Johnson 115 can't get over 2500 rpms

C

clroberts

Recruit
Joined
Jul 6, 2011
Messages
4
Took her out today for a nice run, got up on plane and maxed out at about 5700 rpm, then throttled back to about 4500 for a sweet cruise, then she started losing rpm and never got back over 2500. Motor cranks fine and idles sweetly, and while disengaged, I can run up the rpm fine, but under a load, it will not go over 2500. It doesn't smoke or make funny noises, but there is a miss every now and then which concerns me.
Dead cylinder(s)?, Ignition?, Prop?

Chris.
 
B

bob johnson

Rear Admiral
Joined
Feb 25, 2009
Messages
4,304
Re: Johnson 115 can't get over 2500 rpms

clroberts said:
Took her out today for a nice run, got up on plane and maxed out at about 5700 rpm, then throttled back to about 4500 for a sweet cruise, then she started losing rpm and never got back over 2500. Motor cranks fine and idles sweetly, and while disengaged, I can run up the rpm fine, but under a load, it will not go over 2500. It doesn't smoke or make funny noises, but there is a miss every now and then which concerns me.
Dead cylinder(s)?, Ignition?, Prop?

Chris.
Click to expand...

your motor probably overheated and went into SLOW mode.

that mode restricts the motor from going over 2500 rpm by shutting off the spark to various cylinders at various times....so the motor sounds rough at 2500...but below 2500 rpm the motor probably runs smooth.

maybe your alarm is bad, because you should have had an audible alarm when your motor temps went high enough to engage the SLOW system


once you turn the motor off by turning the key off, and the temps go back below 205 degrees....then SLOW system turns itself off.


bob
 
D

daselbee

Commander
Joined
Jan 20, 2009
Messages
2,765
Re: Johnson 115 can't get over 2500 rpms

No model number...we cannot tell if you even have a SLOW mode.
 
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