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No power when in gear

J

johnnyboy11

New member
I have a 1971 Johnson 20hp. Model 20R71S. Having issues with not being able obey power out of the motor when it is in gear. Forward or reverse, it doesn't matter. It will rev up just fine when in neutral, but as soon as I place it in gear, the RPMs drop and the boat will barely back off the trailer and creates little forward motion. The shear pin is brand new, and I just got back from checking for a spun prop bearing. Everything checks out fine. The prop on there is a 9.25x12. It's the prop that came with the motor when I bought it. I know the prop called for is a 9x9 or 9x10. Could this be my problem or is there something else that I should look for?
 
The motor could be running on one cylinder.----Do a proper ignition check.-On that motor spark must be able to jump 1/4" gap on a test set-up.----Checking with a plug grounded to the block is not a proper test.
 
Ok, I checked for spark on both cylinders by just grounding the plugs and watching for any spark. The top cylinder was not firing. Don't know why I didn't check that before, but it seems it didnt make any difference. I jumped off the deep end and bought all new ignition parts (coils, condensors, point sets) I also had to buy a new magneto cam due to the original one being cracked from the flywheel key being sheared by the previous owner. I got all that installed today. Set the points to .020 and the plugs to .030. All this comes straight from the service manual. Once I got it put back together, I installed a new original slow speed adjustment valve on the carb and got it set. The motor fired right up no problem whatsoever. So I shut it down and checked for spark on both plugs Good to go there. Not sure what you are talking about @racerone with the 1/4" gap other than holding it that far off that block. When I did that, I got a nice little zing. Anyways, hooked it up to take the boat to the river and I am still having the same problem, the boat will not get on plane and the motor bogged down in gear. Not to mention, as I have the boat on the Arkansas river, trying to beat the storms that came through this afternoon, it sheared the flywheel key AND broke the magneto cam again. So now I have TWO issues, no power AND the fact that the flywheel key is shearing. Any thoughts?
 
The flywheel key positions the flywheel for proper spark / timing.------When tapers are clean they lock together when properly torqued.---That fit of the tapers drives the flywheel.------Shops use tools with adjustable spark gaps of up to 1/2" for a proper spark check.--Laying plugs on the block is not a proper spark intensity check.-You may have to use some valve grinding compound and lap the tapers together to get a proper fit between them.
 
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