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Jetting the 650R by
Gary "Pontiac Sr." |
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Special thanks and all credits to Gary for all his hard work making this write-up possible. |
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Though Gary has done a lot of the
footwork for you, this information is in no way intended to be an
instant fix to cure any woes you are having in the jetting
department. They may be exactly what you need, but chances are they
will only get you ballpark. Different pipes, headers, filters and
oiling procedures, backfire screens, and fuel will all make the
figures sway a little either direction.
Learn how to read plugs and don't
ignore what your piggy is trying to tell you via hp, temps, and
feel.
The following information is specific to the XR650R. While the following
jetting charts should be fairly accurate, please use them as a
starting point to work from to find your specific baseline jetting.
Your baseline jetting will be the final jet sizes you end up with
that gives you the very best performance for a given riding
environment. If your riding environment changes from where you’ve
setup your baseline jetting, then simply use the correction factors
listed in your service manual to find your new jetting specs. If
your riding environment varies, then try to choose something that
fits most of your riding needs, but error on the side of being too
rich if you’re in doubt. Running too lean will lead to premature
engine failure. For optimum performance, plan to rejet if the
temperature you’re riding at changes more than 20° F above or below
your baseline. Also plan to rejet if your altitude changes more than
3,000 feet from your baseline.
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***Note: These specs are for an XR650R Uncorked / HRC tip / B53E Comp
Needle***
*** XR650R Uncorked
/stock header with HRC tip / B53E Comp Needle***
- Use a main jet one size smaller when using a drilled stock tip
instead of the HRC tip
- Use a main jet one to two sizes larger when your side panel is
cut-out
- If the stock needle is used, then ad +1 to the clip position
listed below
- Use a main jet one size larger with a high flow aftermarket
exhaust canister
- Use a main jet two sizes larger when using a larger diameter
aftermarket header & exhaust canister
NOTE:
When Gary mentions "Go one size larger", remember that Keihin jets
run in sizes of 0, 2, 5, and 8. (170, 172, 175, 178, 180, etc.) A
170 + 2 main jet sizes should equal a 175 if that makes any sense.
When using the formulas above and more
than one matches your bike, the increases and decreases in jet size
are cumulative.
Examples:
- (XR650R uncorked) + (stage 1 cam) + (drilled out stock tip) = no
main jet changes The cam increases the main jet size by 1, but the
drilled stock tip subtracts 1 so they cancel each other out.
- (XR650R uncorked) + (stage 1 cam) + (side panel cut out) + (HRC
tip) = 2 main jet sizes larger
- (XR650R uncorked) + (stage 2 cam) + (side panel cutout) + (full
exhaust header & canister) = +5 main jet sizes larger
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TEMPERATURE IN DEGREES °F
| Altitude |
20 |
30 |
40 |
50 |
50 |
70 |
80 |
90 |
100 |
| 0 |
182 |
180 |
178 |
175 |
175 |
172 |
170 |
168 |
168 |
| 1000 |
180 |
180 |
175 |
175 |
172 |
170 |
168 |
168 |
165 |
| 2000 |
178 |
178 |
175 |
172 |
170 |
168 |
168 |
165 |
162 |
| 3000 |
178 |
175 |
172 |
170 |
168 |
168 |
165 |
165 |
162 |
| 4000 |
175 |
175 |
172 |
170 |
168 |
165 |
165 |
162 |
160 |
| 5000 |
175 |
172 |
170 |
168 |
165 |
165 |
162 |
160 |
158 |
| 6000 |
172 |
170 |
168 |
168 |
165 |
162 |
160 |
158 |
158 |
| 7000 |
170 |
168 |
168 |
168 |
165 |
162 |
160 |
158 |
155 |
| 8000 |
170 |
168 |
165 |
165 |
162 |
160 |
158 |
158 |
155 |
| 9000 |
168 |
168 |
165 |
162 |
160 |
158 |
158 |
155 |
152 |
| 10,000 |
168 |
165 |
165 |
162 |
160 |
158 |
155 |
155 |
152 |
| 11,000 |
168 |
165 |
162 |
160 |
158 |
158 |
155 |
152 |
150 |
| 12,000 |
165 |
165 |
162 |
160 |
158 |
155 |
155 |
152 |
150 |
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***Clip position counted down from top of needle***
