RB carb CEK, lean (not fault of carb)
Posted: 09:40 am Oct 09 2020
Hey all I have put about eight hours on the bike since I installed the RB carb and I have also put about three hours of tuning into the carb. I’m having an issue with the needle (CEK) needing to be in the richest position so that the bike behaves correctly.
Bike is a 1995 kdx 200 that someone at some point in time has ported for “all bottom end“. I believe this port job has something to do with the odd tuning that this bike has taken.The bike has the following mods: Platinum 2 pipe, V force3 reads with 22 hours on them, Stock silencer, low end oriented porting (done before I got the bike) and the RB carb.
The conditions I ride are: Western North Carolina 2000-2500 ft, humidity usually 50%-80%.
My current jetting is as follows PJ is 38, needle is CEK in the richest position (lean at 1/8 throttle still), And a 150 main jet. PJ is great as is the AS. My best 0-1/8 throttle performance is with the AS 1/4 to 1/2 turn richer than peak idle.
At first I thought the needle needed to be in the richest position because my main was too small. But 2 back to back plug chops at wide open throttle reveal my main is actually still rich. (For my WOT plug chop, I hold WOT uphill in fourth gear with the rear brake held slightly for 5 to 7 seconds at a time before killing ignition & pulling in clutch. I do this 5 to 7 second run three times on each plug before cutting it. With a 150 Main And the above plug chop practice, the ring around the base of the porcelain is approximately 4 mm tall (2mm would be ideal for me).
I apologize for the long winded post, and I feel like I might have answered part of the problem with mention of the porting. But if anyone has any recommendations or suggestions, they are appreciated.I believe the next step to try will be a needle or two with varying richer steps from zero to quarter throttle in the straight section? The better pull at low revs I’m reading about everywhere I’m sure would be improved with more fuel from 1/8 throttle to 3/8.
Thanks everyone!
Bike is a 1995 kdx 200 that someone at some point in time has ported for “all bottom end“. I believe this port job has something to do with the odd tuning that this bike has taken.The bike has the following mods: Platinum 2 pipe, V force3 reads with 22 hours on them, Stock silencer, low end oriented porting (done before I got the bike) and the RB carb.
The conditions I ride are: Western North Carolina 2000-2500 ft, humidity usually 50%-80%.
My current jetting is as follows PJ is 38, needle is CEK in the richest position (lean at 1/8 throttle still), And a 150 main jet. PJ is great as is the AS. My best 0-1/8 throttle performance is with the AS 1/4 to 1/2 turn richer than peak idle.
At first I thought the needle needed to be in the richest position because my main was too small. But 2 back to back plug chops at wide open throttle reveal my main is actually still rich. (For my WOT plug chop, I hold WOT uphill in fourth gear with the rear brake held slightly for 5 to 7 seconds at a time before killing ignition & pulling in clutch. I do this 5 to 7 second run three times on each plug before cutting it. With a 150 Main And the above plug chop practice, the ring around the base of the porcelain is approximately 4 mm tall (2mm would be ideal for me).
I apologize for the long winded post, and I feel like I might have answered part of the problem with mention of the porting. But if anyone has any recommendations or suggestions, they are appreciated.I believe the next step to try will be a needle or two with varying richer steps from zero to quarter throttle in the straight section? The better pull at low revs I’m reading about everywhere I’m sure would be improved with more fuel from 1/8 throttle to 3/8.
Thanks everyone!