Hey ya'll just lookin for a second opinion on jetting for the colder days approaching my neck of the woods.

Quick history of work done for you carby tinkers...

Bought bike at 1600 km with stage 2 dyno installed, k&n filter and fmf q4 muffler. Airbox lid installed, stock gearing. Bike ran great, but got would heat up too fast for my liking when doing city speeds and technical riding.

128 main jet installed, stock pilot jet, DJ needle and spring installed with clip on #3 position, washers set as per DJ instructions. stock gearing (14/39) top speed achieved: 130km/h @9000rpm
dropped a tooth in the front, top speed 124km/h (bike singing, nothing left)

I decided to try my luck with a 132 main, #40 pilot and 2.5 turns on the mix screw to get my exhaust temps down and accomodate for hot weather riding in the summer.

The bike ran like a dream, responded well to my upgrades but with the cooler weather the top end seemed to flatten out. This I assumed was from lack of air flow at high speeds due to lower vacuum? When I decided to remove the airbox lid the other day, I achieved 130km/h with a 13th front sprocket and 39t rear. Bike usually tops out around 124km/h with this set up. This was in my opinion due to the unrestricted air flow at low vacuum at high speeds?

The main question I have is wether or not I should drop back down to the 128 main for the colder weather, as leaning it out (with more air) seemed to really pick up the bottom end and top end yet felt sluggish in the midrange. Is this a needle issue? I understand that air pressure is a factor as well, and it was a cold morning run with the airbox lid off. When I re-installed the airbox lid, I noticed a considerable lack of midrange and top end. It has also become much cooler in temperature. I would like to have it jetted with the airbox lid attached, and in the event of a cold snap or trip to higher altitude simply remove the lid to lean it out a bit.
I'm very interested in all opinions, messing with the jets has become a very fun game for me

 

Eh, just keep the lid off with a 132 main jet if that's where it runs best. Unless you literally drop below 0C I doubt it would be super lean.

I live at 2000ft and when I had my 250 I found airbox off with 13 front sprocket and 124 main it would run great in the winter and summer

 

The main seems fine with the lid off, at high rpms. If I go WOT off the line there isn't as fast a response with revs or acceleration.. I get my best acceleration with a clever snap to about 5/8 throttle.

Half throttle off the mark is a good pull, but anything more than that just seems to poop out. This is why I'm curious about my needle, which effects the flow in conjunction with the main (at around 3/4 throttle if I'm not mistaken)

Since its the only thing I haven't adjusted since going up in jets sizes, would that suggest that its too lean? or is my pilot too rich and not allowing a quick enough jump to higher rpm where power gain is found?

I have a good cruising rpm and dont experience stuttering or lugging at mid throttle. When I blip the throttle my revs return to the original position without hanging up. When I purchased the bike from the PO it had no trouble revving up and down from low rpm to high rpm and had smooth power in between. Now with my steady hand and insatiable curiosity I have great bottom end, the most top speed ive been able to squeeze out of the bike and a lazy mid range that seems to be happy when i rev it, drop it and rev it again.... the mystery continues

Thanks for the words of insight!

 

pulled from supermoto junkie.com:

in response to another person's settings

"your 3 1/2 turns out on the air/fuel screw? wow thats alot. typically its only about 2 or so turns. Uncork the exhaust and the bike really wakes up. I have an 09 tbr slip-on twin air filter. airbox lid off smog deleted and a dj jet kit. I had my bike dyno tuned and it put out 25hp and right around 16 ftlb's. My jetting is dj 134 main 40 pilot needle second clip from the top and 2 turns out on the a/f screw. my air/fuel was reading 12.9 across the board. which is perfect. Im at sea level btw. "

im going to mimic this needle position and see if there is any notable improvement, its the easiest to access

 

132 and 40, that's what I've been running for 6 years, all temps and elevation from 0-3000 runs absolutely perfect!

 

The 40 pilot jet has always been interesting to me. You see a few run it with fine results. However, most run either the OEM 35 or maybe a 38 pilot. And most of us who have tried a 38 or 40 have gone back to the 35...even with a bigger bore kit. There's not really a right or wrong here, as it's more a just "what works" for any given bike or location. Still, I find it fascinating that basically the same bikes at the same elevations can run a 35 or a 40 with apparent success. Two jumps in a pilot jet are huge.

 

You are all over the map on your carburetion, changing too many things at once. I would suggest a more systematic approach. Changing one item at a time and log the results.

First, decide if you are an air box lid on or air box lid off kind of guy. Whichever way you decide, leave it on or off then jet for that condition - pilot, needle, main. Ditto for the snorkel.

Cooler air is more dense than hot air. Since the air is denser (more oxygen) more fuel is usually appropriate, not less. That is assuming the jetting is close to optimum to begin with. In reality, you should not have to modify jetting from season to season.

One of the design parameters of the air box is to provide and maintain high intake velocity at various engine speeds and loads. A CV carburetor is very sensitive to intake velocity. With the air box lid off you are introducing some additional complexities. Intake velocity becomes unpredictable. You have to try to adjust for vagaries in intake velocity with jetting. It is usually a compromise.

BTW, a 40 pilot and 2 1/2 turns out on the mixture screw is crazy rich on the pilot circuit, air box lid or not.

Good luck with the project.

Ron

 

Thanks Ron, I was beginning to get su****ious of my multi tasking when modding.... I did the crankcase mod and pulled the airbox lid at the same time, basically nullifying any noticable changes from whence I had them set at before.

I will no longer do this, ONE MOD AT A TIME MR.

As for wether or not to have the lid on, it seems as though the bike loves the extra air flow, especially with the 132 main. Tuning in my midrange seems a lot harder to do with the lid off. I can understand why my bike is running well with a 40 pilot 132 main and no lid, there is more gas and air going into the bike. Its the mid range that has me stumped. It felt fine in the summer, but now that winter approaches the mid range seems dumpy with my current settings.
I didn't touch the needle when going up in jets, but this didnt seem to matter in warm weather. Now I'm wondering if it needs to be lowered a notch, to compensate for the leaning condition of the colder air combined with more air going into the box. In a perfect world i would run it without the lid on in the winter and with the lid on in the summer, instead of having to rejet.

As for saying you dont need to rejet from winter to summer, that may be true, you dont need to, but you will notice loss of performance, no?

p.s. i still get light poppin on decel with a 40 pilot at 2.5 turns, airbox lid off. Lid back on, no popping unless extreme grade or sudden decel. poppin can be re animated by turning in the idle screw in to 2 turns.. mystery

 

I thought that too. I can only thin of two reasons, perhaps the manufactuer doesnt hve a good quality control and the jet skzes aren't "true" which i think is highly unlikely, or humidity plays a larger role than elevation than we suspect concernin the pilot circuit.

 

deej may i ask what you have your needle height set to? and if you have the slide drilled out?

would help with my pondering

thanks