Freestyle Jetting for 900cc with 44’s

[Wiseguy92]

Anyone got a baseline jet set up high and low for a 900 with stock 44’s . Stock ignition with a Protec pipe. Thanks


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[SmittySX]

Anyone got a baseline jet set up high and low for a 900 with stock 44’s . Stock ignition with a Protec pipe. Thanks


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Going to need more specific info than that.

 

[Wiseguy92]

Dasa 10 mill, old freestyle motor. 110 octane. Stock 44’s with stock main and reeds. Stock water box. Stock electronics. Going in a stock ski


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[Storbeck]

You are very unlikely to find anybody who has run a combination similar to that. Most people with 10 mill race gas freestyle motors use bigger carbs.

But, most 800ish cc motors with 44's use something in the range of a 120-130 low speed jet and 110-120 high speed jet with low 20's psi popoff.

Bigger motors tend to use smaller jets.

So if you put a 130 low and 120 high in there, you'll probably be conservatively rich.

If you're really worried do 130/130 and you'll probably be starting pig rich.

If you're feeling frisky start with 125 low 110 high and you might not have to make any more changes.


You'll need to talk to somebody more knowledgeable than me on the subject, but I would be concerned with that combination running stock ignition. You don't have a very high rev limiter, and you've probably got a lot of compression for a stock ignition to try to ignite. You left out a bunch of details on the motor (pipe?) but if it is some high port motor intended to run a dry pipe, it could be a problem. I've never run a motor like that and I haven't used stock ignition much so no personal experience.

 

[Sparkplug]

I'll offer some grains of salt



My 1100 10 mil runs great on stock ignition. 91 octane also. Running 110 on anything less than 200 psi is throwing money in the trash.

Start fat. 125s. Go down from there. Read piston wash and do the mikuni 1/4 throttle test. Over and over. Should be easy but take your time. 44s will do just fine. I raised my popoff from 18-21 to 29 psi despite what alot of "tuners" say. My wash is perfect as is the mid transition. I actually had a harder time tubing my engine listening to shade tree professionals than I did just sticking to engine theory.

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[Storbeck]

For what reason did you raise the popoff?

I'm pretty sold on the theory that pretty much any popoff can be made to work, but I've never had the ambition to take something that I was happy with the jetting and change the popoff just to try it out. Usually by the time I'm happy with how it runs I'm sick of working on it and don't want to screw with it any more.

 

[Sparkplug]

Popoff is the atmospheric pressure drop required to open the needle.

I had problems with a dribbling venturi. That the builder of the carbs absolutely could not help diagnose. So I did it myself.

I've had an 1200 with 70psi popoff. It still easily pulled fuel. Don't believe all the hype. Oem has way better engineers than anyone on these sites.

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[kevbo]

Start too big and work your way leaner, you may be suprised where it ends up. Set the final fuel mixture just rich of peak power and make 1/4 throttle fourcycle a little. 44s tune very easy and you can use gold springs with whatever N/S you want.

 

[waxhead]

130 low
115 high
2.3 n/s 95 gram spring

 

[Quinc]

You are very unlikely to find anybody who has run a combination similar to that. Most people with 10 mill race gas freestyle motors use bigger carbs.

But, most 800ish cc motors with 44's use something in the range of a 120-130 low speed jet and 110-120 high speed jet with low 20's psi popoff.

Bigger motors tend to use smaller jets.

So if you put a 130 low and 120 high in there, you'll probably be conservatively rich.

If you're really worried do 130/130 and you'll probably be starting pig rich.

If you're feeling frisky start with 125 low 110 high and you might not have to make any more changes.


You'll need to talk to somebody more knowledgeable than me on the subject, but I would be concerned with that combination running stock ignition. You don't have a very high rev limiter, and you've probably got a lot of compression for a stock ignition to try to ignite. You left out a bunch of details on the motor (pipe?) but if it is some high port motor intended to run a dry pipe, it could be a problem. I've never run a motor like that and I haven't used stock ignition much so no personal experience.

Do you happen to have a link to some literature on why that is?

 

[Storbeck]

Do you happen to have a link to some literature on why that is?

Higher air flow creates a greater pressure differential in the venturi so more fuel flows through any given size of jet. The change in fuel flow is usually proportionally more than the change in air flow.

For the same reason putting a larger carb on any given cylinder usually requires larger jets.

Not always true because obviously it depends on a lot of things, but the trend is the bigger the carb is relative to the cylinder it's attached to, the bigger the jets required and vice versa.

The best apples to apples (ish) example I can think of is ktm dirt bikes that switched from 38mm to 36mm carbs of very similar design, or used the same carb on 125/250/380cc motors. You can also see the general trend in the jetting database but there is a lot of scatter.

I happen to have just done this myself on two different skis, one went from 44's to 46's, and one went from 46's to 48's (and the 46's came off of a bigger motor and went on a smaller motor). I make no claims that they are the best tuned carbs of all times, but they followed the trend.

 

[Harbor]

Dasa 10 mill, old freestyle motor. 110 octane. Stock 44’s with stock main and reeds. Stock water box. Stock electronics. Going in a stock ski


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I’ve run older dasa 8 mil, 85mm bore, 865cc, race gas set up, wet pipe and stock ignition with Mikuni 44’s..

currently have 8 mil in 82mm bore, stock 44’s with choke removed, all the rest is as above..

100L
125H
80 spring
14 pop off
1 turn out L
1.5 out H
Sea level

If needed tune you idle to wide open drivability with the low jet… mine didn’t need any adj… very crisp and clean response..

good luck

 

[kevbo]

FWIW, I have a 62T 701 cylinder with sbn44s that needed much larger jets. 140 mains and 125 low.

 

[fastgtfairlane]

I'm running a ported 735 with dual a/m 44s and have tried several netting combinations. Still went back to the 120p,130m 25psi popoff. Reverse jetting was just too muddy on the bottom couldnt get it to clear up. Feels much better with current settings

 

[Storbeck]

I'm running a ported 735 with dual a/m 44s and have tried several netting combinations. Still went back to the 120p,130m 25psi popoff. Reverse jetting was just too muddy on the bottom couldnt get it to clear up. Feels much better with current settings

What ignition are you running? I always seem to end up with way bigger low speed than high speed, my theory is that is because of the high advance down low and low advance up high from a zeeltronic, but I dunno. It's a thing I've wondered about.

 

[Sparkplug]

A properly tuned ski will run exactly like oem regardless of stroke or cc. Or ignition. There is nothing fancy about these engines. They are dinosaur technology. It should fire up with no primer. Idle smoothly with little vibration, transition from the low to the mid cleanly. And pass a one minute wide open throttle test. Any and all 2 stroke engines. 1mm to 100mm. All mine do.

One guys tuning is going to be different than the next. I ride way different than my buddies. I ride faster and blip the throttle constantly. Someone who rides different could get on my ski and say the tuning doesn't work for them.

The general rule with performance is to start conservative and go from there. Mikuni knows more about carbs than all the am carb guys combined. Listen to their manual for dialing in a carb. It is bar none the best and most efficient way to do it.

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[fastgtfairlane]

What ignition are you running? I always seem to end up with way bigger low speed than high speed, my theory is that is because of the high advance down low and low advance up high from a zeeltronic, but I dunno. It's a thing I've wondered about.

I'm running a zeel with a TNT ss chamber.