Jet sizes?

[sean01]

hi,
does anyone know how jets sizes are rated in mikuni's and keihin carbs.

what i mean is a 95 main jet .095 tho or .95 mm...i know there way of but is there a scale they work at..

im looking at buying a jet drill kit for pilots and mains

cheers

 

[sean01]

Cactus Jack, any reason why your post was removed?

i got your post in email but thought it should be up for everyone to see...(if it is a forum issue, let me know if ya want me to post the info)

very good information and has helped me decide which jet drilling kits i need..thank you...

now im not sure if anyone else is interested but ill show you the kits im looking at, and if there not suitable please let me know...

cheers

30PC(0.3-1.6MM)HSS MINI JET DRILL BITS &PIN VISE HOLDER - eBay, Tools, Metalworking, Woodworking, Business, Industrial. (end time 20-Oct-09 22:40:36 AEDST) (shame once it hits 1mm it only gots up in .1mm) but ok for pilots

if anyone knows where other kits available online shoot us some links please...

 

[1fifty1wheel]

Width------Keihin # -- DynoJets # -- 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

i read somewher a dyno jet size is easily converted to mm's, 130DJ = 1.30 mm diameter and a 112DJ = 1.12 mm. But for instance a 130DJ having a diameter of .054" * 25.4 = 1.37mm?
Mikuni Jets are supposed to be sized by cc's of flow per minute.

 

[sean01]

yeah thats the chart cactus jack had posted here but for some reason it was removed

cheers

 

[Cactus Jack]

Yeah I pulled the post to allow myself more time to check things out thoroughly after finding new info in the below Vintage Dirt Bikes forum thread :

Searchable Knowledge Base • View topic - Mikuni specs for MT250

The two jet conversion charts give conflicting comparison specs ... The ONLY real way to know for dead certain is to buy a set of jet drills and use them to measure the actual sizes of various Mikuni and Keihin jets ... maybe Mikuni changed the way they size their jets at some point in time over the years ?

----------------------------------------------------------------------------------------------------------------------

Here's my original post ...

Mikuni jets are rated a cc/minute of flow and Keihin jets go by size in mm ...

I've read where Keihin pilots are #36 = .36 mm / #37 = .37 mm / #38 = .38 mm etc ... and #100 main = 1 mm ... #102 = 1.02 mm etc

I haven't found a Keihin to Mikuni pilot jet conversion chart yet ...

I've had this main jet conversion chart saved for a while ...

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

There are several different types of Mikuni jets ...

mikuni pilot jets

mikuni jets

 

[Cactus Jack]

Here's some more info on jetting and tuning with specs on a 26 mm oval bore carb as an example (they're the equivalent of a 22 mm round bore carb) ...

PZ Carburetor General specifications
Gasoline
Main Jet - #102
Pilot Jet - (slow Jet) #37
Jet needle - CDb 4th notch
Main nozzle diameter - 2.6 mm
Idle Mixture screw turns out - 1-1/2
float Height* - 14.0mm
Torque specifications
bowl screws 17 * 20 in-lbs.
Pilot Jet 9 * 12 in-lbs.
needle Jet 14 * 16 in-lbs.
Main Jet 9 * 11 in-lbs.


1) Float Height :

The float height controls the fuel level in the float bowl,
which can also effect carburetor performance. Set float
height according to specification before any other tuning.
The float height may need to be adjusted for best perfor-
mance on different track types.

2) Idle / low speed :

Tuning of the engine at idle and low speeds is accomplished
by adjusting the Idle Mixture Screw or changing the size of
the Pilot Jet (also called Slow Jet). The jet size or diameter in
millimeters is stamped on the jet (37 = .37mm orifice). The
Idle Mixture Screw is a fuel adjustment, so closing the screw
or turning it clockwise will lean the fuel mixture, and opening
the screw or turning it counterclockwise will richen the
fuel mixture.

To adjust the Idle Mixture Screw proceed as follows. Turn
the Idle Mixture screw in until it lightly seats or stops. Back
the screw out the specified number of turns. Warm the
engine and set the Idle Speed screw slightly higher than
the desired idle rpm. Turn the Idle Mixture screw in or out
to obtain the highest rpm. Turn the Idle Speed screw to the
desired idle rpm. A slightly rich idle mixture is usually better
for acceleration.

If a smooth idle cannot be obtained with the Idle Mixture
screw between 1/4 - 2 turns out from closed, a different
size Pilot Jet may be needed. The proper size Pilot Jet will
allow for smooth acceleration from an idle and steady
engine speed up to 1/4 throttle opening.

3) Midrange / Part Throttle :

The Jet Needle primarily controls fuel flow between 1/4
and 3/4 throttle opening. The Jet Needle has five notches
and a C-clip on the top of it. To richen the part throttle
operation, move the clip to the next lower notch. This will
hold the needle farther out of the nozzle. To lean the
part throttle operation, move the clip to the next higher
position. The highest notch (farthest from the narrow tip)
is considered the 1st position. Needle taper reference
letters are stamped on the needle for identification.

4) High speed / full Throttle :

The Main Jet controls the fuel flow at throttle positions of
1/2 to full throttle. The jet size or diameter in millimeters
is stamped on the jet. Altitude and weather conditions can
effect the engine operation enough to require changing
the size of the Main Jet. High air temperature, humidity, or
altitude could require a smaller Main Jet. Low temperature,
humidity, or altitude would require a larger diameter Main
Jet. Running the engine with an improper Main Jet could
result in a loss of power, high engine temperatures, or
engine damage.

 

[sean01]

thanks cactus jack for making sure your information is 110%

 

[1fifty1wheel]

Keihin in mm's are definately closer then th Dj's. Although going by the inches on the left still not really correct? That is of coarse if the chart is right to begin with?

 

[Cactus Jack]

Those jet drill kits look OK ...

Yes , I checked and according to the chart Keihin sizes AREN'T in mm ... A guy in the link says Mikuni sizes represent fuel flow upwards thru the jets and Keihin sizes represent fuel flow downwards thru the jets ... ONLY Dynojet sizes are in mm ... The guy also says some Keihin jets will screw into the same thread as Mikuni jets ????? ...

 

[mrbrnz]

both keihin and mikuni rounds will screw into my molkt if thats what you mean

 

[sean01]

nah, referring to oko keihin mikuni jet hole sizes...

cant standard molkt carbs, they go in the bin along with china mikuni's

 

[thump*140]

No No Sean, you immerse them in petrol, and let an OKO strike the match...

 

[mrbrnz]

the new deep bowl molkts are really good actually, just gota get the float level right, they even come with a proper 4 stroke needle.

 

[sean01]

yeah, weve had molkts that are shipped from dhz that actually have a different setup inside...no compatible pilots or mains..actually i been meaning to hang a picture up in here showing it...

and i think a member here just fitted a 155z and it was shipped with a mikuni...

but iv come to the conclusion that im going to can my oko because it wont even accept hex jets. they hit the bottom of the bowl... (you may have seen my other thread regarding jetting issue's)

we have a genuine keihin 28mm on the bike now and its awesome...