Jetting for high altitude

[Mt.Mike1230]

Owner of 2 Bombardier 1996 Sea-doo XP.. always kept them in southern CA at lake havasu, but just recently brought them up to Colorado where im living at an elevation a little above 7,000 ft. Anyways, wanting to know if re-jetting them will be as simple as replacing the main jets with a little fine tuning, or will all jets need to be replaced along with more in depth tuning. Can't say im the biggest motor head, but trying to learn more with a bit of reading and online videos.. basically, debating to pay and have them jetted or doing it myself. Any feed back appreciated.

 

[mikidymac]

I run mine at 6,000’ a couple times a year with no issues but less power. I would just try them first as is. If they are a little rich try turning the screws in 1/8 turn and check the plugs.

 

[AKnarrowback]

I will give you my opinion based on snowmobile experience.

To get the best performance you will probably need to tweak most settings on the carb if you want to get the full potential from the machine. If you are staying long term, you are living there, then I would take the time to tune things in.

The good news is you are not going to do any damage to the machines going up in elevation, only run richer and burn extra gas without any performance gain.

I have a lot of experience running Mikuni round slides anywhere from sea level to 7000 feet with temperature ranges from +50 to -50F. I'm sorry, but I don't have a thorough enough knowledge of BN and SBN carbs to suggest jetting changes.

The mantra of all hard core sledders is "test and tune, test and tune, test and tune". Remember this when it comes to getting dialed in. Read your plugs often, have a good selection of jets and a lot of patience. I can't tell you at all what, if any, changes should be made to pop off pressure.

As an example. I spent a while dialing in my 94 XP for 440ft elevation, 65F air with 35 to 55F water temps, river running where I do 90% of my riding. Every time I run out at the lake on the hottest summer days it's 80F with water temps of 70ish and my DOO shows typical signs I would see in a sled that is jetted too rich all around.

I hope someone else can give better "water DOO" info for high alltitude.

Good luck.

 

[AKnarrowback]

If it is just short term go with Mikidymac's direction and enjoy the time.

 

[mikidymac]

It might not hurt to call Impros a have your impellers repitched for the higher altitude if you are going to be there for a while.

 

[AKnarrowback]

The one nice thing about the rotary valve rotax motors was their ability to tolerate rises in elevation with rich jetting but still perform, relatively, well compared to a standard piston port two strokes. I could get around 6000' and not have my machine die on my 580 mx while all the polaris guys had to rejet at least one time going up from our camp at 2000'.

The general rule of thumb for carbed two strokes is you loose 3% of your sea level horse power for evey 1000' of elevation. Calibrating your power to the snow, or water, in this case is another consideration. You will be running around 90hp IF you are jetted right to get the most out of the motor, less if you are still running sea level jetting on the main jet.

Of course water is pretty consistant so getting an impeller set up for your conditions should be a one time fight and then it's set for life.