70 hp Johnson won't develop full power

[mstritt]

I have a 1983 70 hp johnson 3 cylinder. It was running rough at first so the spark plugs were changed, carbs rebuilt, reeds checked as well as the compression. It runs better, starts and idles fine but at full throttle it just seems to creep along. The linkage seems to be okay as at full throttle the carbs seem to be wide open. Also when you increase the warm up lever the RPM seems to increase as it should. Seems like just when it is under a load it does not run properly.<br />Thanks<br />Martin

 

[JB]

Re: 70 hp Johnson won't develop full power

Howdy, Mstritt.<br /><br />You have dropped one or two cylinders.<br /><br />Check spark to all three.<br />Squirt fuel mix into each carb while idling.<br />Search the Forum for loss of power under load.<br /><br />Let us know what you find.

 

[mstritt]

Re: 70 hp Johnson won't develop full power

thanks for the reply,<br />forgot to mention that while the motor was running I removed the leads to each individual spark plug and there a noticeable decrease in rpm, so I assume that each is working-is that true?

 

[JB]

Re: 70 hp Johnson won't develop full power

Yes. If rpm drops you have a cylinder making power.<br /><br />Having eliminated that, does your engine rev up to full rpm? If so, you have spun the prop hub.<br /><br />If the engine is not reaching full rpm at full throttle I suspect you have fuel starvation from the fuel pump or the high speed jets in one carb.<br /><br />Good luck.