Jetting question

4 replies to this topic
  • SLJ

Posted December 02, 2003 - 10:11 PM


Hi all,
What is the difference between a 68 and 68s pilot? I wanted a 68s but the shop gave me a 68 instead. I didn't notice till I got home. Should I use the 68? I also have a 70. I need it yesterday so there's no time to get anything else till I get back :).

  • qadsan

Posted December 02, 2003 - 10:36 PM


The 68s has smaller emulsion holes than the 68. It's not completely uncommon for a dealer to give a 68 instead of a 68s and its also not uncommon for a dealer to tell you there's no such thing as a 68s, but there is. Finding the perfect pilot jet for your specific bike and riding environment often takes some trial and error. If your riding at close to sea level in moderate temperatures, then the 68s might be the way to go, but cooler temps or certain engine mods might favor the 70.

Go ahead and use the 68 and see how it works. Don't forget to adjust the pilot screw and idle speed if necessary.

What altitude & temps are you riding in? What kind of mods have you done to your bike such as the exhaust, airbox cutout, cam, etc?

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  • SLJ

Posted December 03, 2003 - 06:24 AM


I'm going out for the Vegas 200 so will be whatever altitude it is there. I think they say it will be an average of 2,000 feet with starting altitude at 1800 feet. I live at 5,000 feet and ride mostly at around 7,500~10,000 feet so have it jetted with a 65 pilot (stock) right now. I've never had it lower. It's a 650R with drilled tip, airbox parts out, larger carb boot, uni-filter, and no drilled sidecover. Unfortunately I won't be able to run it before the race, so will have to run whatever I start with.
Thanks for the response. I wish I had gotten this straightened out earlier. ???

  • qadsan

Posted December 03, 2003 - 12:10 PM


If my bike had the drilled stock tip, airbox parts out, larger carb boot, uni-filter, no drilled side cover and I was riding at an average elevation of 2,000 feet @ 60F temperatures, I'd use the following jetting as a baseline to work from. It should be pretty close, but if someone else lives and rides in that same area with their bike setup the same as yours and feels their bike is setup correctly, then definitely take their info into consideration as well.

Main Jet = 170 if the temperatures are ~60F to ~70F
Main Jet = 172 if the temperature is ~50F

Pilot Jet = 68s if the temperatures are ~50F to ~70F
Pilot Jet = 65s if the temperatures are ~75F+

Stock Needle = 4th clip from top if the temperatures are ~50F to ~80F
B53E Needle = 3rd clip from the top if the temperatures are ~50F to ~75F

Make sure to adjust your pilot/fuel screw and then adjust the idle speed if necessary at your riding location to get your best performance. Before adjusting the pilot/fuel screw, make a note of where yours is adjusted by turning it all the way in and counting the turns in until it stops (do it gently), but be careful when it stops and don't crank it tight because you can easily damage the screw's seat and then you might be really screwed. Put it back to where it was and make a note of how many turns out it was. To adjust the pilot/fuel screw, first make sure sure your engine is fully warmed up, then set the pilot screw to 1.5 turns out. With the engine idling at the correct idle speed, turn the pilot screw clockwise until the idle slows. Then turn the pilot screw counterclockwise until the idle slows again. Make a mental note of how many turns you made in between the low idle points. Then turn the pilot screw half way between the low idle points to finish the adjustment. If you turn the adjuster counterclockwise and the idle doesn't drop down, then you need a larger pilot jet. If you turn the pilot screw clockwise and the idle doesn't drop down, then you need a smaller pilot jet, but this procedure won't work so well if you have your idle turned up too high to begin with. After adjusting your pilot circuit, re-adjust your idle speed if necessary to the correct spec. If your throttle response is as good as you've ever felt it when you whack open the throttle from idle, then you're done. If there's more hesitation than usual when you whack open the throttle from idle, then turn the pilot/fuel screw 1/8th turn inward and see if that improves your throttle reponse. If it doesn't, try another 1/8th turn inward and see if that makes it better. If it gets worse in this direction, then turn it backward in 1/8 increments until you have good off idle throttle response.

Good luck with everything :)

  • SLJ

Posted December 03, 2003 - 02:34 PM


Wow that's excellent! Thanks for the response, I will do that when I get there in the morning before the race. That helps a lot. Wish I had time to play with it more but this is a good start.

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