1989 Jonson 40 One Cylinder at Idle

Why is it that everybody is so quick to condemn the power pack? That is the last thing to check. The first thing to check is the compression. If that is OK, the most likely cause of your problem is the idle circuit of the top carburetor. That is too new a motor for me, but according to the parts diagram, it looks like it has an adjustable slow speed needle and an idle orfice(?).

Did you have a good spark on the top wire when you removed it? If so, it's not the power pack or anything related.

 

[gsutton]

Re: 1989 Jonson 40 One Cylinder at Idle

I just checked the spark and it is great. I have been chasing what I thought was an electrical problem. I will now look into the carbs.

 

[F_R]

Re: 1989 Jonson 40 One Cylinder at Idle

Never put the cart in front of the horse. Check that compression first. No carburetor can work on a damaged cylinder.

 

[Silvertip]

Re: 1989 Jonson 40 One Cylinder at Idle

If the engine runs fine off-idle to WOT you very likely have a carb issue. Idle circuit is clogged or the mixture screw has worked its way out of adjustment.

 

[gsutton]

Re: 1989 Jonson 40 One Cylinder at Idle

We have removed and cleaned the suspect carb, and it improved a little. What is the proper way to adjust the mixture?

 

[Silvertip]

Re: 1989 Jonson 40 One Cylinder at Idle

Turn it in in very small increments (1/16 turn). Pause and let the engine stabilize. At some point the engine will tend to die. Note the position of the mixture screw. Turn the outward in the same fashon until the engine again tends to die. Note that position. happiness is somewhere in between those two points. As you approach the "sweet spot", you may need to set the idle down a little. Mixture and idle speed MUST be done in the water. There is no back pressure on muffs.

 

[BruceW]

Re: 1989 Jonson 40 One Cylinder at Idle

I have a 1989 40 also,last summer mine was doing the same thing.It was running on one cyl. but when I would open it up it did take off. The problem was the power pack. I had to get an up grade version with the new unit being mounted over the water jacket. It was not hard to install. Runs like new again.

 

[G DANE]

Re: 1989 Jonson 40 One Cylinder at Idle

If the carb clean helped some, chances are it didnt get all the crud. Try to dismantle carb totally, remove all plastic parts and soak in carb cleaning solvent over night. Then blow out all orifices with compressed air. Iddle jets are orifices just above throttle butterfly, often overlooked. Run a hair from a wire brush or so thru the little hole. The 1989 40 had all fixed jets as far as I remember. If you have good equal spark that can jump a 5/16 testgap with strong blue flame at crancking speed, spark isnt the issue at iddle.