Dear Mr. Know-It-All,
I have a 2016 300XC. As you know,
it comes with a 36mm carb. I decided
to try a 38mm carb. I actually ordered
one from a 2015 150SX model, as it
would swap right over. On the Internet
people talk a lot about the best jetting
for these. In the end, the best jetting
I came up with was the stock 300
needle on clip 3, and then the pilot
and main from my 36 Keihin in the
hauls the mail now, but I feel it’s deto-
nating a bit. Premium gas here is 91
octane. I have access to 110 octane,
but straight 110 made the bike a bit
sluggish. I’m thinking maybe 94 or 95
octane in the end is the way to go.
I’m struggling to figure out the math
to get me where I want to go. Can you
enlighten me? Thank you so much.
Well, Zack Attack, I’d love to tell
you that I have both an abbreviated
and a full-score answer to this query,
but even I had to think twice.
Here is how it works. If you were
mixing fuel at 50/50, then even you
could do that, I hope. That would just
be 91 + 110 = 201. Then divide that
by 2, since it’s two equal parts, and
it’s 100. 5. Your end octane would be
When the ratios are not 50/50, you
have to get more creative. You said
you wanted 94–95 range. I agree that’s
advice on what to maybe try first so
that I don’t waste any extra money?
The bike always starts when you kick-start it, if that helps. Thank you.
Dear Jon, that’s a fair question, as
electrical drama is hard to pinpoint.
On your bike you only have four parts
to your charging system.
• The flywheel, which has the magnets and is part of generating the
• The stator, which works with the
flywheel to generate the electricity.
• The regulator/rectifier, which takes
the AC (alternating current) from the
stator and turns it into DC voltage,
plus regulates how much comes out
to the battery.
• The battery itself.
Of course, there are the wires and
cables, too, which should be checked
to make sure they are clean and tight.
So, here’s how I would think it through
and what I would do first.
The bike is still running when you
kick-start it, which means that the
stator and flywheel are still generat-
ing energy. There are three wires that
normally come out of stators, and
they are usually yellow. Look along
the wires as they leave the stator. The
color should be an obvious yellow. If it
a good range for your needs. Since
50/50 is 100. 5, you are going to need
less of the 110-octane fuel, obviously.
Let’s go with a total of 4 gallons and
do the math on finding how much of
each fuel you would need to get in
your desired range.
100% divided by 4 equals 25%.
Each gallon equals 25%. For the
record, if you are mixing 5 gallons,
then each gallon equals 20%.
Let’s try 110 octane x 25% (type
in 100 x . 25) = 27. 5. So that
1 gallon will contribute 27. 5
Then, take 91 x 75% (type
in 91 x . 75) = 68. 25, so that 3
gallons will contribute 68. 25
octane to the mix.
Then let’s add our 4 gallons to get out 100%. This
will be the 68. 25 + 27. 5 =
95. 75 octane in those 4 gallons of gas. So you now
know that 1 gallon of 110
and 3 gallons of 91 will
give you 4 gallons of 95. 75
octane. Not too hard. If you
want 94 octane, then re-run
the numbers on filling your
5-gallon jug with 4 parts of
91 and 1 gallon of 110 and you should
be close to 94.
Now you’re either sticking a Phillips
screwdriver in your eye, or…you get
it. I believe that you’re a screwdriver
kind of guy!
THE BATTERY BLUES
Dear Mr. Know-It-All,
I’m struggling to keep the battery
charged on my 2005 KTM 250EXC.
I put a new one in and the bike
starts for a day, then it just turns
slower and won’t get my scoot
to kick over. My neighbor helped
me check the incoming voltage
to the battery when it was dead
and it was 4. 88 volts. We put a
new battery in and the incoming
voltage was 12. 35. We started
the bike 10 times. The incoming
charge was then 11. 12 volts.
I now know that the charg-
ing system isn’t working. Since
you can’t return electrical parts
to the dealer, do you have any
Compiled, by Dave Simon, owner/operator