jetting....why needles are overlooked

mrviper700

mrviper700

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Numerous threads for why my sled wont run when its warm, burned my sled down,look at these pistons, etc. maybe a common sense approach explanation can take some guess workout of jetting your sled,and why you need to change those settings due to certain conditions. The thing is you see all these people who say "put a bigger mainjet in it", its too lean from not enough wash on the piston, but whats not explained is that unless the person burned the sled down in a certain distance at a certain throttle opening you cant simply have a answer of a bigger main jet because thats false. You need to run a sled wide open for a distance of 750-1000ft to be soley on the mainjet,because all carb circuits overlap.To put this in perspective a 1/4 mile is 1320 feet long!
The reason for most of these burndowns and problems arise from the midrange jetting being too lean,and too low of octane fuel. By richeng up the needle your working the area of the fuel curve where your spending 80-90% of your time if your trail riding, not on the mainjet!
lets give an example of typical trail riding: your riding along a groomed trail averaging 50-60mph, you hit a large straight away, you whack the throttle,the sled speedo hits 80-90 mph,straight is a good 700ft long, here comes a turn,you let off the gas,dive deep into the turn and give it the gas again coming out and getting back up to 80-90mph. Then you come to a field opening after a small turn, on and off the gas,you rip it across the field to the other side to enter the woods again,for a easy 600-800ft again,back into the woods,turn by turn your on and off the gas.
The thing is,in this example scenario,you were never on the mainjet, you were on a combo of the pilot jet and the needle,needle circuit and sometimes getting into the needle/mainjet overlap if the straight distance was 750+ feet long for a short blip.
The needle overlaps with the pilot circuit(lowspeed) and the mainjet(topspeed) circuits. The needle controls how much of the mainjet will be richning up the topend circuit,because of your needle is still down in the nozzle,no mainjet increase is going to save the engine because its being restricted by the needle not coming far enough up out of the nozzle to flow the extra fuel desired. If your lake racing,across vast distances, again, the needle is in play ,because the very instant you let off the gas from a wide open run, your shutting off the main jet, and a lean needle will instantly burndown a engine on decelaration, this is actually what happens alot of times. People will again,put bigger mainjets in and they are working on the wrong part of the fuel curve.
Every sled made yamaha,polaris,arcticcat,evinrude(lol), whatever comes richer then needed from the factory,even a 2000 srx using 146.3 mains. The service bulletin was made for riders running very cold climates to go up to the richer yet 148.8/150 mains if the sled was going to be run for extended wide open periods. The reason they went back to the 00 jetting in 02 was simply the add on of dcs was to take the risk away and cover the wide open running situations. However the leaner jetting also provides more performance.
Simply upping the octane makes the sled richer without ever touching jetting!! The more octane you have the cooler the burn,so keep this in mind as you buy fuel,going cheap on gas fill ups provides less protection with a given set of jets,just simply from the octane level. octane level seems to have come into play alot more in the last couple seasons, 2 stroke sleds are most affected by the lower quality fuels. You need to richen the sled but richen the sled thru the circuit where your spending alot of the time riding the sled, mainjets are not a coverall like some people here like to say, they surely wont protect your piped viper running at 7500-8000 rpm doing 60mph down a trail, its the needle circuit you need to pay attention to. Also, when dealing with a viper,they have leaner needles and nozzles then a srx does,so take that into account when setting up your sled.
 

I am new to the carb tuning , and this made ALOT of sense! If I wanted to lean out a little I should drop my needles? or am I backwards?
 
