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Author Topic:   1970 Johnson 85 Problems
rwill1 posted 05-31-2002 08:26 AM ET (US)   Profile for rwill1   Send Email to rwill1  
I have a 1970 Johnson 85 that stumbles and stalls when given gas above idle. The motor runs perfectly sometimes. I have changed plugs, and it did not change the situation any.

I have ruled out fuel delivery problems. It almost seems that it is timing related (Auto-advance?). Any Ideas?

WHALETEX posted 06-02-2002 02:44 AM ET (US)     Profile for WHALETEX    
I had a similar power problem with a 69 85hp Johnson. It turned out the spark advance arm would not follow the throttle arm in the engine when advancing the throttle at the helm. Generally it would work fine cold and after normal cruising, but it would hang-up after extended idleing. The result was a few seconds of the RPMs picking up as expected followed by big drop in power and in some cases the engine dying.
If it happens to you again pull the cowl and watch the motion of the spark advance arm
(the long arm hooked to the throttle system that has a link that hooks to some stuff under the flywheel) versus the movement of the throttle cable from the helm. The spark advance arm should smoothly follow the throttle cable to about 3/4 thottle when the spark advance hits its stop and the rest of the movement is just moving the throttle butterflies.
I hate to admit it, but for a couple of years we did everything we could think of to fix it right. We replaced most of the moving parts under the flywheel, we replaced the follower spring, made certain every thing was properly clean and lubricated. It would work great for a little while then it would start to act up again. The final "solution" was to wrap a couple of big rubber bands around the spark advance arm to "help" it along. I used the motor like this for over ten years without any problems greater than occationally needing to replace the rubber bands.

Another problem that we had with this motor that affected top end performance was plugged high speed jets in the carburators. On the 69 the high speed jets were fixed and could not be removed. They are located behind each of the four drain screws (two per carb with one each on the left and right side of each carb) Remove both drain screws from each carb. Spray with the little red nozzle on a can of carb cleaner. If the cleaner easily blows in one drain hole and out the other then the high speed jets are clear. If not then the carbs should be removed and fully cleaned.

Another problem that can affect top end performance is the setting of the proper gap on both sets of breaker points under the flywheel. Each set of points fires two of the four cylinders on the 69. If one of the sets of points is too far open it will start to "float" out as the RPM picks up and two of the cylinders will quit firing causing the motor to bog. If one of the sets of points is set too closed or heavily arc damaged the motor will miss at idle, but may run fine at higher RPMs as the points start to "float" out.

The only other problem we had with this engine that caused intermittent performance problems was a small wire that ran from one of the breaker points down the spark advance system toward the back of the engine broke inside the insulation just aft of the little wire clamp on the breaker mounting plate. Inside the insulation this wire made contact some of the time and some of the time it did not. Sometimes the motor would run like it was on two cylinders, sometimes it would run fine, and the last time we ran it before we found the problem it would cause the motor from the flywheel to the prop to run backwards, then forwards, then backwards and so on as we moved the thottle (and the spark advance). Apparantly the intermittant wire contact was sending a signal to the coil like the points were openning and thus causing the spark plug to fire at the wrong time. We found the break by running a continuity check on all the wires within the power head area.

I swapped the 85hp off my Whaler in 1988 for a 100hp, but I saw the 85hp a year or so ago on the back of a friend of a friends old bass boat and he said it was still running fine as long as you remembered to keep some rubber bands handy.

Good Luck

You might also look at some of the input on this thread

rwill1 posted 06-02-2002 01:04 PM ET (US)     Profile for rwill1  Send Email to rwill1     
Thanks! More Info: We have narrowed it down to when the motor is run only in forward gear. Once you shift to reverse, then the problems begin. This may be concidental, but it is repeatable.

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