Jetting Question

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BiancoS3

moped
Hi All,
Last Fall I install BC air box removal kit and pred's on my 08 T100. I started with 135, 140, 145 mains and am now running 150's and the bike is still not running right. I installed new spark plugs with the re-jetting and they are white/gray which indicates a lean condition. The bike starts and idles fine, I tried Thurxton needles and it ran worst so I put back stock. I'm about to order 160 & 165 mains from New Bonneville. Has anyone else experienced this? Any input would be appreciated. Thanks!
 
Easy13

Easy13

Street Tracker
Plugs really aren't the best gauge of main jet size, at least not on these bikes. Take the bike out and get it accelerating strongly at wide open throttle, then back the throttle down just a bit (maybe to 7/8 throttle). If the bike accelerates better at 7/8 throttle than it does at full throttle, then your main jet is too small. Step it up gradually, i.e., don't go from a 135 to a 155, you're looking for the the lowest jet that'll accelerate you better at full throttle.

Once you have that done, then you can work on needles and shims for midrange smoothness, and finally idle adjustment. This is the tried and true for these engines with CVK carbs.
 
Kirkus51

Kirkus51

Hooligan
My Old Man used to "blow the cobs outta it" whenever something ran rough. He just went out and ran the piss out of whatever was acting up (usually Mom's car). Oddly enough it worked pretty well.
 
BlueJ

BlueJ

Blue Haired Freak
BiancoS3 said:
Hi All,
Last Fall I install BC air box removal kit and pred's on my 08 T100. I started with 135, 140, 145 mains and am now running 150's and the bike is still not running right. I installed new spark plugs with the re-jetting and they are white/gray which indicates a lean condition. The bike starts and idles fine, I tried Thurxton needles and it ran worst so I put back stock. I'm about to order 160 & 165 mains from New Bonneville. Has anyone else experienced this? Any input would be appreciated. Thanks!
Click to expand...

Have you adjusted the pilots? With preds and no airbox... 150/45 should be as big as you need to go. You might want to make sure they're balanced, that can make a big difference. Could you be more specific on "not running right"??
 
em_dot

em_dot

Street Tracker
Wow, that's a lot!

I have Preds myself with the airbox removed. I'm running 138 mains and 42 pilots with 1 shim and 2.5 turns out. Here in the Raliegh area we're about 300feet above sea level.

I thought that the 42 pilots were rich, but my bike came from the factory with 42s so I left them in. The bike runs like a scalded dog.

Jenks bolts says 138/40 ought to do it. Check out page 10:

http://www.bonneville.se/nedladdning/Hur man jettar.pdf

Hope that helps!

Joel
 
BlueJ

BlueJ

Blue Haired Freak
I agree with em.dot... 150 is way high although some have reported needing to go that far. 138 is more reasonable.

I actually like slightly richer pilots for easier starting - just slightly fewer turns out.

Whoops! I see by my sig that I'm not running the 45's anymore. :) 135/42 with TORS. Don't remember how many turns out.
 
B

BiancoS3

moped
Thanks everyone for the feedback. I'm running 42 pilot as provided in the BC kit and 2.5 turns out on the adjustment screw. The bike starts and idles fine. Wide open throttle it accelerates OK but not great, sometimes it will hesitate and stumble, especially after its hot. At steady 1/2 - 3/4 throttle it really bucks and hesitates. I tried the Thurxton needles and it was worst in the midrange so I went back to stock, I haven't tried shimming the stock needles. I pulled the spark plugs before the mod's and they were a nice golden brown. I installed new sparks plugs with the mod's and they are white to the point I'm concerned about holing a piston. The bike ran great stock except it sounded like a sewing machine and I wanted a little more power. I'm in the Baltimore Maryland area at about 200-300 feet above sea level. I'll try the 155, then 160 and then 165 main jets and post up the results for general info. Thanks again for the replies!
 
BlueJ

BlueJ

Blue Haired Freak
BiancoS3 said:
..At steady 1/2 - 3/4 throttle it really bucks and hesitates... I haven't tried shimming the stock needles...I'll try the 155, then 160 and then 165 main jets and post up the results for general info..
Click to expand...

Keep us posted. But that's gotta be crazy rich. Trying the shim is what I'd do next for midrange issues - you won't fully engage those mains until full throttle anyway. Also, might want to check that floats are free and set at a good height, and that you have a good seal around your pod filters - when I did my ARK I found it pretty easy to think that the rubber was fully seated on the carb when it really wasn't.

At one point I think Sweatmachine was up in those high main jet ranges, then he put on an a/f monitor and he was, in his words "pig rich" (or was it "bog stinking rich"?).
 
B

BiancoS3

moped
PieMan,
I'm running British Custom Predators and K&N pods. I'm going to try needle shims and the 140 main as suggested by Mikenva. Its going to be a week or so before I'll have time to do it but will post the results when done. Thanks to everyone for their thoughts!
 
H

HepcatBob

Scooter
With the conditions you're describing (the problem being from 1/2 to 3/4 throttle) I would definitely start looking at your needles. You can change main and/or pilot jets from now until doomsday and it won't fix your problem.

Mine was having similar issues a while back. All I had to do to fix it was to move the clips on the Dynojet needles down a notch or two, effectively raising the needles. It's about a 20 minute job to do both carbs.
 
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PieMan

PieMan

Two Stroke
With K&N pods your won't need to go any richer than 145-150 mains using the 42 pilots and try 0.75-1.5 out on the pilot screw. If you put any shims on the needles with 42 pilots, you'll be very rich mid range.
 
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C

Chris in NC

Street Tracker
I installed my NB airbox elim kit yesterday. The kit came with 150s and 42s and K&N pods. I'm running stock headers with Norman Hyde pea-shooters.

I rode 130 miles today, and the bike runs great.. Next step (I should have done this yesterday) is to replace the plugs, then read them after my next day ride.

Unless I notice something between now and then, I don't intend to change anything.
 
TC_Dick

TC_Dick

TT Racer
in '08 they came stock with the same needle as the thruxton. You could look at going to a 3mm hole in your slide.

I haven't been to a dyno, but I'm running k&n filters with the airbox out and a pair of NH toga pipes, with 145/45 jets, 3.0mm slides, 1 needle shim and probably 2 turns out on the idle screws. It stars great, and pulls hard from about 2200 rpm to the redline.
 
B

BiancoS3

moped
Update. Received shims and jets from New Bonneville, installed 2 shims under the needles. She ran much better but is way rich (could smell gas and runs a little boggy, if thats a word). Going to remove 1 shim and replace the 150 main jets with 140's and see what happens. I'm running 42 pilots with 2.5 turns out on the idle screws, as previously posted the bike starts and idles fine. If weather permits I'll do this Saturday and post up the results. Thanks to all for your help!
 
mikenva

mikenva

Rocker
that should put you pretty close to right thats what I ran with your set up.most of the time you dont need 2 shims.138 to 140s should be all the jet you will need with that set up.Alot of guys run way more jet then they need.
 
B

BiancoS3

moped
Removed 1 shim this afternoon (didn't have time to change the mains), 2 turns out on the idle screws and went for a quick 30 minute ride. OMG could not believe the change! She pulls hard all the way to redline, mid-range smooth as glass, no hesitation or stumbling anywhere. She pulled the ton, no problem! I think I'll ride her some and check the plugs before I change the mains. Thanks to all for your help and advice!!
 
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