sanding for SPEED?
just got done sanding two sets for my pals 02 800 mod sled Sunday afternoon.
went through my 9 length needle selection , had about 10 sets..........so needed to sort out and find a couple of set that will never see gas again and use them for the new mod needles.
1. take your stock needle at the area that's too lean and put a veneral caliper ( old mech joke ) your best stainless venier or dial caliper on that spot and lock in place. Now start testing the needle to mod and see if it will slide down further than the stock needle........ok sit and think, if it slide down further its SMALLER AND RICHER !! won't slide down as far its FATTER AROUND AND LEANER.
2. Now you know where you need to be, a needle that's smaller and slides down a little further, going to be leaner. Don't worry that much about the actual measruement unless you have good micrometers and know how to use them, if you do about .0015 ( say one and a half thousandsth ) at the critical area will give you on site noticable feels richer running. I sanded a set so when dropped in next to the stock neddles, the sanded needles slid about 4 clip notch's further down through the caliper. Then of course sand a match up a set.........well maybe not if one side always runs richer........oh crap.....like a boonie box, its getting complicated.
Don't worry, aint as big a change as you migh think.
3. What I have found on the 9 series ( FLAT RACK MOUNTED MIKUNI SNOWMOBILE CARBS IS)
Most issues are around the 1/5 to 1/3 range, and that's the first letter.
Cats you find a lot of 9DH6-59 in that area. The mikuni book and charts rate these needles by OVERALL RICH OR LEANNESS, meaning when you subject some of the supposedly richer needles to the caliper test you find that thay are lean in the bottom and just have a skinney end.........where in the upper end of throttle opening any idiot with a main jet can compensate.
You need that first straight section most of the times, just below the clip notch's smaller in diameteer to pass more fuel and be richer. Its usually the modest speed / very small throttle opening thats lean and needs gas and when you view your needles just crawling up out of that needle jet, you see that fat lean section of the needle screwing with you.
If you have a 9EH or 9FHY etc you can measure that small difference between the d/e/h needles and it's less than a .0005.
And after accumulating lots of $25 needles with bigger letters that didn't cure lean conditons I began sanding.
So.....when you want to see some richer piston saving deto avoidance jetting, hunting up lots of needles is usually not going to do the trick!!
The 2nd 3rd and 4th letters indicate how much bigger or small your mid and upper mid range is going to be.................and I''ve found you can fairly easily adjust that with your main jets for almost any of the really different oddball letter and tapers that all seem to be not that different in mid and upper ranges or only a couple of jet changes different.
Sunday I used a corless drill, 180 grit to knock some off and 400 grit to put a polish on the needles..........just seemed like I ought to polish them ?
Years back I was told by the great tuners never to file Mikuni needles cause they were special hard anodized, once you broke that surface they would'nd wear and............ awh bullcit. When I wanted custom needles for my yzf250, they came made of .......BRASS? maybe they were hard anodized by a special method unknow to us guys? Your needle jets are brass.......just another old wives tale.
So when we planted this new set of UNCLE MIKE'S custom made needles in Keith's rompin stompin 800 with the lean spot it knocked about 150 degrees out of the low mid...... well......just a few toots around the shop. Got another really skinny set to try, won't get that sled on the snow for another 10 days, but it'll be fun to see what happens. Still got the stockers so we can burn down the old girl anytime we feel like it. So......go to the woods with your sandpaper, your stock needles in case you make this thing a flushing toilet, and experiment.
Any time you pickup sandpaper you done left science behind and are entering the world of ART. This all works..... cause jetting is an art, good jetting is a thing of beauty, so with some sandpaper and stick of aluminum you got the whole world ahead of you.
