Carburetor Tuning - Rich and Lean Spikes

Zyconic17 · May 13th, 2012, 12:08 PM

Hi everyone. I have started tuning my carburetors on the dyno. My first run (the red line) shows that i was running incredibly rich, and there are many spikes in the Air/Fuel ratio throughout the rev range. My biggest goal is to smooth out the Air/Fuel ratio line across the entire rev range and have it sit at about 14:1 but i am unsure how to get rid of the spikes. the red line is my first run where i had a 98main jet in, and the needles were on the third clip from the top. The blue line is my second run, where i moved to a 94main jet and dropped the needles to the 2nd clip from the top (to lean out the A/F mixture.) I know that the dyno sheet i have provided is not the most accurate comparison between the two different runs because of the relatively large difference in ambient air temperatures. (66F and 83F) but i am not worried about that. i just want to smooth out the curve. any help would be appreciated! thanks!

alex.s · May 13th, 2012, 12:26 PM

i think i read somewhere the needle taper is whats responsible for the midrange mix curve. so maybe drop one more main size and lean out the needle more and put a bigger idle jet in?

Zyconic17 · May 13th, 2012, 01:01 PM

Yeah i have heard that about the needle too. the only thing I am concerned with is dropping another main jet size. as you can see, at redline it is already pretty lean (approx 13.5:1). if i go much leaner than 14, the engine could be damaged. I will try dropping the needle some more, but the hard part will be finding a way to make a spacer to go in between the spring and the needle so that it will not bounce. I really want this midrange cleared up because its killing my lap times. so ill give what you said a shot and post the results.

May 13th, 2012, 12:26 PM	#2
alex.s wat Name: wat Location: tustin/long beach Join Date: Sep 2009 Motorcycle(s): wat Posts: Too much. Blog Entries: 5 MOTM - Oct '12, Feb '14	i think i read somewhere the needle taper is whats responsible for the midrange mix curve. so maybe drop one more main size and lean out the needle more and put a bigger idle jet in? __________________________________________________

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May 13th, 2012, 01:01 PM	#3
Zyconic17 ninjette.org member Name: David Location: Arvada Join Date: Apr 2011 Motorcycle(s): 2010 Ninja 250r Track bike, Honda CRF250r Dirt bike Posts: 137	Yeah i have heard that about the needle too. the only thing I am concerned with is dropping another main jet size. as you can see, at redline it is already pretty lean (approx 13.5:1). if i go much leaner than 14, the engine could be damaged. I will try dropping the needle some more, but the hard part will be finding a way to make a spacer to go in between the spring and the needle so that it will not bounce. I really want this midrange cleared up because its killing my lap times. so ill give what you said a shot and post the results.