Author Topic: 2021 300 SE Factory - Getting brand new bike jetted  (Read 962 times)

DEL107

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Re: 2021 300 SE Factory - Getting brand new bike jetted
« Reply #15 on: April 20, 2021, 05:02:14 PM »
I'm a little surprised by the instruction to raise the idle speed slightly above normal to set the air screw. If your pilot jet is too rich, it'll require the slide to be lifted a fair bit (in relative terms) to get a fast idle. The problem with this is the carb will be starting to draw fuel through the main jet. When adjusting the airscrew, the method I use is to warm the bike up and back the idle down to slightly below normal before adjusting the airscrew until the highest rpm is reached. Then I'll drop the idle a little more, screw the airscrew in half a turn and do it again. If it peaks at the same point, I screw the airscrew in 1/8 turn from there and call it good. As others have said, if the final setting is more than 3 turns out you should put the next size down PJ in. If its less than 1 turn out, go up a size (you don't have to if you have found the sweet spot but it gives you a wider range of future adjustment to compensate for weather/altitude variations). My 2 cents YMMV

I also used to do it using the low idle technique. I was surprised when all I could find were sources saying to use the increased idle to set the AS while brushing up on my jetting skills after a period on FI bikes
 

KTRacer14

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Re: 2021 300 SE Factory - Getting brand new bike jetted
« Reply #16 on: April 29, 2021, 05:16:09 PM »
I think some of you are very confused at to what 1/8 throttle is, and where the pilot circuit is active.  The pilot circuit is active everywhere.  That is why you adjust it first.  Other circuits simply overwhelm its effect with increased throttle opening.  The needle taper starts to be active at about 1/8 throttle.  Go see how much throttle adjustment it takes to bump the idle RPM by 500.  It is tiny tiny fraction of 1/8 throttle.  Adjusting the idle up by 500 is going to come nowhere close to using up 1/8 throttle.

FYI...I got tired of re-jetting for Alt changes so I took off the Keihin and put on a SmartCarb SC2.  Problem solved.   

erdat

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Re: 2021 300 SE Factory - Getting brand new bike jetted
« Reply #17 on: April 30, 2021, 08:39:55 PM »
KTRacer14 good info. what kind of a SC2 setup do you have? A friend of mine has a 38 installed (not a sherco, an other popular brand). He is kinda happy, but commented that he should have bought a 36.
I am considering of getting one but the price is an important factor.
cheers, erdat
'15 SE-R 250
Ankara, Turkey

KTRacer14

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Re: 2021 300 SE Factory - Getting brand new bike jetted
« Reply #18 on: May 04, 2021, 03:46:41 PM »
KTRacer14 good info. what kind of a SC2 setup do you have? A friend of mine has a 38 installed (not a sherco, an other popular brand). He is kinda happy, but commented that he should have bought a 36.
I am considering of getting one but the price is an important factor.
cheers, erdat

erdat,

I went with the Mfgs (Technology Elevated) recommendation.  For the Sherco 300 2T, that is 36mm.  I think they also recommend 36mm for other 250-300cc 2Ts. 

So far it runs great.  I am about 12 clicks leaner than the baseline they set the carb at.  I would say that initial throttle response is about 90% as good as a well jetted carb set up.  It is good...but not quite perfect.  Throttle feel/control (holding traction, lugging, etc) feels better than a std carb.  Mid to top end power feels the same.  Fuel mileage is noticeably better.  500'-5,500' elevation....no change in how it runs, which was the whole reason I decided to go with the SC.  That to me is worth a lot.  Spooge is reduced to about 20% of what it was with a carb.

One thing I have found is the bike idle RPM changes quite a bit as the bike warms and get hot.  If the idle is perfect 5 minutes into a ride...it will be 300 RPM higher 10 minutes later.

Another weird nuance is if you lay the bike down to the left, when you get the bike back up and re-start...it is really rich and takes a bit to get it cleaned out again.

It was quite a bit of work modifying the air boot to fit for proper installation.  I did a lot of careful grinding to get the shape right, and allow for the compensation port to be properly exposed.  They have a good video showing how to do this.

So far, I give the SC2 a 9/10 rating. 
« Last Edit: May 04, 2021, 03:53:54 PM by KTRacer14 »