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Random High Idle That Wont Adjust

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Matthew72Johnson115

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1970 Johnson 115 will randomly acquire a high idle 2000 to 2300 rpms on the muffs. This issue is sporadic and will not adjust down. Other times its perfect at 900rpms. Any suggestions for troubleshooting?
 
You cannot properly set idle on muffs, it needs to be a barrel/tub/lake so engine has backpressure. You can get close by setting it at 1100-120rpm
 
On a flushette, idle =

20" shaft engine = 1000 rpm

25" shaft engine = 1200 rpm
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It sounds like you may have quite a bit of play/slack in that throttle cable or the control box.
 
faztbullet idle has already been set. What I meant about not being able to adjust is that the throttle linkage is all the way back. What could make it increase on its own?
 
Matthew72Johnson115 said:
joereeves there appears to be no slack. The throttle linkage is at its minimum setting when looking at the motor.

faztbullet idle has already been set. What I meant about not being able to adjust is that the throttle linkage is all the way back. What could make it increase on its own?
Click to expand...

When this idle increase takes place on the flushette, is the hood off, and are you standing right there where you can see if anything on the power head is moving.... timer base under the flywheel, anything?

You say that the throttle linkage is all the way back... does that mean that the idle stop adjustment screw is backed clear away from the block? If so, that would indicate that the cam with the scribe mark would not be touching the throttle roller... is this correct?

Does pumping the fuel primer bulb up hard while this is happening create any difference?
 
Hood is off and I haven't caught anything moving yet, screw is backed loose and cam is not touching the butterfly's. I have not tried to pump the fuel primer bulb but will.
 
I've been wondering if possibly the fuel pump may beginning to fail or if there is a slight leak somewhere that is affecting the fuel pump, causing the carburetors/engine to start running lean.

This would coincide with a engine that is running out of fuel... as this takes place, with the throttle locked in place, the rpms will increase until eventually the engine stops running.
 
Sounds to me like it is about to go into a serious runaway condition. Make sure the link & sync is correct, and don't rev it up under a no-load condition.
 
Put a timing light on it and watch to see if something strange is happening to the spark advance when the problem occurs.
 
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