20 HP Johnson cuts out when accelerating

[riverso]

1969 Johnson 20hp SN# = J310 7794 Mod# = 20R 69D Engine starts ok and runs out great at full throttle, but cuts out when accelerating. It actually seems to run on one cylinder and surges (cuts out and in) until the unit is up to top speed? Suggestions on what to look for??

 

[NathanY]

Re: 20 HP Johnson cuts out when accelerating

Is it like a stutter? My 25hp is doing the same thing I think. I am going to rebuild the carb, and I will get back to you. I have been told that it might be the highspeed jet causing the problem.

 

[alcan]

Re: 20 HP Johnson cuts out when accelerating

Hi Reverso<br />The first thing to look for is a repair manual. Sounds as if it has been a while since this unit has been serviced. You may be able to obtain a copy of an after market manual at the library. If not buy one, they are well wroth the cost. It sounds to me like the main problem is ignition related, points, coils or wires, etc. So many times these things end up being a combonation of problems. A person will focus on one area and make a repair and break down again on the very next trip. Then they say, the motor is old and a piece of junk, wore out. If you follow the book, take an evening or day off and do a complete service and inspection job, you should have a depenable motor for the next couple years.

 

[riverso]

Re: 20 HP Johnson cuts out when accelerating

I'll look for a service manual. I tend to think it is electrically related too. It does run excellent at the top end, it just getting it there. The unit has new plugs and fresh gas. Plug wires 'look' good, but I have never changed them in the 20 years that I have had the motor, so wires and points may be the best start location.

 

[alcan]

Re: 20 HP Johnson cuts out when accelerating

Hi Riverso<br />Unless you test the sparkplug wires bad. Find them leaking or a worn spot or some defenate corrosion, etc, They should be fine no real need to replace them. Do inspect them carefuly along with the coils. Always remove and look under the coils. You may find evidence of leaking, a black smug or spot (arcing). Just my guess, but I think you will find worn points.

 

[OBJ]

Re: 20 HP Johnson cuts out when accelerating

Hi reverso....<br /><br />Alcan makes a good point on the points (no pun intended). If it were me, that's the first thing I'd look at. Remember, if you replace the points, replace the condensers also. I'd bet that would take care of the problem.

 

[riverso]

Re: 20 HP Johnson cuts out when accelerating

Thanks for the advice, I will start with the points/condensor and check the coil.