15hp Johnson problem

[Xeenan]

I have a 15R75C Model Johnson. I recently installed a new ignition tune-up kit on it cause it wasnt getting spark. I timed the points and now have great spark. This past weekend I launched the boat on the river I fish out of, the motor started normally and I let it Idle for a min. or two, but when I went to give it full throttle it didnt have full power so I messed with the Idle till it ran at full. Then when at our location to fish I shut it down to use the trolling motor. BUt when I whet to start the motor again it took forever and didnt want to run right., I had to full choke it to get it started and mess with the idle to get it to run and when it did run it would only run a full for about 100yrd then shut down like I flipped the off switch. It did this several time in a row during the day. But then for some reason it just started running great. I haven't had this boat very long I did the ignition tune-up, cleaned the carb, new plugs, and new Fly Key. I have noticed that the carb bowl gasket is leaking though. Anyways any thought on what the problem is would be greatly appreated

 

[oldcatamount]

Re: 15hp Johnson problem

Get that float bowl leak fixed first. A leak will allow air to interrupt the fuel flow and cause the symptoms you described. Also, check the fuel tank vent.

 

[OptsyEagle]

Re: 15hp Johnson problem

Tough to say what your problem is but since you need to fix that carb bowl leak you might as well clean the carb again when you have it off the motor. Put a new carb kit in it and make sure you clean under the welch plug and replace the little plastic bearing that is deep inside your slow speed jet.

Now once you have done that if the problem happens again try to squeeze the primer bulb and see if that temporarily fixes the problem. This quick fix would indicate a fuel pumping problem caused by a malfunctioning fuel pump, fuel hose, fuel tank or an air leak.

Anyway, that is what I would do ... and I would make sure I am using NGK B7HS spark plugs and not the champion recommended ones. Those motors (1974-1976 9.9/15HP) do not like champion spark plugs.