ridgrunr Posted November 21, 2014 Report Share Posted November 21, 2014 (edited) I leaned out the needle and main jet on my '08 Yamaha powered SY250r, but never messed with the pilot. I'm getting ready to some winter time maintenance and thought I'd mess with the pilot. Bike runs great, but I get some back firing occasionally while starting the bike between sections, and the bike seems to use more fuel than most of the others, so I wonder if it's running really rich with the stock #40? Looking at what's available, it seems there's a #38, and a #42, #44 and #46. Now my pea brain tells me should lean it out (I operate between 3000 and 7000 feet) and the #38 would be leaner than my stock #40, but my buddy swears it's different with pilot jets and the bigger the number, the leaner they are, which is why they offer more bigger (leaner?) jets than the one smaller (richer) jet. Anyone know what the scoop is with the pilot jets? Edited November 21, 2014 by ridgrunr Quote Link to comment Share on other sites More sharing options...
lbhbul Posted November 21, 2014 Report Share Posted November 21, 2014 Is it a Mikuni? If so smaller number = smaller bore on pilot jets. Larry Quote Link to comment Share on other sites More sharing options...
ridgrunr Posted November 21, 2014 Author Report Share Posted November 21, 2014 Scorpa's us a (TK) Teikei carb. Quote Link to comment Share on other sites More sharing options...
lbhbul Posted November 22, 2014 Report Share Posted November 22, 2014 My experience Mikuni,TK,Bing, as above. If you can hold them in your hand one can see the difference. If you think its rich, back out the air screw and see if that helps. Call Mike @ Tryalshop in New York he can help. Larry Quote Link to comment Share on other sites More sharing options...
lineaway Posted November 22, 2014 Report Share Posted November 22, 2014 It is a bit of a mystery. On the modern bikes we go larger at altitude. It`s been this way awhile. Although 7000ft is not real high. It has to due with atmospheric pressure, totally backwards of reason. The TK was a strange cab though. Quote Link to comment Share on other sites More sharing options...
b40rt Posted November 22, 2014 Report Share Posted November 22, 2014 It is a bit of a mystery. On the modern bikes we go larger at altitude. It`s been this way awhile. Although 7000ft is not real high. It has to due with atmospheric pressure, totally backwards of reason. The TK was a strange cab though. Where were you when billyt was wittering on about his 4rt ? 1 Quote Link to comment Share on other sites More sharing options...
baldilocks Posted December 13, 2014 Report Share Posted December 13, 2014 Tk pilot jets are strange. There is a bore hole but also 3 or 4 holes at the top. Its these 3 or 4 holes that increase in size with bigger number jets. I think more fuel is sucked through the bore hole as these holes increase in size. Definitely bigger number is richer on tk Quote Link to comment Share on other sites More sharing options...
toshy Posted February 22, 2015 Report Share Posted February 22, 2015 How did your jetting issue go? My bike also seems to run on the rich side. I replaced the needle and nozzle with new stock items, needle on the top clip, I am running a 38 pilot and still feels a bit rich. I even fitted new reeds. I also use almost double the fuel as the rest of my crew. A bit annoying to always be worried about running out of gas. Quote Link to comment Share on other sites More sharing options...
b40rt Posted February 22, 2015 Report Share Posted February 22, 2015 What colour is your plug ? Quote Link to comment Share on other sites More sharing options...
toshy Posted February 22, 2015 Report Share Posted February 22, 2015 My plug? Not sure to tell the truth plug chops are alittle tough with having to he move the tank each time. You can smell that it runs rich. I run the air screw out 2.5 turns. Quote Link to comment Share on other sites More sharing options...
ridgrunr Posted December 21, 2015 Author Report Share Posted December 21, 2015 With some help from lineaway, I finally got the SY250R jetting sorted out. Stock jetting was 40 pilot, 140 main and the needle on the meddle clip. Am now running a 42.5 pilot, 135 main and needle clip is set on the second from the top slot. Air screw is out 1.5 turns. Bike starts second kick, and the air screw. Make sure you use TK (Teikei) jets. It makes a difference. The Delorto jets fit in there, bu they seem to be calibrated different. Quote Link to comment Share on other sites More sharing options...
beta_blocker Posted December 22, 2015 Report Share Posted December 22, 2015 The first things to check before deciding to alter your carburetor jetting: 1. Is the air filter clean and the airbox intake unobstructed? 2. Is the carburetor and the jets and all passageways clean? 3. Is the carburetor float level correct? 4. Is the air boot from the air filter tight to the carburetor and not leaking. 5. Is the intake boot from carburetor to cylinder (or Reed valve cage) tight, sealed and not leaking? 6. Is the exhaust gasket properly sealing and any exhaust pipe connections tight and not leaking? 7. Is the proper heat range spark plug installed (and is it new or clean)? 8. Throttle cable runs free and slide returns to the carburetor stop? Until you can confirm (and there are more but this is a start) that these basic needs are met you can waste a lot of time and can become extremely frustrated chasing what symptoms you think might be improper jetting (and then "correcting" that) and getting even further from the goal. Backfiring may make you think the jetting is lean but it could be an air leak in the Reed cage gasket or a low float level or your throttle cable is hanging up. You might look at your spark plug and think it's running rich but it could be a dirty filter, a pinched air boot or float level out of whack. Back off the throttle and it backfires? Could be a bad exhaust gasket or air intake leak or partly blocked pilot jet or? Most carbs have some pretty well thought out jet settings for sea level and are basically a good place to start. Float level plays a larger then you might think influence on rich and lean conditions. I have purchased bikes that have had the float level altered as much as 7mm from stock which throws your whole attempts at jetting out the window until it is back within the proper tolerances. Make sure it's correct. This site has a good information page on jetting sequence and altitude / temperature correction. http://jetsrus.com/FAQs/FAQ_rejet_elevation_and_temperature.htm http://www.jetsrus.com/FAQs/FAQ_rejetting_101_how_to_rejet.htm I'm not associated with this site but have bought many jets and parts from them and have been very satisfied with my purchases. Happy Jetting! Quote Link to comment Share on other sites More sharing options...
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