Super Jet SJ limited Mods High Altitude; How to tune?

For those of you that are experienced high altitude riders......


I have a new SJ. I'm in New Mexico and will be riding mostly at 4,500 feet elevation. I'm trying to determine a starting point for tuning. I'm not a mechanic, and fairly new to this. Unfortunately, finding help from someone who knows what they are doing around here is limited, seeing as it is the desert and all.

Mod List:
ada girdled head with 33cc domes that should put me around 175psi at this elevation
Factory B Pipe
MSD enhancer
MSD spark coil
Flame arrestors
Boysen Carbon Reeds
Hooker 10/16 impeller

I have the screws on the Head Pipe set as follows: top = closed, middle = closed, bottom = 3/4 turn open
The carb jets are stock.
It has been suggested to me to leave water screws on the pipe set as I have them
To leave the factory carb jets in place.
To set low carb screws at 2 1/4 turn out and to set high screws at 2 turn out.

I put around 12 hours on the stock machine at the end of last season. I have not yet fired this up with the mods.
Does this sound like a good starting point? Anyone have additional advice?
Thanks ahead of time!
 
Location
kalispell
Subd, I'm curious as well. Riding around 5000 ft here in Montana. My setup was jetted for sea level and seems to be a little rich up here. What carbs are you running @awake?

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RMBC Freeride

Vintage
Site Supporter
Location
Pueblo, CO
The 2 best things you can do for elevation are to run higher compression and a lower pitched impeller.

Sounds like you are somewhat on the right track, but I would suggest 31cc domes at your elevation. I am at 4700 feet and always recommend 31cc's. That being said, the 33's will be OK (and very safe) but will probably not yeild 175psi. As for impeller, I would recommend pitching that Hooker down to 9/15. 10/16 is pretty tall even for sea-level on a freestyle setup (if that's what you're going for). For top speed it might be OK. Some guys even run 8/14 here. Nozzle bore is a big player too, is your nozzle bored at all?

Jetting, follow Factory Pipes recommended jetting as a starting point. You might be a bit rich but that is the safe place to start. Might need to drop the popoff pressure a bit if it hesitates on acceleration. I can almost guarantee that leaving the stock jetting in will run like poop.

@CarbonCorban is in ABQ NM and I am about 4.5hrs north of you. The CO group usually has a get together in southern CO in the beginning of June that you might want to check out...
 
I called impros and talked to them about the right impeller for my situation. They suggested the 10/16 hooker. I replied that I thought the hooker was for free ride, of which i'm not interested. He said correct, but running the 10/16 should give me good results.
What psi do your 31cc domes produce?
The nozzle is not bored. what am I going to get out of boring it? Does it just go to a machine shop or what?
Leaving the stock jetting settings, or leaving the stock jets will make it run poorly?
 
we have lakes at 4500/5500 and mostly noticed in all tuning to shrink to 1.5 N/S on applications that run 2.0 N/S , jetting was the same for heads , aftermarket pipes etc but high and low screws had to be turned out 1/4 to 1/8 .

B- pipe middle open 1/2 and the hooker was 11/17
 
we have lakes at 4500/5500 and mostly noticed in all tuning to shrink to 1.5 N/S on applications that run 2.0 N/S , jetting was the same for heads , aftermarket pipes etc but high and low screws had to be turned out 1/4 to 1/8 .

B- pipe middle open 1/2 and the hooker was 11/17

So were the adjustment screws turned out from a baseline of completely closed, or from a baseline of where the factory set them?
 

RMBC Freeride

Vintage
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Location
Pueblo, CO
Well, there you go.... lesson here is that there is no "one" right answer... @orangefinger 's suggestions are nearly opposite of mine. But I can agree, I have had several occasions where dropping the seat size does clean up the throttle response.

orange - Really surprised at the 11/17 suggestion - is that on an OEM SJ hull with a "limited" engine? or are you talking about some of your lighter weight A/M hulls - makes a big difference... Is that with a bored nozzle as well?

awake - Again, so many variables here, no single correct answer. What kind of riding are you looking to do? All-around playing/criusing, racing, freestyle, etc.

As for the lingo - carb screw settings are generally given in a total number of turns out from closed. However when orangefinger says "high and low screws had to be turned out 1/4 to 1/8" he is talking about turning them out from their current setting. You would pretty much never run the screws only 1/8 to 1/4 turn out from closed. I can see how it sounds confusing but over time you start to understand.

