Mercruiser470 Idle problem .

[kjohn2007]

Hello.
I have a 1979 Starcraft boat with a Mercruiser 470 motor on it. I just recently had a throttle cable replaced on the boat by the marina. I took it out yesterday for the fast time. I started the boat up and it was ideling fine it was around 900 to 1000 rpms. Then I backed it off of the trailer and noticed it was running around 2000 rpms and it just kept on doing that. I was wondering if anybody would be able to help me out with this situation. I didnt know if they didnt get the cable adjusted right or if it is something else.

Thanks.

 

[bspeth]

900-1000 seems high to start with.You could disconnect the cable to eliminate that from the scenario,work the throttle by hand and you should be able to to tell if the cable needs adjustment or the carb.

 

[kghost]

As said remove the cable from the carb throttle shaft, in the water idling. Adjust idle in neutral to about 700-750 rpms.

now with the cable in hand see of the trunion and end plastic piece line up at the mounting point and throttle cable end to the throttle shaft on the carb. If not the adjust the trunion so they do.

once you have done this adjust the trunion two or so more complete turns to add additional force to push the throttle shaft against the idle cam on the carb.

install and secure the cable and test. Every time you return to the neutral position with the shift control the motor should return to idle.

Idle rpms should be, while in gear idling in the water so the motor is under load, rpms should be 650-750 rpms. If idling around 1000 that is not good for the shifting of the outdrive and or getting out of gear when shifting back to neutral.