1975 6HP Johnson surges

[rainycity1]

When I try to troll with my 6hp Johnson it runs fine for about 15 minutes and then drops from trolling speed to a slow smooth idle, then will rev up all by itself. I tightened sloppy throttle linkage to no avail. It is almost as if one cylinder drops out and then kicks back in but the idle is not rough at all and I can manually increase the speed. There doesn't seem to be anything in between fast and idle when it starts acting up.

 

[lexkyboater]

Re: 1975 6HP Johnson surges

Sounds like a cylinder is dropping out maybe? Have you had it long? Have you replaced coils and/or checked spark - see http://forums.iboats.com/showthread.php?t=213548&highlight=spark+tester for info on how to make a tester. Have you checked compression? One problem may be plug wires - you can try using an ohm meter connected at both ends and wiggle the wires to make sure there's no open circuit.

I suppose it's possible something's in the fuel delivery that's causing a problem. After you verify compression and spark, you can check things like fuel pump and carb. You want to make sure there's no splits in the fuel lines from the tank the carb. We've seen issues with check valves in the tank to check valves in the fuel bulb. If you pump bulb and it runs better, then you have a fuel pump problem. If you choke it and it runs better, that indicates it's not getting fuel and might need a carb rebuild. Could be trash in the carb float chamber that's preventing fuel flow. If you can isolate the problem, that will help. If you fix the problem, please post the results so we know what resolved it. That helps us and others. --Steve

 

[Rick.]

Re: 1975 6HP Johnson surges

I had the same problem with a 1973 4HP. Put new coils and wires on it and it runs smooth as silk now. Good luck. Rick.