Drilling out jets?

[lowliferat]

I have a set of bs38s and was needing to go with bigger jets. I heard of some using drill bits to up the orifices of them. Anyone have any info as to what size bit equals what jet size? Thanks

 

[lowliferat]

I just foundy post that went through when I was thinking about this before. Thanks for the answers.

 

[Brian902]

Drilling jets is the redneck method to fine tuning.

Lots of good advice here on jet sizes for most configurations, you just need to do some searches for 5twins carb jetting articles.

Mikuni original jets are the best to buy for consistency and accuracy.

Drilling jets is a bit like going to your dentist and having him use a 18v makita cordless drill with a spade bit to remove cavities before a filling.

my 2 cents.

 

[5twins]

I have to agree, drilling jets is rude and crude. A jet is a precision part. That's why many of us prefer the genuine Mikuni jets.

 

[yamahammer]

My mikuni main jets started as 130's, which is 1.3 mm's. I opened em up to 145's in increments til it pulled hard up top and didn't surge. I never even took the carbs off.

But I am a redneck

 

[5twins]

..... and destined to become one of those notorious P.O.s when the next guy who owns that bike wonders why the 130 mains run so rich, lol.

 

[Jaydela180]

I thought mikuni jets were numbered by some weird flow rate equation unlike keihins that use a orifice diameter. Or do I have it backwards?

 

[jd750ace]

I buy the Mikuni jets so I never have to know the answer to that one!

 

[5twins]

I thought they were flow rated too but I don't know for sure. On the other hand, where the heck would I get 1.3, 1.4, and 1.5mm drill bits?

 

[Iowa Mark]

Several years ago I was at an auction of a heating and AC business. One of the things up for sale was a complete set of drills and tapered broaches for sizing gas burner nozzles and such. They ranged from beyond tiny to "holy shit". I thought about all the jet doctoring I could do with a couple hundred little drills and reams. Then in a fit of surprising clarity, I reminded myself of how little I knew about jet drilling. Most of the time it's not just a single jet that needs to be a new size. You change the fuel, the air has to change too. Now the transition from idle to wide open throttle has changed and we are back messing with the whole works again.

 

[Johnt3]

5twins, I just googled them and yes they are available! I'll be damned, although for the price I'd just buy the damn jets.

 

[gggGary]

Please if you drill file the old size off the jet.

 

[yamahammer]

I've been on the shit end of that stick myself. I have a little engraving gun to keep track.

 

[itrguy]

Its Hillbilly shit but Ive done it a time or two.....

 

[lowliferat]

Yeah I guess for the price of the drill bits I could get jets. I was just trying tort my other one running better, yes it's redneck ish but I didn't want to wait for the mail . Plus I just wanted to know if it could be done and how to in a pinch. Are welder tip cleaning files reliable? Or too imprecise to work? And yes I will file off the jet size. What a thing to do to someone, having to figure that cluster F out ?

 

[XSLeo]

Well now you know the size just get the jets the same size. This way the next guy won't cuss you out for being one of those PO's.
Leo