1997 Force 120 crazy idle

[Grant Ingle]

Working on a 1997 Force 120 HP. Customer had tinkered with linkage and carb idle needles. Ran motor on the hose and managed to get a decent idle and throttle response out of the lake. With an inductive tach I got @1150RPM's. When the boat was launched, the RPM's doubled to around 2400 in idle. Normally the addition of backpressure will cause a drop in RPM but not so with this one. Is this a sign of an internal leak at the powerhead? Compression was fine with all cylinders around 140psi. Good spark and new plugs also.

 

[sony2001]

Re: 1997 Force 120 crazy idle

A lot of Forces have idle speed bolt on tower bar that should be inactive when setting idle mixtures<br />to 7-900 rpm. Do you have it on the 97?

 

[Grant Ingle]

Re: 1997 Force 120 crazy idle

Yes, there is a timing bolt on the motor. On a hose with zero backpressure the motor idles just over 1000. In the lake, when it should be at @ 900 in neutral, it idles at over 2000. I know, totally backwards from what it should be. Used an inductive pickup tach just to confirm it. Later learned that this boat was recently purchased from another local dealer and I'm now wondering if the throttle and spark advance were mis-adjusted to cover another internal issue. Unless someone has some ideas I'm going to remove the powerhead Tues. and have a look inside.

 

[sony2001]

Re: 1997 Force 120 crazy idle

I was indicating the other end of the towershaft where the throttle link couples to it. That idle speed bolt has to be off the block before setting the idle mixture screws. Throttle cam WOT line at roller. All this before timming check.