Anyone Ever Make Jets For A Carburetor?

[chips&more]

Did lots of it decades ago. Found out that drilling the hole was not the best idea. Because drill bits do not cover every hole diameter needed. And the hole diameter is critical, at least for my engines running their best! You need to get a watch/clockmaker broach set. There is no better tool for the job. And get an exhaust analyzer. And get some small pin gages too. And get ready to take that carburetor apart more times than you would like to. …Good Luck, Dave.

 

[TOOLMASTER]

glad those days are over....i don't miss jetting carbs...still have a box full of jets and my jet reamers though ;-)

 

[great white]

I like my early to mid 80's bikes so carbs it is for me.

Which is not to say I don't work in fuel injection too. I just do that in 4 wheeled contrivances.

Pretty hard to beat plugging in, a few keystrokes and adjusting up the fuel/timing/transmission.

I mostly work with tunercat OBDII. Diesel and gas although I prefer diesel....

 

[G MORSCH]

I had a similar situation about a dozen years ago. I picked up a great deal on an RD125 Yamaha. The guy who had it before me drilled the high speed jet way oversize. So, I simply bored it out, pressed in another brass cylinder, and drilled it out one number size at a time till it purred like a kitten. 55 MPH before and 75 MPH after, even with my 190 lbs. in the drivers seat. Got it right on about the forth try.

Can't wait for warmer weather, love it on a two wheeler.
Good luck!

 

[FOMOGO]

I used to do a lot of HVAC work including re-jetting furnaces, etc.. As said above, solder shut and re-drill. Have used the same method on cars and bikes and seems to work just fine. Mike

 

[chips&more]

I used to do a lot of HVAC work including re-jetting furnaces, etc.. As said above, solder shut and re-drill. Have used the same method on cars and bikes and seems to work just fine. Mike

Really! I didn’t know my 427 ran like your HVAC. You must have a nice HVAC!!!

 

[Grumpy Gator]

First I'll start with my "Bonney Fides". I had a bike shop for over 15 years. Mostly American made stuff. But we would work on anything on two wheels. I was never brand stupid. If you were up on two wheels it was good enought for me. That being said what are you tuining for ?
Speed , economy , Mid range power , bar hopper ???
The make and motor size and your expectations are the guiding factors. I can build you a motor that will take you coast to coast and be reliable or I can build you one that will be a LSR contender for the salt in Utah. Or it can be a bar to bar racer.
So from my point of view more input is needed to answer your question
*******Justing Saying*******G****

 

[great white]

I'm not going very deep.

Just decent stoich by plug chop indications.

It's just a street bike. Back and forth to work, around town and freeway cruising.

It's a 1983 Yamaha Venture:



rated 99 hp at the crank.

I've just installed VMax heads and cams, the Vboost is going in too, all controlled by an Ignitech controller. Coil on plugs are also going in. The transmission has been swapped for a 2002 royal star venture transmission and the rear differential is also from a VMax. Still using the stock down pipes and collector box. Mufflers are from a Yamaha R1, so essentially the same as a set of "slip ons". Likely less restriction than the stock venture mufflers as the R1 model these muffs came from was rated around 170HP, they should flow fine on my bike, but will also mess with the jetting.

I'm hoping for somewhere around 130 crank and/or 100 RWHP. VMax is rated 145 crank, but hte exhaust is different and it has a skootch more compression (about .5).

Its highly unlikely the stock carbs will be right for the modifications (venture uses Mikuni 117.5 main jets, Vmax uses 155-160), hence the need to rejet. Like I said, not fussy. Just going to do plug chops and get it "in the zone".

Biggest concern is that I don't go lean.

I'll likely have to fool with needle height, float levels and pilot air jet sizes as well to get it dialed in.

No big. Been there, done that.

 

[Str8jacket]

The chamfered edges leading into the jets make as much difference to the flow rate as the diameter of the hole. I had made an excel spread sheet for hyd orifice calcs using all the formulas. I'll be honest i dont half understand some of the components of the formula just learned to manipulate the inputs to get the results i needed. But a square edge hole can have a flow coefficient of as low as .7 where as the same diameter orrifice can be 1.2 with a chamfer leading in and out. Also from playing around i found chamfered hole orifices to be more stable in the flow rates as pressure changes.
How this helps you is sneak up on your hole sizes but dont fully drill out to the next size wire guage just put a small leading and exit chamfer on first and try that. If you look at most holley jets they're chamfered.
A lot of messing around but the results where quite amazing.

 

[great white]

The chamfered edges leading into the jets make as much difference to the flow rate as the diameter of the hole. I had made an excel spread sheet for hyd orifice calcs using all the formulas. I'll be honest i dont half understand some of the components of the formula just learned to manipulate the inputs to get the results i needed. But a square edge hole can have a flow coefficient of as low as .7 where as the same diameter orrifice can be 1.2 with a chamfer leading in and out. Also from playing around i found chamfered hole orifices to be more stable in the flow rates as pressure changes.
How this helps you is sneak up on your hole sizes but dont fully drill out to the next size wire guage just put a small leading and exit chamfer on first and try that. If you look at most holley jets they're chamfered.
A lot of messing around but the results where quite amazing.

Thank you. That's info I can use and I pretty much figured as much.

Part of my loose plan was to duplicate the stock jets as they are and then drill for size. Iirc. The oem jets have the mentioned chamfer, at least at the entrance. Not sure about the exit side but will for sure check when building them.