mrviper700 said:
Numerous threads for why my sled wont run when its warm, burned my sled down,look at these pistons, etc. maybe a common sense approach explanation can take some guess workout of jetting your sled,and why you need to change those settings due to certain conditions. The thing is you see all these people who say "put a bigger mainjet in it", its too lean from not enough wash on the piston, but whats not explained is that unless the person burned the sled down in a certain distance at a certain throttle opening you cant simply have a answer of a bigger main jet because thats false. You need to run a sled wide open for a distance of 750-1000ft to be soley on the mainjet,because all carb circuits overlap.To put this in perspective a 1/4 mile is 1320 feet long!
The reason for most of these burndowns and problems arise from the midrange jetting being too lean,and too low of octane fuel. By richeng up the needle your working the area of the fuel curve where your spending 80-90% of your time if your trail riding, not on the mainjet!
lets give an example of typical trail riding: your riding along a groomed trail averaging 50-60mph, you hit a large straight away, you whack the throttle,the sled speedo hits 80-90 mph,straight is a good 700ft long, here comes a turn,you let off the gas,dive deep into the turn and give it the gas again coming out and getting back up to 80-90mph. Then you come to a field opening after a small turn, on and off the gas,you rip it across the field to the other side to enter the woods again,for a easy 600-800ft again,back into the woods,turn by turn your on and off the gas.
The thing is,in this example scenario,you were never on the mainjet, you were on a combo of the pilot jet and the needle,needle circuit and sometimes getting into the needle/mainjet overlap if the straight distance was 750+ feet long for a short blip.
The needle overlaps with the pilot circuit(lowspeed) and the mainjet(topspeed) circuits. The needle controls how much of the mainjet will be richning up the topend circuit,because of your needle is still down in the nozzle,no mainjet increase is going to save the engine because its being restricted by the needle not coming far enough up out of the nozzle to flow the extra fuel desired. If your lake racing,across vast distances, again, the needle is in play ,because the very instant you let off the gas from a wide open run, your shutting off the main jet, and a lean needle will instantly burndown a engine on decelaration, this is actually what happens alot of times. People will again,put bigger mainjets in and they are working on the wrong part of the fuel curve.
Every sled made yamaha,polaris,arcticcat,evinrude(lol), whatever comes richer then needed from the factory,even a 2000 srx using 146.3 mains. The service bulletin was made for riders running very cold climates to go up to the richer yet 148.8/150 mains if the sled was going to be run for extended wide open periods. The reason they went back to the 00 jetting in 02 was simply the add on of dcs was to take the risk away and cover the wide open running situations. However the leaner jetting also provides more performance.
Simply upping the octane makes the sled richer without ever touching jetting!! The more octane you have the cooler the burn,so keep this in mind as you buy fuel,going cheap on gas fill ups provides less protection with a given set of jets,just simply from the octane level. octane level seems to have come into play alot more in the last couple seasons, 2 stroke sleds are most affected by the lower quality fuels. You need to richen the sled but richen the sled thru the circuit where your spending alot of the time riding the sled, mainjets are not a coverall like some people here like to say, they surely wont protect your piped viper running at 7500-8000 rpm doing 60mph down a trail, its the needle circuit you need to pay attention to. Also, when dealing with a viper,they have leaner needles and nozzles then a srx does,so take that into account when setting up your sled.
Click to expand...
Nice summary of carb tuning. Good point on the fine tuning of the needle jet. I like to drop my needle 1/2 clip with needle shims when neccessary. I think E-10+ fuel has A LOT to do with the recent couple yrs burn downs and fuel related issues. I agree though, tune it and run good fuel, dont just poor fuel in the engine with a big main then gripe that its a dog in mush snow and warm weather.
 
I have the clutch tuning manual from Aaen's I'm going too order the carb tuning one also Thanks mrviper for clearing up the jetting + needle issues

So can I go down a size on my main jet for 660ft drags


















Just kidding LOL!!!!!!!!!!!!!
 
Definitely a great write up. After owning a Viper with DCS, I've learned about what needles do in a hurry, since they came with a lean midrange to begin with.

As always thank you for the great information and the amount of knowledge you share with this great forum.
 
Hey there mrviper700,,, welcome back.... first start post -- with great info,,,- in a couple years.... Been missed by many....
 
Hi Don, good to hear from you again.

Great info in this post guys.

Maybe one of us could format the info in an eye-catching format and add to the Tech Pages
 
Yeah this reAlly opened my eyes on how it all works. So In my case on my srx my dcs only comes on at wot so that would mean it is a little lean on the top end. Some people say to change to 01 jetting witch would hinder performance on the bottom end am I right? I should just change the main for my top end and adjust needles for temp
 
I have my 02 SRX jetted to 01 specs.The DCS never kicks on,but I know I am on the rich side and lost some performance.Going back to stock next season and watch the DCS reaction.When I first got that sled few years back..it was jetted stock and the thing was a wild beast even in above 0 temps,now it is a dog for performance.The needles is something I have never taken out,am a little hesitant to touch something I know nothing about.Would be nice if someone could make a video on how to remove,adjust and re-install those damn needles. :o|
 
It's not that hard there are three notches middle one being stock setting top lean bottom rich I believe correct me if I'm wrong. I think that is all you have to do. Again sombody correct me if I'm wrong
 
teamblue02SRx said:
Yeah this reAlly opened my eyes on how it all works. So In my case on my srx my dcs only comes on at wot so that would mean it is a little lean on the top end. Some people say to change to 01 jetting witch would hinder performance on the bottom end am I right? I should just change the main for my top end and adjust needles for temp
Click to expand...

If its coming on after being held wide open for 10 miles then dont do a thing. If its coming on before you can get wound out then your octane is probably to low. But if you insist on hurting your performance, jet up. Otherwise dont go any richer than the stock 02 mains and dont panic if the light blinks every once in a while. In my case with 100 octane I was able to hold it WOT for miles in zero (F) weather and no light. With 90 octane in 35 degree weather it was blinking on and off all day--sometimes at 1/4 throttle cruising. Octane and fuel QUALITY has a lot to do with the DCS light. Increasing the QUANITY of fuel is a small portion of detonation and in the case of the 02 SRX, isnt the fix.
 
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