1980 70HP Johnson kills under load

[Minnesota Ernie]

I have a 3cyl. Johnson that idles fine but bogs down when I begin to throttle up. This is especially noticeable when trying to pull someone on a tube. I have to throttle 1/2 way and wait for the motor to catch up and then gently bring it to full throttle. <br /><br />I have tried to run SeaFoam through the gas for 2 tankfulls but this hasn't helped the problem. Some friends believe it is a carburator problem while others believe the advance may not be functioning properly. Any suggestions for troubleshooting the cause would be greatly appreciated.<br /><br />Thanks.

 

[G DANE]

Re: 1980 70HP Johnson kills under load

Hi Ernie<br /><br />Try to pull one plug wire at a time while the motor iddles. Use a cotton cloth or insulated plier.<br /><br />You could have bad spark or low compression on one cylinder, it happens and 3 cylinders iddle well anyway. A compression test also tells a lot if you have access to a meter. Otherwise a gummed up carb would be a good guess.<br /><br />Try and post back.

 

[Greg Lawrence]

Re: 1980 70HP Johnson kills under load

push the choke in when it starts to bog, if it starts to come alive its probly the carb. I am lickin this problem as we speak. (type)

 

[Minnesota Ernie]

Re: 1980 70HP Johnson kills under load

Hi GDane,<br /><br />I pulled the plugs and it seemed to have good spark from the plugwire to the plug. I also did compressions on the three cylinders and then also squirted oil into the cylinder to compare compressions. On the top cyl I got 130 and 160(oil), middle was 130 and 165(oil) and the bottom cylinder was 130 and 160(oil).<br /><br />After this I ran it for a while and would hear a periodic metal ping on metal. Further investigation seemed to indicate the starter was getting a jolt of electricity from somewhere and the starter gear would try to jump up and catch in the flywheel. <br /><br />I am not sure this is a related matter but what is happening here?

 

[G DANE]

Re: 1980 70HP Johnson kills under load

Hi Erni<br /><br />I think you ought to clean your carbs realy carefully, it probably is your problem.<br /><br />Remember the small casted-in jets in top of carbs, for iddle and intermediate supply.<br /><br />I think it will solve your problem.

 

[Minnesota Ernie]

Re: 1980 70HP Johnson kills under load

Well, I cleaned out the carbs-found a couple bad gasket pieces that sit over the stem in the carb., reassembled and it still needs to catch up to itself when moving from idle to WOT. It definitely runs quieter than before the carb cleaning.<br /><br />Any other ideas what would make it difficult to go from idle to WOT without stopping to let the motor catch up to itself?