Carby Jets?

Discussion in '2-Stroke Engines' started by canalcat, Jan 19, 2016.

  1. canalcat

    canalcat Member

    Drill bit set for jets / conversion chart millometers vs JET size// like A # 72 jet= how many MM? Thanks!
    Last edited: Jan 19, 2016

  2. butre

    butre Well-Known Member

    I know a .0250 wire gauge drill is about in between a 63 and a 64 jet so I would have to say they're sized in hundredths of a millimeter, ie. #72 is .72mm

    I keep a handful of .0250 wire gauge drills and then embiggen the hole with a torch tip cleaner until it runs right. way cheaper than keeping an assortment of sizes with backups.
  3. Fabian

    Fabian Well-Known Member

    Unless you have a very accurate and expensive drill press and jig holder, it is much better to simply buy a range of jet sizes from No #65 to No #86, in individual sizes, eg #65, #66, #67, #68 etc
    I have every numerical jet size from No #65 to No #90.

    A full compliment range of jets is the only way to properly dial in your carburetter.

    In the lower south eastern part of Australia, using the highest octane (non ethanol) pump grade fuel, most of my engines fall into a jet size zone of No #76, though i have had one engine that ran optimally on a No #70 jet and another engine that ran optimally on a No #86 jet.
  4. sbest

    sbest Active Member

    Figure out if you are rich or lean (rich I'd bet). Jets here are $3-$6 apiece. Use a tip-cleaner to see what size you have and buy several sizes in the direction you need to go. in a worst case you've spent less than $20.

  5. butre

    butre Well-Known Member

    I don't use a drill press for micro drills. mine doesn't go slow enough, so I just turn the bit by hand. I've had a few break, but they're cheap. at the rate I buy them it's cheaper than buying jets.
  6. 45u

    45u Active Member

    I hate folks that drill jets as when I work on a motor trying to get it right and the jet has been drilled I have no way to tell other then spend more time to figure it out. I have run across this MANY times working on motorcycles so from now on if I think it has been drilled I just charge the customer and put a new one in. Yes I know you can spend time using bits to figure this out but cost the customer more time and the jet is cheaper. All so when drilling a jet you can sure mess one up.
  7. butre

    butre Well-Known Member

    I don't drill other people's jets and I do all my own repairs so you'll be happy to hear that you'll never have a bike come in that I've drilled the jets in.
  8. 45u

    45u Active Member

    I feel sorry for who ever ends up with later on which I hope is a long time.
  9. butre

    butre Well-Known Member

    I don't get rid of anything, I use it until it breaks, fix it if I can and keep it for parts if I can't. if there's nothing worth keeping on it I'll send it to the scrappers, and if you're buying engines from the scrap yard you better be able to figure out something as simple as a drilled jet.
  10. 45u

    45u Active Member

    Can not take it with you when you die!
  11. HeadSmess

    HeadSmess Well-Known Member

    someone has a lot of misplaced faith in the longevity of chinese throw away engines... :rolleyes:

    anyways...jets are NOT sized on the size of the hole, but on the amount of FUEL THEY FLOW in a given time.

    yes, a 78 may actually have a SMALLER hole than a 72... depends how LONG the hole happens to be as well...

    at least, thats how mikuni does it, and well...mikuni does have a reputation for reason.

    no manufacturing process is that consistent that each and every bit coming out of the machine is identical... not when .005 mm makes a BIG difference.

    jets are numbered AFTER being drilled. (and reamed...they ream them too)
  12. HeadSmess

    HeadSmess Well-Known Member

    for what we do, with these engines... a plain old set of micro drills, be they metric or number types, suffices.

    having both types on hand does allow one to get even finer...but why? why bother?
  13. Hello Moto!

    Hello Moto! Active Member

    I just bought a jet kit. Gonna try and figure this shit out man! I know I'm running rich and having issues towards full throttle. It almost sounds like boggy or four stroking past 15mph. Not sure but I WILL figure it out.

    I didn't figure I would have to mess with a stinkin jet livin close to 1500ft in the land of OZ. I'm gonna give it a shot though!