XR Tuning with NGK AFX kit
I finally have the ultimate tool to get the carb tuning right. The final result surpassed all expectations and reminded me of
a statement a Porsche engineer made to me in the 80s: "we were looking for fuel economy and what we found was power,
power and more power..."
Anyway, going by the book (the NGK AFX tuning manual) I started setting up for max economy running close to the
stoichiometric ideal. Interestingly that required amongs other jetting surprises a 150 main (down from 170). Result - instant
power over a wide rev band, amazing!
However when riding at higher altitudes it appeared to lean off - flat spots when accelerating. So I tuned again for max power
(on the richer side).
Had lots of fun going back and forth between pilot jets, needle pos & main. Ended up with the 150 main,
stock needle in middle, 60 pilot. But this is with a modified stock muffler (see home page) and the intake uncorked.
The secret of good tuning lies in the fact that you simply cannot follow a receipe - every bike has different parameters -
the only way is to tune individually. AFX makes this possible.
To give you an idea how puzzling this can be, when I switched from the stock header which made good power to the
aftermarket stainless one which has 4 mm more diameter in the dual pipe part, the tuning suddenly was very rich and
power was down in the mid revs - I had to reduce the main jet substantially and only then it the power improved.
This was all before I used the AFX. As it turned out, I still had the tuning too rich when going by feel alone.
By the way, fuel economy is now an honest 5.5 litres per 100 kms (converted, hopefully correct: 44 US MPG, 51 UK/Aus MPG)
based on a NGK's wide band O2 sensor* this is a tuners dream come true - I reckon it's superior to dyno tuning as
it can be done in the filed under true riding conditions.
*) NGK makes these for major brands, amongst others for Bosch. Wide band sensors have a number of advantages over
narrow band types used in common closed loop fuel injection systems - study details via Google...
temp mounting of display unit. The latency of the display is a claimed 0.3 seconds - this appears to be right.
permanent socket welded into header (ss aftermarket header).
normally this is bunged of course.
sensor in place for test runs.