Jetting in advance of riding

mary ann over ginger anyday...

I've decided that I'm punting the whole mary ann vs. ginger argument
in favor of a new Diane Chambers (Cheers) vs. Christine Sullivan
(Night Court).

Damn, that's a hard one. Eh, I've always been a diehard Markie Post
fan anyway...

Incidentally, I found this floating around the net - no guarantees on
accuracy:

Correction Factor (CF) = 1.0778-.00111*T + (2.38554*10^-10)*A^2 -
(1.0777*10^-5)*A

T is temperature in degrees F; A is altitude in feet (CF=1 at 70F and
0ft.)

JayC

 

That may be true of hex jets.

That is simply NOT true of Mikuni and Keihin *round jets*, which are
are based upon a #100 having a 1.00 millimeter orifice hole.

While Mikuni has half-sized round jets, like 107.5 (1.075 mm), the
equivalent Keihin round jet is a #108.

I have a Mikuni #17.5 pilot jet in my KLR, to replace the Keihin
#17...

 

That is simply NOT true of Mikuni and Keihin *round jets*, which are

Not to my knowledge. According to my research, Dynojet jets are
numbered by diameter, with a system corresponding to what you posted
(10 mils per #) - however, they are the only company that does so.

Evidently, the difference between the Amal jets (hex) and button jets
(round) are that the Amal jets are stamped with calibration volume,
and button jets are stamped with operational volume, although both
systems are flow in cc/minute

Excerpt from article regarding Mikuni jets:

**************
1) the “long (or large) hex” style main jet is known as the “Amal”
style in Mikuni-speak. It’s also Mikuni type 4/042. This style of jet
has its fuel flow calibrated in the “wrong” direction i.e. from the
threaded end through the orifice and out what we consider the inlet
end. The number stamped on the jet corresponds to the number of cubic
centimetres of gasoline which will flow through the jet when poured in
the calibration direction from a height of 50 centimetres. Since the
direction of flow during calibration is opposite to what the flow is
during actual operation when installed in the carb, the OPERATIONAL
flow rate does NOT correspond to the number stamped on the jet.

2) the “button” or “slot” style main jet is properly known as the
“reverse” style in Mikuni-speak. It’s Mikuni type N100/604. The fuel
calibration flow can be done from either side of the orifice. This
also holds true for actual fuel flow volume when in operation in the
carb. I assume it’s called the “reverse” style because the calibration
can be done in the reverse direction compared to the Amal style jet.
Regardless of that, although none of the info I have specifically
states so, you can PROBABLY ASSUME that the number stamped on the jet
is the operational flow volume in cubic centimetres of gasoline as
well as the calibration flow volume.
************

JayC

 

"JayC" <

who?? , searching, oh, neither do it for
me... they just don't seem like fun... they
don't have what i'd consider practical qualities
yet this is hypothetical not practical, so the
dark haired one looks like she requires less
maintenance.

neat formula
I hope the next bike for me is going
to have a computer to do that calculating for me.

oh side note, met another gasgas guy today...
wuds guy... might have another riding spot <grin>
john




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If any *ass*-uming needs to be done, you go ahead and *ass*-ume all
you want.

 

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/ \ \ |
/ _ \ \ ----------------------
/ |\____\ \ ||
/ | | | |\____/ ||
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* ___ c_c_c_C/ \C_c_c_c____________

 

Not saying you're wrong, but Dynojet company would disagree with you.

From the Dynojet site:

Dynojet numbers are simply the hole diameter. A 140DJ main has a
1.40mm (0.055") diameter hole in it at the threaded end. A Mikuni 140
has 140 cc of fuel flow per minute. We're not sure where the Keihin
scale comes from.

Width------Keihin # -- DynoJet # --- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90.0
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105.0
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120.0
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135.0
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150.0
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 157.5
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165.0
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180.0
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5


JayC

 

WTF is this *shit* from DumboJet? Keihin does NOT make jets in half
sizes.

