50hp johnson only starts with top spark plug remove.

ahmongboi

Recruit
Joined
Jan 4, 2013
Messages
2
Hi there iboaters I need help here, i have a late 70s to early 80s 50 hp johnson that was running fine untill I let it sit for a good few months and now it's not starting anymore. I've try pulling the spark plug to check for spark so now it starts fine with the top spark plug remove, but as soon as I put in the top spark plug in it will turn but will not start. So far here's what i've gotten check. I don't think this motor has a kill switch, there's still spark in both plugs, theres fuel going into the carb, try taking off the bottom plug and only run the top plug but still wont start. Try switching plug wires still not working. So I've at the end of the road here does anyone have encounter anything like this.
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Re: 50hp johnson only starts with top spark plug remove.

Is the starter mtr spinning it fast enough? Have you got a good battery thats been load tested ?? Are all the battery connections on both the battery and the mtr good, clean and tight ??
 

Home Cookin'

Fleet Admiral
Joined
May 26, 2009
Messages
9,715
Re: 50hp johnson only starts with top spark plug remove.

are you removing the whole plug or just its wire? Does it shut off if you start it with one plug, and then plug in the other while it's running?

By removing one plug completely you make the compression lighter and the motor will spin faster. So I think boobie is on to something.
 

ahmongboi

Recruit
Joined
Jan 4, 2013
Messages
2
Re: 50hp johnson only starts with top spark plug remove.

Thanks for the fast reply guys. Yes the starter mtr is spinning fast enough. What I did was take out the whole spark plug on the top and then with just one easy turn key it starts fine with only the bottom plug, a lot of pressure so i couldnt insert the top spark plug in while running so I'd have to turn the motor off and then insert the top spark plug in to try to start it again but it would not start with the top plug inserted. Top compression was 70 and bottom compression was 80.
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Re: 50hp johnson only starts with top spark plug remove.

Will the spark jump a 7/16" open air gap on a spark tester ??
 

coolguy147

Commander
Joined
Jul 14, 2008
Messages
2,817
Re: 50hp johnson only starts with top spark plug remove.

Thanks for the fast reply guys. Yes the starter mtr is spinning fast enough. What I did was take out the whole spark plug on the top and then with just one easy turn key it starts fine with only the bottom plug, a lot of pressure so i couldnt insert the top spark plug in while running so I'd have to turn the motor off and then insert the top spark plug in to try to start it again but it would not start with the top plug inserted. Top compression was 70 and bottom compression was 80.

Check for spark on both cylinders then I would do a decarb with the BRP engine tune stuff. follow the directions. Get those numbers up!!
 
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