Anyone Ever Make Jets For A Carburetor?

[great white]

My bike is going to require some re-jetting this year since I've made more changes than I can count to the engine and exhaust.

It's not that jets are expensive, but it can take a couple rounds of changes before you get it dialed in.

Unless you have a stock on hand, at 20-30 bucks a set (4 jets needed per set) it can get expensive before you dial it in properly.

The jets themselves seem pretty simple:


OVERALL LENGTH = 9mm
HEAD DIAMETER = 8mm
THREAD DIAMETER = 4.9mm
THREAD PITCH = 5.0 x 0.7

They're basically a restricting orifice and it's made in nice simple brass.

I can't see any reason why I can't turn out a bunch of blanks and then drill out to size.


Anyone ever done this job before? Anyone see a reason why I should buy them instead of make them?

 

[royesses]

I used to help my dad make return jets for the hilborn injection system on his nascar modified and on carburetors. While it is easy enough to make, the length of the drilled orifice, diameter and entrance and exit angles all have an effect on the jets flow rate. If you duplicate whats in there from the factory as close as possible and just vary the bore size there is no reason it won't work.

 

[Steve Shannon]

Here's a YouTube video (not mine).

Steve Shannon, P.E.

 

[ch2co]

In the distant past, (early 60's) we used to do a lot of re-jetting carbs for high altitude operation. We simply took the jet, soldered the orifice up, and carefully drilled the
desired diameter hole. No need to try to find another jet or in your case machine a new one. I still have my sets of tiny number drills the smallest which is an 80 or 0.0135".
I don't think that I ever needed that one.

CHuck the grumpy old guy.

 

[Kernbigo]

bore 1 jet out to a nominal size not all the way through, make inserts of different inner drill sizes and press them in the jet you have, if that one don't work try another drill size one( i rejet small engine all the time honda is a good one )

 

[Bob Korves]

You can save a lot of time and effort if you start with what you are running now, decide if it is too rich or too lean, measure the hole with gage pins or number drills, and then drill the replacement slightly on the lean side of what you expect might be correct. It is a lot easier to open them up a little at a time than to make them tighter...

 

[great white]

I've done lots of jetting before.

Swapping jets and drilling.

But I've never made one from scratch before.

I'm just wondering if there's any good reason why I couldn't just turn out my own blanks and drill from there.

The jets themselves look simple enough to make. Just pretty small.

I guess I'm wondering if there's a taper or bevel that I should be aware of. I don't think there is...

 

[rgray]

+1 on the solder and redrill. Done that many times. As royesses says the lead in and the lead out of the hole will effect flow so soldering a jet up and redrilling the same size will likely flow different....not a deal breaker all can be adjusted by hole size.

 

[Bob Korves]

Unless you are a racer and change them back and forth a lot to match different ambient conditions, I really don't see much value in making whole sets of them. But then, I am not a tinkerer by nature. Make the damn thing run good and forget about it is my approach!

 

[great white]

I make lots of changes on a running basis.

The bike has had lots done (vmax heads, cams, custom exhaust, etc) and there are still several more rounds of changes to come.

I'd just turn out 12 or 16 blanks (4 carbs). That way I can dial in one set and if I go slightly over it's just re-drill a blank to the last orifice.

Turning out a couple sets while I'm making one just seems to make sense for tinkering later on down the road.

Yes, I am a tinkerer...