Why would *anybody* believe information from DumboJet? Giving out
false info is to their advantage if it convinces a naive ride to buy
their homemade crap instead of buy precision-machined OEM jets.

 

Knowing what jets work in my XRL with both dynojet jets, and keihin
jets, I think dynojet has something wrong somewhere in how they
arrange that chart if there's supposed to be some equivalence for the
jets on a given line.

A DJ 160 (in flow) is much more like a keihin 158 or so, not like a
177.5.

Dave

 

Well, they aren't succeeding, IMO.

No, I don't think so. I think they are trying to compare fuel flow in
cc's/min but don't know what they are up to.

The DumboJet "technicians" are comparing Mikuni HEX jets and Keihin
ROUND jets to their homemade STRAIGHT HOLE jets which do not have a
venturi cross section at all.

I have a graph right here. It compares the flow of a Mikuni HEX jet to
a Mikuni ROUND jet. Mikuni ROUND jets are also called "Reverse Type".
A cross section of this jet is venturi-shaped like a rocket nozzle.

The Mikuni #140 HEX jet flows 140cc's of fuel per minute.

The Mikuni #140 ROUND jet flows 280cc's per minute.

 

Knowing what jets work in my XRL with both dynojet jets, and keihin

Also, one of the motor tuning guys on TT mentioned that the Dynojet
numbers roughly correspond to Mikuni numbers in actual flow.

Everyone I've seen that is somehow connected with the jetting industry
tends to support a "black magic" air with what they do. From the carb
manufacturers esoteric numbering techniques, to the OEM guys and their
mysterious cross-referencing, to the jetting "gurus" who won't give a
straight answer no matter what. Pththththth. If decent carb/jet data
was available, anybody with a pen, and calculator, and a pad of paper
could do a first-order set up of any motor/carb combination in 5
minutes.

Man, I can't wait until everything is fuel-injected. At least you can
generate real data putzing around with sensors and software.

JayC

 

I'd settle for jets that I can change without removing the bowl.

Dave

 

Giving out the true information won't sell a DumboJet kit to a squid...

 

That is one of the things the JD spreadsheet was supposed to
address... the other was temp.

 

Give me your current specs... pilot, main, needle and clip number,
altitude, temp and slide number.
Then the temp and altitude for where you are going and I'll try to run
the numbers.

 

I couldn't help Strud directly with my spreadsheet because his carb is
not compatible with the spreadsheet.

However, I will offer this little gem that may help someone out
there.
I use 1200 ft for my average KY altitude and my bike is currently
jetted for 80-85 degrees. I'm planning a ride at up to 6000 feet and
temps probably around 60... since the increase in altitude and
decrease in temps partially offset each other, my KY jetting *SHOULD*
be pretty close without any changes...

I just hope it works as well in the real world as it does in the
spreadsheet.

 

Just as a datapoint, heard back from someone who was jetted for about
sea level, went on a high-altitude trip (10,000 ft or so) and the XRL
just needed some pilot mixture tweaking. Ran great, he said, the
powerloss was of course much less than the poor 450s on the trip.

Dave

 

With all this talk are the riders going to rejet before they leave on
their trip and suffer til they get there? Or are they going to get
there, tear out the carbs, rejet and hope is easy and nothing breaks?

I know when I pulled carbs of 81 and 83 GS650 I swore and needed a 2x4.
I am doing everything I can to not pull them on an 82 KZ750-R1.

Ian Singer

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I can change the main with the carb on my bike. I can change the
needle or pilot in about 15 minutes without breaking a sweat... I do
have a serious dislike for opening it up on the trail once it gets all
muddy though so I like to do it before the ride while the bike is
still clean. Plus it's easier to lose tiny parts on the trail than in
the trailer or garage.

 

If you have to run so slow because of difficult terrain that you can
never use full throttle, it doesn't matter what size the main jet is.