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

Discussion in 'Performance Mods' started by quarkdude, Jul 24, 2007.

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  1. Mogyver69

    Mogyver69 Guest

    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.

  2. Mogyver69

    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.
  3. quarkdude

    quarkdude Guest

    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.
  4. SchwinnHS

    SchwinnHS New Member

    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!
  5. azbill

    azbill Active Member

    motorbikemike (simpson motorbikes) has the only jet kits i am aware of
  6. SchwinnHS

    SchwinnHS New Member

    Carb Jets

    Thanks for the information. I'll give em a try and let you know.
  7. quarkdude

    quarkdude Guest

    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:grin:
  8. ravo

    ravo New Member

    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.
    Last edited: Nov 6, 2008
  9. TWalker

    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?
  10. arceeguy

    arceeguy Active Member

    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.
  11. TWalker

    TWalker Guest

    Thanks but I did get it figured out, I was gouing about it the wrong way. The procedure for this motorcycle is the same as the bikes.

    But this bike is even more rare/unusual than our china engines, which is why I was considering soldering. This is a 34 year old bike out of east germany, very unusual an MZ 250.

    But now I know the proper procedure all thanks to the MB forums.
  12. rule413

    rule413 New Member

    what would work for an elevation of 70 feet??? should i leave it stock or could i benefit from some adjustments? i cut the baffle out of my stock pipe and installed a amsoil air filter. thank you in advance.
  13. fetor56

    fetor56 Guest

    70 feet in the grand scheme of things is nothing...leave it stock.
    SRPM likes this.
  14. quarkdude

    quarkdude Guest

    Re-Jetting by soldering

    I'm glad this helped you out. I went thru the same thing when I built my bike and was fustrated that I couldn't get a different jet. But soldering it and re-drilling it was actually pretty easy and only takes about an hour the first time.

  15. quarkdude

    quarkdude Guest

    Thanks Ravo for the pics

    Thanks for the great pictures of the jet and the carb apart. I never got a chance to take pictures of the mod and then I sold my bike to fund a screamin deal on a 1973 Yamaha RD350 cafe racer that I purchased. Still very much into Motor bicycles.

  16. jack stewart

    jack stewart New Member

    Your instructions seem to work for me!

    I followed your instructions and soldered the existing jet port and drilled a smaller hole to reflect my current elevation, 1900 ft.

    No more 4 stroking!!!!

    Thanks for the tip and keep up the excellent work!

    I love this cite!


  17. jaguar

    jaguar Well-Known Member

  18. GreenMantis

    GreenMantis Member

    I want to rejet one to burn r/c glow fuel (nitromethane) if I want to. It will have to flow 8 times as much fuel as gasoline, more or less. That's a lot of jetting, I'm not sure if the jets can be drilled out that much. Any thoughts?

    I just noticed someone said the stock jet size is .o30, if my math is right, then I would need to open it up to .24, at least. Does that sound right?
    Last edited: Sep 15, 2017