I am looking to re- jet my sons carb for the elevation that we live in. 3655ft. The carb is from a 90cc engine.
same as a polais 90. I'm up in Alberta and the cost to play around with some diffrent jets gets a little high.
Does any one here know of a good supplier for these jets. My local shops all seem to think that $30 bucks a jet is o.k. ! The jets were set for 0-2000 ft from the factory.

 

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$30 for each jet? Man, that's pretty darn expensive. In Canada, Pred-90 main jets should be around $7 - $9. Most are $7 ish. Wonder if he was thinking of a Jet Kit - which are several Main Jets included in a single package? If you can't get a good price in your region, perhaps you can buy from USA and get them to ship it to you via General US Postal. May take a few days via Snail Mail but it will eventually get to your house. Worked for me.

Note: Most Pred-90 main jets are around $3 / $4 (USD) in the central part of North America.

Hope this idea helps....

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Check out sudco.com

 

Thanks for the replies. I checked out sudco's cataloge and will try to pick out the ports I want. I dont know what it is about parts up here, but the costs on some items are nuts.I checked out ronnies store parts list, and (yike's) same costs of the parts as up here. If any one else has had to rejet due to elevation changes, please tell me how it went. My boy is tired of being left in the dust and he's starting to think he's a mechanic and tries to tune it up himself now. Ill have to lock-tight every screw on the carb to stop him from leaning it out.

 

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My son has an '03 Pred-90 and we had to re-jet it main because we install a larger size snorkel on the factory airbox and also went pre-mix. Just by luck, I nailed it first try with a 90 main jet and its needle all the way up (re: its C-Clip in the lowest postion) - to obtain Beer Bottle Brown spark plug. Due to our extreme winter cold, I need to re-jet higher 1 more jet in a few more months. Instead of doing this, I'm going to add a 12" long rubber hose on the end of our air box snorkle. We only do "around the house" riding in the -35s / -40s winter and thus, don't need the extra air flow. I remember reading some where that if one goes higher then a 90 main jet in a Pred-90 stock carb, they have to drill out its carb. Not too sure what that really means (could be something simple) but adding a longer snorkel pipe sounds much simpler. If you go larger then a 90 Main jet, you may have to drill your carb as well. Not too sure on your Pred-90 clone. Instead of changing jets because of different elevations, I wonder if 3 different size snorkle pipes on your 90 might work as well??? Something to think about....

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For some good carb jetting info, surf: http://justkdx.dirtrider.net/printcarbtuning.html


If you go higher in altitude, then jet(s) need to be smaller size. If you go lower in altitude, then jet(s) need to be bigger size. Most of the time, the Pilot jet size is ok. Most people have to change the Main Jet size (and tweak its Needle setting). With this in mind, try to purchase 3 different jet sizes. One at a "good guess", one size above and one size below. With these 3 jets and by tweaking with the Needle's C-Clip (aka: Needle height), you should be able to "hit the target" right one. Target meaning beer bottle brown spark plug color.

Hope this helps as well...

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Go to your local welding supply store and buy a micro drill bit set for cleaning cutting torch tips, $8-$10. The set I have comes in a handle that is used as a hand drill. Medium size bits in this set are good for our application 70-120's jet size. Only draw back is if you don't have a micrometer to measure drill sizes. After that just solder jets and re-drill for different size. I only need two jets to cover all conditions when we race or play ride. Keep a note book for conditions and best jetting so you can change as they do, without having to test agiain. Somewhere on this site or Miniatv site there is a pdf chart for drill size to jet size. I didn't save a copy but maybe someone here will have it. Also if you know the size bits you need check the auto parts store. The one buy me has a good assortment and they are $1.99 each.

 

Thanks again, I Know I have to go smaller with the port but how many sizes I am not sure. I was going to change the air intake as many other people have, but have been avoiding streams and deep puddles untill I did. I have a orfice tap drill set for gas furnaces change overs and I think I'll buy the smallest orfice and work my way up.( this will let me have the original and one to play with as bengen has suggested to change the sizes .) I am at the point where my son wants more from his ride and like Spike 99 this winter we may have to play with some engine, carb, and exshaust upgrades.

 

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The Pred-90's 16mm stock carb comes with a 82.5 Main Jet. If you install a smaller Main Jet, you don't have to Drill the carb. I've read that if you go bigger then Main Jet 90, then you need to drill the carb larger. If streams, mud and crud is your passion, perhaps it might be best to keep the original factory air box and install a larger snorkle. For pictures of our modified snorkel, surf top 3 pictures within: http://community.webshots.com/album/283726905AgWkij


As a long term suggestion, remove the factory air box and use vacuum nose, rubber hose, steel bent hose, etc. and install a uni filter under the front hood. For a picture that was posted on another forum, surf: http://community.webshots.com/photo/...92389209vbjDzv

Hope these pictures help...

Regarding Jet size (smaller then factory or larger due to factory air box replacement), I'm not too sure of your perfect size. Most of the time, it's one of those "best guess" with trial & error things. Luckily, I got mine on the 1st guess. Should have bought a lotto ticket that day. LOL!!!!

Good luck in your jet size guessing....

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