Idle Mixture Screw

[kcg646]

I was wondering if someone can tell me how far to screw out the idle mixture screws on my 98 air nautique. It has a 351 HO. It also has a holley carb. I just finished the carb rebuild and looking at different article, I have seen anywhere from 1-1/4 to 2 1/2 turn out. Any info on this topic would be greatly appreciated.

[81nautique]

Start with 2 full turns out. 2 ways to set it properly. First is to hook a vacuum gauge to the motor, with engine warmed up and in gear( I do this tied to the dock or better yet on the trailer if the ramp is open) adjust the mixture screws equally on each side until the engine pulls the highest vacuum reading. Second method is if you don't have a vacuum gauge again with motor in gear set the mixture screws until the engine rpms peak while at idle, that should represent your strongest idle, then set your idle speed back to the correct level for your boat. I find 1-1/4 to 1-1/2 to be about right for most of these boats.

[surroundsound64]

It will depend on your elevation. It's about 2 full turns at 1000' MSL. And that's about... depending on the rest of the carb settings.