1957 johnson 18 hp runs rough

[codykoke]

I took this motor out for the first time after carb kit new coils and impeller. It ran fine for the first 20 minutes then started stumbling every few seconds. Adjusting the carb does not help. I'm wondering if a small leak in the tank around one of the bolts could cause this but the filter bowl remains full.

 

[lindy46]

Re: 1957 johnson 18 hp runs rough

What do you mean by "stumbling"? Cutting out? Sneezing? Does it do this when idling or at higher speed?

 

[codykoke]

Re: 1957 johnson 18 hp runs rough

It will jerk to the side than resume normal running and that happens every few seconds. It occurs at idle and throttle

 

[HighTrim]

Re: 1957 johnson 18 hp runs rough

May have an air leak, did you replace the fuel lines?

 

[codykoke]

Re: 1957 johnson 18 hp runs rough

That's what I was thinking. The lines are all new but could a leaking bolt on the tank cause this problem. I must admit that i didn't remove the welch plug thing on the carb when i rebuilt it but if there were any thing stuck in those holes would it run bad at all speeds or just slow speeds

 

[lindy46]

Re: 1957 johnson 18 hp runs rough

Almost sounds like a lean sneeze, but that should adjust out with the low speed needle, and shouldn't really occur at higher speed or once motor is warmed up. If you loosen the cap on the gas tank, does pressure release with a "whooshing" sound? If you push the primer button, does it help? You may want to go back through the carb and clean that idle circuit and make sure the high speed circuit is also clean. Did you install a new kit and put the fiber washer on the high speed nozzle?

 

[codykoke]

Re: 1957 johnson 18 hp runs rough

The tank does hold pressure, but what is this fiber washer you speak of. I have the the thick rubber washer on the nozzle. I will tear the carb down and rebuild it again.

 

[lindy46]

Re: 1957 johnson 18 hp runs rough

The tank does hold pressure, but what is this fiber washer you speak of. I have the the thick rubber washer on the nozzle. I will tear the carb down and rebuild it again.

Yeah the thick rubber or fiber washer which goes on the nozzle and seals to the float bowl.