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Jetting the Carb

 
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Jetting the Carb
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The Offscootinovs



Joined: 08 Apr 2007
Posts: 77
Location: Columbia County, NY

Post Jetting the Carb Reply with quote
Hi, All. I have an HRS pipe on order and just ordered a K&N air filter. Can anyone fill me in on the process of jetting the carb? If I understand correctly the stock jet is 120 (120 what?). Any info you can share would be appreciated.
Sun Jul 08, 2007 4:06 pm View user's profile Send private message
lex



Joined: 18 Jun 2007
Posts: 18

Post Reply with quote
now i may just be inexperienced and or dumb buti dont know what jetting is
can you telll me and possibly post prosedure pics
Sun Jul 08, 2007 10:11 pm View user's profile Send private message
monza



Joined: 26 Mar 2007
Posts: 343
Location: Kansas City

Post Reply with quote
Jets are measured in hundredths of a millimeter, so a #120 jet has a hole in it with a diameter of 1.2mm, a #60 jet has a hole in it with a diameter of 0.60mm. The purpose of the jet is to meter the fuel flow to the engine from 75% throttle to wide open throttle. (There is another part of the carb that restricts that flow from the main jet from 25%-75% throttle called the needle, and the idle circuit takes care of the 0-25% throttle.) Increasing the jet size increases the fuel to air mix (making it "richer"), but only for the 25% to wide open range.

Changing the jet on the Chetak is a breeze (I will post some pics later). You first disconnect the air inlet hose from the bellows, and then take out the two bolts that hold it onto the intake. Make sure to turn off the fuel valve, and then open the small screw on the bottom of the bowl. The fuel in the bowl will drain out of the tube attached to the bowl. Close that screw when the fuel stops. Then take the screws off the bowl to remove it. The main jet sticks down smack dab in the middle of the bowl. it can be removed with just a flat headed screwdriver. When changed, put the bowl back on, re-attach to the intake, re-attach the inlet tube (or install K&N), and you are done.

*make sure to take care when taking the bowl off to not let the needle valve fall out. It is attached to the float (pink thing in the bowl). If it falls out, it can be re-inserted, but can be tricky.

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75 Vespa Primavera "Parmakit 130", P200E,
Mon Jul 09, 2007 3:03 am View user's profile Send private message Visit poster's website
The Offscootinovs



Joined: 08 Apr 2007
Posts: 77
Location: Columbia County, NY

Post Reply with quote
Thanks, Monza. Look forward to the pictures. Where do you get different size jets from and what do you look for?
Mon Jul 09, 2007 5:28 pm View user's profile Send private message
Angry J



Joined: 25 Mar 2007
Posts: 496
Location: Kansas City

Post Reply with quote
Here's a document I found a while ago that explains carburetor tuning fairly well. This article was written regarding much larger carbs than our Bajaj's have, but the principals in the first couple sections are the same. It has illustrations to help folks like me. Smile

http://docs.google.com/Doc?id=dd7mpwxc_5c2frkr

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Mon Jul 09, 2007 6:20 pm View user's profile Send private message Visit poster's website
cowboyrob



Joined: 26 Mar 2007
Posts: 831
Location: Fayetteville, AR

Post Reply with quote
Angry J wrote:
Here's a document I found a while ago that explains carburetor tuning fairly well. This article was written regarding much larger carbs than our Bajaj's have, but the principals in the first couple sections are the same. It has illustrations to help folks like me. Smile

http://docs.google.com/Doc?id=dd7mpwxc_5c2frkr


Nice article J!


Note to anyone really new to motorcycles. When he starts talking about your gas oil mix, premix, and so forth pay no mind, he is talking about 2 strokes and your bajaj is a nice clean 4 stroke!

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Mon Jul 09, 2007 9:10 pm View user's profile Send private message
seeshores



Joined: 04 Mar 2015
Posts: 2

Post Reply with quote
I'm having a sputtering issue at WOT in the high gears and I wanted to see what I could diagnose with jetting the carb. I know the previous owner I bought from a few weeks ago cleaned the carb and I'm not sure what he may or may not have done. Does someone still have access to this google doc? It says viewing it requires permission now and I can't seem to find a walk through on the forum that details how to do this.

Thanks for any help anyone can offer!
Wed Mar 18, 2015 3:42 pm View user's profile Send private message
donarntz
Site Admin


Joined: 01 Jul 2007
Posts: 235
Location: Austin, TX

Post Reply with quote
It may be WOT fuel starvation, it's a common thing for stock. Search the forum for the fix. Take out the inline fuel filter if you have it, buy some better fuel line to the carb and replace. You can even drill a tiny vent hole in the gas cap.

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