Manufacturing Replacement Jets

[Tobias Funke]

it's still possible to buy replacement jets, but this thread will explore the idea of making our own. eventually i want to be able to make any replacement part for any petrol driven engine, so let's look at some engineering ideas here.

talon kindly provided an image of a slow jet. here i'm using it as an example of trying to find the total surface area of jet bores in a jet, using high resolution photos. we may even be able to calculate the resolution required in order to accurately calculate the areas with necessary precision. of course, if there is a datasheet out there then we could use that instead..

the photo needs to be calibrated first. we take 'A' as the measurement of the actual jet, using a micrometre, to the greatest precision available. then we measure 'B' of each bore in the photo. by using 'A' we can find the area of 'B' without measuring it directly, only from the photo.

exercise : would anyone care to draw up a formula for that, i.e. B as a function of A ?

next episode : how do we reproduce a jet using only commonly available tools ?

( any ideas, feedback or constructive criticism are welcome ! )


20220902_204909.jpg

[6]

a jet is about $2-$4

Tobias YOu are a nut.

[Tobias Funke]

haha yea. well maybe ... but even if you can get them that cheaply, its great to learn self sufficency

mark my words, a day will come when any kind of carb or petrol engine will be either :

- hard to find
- impossible to find
- very expensive

do you feel like driving vehicles that dont have any voice or any soul ? rhetorical ...

[squirrelman]

OMG !!

this guy is full of it (theory) with little practical knowledge or experience.

most riders here can manage a simple carb cleaning without resorting to deluded and abstruse thinking to explain why it can't be done. and there is NO WAY he could make a useful idle jet from scratch, no matter how many measurements he might make.

[Tobias Funke]

ah brother, you just wana troll on me huh ?

i did pure math degrees, so engineering is more entertainment than work haha

cant be done ? of course if i want someone to clean carb only, its a nice boring and simple task for my little child. i hope he doesn't get bored quick too, poor little guy !

anyway let's get to work. if anyone can find for me the typical vacuum levels of bros400, i'll show you guys the magic

exercise 1 : draw up a formula for calculation of bore size from photo, i.e. B as a function of A ?

exercise 2 : vacuum data for a bros400 engine as it's meant to run

or just sit around with telescope and complain that the moonwalkers are doing a bad job

[ParcNHawk]

Does one have to be an astrophysist to recognize a limp?

[Tobias Funke]

Does one have to be an astrophysist to recognize a limp?

haha

[Tobias Funke]

slow jet measurements.png

here's measurements from the two jets i have.. obv we can round up to guess what they are meant to measure as

[Tobias Funke]

current open questions for the team :

exercise 1 : draw up a formula for calculation of bore size from photo, i.e. B as a function of A ?

exercise 2 : vacuum data for a bros400 engine as it's meant to run

exercise 3 : why is there a standoff (slightly larger diameter of cylinder) at the end of the jet stem (slow jet) ?

exercise 4 : does the homemade jet need to have the same number of holes as the original ? what are the main parameters for good jet operation ?

exercise 5 : why are jets commonly constructed from brass and not steel ?

[bitzz]

ah brother, you just wana troll on me huh ?


exercise 2 : vacuum data for a bros400 engine as it's meant to run
:

Intake vacuum or throttle plate vacuum?
You DO know the difference... right?

[Tobias Funke]

Intake vacuum or throttle plate vacuum?

everything thanks

[Tobias Funke]

slow jet seating.png

here's how i think the idle jet is seated

[Tobias Funke]

aluminium rod.png

if you can find 6mm OD with 2mm ID then it's going to save you some time on this. otherwise buy the 6mm bar as i am. note : we aren't going to copy the same original design, so it's ok for the inner channel to be larger.

[Tobias Funke]

men watch this for inspiration !

https://www.youtube.com/watch?v=FBi3TKDdwT8

did we progress to a more ' enlightened age '

or perhaps humans are starting to drift from things they can understand and control ?

i'll always be fine buddies, no matter how complex and abstract things get

but our countrymen, i fear they are ill equipped for the future of my darkest suspicions

( rant completed )

[riot]

Well, I have to say, you got me to read the thread!

I would suggest using brass, rather than aluminum. I suspect this is done on OE carbs to prevent corrosion fusing the parts.

That said, I gotta ask the obvious question of why?

A jet would be really easy to make, but they are cheap and plentiful. If you just want to build an engine, why not build a whole carb? Or for that matter, a whole engine? There are people who do this, and it’s really neat.