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Merc 1989 3.0L Carb Jets for different altitudes

sparks75

New member
All,
Any help is greatly appreciated.
I am currently running the stock 1.45 jets in my 1989 3.0L merc 15P 4 blade prop, at high altitude, there is a little bogging...
I'd like to change the 1.45s out for the Merc recommended 1.40's for altitude between 5000'-9000', which will cover most of my needs, chatfield ~6000, Steamboat lake ~7000, green mountain res ~80000., Dillon 9000, etc etc
But what about when I go to Lake McConaughy which is I believe about 3250'
Will I need to change the jets back in order to keep from running too lean and burning a piston? or is that not enough altitude change create a problem?
I hope to put the 1.40's in leave them alone.
Any other altitude tweaks?
I hear advancing the timing also helps...
Not sure if it is relavant, but this week I am installing the following ignition components:
PerTronix Ignitor II
Flamethrower II Coil
So spark should be strong…

Thanks for the help
 
Re: Merc 3.0L Carb Jets for different altitudes

make one change at a time and make sure it does what you intended.

As far as the jets go, the 40's should be fine for all the altitudes you listed unless your boat is a big load on the engine. If in doubt at the lower altitude, go slow and steady the first visit. Keep your ears open and if all is ok, increase the rpm a little bit at a time. The change you are talking about is very small.
 
Re: Merc 3.0L Carb Jets for different altitudes

Thanks for the info, I was thinking the same with regard to the lower altitude lake, the change is only 1700' lower then Merc's owner recommendation...I'll take it easy and listen for trouble.
With regards to the other things,
I am doing those to get away from points, I'll install them first, test, then run the new jets
thanks
 
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