Carb needel settings

[OVERKILL 19]

Have read when guys are re-jetting their revs they move the c-clips on the needles up or down. My ? is what is the purpose of this? Tried to research it but no luck on a clear definition.
Thanks

 

[teeroy]

needles control mid-range fuel delivery. drop needle, less fuel. raise needle, more fuel. needle effects throttle application from approximately 1/4 - 3/4 open.

 

[OVERKILL 19]

needles control mid-range fuel delivery. drop needle, less fuel. raise needle, more fuel. needle effects throttle application from approximately 1/4 - 3/4 open.

So do needle adjustments go hand and hand with jet changes? Jet up=needle up or I'm I on the wrong page.

 

[teeroy]

So do needle adjustments go hand and hand with jet changes? Jet up=needle up or I'm I on the wrong page.

not necessarily, main jet feeds fuel unobstructed at WOT. have you done some mods to require adjustments? EGT's are invaluable for such, especially when you get into mid range tuning. should be first purchase when modding

 

[OVERKILL 19]

not necessarily, main jet feeds fuel unobstructed at WOT. have you done some mods to require adjustments? EGT's are invaluable for such, especially when you get into mid range tuning. should be first purchase when modding

06 RevX single pipe, ported,vforce, can
08 Rev XPX Motts head,vforce, can

I went up one jet size on my 06 as per Tom, but I think I'm rich so I was going to go back to the factory 440's and give that a try. My plugs did look better than before the port job though. I was rich even with the pipe and no other mods.

The 08 we have not touched the jets...yet have read were guys went to 500's and up one clip on the needle. but would like to wrap my "small"brain around why change the needle posion first before I go changing things "willy nilly"......that sounds really gay "willy nilly" once you type it the first time.LOL

 

[teeroy]

06 RevX single pipe, ported,vforce, can
08 Rev XPX Motts head,vforce, can

I went up one jet size on my 06 as per Tom, but I think I'm rich so I was going to go back to the factory 440's and give that a try. My plugs did look better than before the port job though. I was rich even with the pipe and no other mods.

The 08 we have not touched the jets...yet have read were guys went to 500's and up one clip on the needle. but would like to wrap my "small"brain around why change the needle posion first before I go changing things "willy nilly"......that sounds really gay "willy nilly" once you type it the first time.LOL

sounds like you're on the right track with the '06, drop one and check your plugs after a good pull. porting improves flow, and will move more air requiring more fuel. you may have been rich before and improved flow to where it's better with same jetting. almost every stock sled comes jetted rich, to avoid warranty claims. not sure about increasing compression and relation to fuel flow, over my head it is.

pretty sure the '08 XP's have no needle adjustment, you have to add shims under the clip to richen the midrange. heard of guys swapping needles with '07 carbs to get adjustability. I've never changed jetting on my '08, it seems to work well. mind you, I've never checked wash or even had the plugs out of it yet...lol.

my experience with mods is that what they tell you should work hardly ever does. only kit I've ever bought that worked with the settings in the instructions was for an '02 XR650L. elevation, temperature, humidity, and snow conditions can vary, part of the "fun" in tuning. sorry I can't be more help, I feel your frustration.

 

[OVERKILL 19]

No frustration here, Its kinda fun, I would like to get it as close as I can. But for me I will gladly stay rich than too lean for the sake of a couple HP, cause I'm gonna get stuck anyway.

I just don't want to have my hood up half the day, or at all.

P.S You are 100%correct about shimming the needles for the 08 my bad,Thanks for your help

I'm thinking that if we add more air "vforce/ port or heads" we should richen the mid range.

 

[Modman]

Have read when guys are re-jetting their revs they move the c-clips on the needles up or down. My ? is what is the purpose of this? Tried to research it but no luck on a clear definition.
Thanks

Moving c-clips up or down will change mid-range mixture as stated. You don't necessarily require a complete carb jetting overhaul if you go up on one compenent or the other, it depends on your current jetting. Read F-Bomb's article attached but disregard the part about correllating it to your EGT readings. The key will be to inspect the plugs after idle, 1/4 throttle, 1/2 throttle, and full throttle passes and see what your plugs are reading. Then you will know if you are rich/lean in any of the throttle circuit areas and where you can compensate. If you are rich at WOT but good on the midrange, you only need to adjust the main jet, or vice versa if you are rich in the midrange but good at WOT.
DigatronTech

There are two components of the needle - the needle jet and the jet needle. The needle jet is also known as the emulsion tube and is the part the that the needle slides into on the bottom of the carb throat. The jet needle is the needle itself. You can change needles, jets, c-clip positions, or all of the above to vary the mixture in the midrange alone. Run the sled at different throttle settings as per F-Bomb's procedure and see what the plugs say, then jet from there. You have to start with a baseline on all circuit points.

 

[teeroy]

I think V force do more for proper atomization of fuel, as compared to flowing more. but porting will definitely increase flow. the throttle response after installing v force is wicked, not to mention better fuel mileage because of not havin the flipper pushed as far to keep up speed when cruising. that was on my '01 800, first series 3 rotax I owned. like you say, better to be safe than sorry with the needles.

tuning was a lot of fun back when I was into it. it was before internet was happenin', and a lot tougher to get solid info....magazines, and trial and error was the way I learned...lol. the ol' rotary valve 'Doos were a great motor to play with, not near as finicky and sensitive to tuning changes as these high strung/high horse engines out now. 'Doo is famous for not leaving much on the table hp wise. I miss the days of putting 10,000 miles on a Rotax with minor maintenance....besides smokin' your buddies with the same sled...

 

[teeroy]

modman has good info, he prolly forgot more than i know on carb tuning. Lonn Peterson from TPI was a big help when I was playin with this stuff, spent a lot of time on the phone with him asking questions. settings are infinite once you get into jet tubes, needle tapers, etc...

 

[OVERKILL 19]

I'm not trying to set land speed records, for the most part I want to pull the rope and go....I know leave it stock!

If I can learn alittle and not get carried away with the mods thats all I'm after.
Thanks for all the good info

 

[Modman]

modman has good info, he prolly forgot more than i know on carb tuning. Lonn Peterson from TPI was a big help when I was playin with this stuff, spent a lot of time on the phone with him asking questions. settings are infinite once you get into jet tubes, needle tapers, etc...

LOL, doubtful. I had a great teacher, I was smart and be-friended a sled mechanic when I was younger and he taught more than I could possibly ever have thought possible in a very short time. Ski Doo used to fly him down to Hay Days every year to tune their sleds for the drags. He had a 440 that would take down most 700's. He could tune a sled like no one I have met.

Best bet is to read lots and learn as much as you can. One of the best things you can do IMO is read Mikuni's tuning guide to get the basics Mikuni American Corporation

and then read the tuning manual for flat slides http://www.mikuni.com/pdf/rs_app_parts_lists.pdf

and round slides
http://www.mikuni.com/pdf/vmmanual.pdf

It may not be your exact carb setup, but a lot of the functions and theory of the carbs are the same and will give a good understanding of what components do what and how carbs generally work.

Hope that helps!

 

[Modman]

I'm not trying to set land speed records, for the most part I want to pull the rope and go....I know leave it stock!

If I can learn alittle and not get carried away with the mods thats all I'm after.
Thanks for all the good info

Tuning is fun!!! and knowing how things work and how to optimize your setup will really make that sled shine! Get a good air/fuel gauge or EGT and play around with it.