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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4725
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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I read what you replied to another person who was trying to

Customer Question

Jason I read what you replied to another person who was trying to adjust the idle on his Johnson 150. My idle is too fast and currently idling about 1100 rpm. This is a fresh rebuilt powerhead and the old engine did not idle at this speed. I found the plastic tab on the top of the flywheel cover and adjusted it first one direction then the other. No change whatsoever. The throttle plates/valves are fully closed and I checked for vacuum leaks and none were found. Some of the evac hoses were seeping a bit of oil but now that has been tightened up. The model is a J150VXSIF and model year is 2001 with the OIS ignition. The port side motor which was not reconditioned is idling at about 800 rpm on the water hose which from what I read is ok.
Submitted: 1 year ago.
Category: Boat
Expert:  Jeff G. replied 1 year ago.

Your engine is idle speed controlled by the timing. You can not simply move the timing levers. It takes a special ignition tool to set the timing on all the OIS engines. On yours the idle timing will end up being about 6*ATDC this will give you an in gear idle of about 700 rpm.

All idle speeds are measured with the engine in the water not on the hose. In the water you have the proper backpressure on the exhaust. Johnson/Evinrude also looks for in gear rpm, not neutral rpm for that motor.

The timing can be set on dry land, then checked in the water. You may find that once the engine is warmed up and in the water the rpm will drop to a proper idle.

Was the timing properly set after the engine was rebuilt? It MUST be set with the special tool.

The WOT timing is set in the same way. If it is too far advanced then you could damage the new rebuild. I would take the boat to a qualified shop and have the timing set. Double check the throttle shutters are closed all the way, put the boat in the water and see where the idle is.

Just by putting the engine in the water I would expect the idle speed to drop 300+ rpm, then another 100-200 in gear giving you a proper idle speed.

The other engine at 800 out of the water is too low. I would have the timing done on that engine as well.

Finally only check the idle speeds after the engines are warmed up with no starting spark advance.

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