Mercury 9.9 4-stroke at 4500 ft

Shark Racer

Recruit
Joined
Jun 23, 2013
Messages
2
Hi all,

I'm planning on running my Mercury 9.9 at 4500'. I have no problem getting into a carburetor; I've overhauled a number of QuadraJet carburetors, as well as a couple Keihin and even Zenith-Strombergs off old Jags. I know that to make this thing run well I'd have to downjet a size or two, but I haven't had any luck finding a place that offers jets. I can only find stock replacement.

For what it's worth, this should be the 2011+ variant. I live at roughly sea level and will return to stock jetting before running it again. The last thing I need is to burn a hole in the piston. :)

I also have read that people go with "quicker" props to make up for the lost power. I'd still like to get the air-fuel ratio a bit closer to perfect for better throttle response, MPG and power at altitude.

Also - I'm a new member, and this is my first post, so hello. :) I'm a car nut and this will be the first boat *I own* to hit the water with a motor strapped to it. Looking forward to it. (It's a Zodiac Cadet 310S FWIW).
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Re: Mercury 9.9 4-stroke at 4500 ft

Also - I'm a new member, and this is my first post, so hello. :) I'm a car nut and this will be the first boat.

Welcome, you are only required to be a nut to hang out here, the type isn't important.

I don't know if there is a high altitude kit for that motor, try a google search on that.

You won't burn a hole in the piston, it will run rich and cold at high altitude, not hot and lean.

You may need a lower pitch prop, but you won't know exactly which pitch until you try it, one step lower may be enough though.
 

Shark Racer

Recruit
Joined
Jun 23, 2013
Messages
2
Re: Mercury 9.9 4-stroke at 4500 ft

Welcome, you are only required to be a nut to hang out here, the type isn't important.

I don't know if there is a high altitude kit for that motor, try a google search on that.

You won't burn a hole in the piston, it will run rich and cold at high altitude, not hot and lean.

You may need a lower pitch prop, but you won't know exactly which pitch until you try it, one step lower may be enough though.

Thanks! I did find a company that sells kits for Tohatsu and Nissan 9.8s, I've contacted them to see if they can help at all.

As for burning up - I meant I'd return to the sea level jets before running on my home lakes. :)
 
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