Half throttle stuttering
Posted January 30, 2013 - 10:30 AM
I am riding a WR400 with both intake and exhaust Hotcams, a high compression piston, and am running a California WR muffler with a modified sound reducer.
My jettings are 165 main, 42 pilot and 72 starter jet with a Power now and a stock needle off an 04YZ450F.
I am running a motard set up and uses my bike for commuting.
Each time when I slowly pulls to half throttle, the bike felt like choking and stammering bad. But if I rev beyond half throttle, it will be fine.
Anyone can identify the issue? I will try my best to provide more info. I am not sure how to put it, so i hope for your kind patience.
Posted January 30, 2013 - 10:33 AM
Posted January 30, 2013 - 04:27 PM
Like William said....ditch the powernow to eliminate a big variable. If your AP is tuned and jetting is right then the Powernow is pointless.
Posted January 30, 2013 - 06:37 PM
Posted January 30, 2013 - 10:47 PM
Test ride it, and the stutter remains. A short, slow bog was reintroduced when rolling throttle off traffic without the PN.
Continuing without the PN, I shifted the needle to the 2nd clip position from 3rd clip, the stutter did move to a higher range.
Originally at half throttle, the stutter kicks in at around 64-67km/h or higher speed/rev from 78-83km/h
After shifting the clip to 2nd, the stutter kicks in at 71-74km/h or higher speed/rev at 84-88km/h
I am running a NCY R needle.
Is this needle too rich for my settings?
Is there a recommended needle or chart for the Keihin/Yamaha part I can follow?
Thank you guys.
Edited by austinmation, January 30, 2013 - 11:28 PM.
Posted January 30, 2013 - 11:31 PM
Rather than a new needle.
Try a 162 or 160 main. Only about $6 to test it and a lot less hassle to swap.
Posted January 30, 2013 - 11:57 PM
Make sure your float is set correctly.
Height Could be set too low making it rich.
Posted January 31, 2013 - 12:05 AM
Posted January 31, 2013 - 06:24 AM
The flow bowl is within 8mm.
The emulsion tube is fine.
I had adjusted the following:
165 drop to 158 MJ
Needle to first clip
Still have a little "cough" or "tripping" during half throttle. More can be felt during quick acceleration at 70km/h and if gradual roll during highway at 82km/h. With or without PN.
Should I continue to lower my MJ?
I have an NCV Q from a friend. Is this a leaner needle compared to NCY R?
Posted January 31, 2013 - 02:48 PM
The Taper angle (lower 1/2) of the needle effects how lean or rich it is from 1/2 to Full Throttle. I am running OBEKP needle, E is 1 step leaner on the Taper and P is 3 steps leaner on the Straight portion and than stock OBDTM.
This means in your case the Q/R/S options of the NCV needle are only the straight portions (which is up to 1/2 throttle).
To go leaner at wider throttle openings you need a leaner taper ( 2nd letter) or leaner main.
Keep trying....you'll get it.