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1987 Johnson 150 hp RPM reduced with Cowling on

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Katyjinny

New member
The engine has done 180 hours from new. To keep tick-over at around 1000 on the water it has to be set at 1500 with the cowling off. As soon as the Cowling is replaced the revs drop. The only possible answer I've found on the forums is a leaking exhaust gasket but there are no visible signs to suggest a leak anywhere.
 
Check the plug wires,---------------sounds like on maybe shorting out to the cover-----------Not common but it does happen.
 
Does the drop in RPMs happen immediately when the cowling is replaced? If so, it wouldn't be an exhaust gasket problem. More along the lines of what racerone suggests.
 
Has this engine ever run normally? Is the engine located normally on the back of a boat OR is it situated in a well of sorts, such as being installed inside the boat?

Have you checked the air intake areas of the hood?
 
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