Mercruiser power valve

[redlaw]

I have a 2000 Maxum SCR with a 220HP, 5.0L, 305 CID engine. I bought the boat at 200 ft elevation. Now run it at 6100 ft elevation. Stock main jets are 165's, stock power jet is a 90. At 6200 ft elevation I am putting in 150 mains and I need to know what power jet to install. Calling Merc Marine in Stillwater Ok., has been frustrating because I get different answers every time I call. They had told me a year ago to put in 145 mains and a 74 power, now I find out that the 145's are for elevations over 9000 ft so I am going to the 150's which are for 6000 ft elevation the guy stumbled and fumbled when I asked about the power jet. I asked a few questions and he then changed his recommendation from 90 with the 150's to 74 with the 150's. Any help would be appreciated.

 

[achris]

The 'official' Merc recommendation is to leave the carb jets the same as sea-level and just change the prop for the higher elevations. (It would need to be shorter in pitch)...

However, the service manual for your engine does show different jets for the different altitudes (you need to know exactly which carb you have (should be a red tag on the carb, attached with one of the top cover screws).. It doesn't specify the power jet, just gives the options. I suspect it's a 'trial and error' thing. For the power valve. You need to be able to check if the mixture is rich or lean.

And since you're only about 400m above the sea level jets anyway, I'd be just leaving the jets as is and using a 2" smaller prop...

Here's the chart...



Chris........

 

[redlaw]

Chris, thanks for the help. I have already changed the prop. I guess you are correct that it will be a trial and error thing. Do you know how to determine if my mixture is rich or lean? Is there a simple way to do this? Ron

 

[achris]

Difficult without an exhaust analyzer, but you can get an idea by reading the spark plugs...

Chris......