Re-jetting Your Carb, As Easy As 1,2,3 ( quarkdude )

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Mogyver69

Guest
Hello Mogyver69,
I checked the site again to make sure I didn't post something we couldn't reference: http://www.ehobbytools.com/en-us/dept_8.html
This site uses the drill# which also has a decimal equivalent. Most of the kits on that site have the drill sizes we need so it is a good reference. A good kit for us would be one that has Drill#65 to Drill#78 or so. The decimal equivalent of a Drill#65 is 0.0350 and the Drill#78 is 0.0160. Most of the carb jets I have redone on these Chinese 80cc carbs start out around 0.030 and you go up or down from there as you know. I would guess that if you were to drill your jet ( I know you already filed it ) it would be good to step it up 1000ths of an inch at a time. Using Drill#68(0.310) do a test ride and see if the engine runs smooth thru the whole RPM range, if it hesitates on the low end go up one thousands to Drill#67(0.320) and keep going up one at a time until the engine runs smooth thru the whoe rpm range. Then when it feels good riding it - the spark plug will tell you when it is perfect by looking for a light brown to grey color on the electrode. Black and sooty sometimes wet=too rich. Hope this helps
................quarkdude

Hey quarkdude, I finally got my drill bit set the other day. this evening I decided to pull apart the new carberator I havent messed with and check the initial jet size. I came up with a #71 .027 I went ahead and drilled it up one size to a #70 which I believe is the size you ended up using at .028. Ill start with that and see what happens. I must say people dont follow my example with the file idea its a no no.
 


M

Mogyver69

Guest
Well I just pulled apart the other carb and the biggest bit I could fit in it was a #65 but it was alittle out of round. I was able to round it back out going back up one size to a #66 but wow thats much bigger than what I started with. I maybe soldering this jet to fix. Gonna try the other carb for now and will let you know what I end up with. Thanks again for your help quarkdude.
 
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quarkdude

Guest
Well I just pulled apart the other carb and the biggest bit I could fit in it was a #65 but it was alittle out of round. I was able to round it back out going back up one size to a #66 but wow thats much bigger than what I started with. I maybe soldering this jet to fix. Gonna try the other carb for now and will let you know what I end up with. Thanks again for your help quarkdude.
Hello Keith,
Glad to see that my instructions are being used to tune your carb. Sorry I dont have any pictures yet, I will put some on sometime in the future when I get a chance away from work. You got it - one drill size up at a time and you will find the magic jet size. Unfortunately is takes a little patience and time to find out where your engine wants to be ( this is the simple art of it ). But the engine will tell you when it is happy along with the spark plug. Good luck - definitely like to hear how it works for you.
................quarkdude
 

SchwinnHS

New Member
Joined
Jun 18, 2008
Messages
10
Albuquerque altitude

This answers aot of my questions. My bike has been running too rich and I was looking around to see if there was a place you could just buy these carb jets for higher altitude. Haven't had any luck yet so I'll end up making this modification myself.

Thanks quarkdude!
 
Q

quarkdude

Guest
This answers aot of my questions. My bike has been running too rich and I was looking around to see if there was a place you could just buy these carb jets for higher altitude. Haven't had any luck yet so I'll end up making this modification myself.

Thanks quarkdude!
Hello SchwinnHS,
Glad you found the directions for modifying your carb jetting that I posted awhile back. I to, at first, was looking for jets and could not find them at all. I checked with (Simpson motorbikes ) and the kit cost's around $60 or $70 dollars. I was very cash strapped at the time so that is when I looked for a more desperate approach, I searched the internet and found a site that talked about soldering the jet closed and redrilling it to what ever size you wanted. I did this and it worked.
Now that the gas prices are getting higher, these engine setups on bikes are hitting an all time high in popularity which means a lot more people at higher altitudes, like us, are running into the jetting issues that you and I have seen.
........thanks SchwinnHS, quarkdude:D
 

ravo

New Member
Joined
Oct 22, 2008
Messages
8
Bumping for a few pics because I drilled today.


That brass thing is your jet. Remove the tip if youre going to fill it with solder, or you can remove the entire brass tube part if youre just going to drill (like I did)


yes, you drill the smaller side. Don't use much force and blow on it real hard to clear out any brass junk after youre done.
 
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T

TWalker

Guest
Maybe someone can clear this up. I am workining on rejetting a motorcycle and my bikes for altitude. On the motorcycle and some other jets Ive seen online there are tiny holes on the side of the brass jet, I assume these are the actual holes to solder, yet on the pictures you are drilling the part way down inside the bowl.

Am I missing something? On the motorcycle should I be soldering/drilling the part down in the bowl as well?
 

arceeguy

Active Member
Joined
May 20, 2008
Messages
1,157
If you are re-jetting a motorcycle, just buy replacement jets at your local powersports dealer. The soldering/re-drilling procedure outlined here is done because there are no other alternatives for the "HT" type engines.

Also - if you are looking at a tube with holes on the side, you are looking at an emulsion tube type of needle jet. The holes on the side allow air to mix with the fuel. This type of jet usually controls low speed mixture.
 
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