1972 Johnson 9.5 Hesitation/Stumbles at Mid-Range

[thull]

Hi All,

I inherited this motor from my uncle. Compression is an even 65psi on both cylinders. I know it sounds a bit low, but many folks indicate this is fine compression for this motor, evidenced by good idling and starting discussed below. Before I invest a $100-$150 on new consumables I thought I'd see if I could just file the points, clean the carb (w/o kit) and see if she'd run. Well, she does. Starts on first pull usually, runs great at idle and WOT. However, it stumbles/hesitates as I move the throttle from idle to high speed. On the lake test, it ran for about 1/2 an hour and then died and wouldn't start back up. Had to paddle my 14' jon boat into the dock about 1000 yards away. Not great, but not the worst that could have happened. Got it home in the barrel and it started right back up the next day and ran the same. Idles fine but stumbles in mid-throttle.

I'm thinking either the hi speed fixed jet is not totally clean or perhaps a coil is going bad (they are the German sea-green ones but are showing some cracks). I tested the coils B4 the lake run and both had 5K-6K ohms of resistance on the secondary winding and no resistance on primary winding. I replaced the spark wires and have great spark on one cylinder and mediocre spark on the other (spark jumps 1/4" gap but doesn't spark on every pull of the rope). I did not replace the condensers yet, so maybe one of them is the culprit. Any advice is appreciated. Thanks!

 

[gm280]

thull, I don't thing your condenser is a problem. They either work or not. They are merely a capacitor and usually there is not erratic issue with caps. So I would seriously look at replace BOTH spark coils because while they work cold, how do they work after getting hot. And the fact that you stated they have cracks is a sign they are tired and wanting to go to the retirement old parts can now. You could use a heat gun or hair drier to test their function and see if they break down when hot. Because that IS what I think is PART of the problem. Your reading on the secondary's are good and there is resistance on the primaries as well but being so small in their resistance, they probably read shorted on your meter. An RX1 scale may show their resistance. The next thing is to buy carb kits and time for a good break down and cleaning for the carbs. I think if you do those things, you will enjoy a nice running engine again... JMHO!

 

[racerone]

I use a MERC-O-TRONIC ignition analyzer to test condensers.---They often pass the test when cold but fail when put in an oven to warm them a bit.---They are cheap so replace them.----The intermittant spark is a sure sign of problems.----Perhaps look in the dark when pulling it over, look where the plug wires come out of the magneto plate.

 

[reiddo1]

thull, I don't thing your condenser is a problem. They either work or not. They are merely a capacitor and usually there is not erratic issue with caps. So I would seriously look at replace BOTH spark coils because while they work cold, how do they work after getting hot. And the fact that you stated they have cracks is a sign they are tired and wanting to go to the retirement old parts can now. You could use a heat gun or hair drier to test their function and see if they break down when hot. Because that IS what I think is PART of the problem. Your reading on the secondary's are good and there is resistance on the primaries as well but being so small in their resistance, they probably read shorted on your meter. An RX1 scale may show their resistance. The next thing is to buy carb kits and time for a good break down and cleaning for the carbs. I think if you do those things, you will enjoy a nice running engine again... JMHO!

These coils also depend on a solid connection where the plug wire goes. I found on mine that the only way to ensure this is to remove the timing plate completely, pull both spark plug wires up into the plate with the coils removed and then thread the plug wires into the coils before setting them back in place. This was not done with the previous owner and I was experiencing misfiring issues. Hope this is clear. Good luck