Weird thing, I was unable to find the same same jetting that you provided. I am curious what manual that you are looking at.

 

This is out of the shop manual for the 98 sleds but it just seems wild to me to have to do such a drastic jet change

 

This is out of the shop manual for the 98 sleds but it just seems wild to me to have to do such a drastic jet change

I see you got this from the High Altitude Technical Data (HATD). When I couldn't find the Summit in the HATD then I understood why you used the one from the MXZ. The changes that 396F/A refers to is shown in the HATD. Below is what I got from the Shop Manual, and the difference with HATD shown in parenthesis.

The change in Main Jet size per 1000 feet of elevation is also a function of the carburetor size (VM34 vs a VM32 for example) versus the engine size or more specifically air intake volume. I am not even sure there is an explanation of this anywhere, so take what I write for what it is worth. I have done more detailed charts in spreadsheets per 1000 feet in elevation for a few engines which left me scratching my head with the same question you raised, and that is what I figured out. I should check the HATD for the 583 as it came with different carb sizes, or maybe I have and just don't remember. I was actually more interested in the part and mid throttle positions to look at the pilot and needle position more closely since this is a common range to ride in. The smaller the engine, the more time is spent with the throttle pinned, so the percentage of failures for each range depends in part by the engine size. The point is that it become interesting when charting it out for different jets for different engines. So you have a comparison to show how the MJ looks to be a drastic change in elevation, then please mention the other engine that you are comparing to.

FYI, the Needle Jet is what 396F/A refers to as the emulsion tube.




1998 MXZ 500 from Shop Manual
VM 38 380/381
Main Jet 330/300 (300/280 showing in High Altitude Technical Data)
Needle Jet 480-Q4
Needle 6DHY48-3 (6DGY9-3 showing in High Altitude Technical Data)
Air Screw 1.5 (2.5 showing in High Altitude Technical Data)
Pilot 50
Slide 2.5


1998 Summit 500 from Shop Manual
VM 38 (H.A.C.) 384/385
Main Jet 350/330
Needle Jet 480-Q6
Needle 6DHY48-4
Air Screw 2.0
Pilot 75
Slide 2.5

 

There was a recall on jetting for the 98 MXZ and Formula 500. Possibly the shop manual does not reflect this.
1998 MXZ - 500: mains 300P/280M, intermediate jet ( emulsion tube ) 480-Q4, jet needle 6DGY9-3, pilot 50, air screw 2.5 out
1998 Formula 500: 300/280, intermediate 480-Q3, jet needle 6DGY9-3 pilot 50, air screw 2.0 out.

Note there is a difference in the emulsion tube and jet needle from the Summit to the ones above. If you are a believer in horse shoes and hand grenades you may not bother to change them, but if you want it to perform correctly with the HAC delete I firmly believe you should change them. Some don`t change them and claim good performance ( I question that )
The above specs are the factory specs, you may need a tweek on the mains for altitude.

 

Well i went with a 290m/270pto and a 50 pilot just gotta take it to the mtns and see how she does hopefully dont burn it down😂

 

Hope they work for you.