no idle in water

[markoc85]

Hi, just wondering if anyone can give me a lead on this - my 1990 90hp Johnson has strange behaviour at idle.

When flushing on the hose it idles fine without any throttle required.

However when the boat is in the water it requires me to lift the throttle to avoid stalling.

What is this caused by, how do I fix this?

 

[tashasdaddy]

Re: no idle in water

low idle speed, set your idle at 1,000 on muffs, then fine tune the idle in the water. on muffs there is not any backpressure on the exhaust, which there is when in the water. the motor has to tune fast enough to force exhaust out the prop. that simple.

 

[markoc85]

Re: no idle in water

Ok cool. which of the following adjustments is the idle speed one because they both affect the throttle...Thanks

 

[emdsapmgr]

Re: no idle in water

You don't adjust the carbs. The idle speed is adjusted by changing the ignition timing at idle. If you screw the A screw clockwise, it should raise the idle timing and subsequently the idle speed. Adjust the idle when the boat is floating at normal level in the water. It should be set when idling in forward gear to 650-750 rpm. That will probably equate to around 900-950 in neutral.

 

[markoc85]

Re: no idle in water

Mint thanks. Should I adjust the B screw aswell to remove the gap (about 3mm) between butterfly cam and roller or is that gap meant to be there?

 

[emdsapmgr]

Re: no idle in water

Normally at idle the roller should be spaced away from the cam about the thickness of a sheet of paper. This is all part of the "sync and link" process-a rather detailed procedure of numerous steps to insure that the carb butterfly opening is perfectly coordinated with the spark advance timing. It is detailed in the factory service manual. If you don't have a factory manual, it is best to acquire one before making any adjustements to these linkages. You can get an original factory manual from the publisher, Ken Cook Co. in Milwaukee.