Drill size vs jet size
- Thread starter Baja 252
- Start date
- Location
- Saskatoon,SK
I have found jet sizes normally go up in number drill sizes.
- Location
- Stouffville, Ontario
You better own the bit you need to drill it. If you buy the drill bit it definitely ruins the point of trying to save $5 on a jet.
Sorry I don't have the answer to you OP. Good luck
Sorry I don't have the answer to you OP. Good luck
Quinc
Buy a Superjet
- Location
- California
Someone posted an exact chart on one of the Facebook page. I thought I saved kt. But can't find it.
- Location
- Ontario, Canada
I went through this as well and did end up drilling. I found a hobbyist drill kit for about 7$. I just locked the drill bit into a bench vice and spun the jet down over the drill. It worked but this is a method that really should only be a very last resort. If you have the downtime then you should order the proper jets. Drilling them so I have read will reduce the inlet and outlet flow angles changing how the jet collects and directs the fuel, and certainly if the drill bit is not even on both flutes, it can leave gouge lines. I would assume that when Mikuni makes them they also have special reamers to give the best finish inside you could ask for. Drilling realistically should be only used for testing purposes, once you have determined the approximate size you need you should then put an order in for the new ones. For reference purposes though, I found these, and also a nifty little Mikuni pocket tuning guide...
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Vumad
Super Hero, with a cape!
- Location
- St. Pete, FL
You have like $40,000 in jetskis in your signature and you don't want to buy a $5 jet?
Just order one from JetManiac dude. He'll put it in his teleporter and you'll have it yesterday.
Just order one from JetManiac dude. He'll put it in his teleporter and you'll have it yesterday.
Unfortunately, no. Jets are metric, not decimal inch sizes. A #120 Mikuni main jet is 1.20mm or 0.0472". A #31 drill is 0.120" and about 4X the volume that you want.
@Pro-pulsion has it correct. Mikuni reams their jets to size using the world's smallest reamers. It's why jets are expensive.
You can drill jets for waterlines no problem since it's water and not fuel. I've done this plenty of times myself for water but never for fuel. Never drill jets for fuel as the results won't be accurate. The hole will be slightly oversize and possibly oval depending on the rigidity of your setup, your drill bit and the concentricity of your chuck and spindle (which at 1.2mm surely will be off a few thousandths or more on your average drill press).
@Vumad is correct if we're talking fuel. Since this is just water I'd say drill it for testing and run it. Water doesn't care as much about jet orifice accuracy.
the funny thing is that decades ago weber and solex carbs sold drill bit sets for their carbs.plenty of mechanics used them with no ill effects for the longest of time.
holley always mentioned how their jets where reamed/flowed etc..etc.. etc.. blah blah blah but yet guys at the track where re-drilling jets for tuning with good results.
makes me wonder if we haven't been all suckered into this jet bs by the manufacturers.
the important part is how much flow the jet has,whether it's oval square or oblong,the amount of fuel going thru it is afterward going down narrow passage ways and bends before it gets sucked into the venturi .
hey,just my $0.02
holley always mentioned how their jets where reamed/flowed etc..etc.. etc.. blah blah blah but yet guys at the track where re-drilling jets for tuning with good results.
makes me wonder if we haven't been all suckered into this jet bs by the manufacturers.
the important part is how much flow the jet has,whether it's oval square or oblong,the amount of fuel going thru it is afterward going down narrow passage ways and bends before it gets sucked into the venturi .
hey,just my $0.02
@restosud Absolutely. Assuming all jets being used have been drilled to the same level of inaccuracy, they're technically accurate due to matching each other. But, for example, if you were to drill one jet to 1.2mm and use a factory 120 jet in dual carbs, the chances of the two matching is slim. The drilled jet will almost certainly be larger and act like a 122.5 or 125 jet. That's where the high-speed adjuster can help mask that issue.
I'd still recommend buying proper jets for fuel applications. Whether jet orifice size is considered myth, hype or reality, having a known level of accuracy makes tuning easier. Just because someone sells a tool for a job (ie: jet drill kits) doesn't mean they're a good idea.
Edit: I should add that a jet drill kit can work quite well if drilling in small increments. Going from 1.20mm to 1.25mm should leave a fairly round hole if your drilling setup is reasonably true. A larger jump (ie: 1.00mm to 2.00mm) will certainly leave a misshapen or oversized hole.
I'd still recommend buying proper jets for fuel applications. Whether jet orifice size is considered myth, hype or reality, having a known level of accuracy makes tuning easier. Just because someone sells a tool for a job (ie: jet drill kits) doesn't mean they're a good idea.
Edit: I should add that a jet drill kit can work quite well if drilling in small increments. Going from 1.20mm to 1.25mm should leave a fairly round hole if your drilling setup is reasonably true. A larger jump (ie: 1.00mm to 2.00mm) will certainly leave a misshapen or oversized hole.
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