TEMPERATURE IN DEGREES °F
| Altitude |
20 |
30 |
40 |
50 |
50 |
70 |
80 |
90 |
100 |
| 0 |
4 |
4 |
4 |
3 |
3 |
3 |
3 |
3 |
2 |
| 1000 |
4 |
4 |
43 |
3 |
3 |
3 |
3 |
2 |
2 |
| 2000 |
4 |
4 |
3 |
3 |
3 |
3 |
2 |
2 |
2 |
| 3000 |
4 |
3 |
3 |
3 |
3 |
2 |
2 |
2 |
2 |
| 4000 |
3 |
3 |
3 |
3 |
2 |
2 |
2 |
2 |
2 |
| 5000 |
3 |
3 |
3 |
3 |
2 |
2 |
2 |
2 |
1 |
| 6000 |
3 |
3 |
3 |
2 |
2 |
2 |
2 |
2 |
1 |
| 7000 |
3 |
3 |
3 |
2 |
2 |
2 |
2 |
1 |
1 |
| 8000 |
3 |
3 |
2 |
2 |
2 |
2 |
1 |
1 |
1 |
| 9000 |
3 |
2 |
2 |
2 |
2 |
1 |
1 |
1 |
1 |
| 10,000 |
3 |
2 |
2 |
2 |
1 |
1 |
1 |
1 |
1 |
| 11,000 |
2 |
2 |
2 |
2 |
1 |
1 |
1 |
1 |
1 |
| 12,000 |
2 |
2 |
2 |
2 |
1 |
1 |
1 |
1 |
1 |
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TEMPERATURE IN DEGREES °F
| Altitude |
20 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
100 |
| 0 |
72 |
72 |
70 |
70 |
68s |
68s |
68s |
68s |
65 |
| 1000 |
72 |
70 |
70 |
68s |
68s |
68s |
68s |
68s |
65 |
| 2000 |
70 |
80 |
68s |
68s |
68s |
68s |
65 |
65 |
65 |
| 3000 |
70 |
70 |
68s |
68s |
68s |
65 |
65 |
65 |
65 |
| 4000 |
70 |
68s |
68s |
68s |
68s |
65 |
65 |
65 |
65 |
| 5000 |
68s |
68s |
68s |
68s |
65 |
65 |
65 |
65 |
62 |
| 6000 |
68s |
68s |
68s |
65 |
65 |
65 |
65 |
62 |
62 |
| 7000 |
68s |
68s |
65 |
65 |
65 |
65 |
62 |
62 |
62 |
| 8000 |
68s |
68s |
65 |
65 |
65 |
65 |
62 |
62 |
62 |
| 9000 |
68s |
65 |
65 |
65 |
65 |
62 |
62 |
62 |
60 |
| 10,000 |
68s |
65 |
65 |
65 |
65 |
62 |
62 |
60 |
60 |
| 11,000 |
65 |
65 |
65 |
65 |
62 |
62 |
62 |
60 |
60 |
| 12,000 |
65 |
65 |
65 |
65 |
62 |
62 |
60 |
60 |
60 |
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One of
the most common questions asked on the subject of jetting is "What's
the difference between a 68s and a 68 pilot?".
Only a little, but it makes a big
difference in fuel flow! Below are two pictures of pilot jets. The
top is a normal 68, while the bottom is of a 68s. Notice that the
68s has smaller emulsification holes. Though hard to see in the pics,
the "s" has an "S" in the stamped markings.
Here's what Gary thinks of the different
jets:
The 68 pilot jet is similar to the 68s. They both share the same
main orifice size for the discharge nozzle, but the 68s has smaller
emulsion holes on the sides of its tube as you can see by the
picture. The smaller holes on the 68s pilot jet reduces the amount
of air that mixes with the fuel before the emulsified mixture is
discharged through the jet's nozzle.
Now for a bit of Haymakers free trivia:
Websters defines "emulsification"
as "To make into an emulsion", where the definition of such is the
following:
- A suspension of small globules of one liquid in a second liquid
with which the first will not mix: an emulsion of oil in vinegar.
Now substitute "oil in vinegar" for "fuel
in air", and there you have it!
"What does all this mean?" You ask? The
size of globules into which the fuel is made by the jet drastically
changes the rate in which it will burn. A Charge of air and fuel
will burn much faster and with more force when there are more,
though much smaller, droplets of fuel involved. I believe that the
different jet has a direct correlation to the fact that the big XR
is epa certified for emissions. Maybe I can get Gary to provide a
little more insight as to why this change has been made.
Here's a bit of real world theory to help
you understand how fuel burns. If you were to light a cup containing
gasoline, only the surface of the cup would burn. You'd get a
orange, smokey, flame, meaning that it was not burning efficiently.
If you were to take that same cup of
fuel, atomize it into a fine mist in an enclosed space with the
proper 15:1 ratio of air, then light it, you'd see the difference
small globules make. Something I once read stated that "1 cup of
gasoline will lift 1 ton, 100 feet, in one second." Maybe it's not
correct, but it's something to think about as you are trying to put
out your eyebrows because you had to check and see if I know what
I'm talking about.
Well, that's about all I have for now. If
anyone has any constructive criticism or recommendations, please let
us know.
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