31cc domes here produce around 175~180 on a good quality Snap-On gauge. At this point I'd say stick with the 33's and your 10/16, you'll be more than happy over stock and be plenty safe even if you get bad fuel, drop a little in elevation at a different lake or just want to run wide-open a lot.
 

Big Kahuna

Administrator
Location
Tuscaloosa, AL
I dont see how people with larger DASA PV Motors were running 9/15 Hookers. Dave recommended the 10/16 when I was running an 84mm big bore. He was spot on. I went back to an 82mm ported motor and it still ran good, I felt I could stand a lower pitch and had Dave send me a 9.5/15.5. Running currently. I mainly do flat water "Old School" freestyle.
 

Philip Clemmons

Owner, P&P Performance
Location
Richmond, Va
I dont see how people with larger DASA PV Motors were running 9/15 Hookers. Dave recommended the 10/16 when I was running an 84mm big bore. He was spot on. I went back to an 82mm ported motor and it still ran good, I felt I could stand a lower pitch and had Dave send me a 9.5/15.5. Running currently. I mainly do flat water "Old School" freestyle.
No, you are mainly a keyboard warrior! Get off the keyboard and ride; then you'll get some respect!
 
Well, there you go.... lesson here is that there is no "one" right answer... @orangefinger 's suggestions are nearly opposite of mine. But I can agree, I have had several occasions where dropping the seat size does clean up the throttle response.

orange - Really surprised at the 11/17 suggestion - is that on an OEM SJ hull with a "limited" engine? or are you talking about some of your lighter weight A/M hulls - makes a big difference... Is that with a bored nozzle as well?

awake - Again, so many variables here, no single correct answer. What kind of riding are you looking to do? All-around playing/criusing, racing, freestyle, etc.

As for the lingo - carb screw settings are generally given in a total number of turns out from closed. However when orangefinger says "high and low screws had to be turned out 1/4 to 1/8" he is talking about turning them out from their current setting. You would pretty much never run the screws only 1/8 to 1/4 turn out from closed. I can see how it sounds confusing but over time you start to understand.

31cc domes here produce around 175~180 on a good quality Snap-On gauge. At this point I'd say stick with the 33's and your 10/16, you'll be more than happy over stock and be plenty safe even if you get bad fuel, drop a little in elevation at a different lake or just want to run wide-open a lot.

Thx for clarification on carb screws. It's my understanding carb tuning can get scientific.
Assuming my stock mikuni is with a 2.0 N/S?? Planning on adjusting pop off to 18.
What elevation are you riding?
I'm looking for all around riding. Prob some buoy courses ect.
 

RMBC Freeride

Vintage
Site Supporter
Location
Pueblo, CO
Your stock mikuni 38's have 1.5's OR 1.2's - I don't remember for sure.

I should have notes from a friends ski that we built a couple years ago. Almost the exact setup you are trying to put together. I can give you those jetting specs and it will be a great place to start. But I guarantee, it isn't too far from the suggested Factory Pipe specs. I'll see if I can find it tonight and post here. Maybe he can chime in on how it runs... not sure if he gets on here much anymore @JHD ????

We ride at 4300~4700ft here
 

RMBC Freeride

Vintage
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Location
Pueblo, CO
Sorry, I went through all my notes and don't have anything on the ski I mentioned above ^^^^^^

I had also forgotten that @JHD installed the pipe after he bought the ski from me. So what I likely did was tell him to start with Factory Pipe's recommended jetting.
 
to clarify the engine was a 771cc and 876cc both equipped with dual 46's , b pipe, enhancer, 144 mag pump , modified square nose hull, Ported engine 31cc domes ( sea level 33cc )

We ran the BOB later on with an 8/13 for best performance

The Exit nozzle was bored to 87, end nozzle stock ,did not run stubby cone, had better results with oem cone...

I did personally not want to get into this ordeal having to change jets/impeller etc with alterating elevation rides, so we attempted to keep it simple , just switching domes. I am aware that this is not the 100% best solution and there was a compromise, but u can also make this a science and we wanted to ride rather than wrench...All engines ran good and we never had any problems.

Again at altitude lots of variables change, barometric pressure, air temperature, water temp ( we did work with restrictors ) etc all important , and opinions will differ, I am just reflecting what we had good success with simple soluton....in all honesty its a pita and we no longer ride elevation due to the complexity of skis we run now.

I think everyone will have to inch forward with lots of R&D for their own specific best results riding at altitude...
 
"I think everyone will have to inch forward with lots of R&D for their own specific best results riding at altitude..."

I reckon you are right, @orangefinger. But thanks for all of the helpful info. It's good for a starting point. Hope to be on the water within 2 weeks.
 
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