1973 johnson 9.5hp intermitent throttle

[bowtieboy77]

I took my motor in to a marine shop last year for a tune up and to diagnose why it would rev in nuetral but not rev up in gear. The problem was a bad plug wire. I will not take it back there as I caught him lying about repairs billed but not performed. I took it north Moose hunting and it starts and runs great the problem is if you are travelling down or up river at full throttle at times it feels like its only 3/4 throttle and suddenly it will just take off and it runs the way it should. If you let off throttle to go through a shallow section and then return to full throttle it might rev up to max throttle/rpm or it might again be lacking in top end power for awhile until it suddenly revs up again if it does at all. I took the cover off in a open section of the river and traveled at full throttle I checked for the choke linkage sticking but choke was wide open. I also watched the trottle linkage and gear mechanism and its not binding up and its going to full throttle no problem found. Could this be more electrical then mechanical? Any help is greatly appreciated.

 

[Joe Reeves]

Re: 1973 johnson 9.5hp intermitent throttle

Assuming you're using the correct spark plugs, Champion J6C plugs gapped at .030 and have the proper comnpression and spark, perhaps the timer base has a wobble that is affecting the point setting, as follows.

(Magneto Armature Plate)
(J. Reeves)

If the armature plate has a a loose fitting, wobbling motion (the plate that the points, coils etc are attached to), it is usually caused by a slightly worn support ring. This allows the point setting to change erratically as the armature plate turns.

The cure is to remove the armature plate so that the support which is attached to the powerhead with 4 screws is visible. Then, with a screwdriver and hammer, or some tool of your choosing, and looking straight down at the support ring, make an indentation at what would be called the 12, 3, 6, and 9 O'clock positions. Install the armature plate and check for a smooth turning wobble free movement.

You may need to do that procedure a few times to obtain the proper fit (not too tight, not too loose), but it's worth the effort.

Use a small amount of anti corrosive grease between the aluminum ring and the brass support plate and also on the brass bushing of the armature plate when all is well.

 

[F_R]

Re: 1973 johnson 9.5hp intermitent throttle

Whatever the cause, the bottom line is that your motor is cutting in and out on one cylinder. Your mechanic knew this, which is why he replaced the plug wire. Only trouble is he failed to find the correct cause of the problem. The possibilities are several, in addition to what Joe mentions. Don't ignore the spark plugs...even a new one can be shorted. Easy things first.