Jetting Help

[6sic6]

I finally got FMF SST's and jetted them per ALBA's instructions this summer. I live in Minnesota (1000' elev) and am running a K&N with the lid off. They told me to use either 300 or 310 mains, 32.5 pilot with air screw out 1.5 turns, and aftermarket needle in the 4th clip position. Top end was great, but the low and mid seemed alittle week. What can I do to improve this?

 

Also, now that winter is here, what do I need to change for the cold temps?

 

Any help would be greatly appreciated.

[BenBB]

Could be rich or lean on the pilots and needle, and MIGHT even be a little lean on the mains...

 

Briefly, the pilots control mixture from idle to about 1/8 throttle, and the airscrews fine tune the mixture. The needle length & taper control mixture from about 1/4 to 3/4 throttle, fine tuned by the clip position. From about 3/4 throttle to WOT mixture is controlled by the mains.

 

So, if it bogs or hesitates right off idle, start by adjusting the airscrews in (richer) or out (leaner) and see if it helps. If going out on the pilots helps but the problem persists after you get to about 3 turns out from seated, try the next size smaller pilot (30) and start over with the airscrews 1.5 turns out. If going in helps and it still bogs or hesitates with the airscrews a half turn out from seated, try the next size larger pilot (35) and start over with the airscrews 1.5 turns out.

 

Similarly, if it's boggy or hesitant between 1/4 and 3/4 throttle, try adjusting the needle clip position (if you already have aftermarket needles no need to worry about changing the needle itself unless you've tried everything else possible, and in that case try stock needles). Move the clip up towards the blunt end (leaner) or down towards the pointy end (richer) and see if it helps. If you're not sure which way to move it, go richer first, or try popping the choke out to the first notch and see if it helps or not (if it helps, go richer, if it gets way worse, go leaner).

 

Anyway, one way to dial in the mains is to jet them higher until it bogs at WOT and then drop a size. It might be fine where it's at now, but it could also be lean (another way to verify the mains is by doing a plug chop).

 

Once you get the jetting dialed in, for winter all you usually need to do is adjust the airscrews if neccessary, and jet the mains a size larger for every 20 degrees colder or so (so if it's perfect for 60-80F, go up on the mains one size for 40-60F).

 

Hope this helps, you might want to check out the Jetting FAQ for more details. Good luck.

[6sic6]

Thanks BenBB.

That will get me going. I'm still alittle unsure of myself when it comes to playing with the carbs and I definetly don't want to burn up my motor. I have read the "Jetting FAQ" many many times. I've got it bookmarked under "My Favorites" and have been thinking about making it my start page! I'm just wondering what everybody else is running with a similar set-up so I know I'm at a good starting point. Also, I'm looking for short cuts because I'd rather be riding than messing with my jets.

[BenBB]

You should be pretty close, start with the airscrews and see if you can get a good off-idle response (you might need 30 pilots), then try moving the needles...and I'm just guessing but you might try a size or two larger on the mains just in case the 310's aren't big enough (if you hadn't gotten a recommendation already I would've said 30 pilots, needle in the stock position, and 320 or 330 mains to start out).

 

Unfortunately jetting is alot of trial and error, but the good thing is, it's worth the effort. Just dial in one circuit at a time (adjust the airscrews, go ride it, readjust, etc.). Good luck.

[Banchetta]

My friend went staight to 30 pilots like fmf suggested and had a numb spot on the off idle.. He lowered the pilots to 27.5 and it ran better. Went back to stock pilots and really rips on the throttle response....He has 290 mains, 25 pilots, and needles in the 5th clip from the blunt end.....good luck..and let us know how you make out...

[6sic6]

So should I start with the mains, dial them in and then start playing with the pilots and airscrew? Then the needle clip position? Or what order should I work in?

 

Thanks for all the help. I'm going to play with it this weekend. I don't know what I'd do without this site. You guys are awesome!