high altitude tuning

[bassnmamma]

I have a 1990 Evinrude 150XP and moved from TN to Colorado. Just had the VRO pump replaced and tune up. Bogs down on hole shot just a bit. <br />Seems to be a bit rich. Should the carbs be re-jetted? The shop recommended a different prop. I ran a 14.5 x24 Raker SS with a HiJacker jack plate. They gave me a 14.5 x 15 to try out. WOT rpm about 5500 with that prop, but top speed only about 45mph on boat that ran 55-58mph at sea level.

 

[clanton]

Re: high altitude tuning

Rejet the carbs depending on how high the engine is. Shop working on engine should have a chart with correct jet size.

 

[ob]

Re: high altitude tuning

I'm thinking once you get it jetted properly for the altitude change that a 15" prop form a 24" will overrev.You may drop back to a 21".<br /><br />Also consider your carbs could be fouled a bit from engine down time.

 

[walleyehed]

Re: high altitude tuning

I can tell you by personal experience you will not turn a 21"p at this alt. A 19P is about all you can get by with.<br /> Pull a main jet and read the number and letter following....Go 2 steps (.002)smaller-leaner, and that should be darn close. some of the 115's we go 5 steps leaner.<br /> As far as the 21"p, you could turn that at say 2500-3500ft above sealevel.<br /> I also found out last week that the Denver area dealers are recommending NO jet change, and just dropping prop pitch, their reason is on this vintage of engine, the fuel produced at that time was much higher quality, and NOW we need to go back to the sealevel jets????????????

 

[NOSLEEP]

Re: high altitude tuning

If you drop jet size to lean out your rich <br />Idle & WOT ,you will definitely run the risk of<br />having a lean burn problem when you use the boat<br />at a lower elevation. And it dosent take much of<br />a drop to start leaning out and cause serious<br />damage to your motor. That is why they recommend<br />switching the jets back to factory specs. See if<br />you cant advance your base timing a little.That<br />should help it run a little smoother.But it would<br />be hard to make it run like it does at sea level<br />unless you can change the density of the air.