460 Altitude Adjustment

[77_Tahiti]

What adjustments should be done with timing and carburetion for high altitude water? I'm running on water that ranges from 4200 to 6500 elevation.

[mister460]

Don't hold me to it but I think the rule is one jet size leaner for every 2000ft. I know you need to run the carb leaner at higher altitudes because there's less air. I never had to deal with it cause I lived at sea level. Anyone else know the rule?

[spectras only]

I would go down one jet size ,run run the boat to operating temperature.Shut the engine off and check plug colour.Run jet size down incrementally until you achieve a light tan colour.Jetting down starts around 1300-1500 feet above sealevel.
[This message has been edited by spectras only (edited July 16, 2001).]

[Timer]

Holley Carburetors & Manifolds book says go 1 main jet size down for every 2000' up. The same for every 40*F in temp up. It's assumed that there is a 4% change in fuel flow between jet sizes.

[spectras only]

We keep my buddy's boat in the Penticton area [1320 feet above sealevel]in the summer,and I go down one jetsize in his 850 Holley on the 460 to achive the right plug colour.Don't notice any performance change at all at that altitude!

[mister460]

I say put a blower on it and not have to worry about altitude ever again! That's just me though.

[77_Tahiti]

Thanks Guys,
I have also heard that the timing should be advanced 4 degrees or so for every 2000 feet, any comments on this? Also I think that my Carb is an "ASE" brand or something like that, does this sound correct? If so were do I buy the jets for this carb?

[nitro557]

even with a blower you have to back up 2% of overdrive for every 2000 ft, carbs are easy try a constant flow system on nitro or alky , even a constant floww on gas can give you fits