Mercury 175 xri idles at 2500 RPM
#11
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The throttle arm controls both the intake butterflies AND the timing plate under the flywheel. There are separate adjuster screws for both of them. Even a low butterfly openings, the timing advance alone will make those motors rev when there's no load on them.
Pull the cover. Disconnect the throttle cable from the big arm. Make sure it all moves as it is supposed to from idle position to wide open throttle position. Hold the arm and let somebody fire it up. See if you can move the arm far enough to let the motor idle down to under 800. Vacuum leaks can also contribute, but chances are that you have something out of adjustment from the throttle cable itself to something in the arm and actuators.
There are stop screws for max timing advance, minimum throttle plate opening, etc. Just take a look while you move the arm and watch it all. It will make sense.
You'll notice that the throttle plates only open a tiny amount as you increase the throttle until you get most of the timing in, then the throttle plates start opening.
MC
Pull the cover. Disconnect the throttle cable from the big arm. Make sure it all moves as it is supposed to from idle position to wide open throttle position. Hold the arm and let somebody fire it up. See if you can move the arm far enough to let the motor idle down to under 800. Vacuum leaks can also contribute, but chances are that you have something out of adjustment from the throttle cable itself to something in the arm and actuators.
There are stop screws for max timing advance, minimum throttle plate opening, etc. Just take a look while you move the arm and watch it all. It will make sense.
You'll notice that the throttle plates only open a tiny amount as you increase the throttle until you get most of the timing in, then the throttle plates start opening.
MC
Thanks MC! I did mess with the timing arm and got it to slow down a bit. I need to put it in the water and bring a buddy with to run the throttle. I'll let you guys know if I get it running better!
#12
If you mess with that linkage at all, you really should run thru the entire link and sync procedure, having the timing off can cause poor performance, or too much advance(boom), depending on which way ya went.
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Had the boat back at house and did more investgating. Found that 2 of the 3 intake gaskets hanging out. The gaskets are in between the throttle bodies and intake manifold. Already have torn apart just waiting on new gaskets. So thats where the engine was getting the extra air to run so fast at idle.... I hope!
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Intake gaskets $8. Two hours of work in the driveway. Stopped at the boat shop on the way to the lake to set timing, throttle stops and oil pump settings. Boat ran good! Ran it to 6,000 RPM 51 MPH ON GPS. It has a Mercury high 5 19p on it. Thinking about trying a 21p 3 blade prop. The boat is a 1993 Ski Ray 190. Burned a half a tank of fuel. Had a bit of a stumble from 4,500 to 5,000 Rpm. Hope that goes away when I have a full tank of fresh gas!