changing altitude question

[donaldm]

just bought a 2004 4.3 volvo carborated with 80hr. on it. i don't know what altitidut it has been running at. I'm going to use the boat at about 5000 ft lake. if its not jetted right how will i know? and assuming it was jetted for 1000 ft will i deffinitly need to re-jet the carb? thanks for any input.

 

[bruceb58]

Re: changing altitude question

Are you going to be using this boat ONLY at this lake? If not, I wouldn't do it as you will run lean if you ever brought it down in elevation.

 

[Don S]

Re: changing altitude question

I have never worked with high altitude boats, so not much help with the carb question, but here is a service bulletin from Volvo on drive ratios for high altitude.

View attachment 44-0-8 Volvo gear ratios.pdf

 

[Jammer864]

Re: changing altitude question

You do not have to re-jet it. You will need to re-prop it though. I had good luck with re-propping when going from 5000ft to 1000ft and visa versa. If you plan on staying only at 5000 ft though, you will see an increase in gas mileage if you re-jet it. For example, I re-jetted a pickup with a Chevy 5.7 (350) in it and it went from 10mph to 14mpg. That was a Quadrajet carb and took 30 minutes to accomplish the first time and about half that on subsequent vehicles. No power change was noted but a tank of gas lasted noticeably longer.
Just re-prop it with a smaller prop and you will be fine and its easy to change if you go somewhere lower.