Carburettor Clean

[Tobias Funke]

hi guys, please help me clean her up !

the jets look undamaged and light goes through the holes to the other side, so they seem ok ?

there are two stems in the float bowl, one with what looks like a check valve. anything to do there ?

also it begs belief that the float ventilators are open to air. those should be filtered

i think perhaps some channels are blocked, even from metal particles or oxides in the air, since i do a lot of grinding in the workshop ...


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p.s. i figured out why only one float valve has a baffle plate. due to the seating of the carburettor, splashback into the vent is only a potential issue on the front cylinder

[Tobias Funke]

it looks like the main jets have flow right through, plus the spray holes are fine and not blocked, i guess the end is sealed when it's screwed in so that spray works, presumably ?

the idle jets seem blocked halfway, even a pin can't clear it, so the flow for those is sent the other direction ? if not, we have a problem ...


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[ParcNHawk]

Um... there's your problem.

Clogged pilot jet. You might remember that from the video you posted that named it the number one cause of the issues you're having.

Also: NOT how that jet works. It gets the fuel from the bowl. Which is from the direction of your orange arrow.

Jerry isn't a troll and Andy is right about your troubleshooting being all over the map.

[Tobias Funke]

ok thanks. i just don't get how both jets can be completely 100% blocked, as though they were designed that way

anyhow i'll see if i can carefully drill through them with a small bore twist. obviously it gets fuel from the bowl, i was wondering if one of the other channels suppied it from the reverse. as you said - not the case

yes, my diagnostics need work. call it a lack of patience combined with eagerness to jump right in. haha

[ParcNHawk]

I would NOT drill out the jets. You may make the bike untunable. Your hole may end up being the wrong diameter and it will not be perfectly smooth inside. The non-smooth inner bore may have problems emulsifying the mixture consistently. You may end up chasing even more difficult problems.

The holes on the side of the jets is where air enters the fuel stream and is mixed with that stream of fuel. This is of fundamental importance to carburetion.

Fuel injection atomizes the mixture by using tiny holes fed by a super high pressure. Carburetors work with a pressure differential between partial vacuum and atmospheric pressure so everything about how it makes a usable fuel ratio in a usable state (vapour) is fundamentally different than FI.

The old-school way of enlarging jets is to use a reamer, although some tuners do use drills to find the right size before buying new jets.

I would try to chemically strip the jets or replace them.

[ParcNHawk]

The jets clogged up the same way because the bike probably sat for a long time. The pilot jet inlet is highest so as fuel slowly evaporates out, it dries out first. And when it dries, the heavy parts are left behind to clog the hole as the lighter volatile parts make their way to the upper atmosphere to do things like deplete ozone.

[Tobias Funke]

we might need a new theory ? both are completely blocked in the same location.. as though they're meant to inject from the reverse direction

i drilled a *tiny* amount out with a 1.5mm bit. what came out was a small amount of brass shavings, looking like part of the jet, not any obstruction. if it were some sort of blockage it would have cleared immediately without presenting resistance to the drill ..

note i'm being careful and not drilling the spray holes, just the main channel. perhaps i have a different type of carb and this is causing the ambiguity ?

p.s. is there a diagram of how the whole fits together ? the workshop manual is good but there's still some guesswork at this point ..

[Tobias Funke]

The holes on the side of the jets is where air enters the fuel stream and is mixed with that stream of fuel. This is of fundamental importance to carburetion.

btw have you heard of anyone making their own jets ? i think it would be pretty easy as long as there's bits small enough for the spray holes. there's a reason for my parsimony, in that the rebuild kits cost the same as a new carburettor (cheap generic type). if we can make our own jets and gaskets, the existing carbs can be recycled at very low cost !

proposed method:

- take brass or copper hex bar
- drill hole through middle for channel
- lathe the part that is to be cylindrical (but leave room for thread)
- drill holes for the spray holes
- use die to make a thread in the right location

i think this is why they use soft metal, it'd be a lot easier to drill very small holes, when compared to steel

[ParcNHawk]

Jets themselves cost next to nothing.

[bitzz]

If you're making jets to get something to run, usually out of desperation, go nuts.

You can't TUNE with homemade jets. The difference in jets sizes is thousandths of an inch.
What's the runout on your drill press?
After ya' figure that out: read some of this Laminar and turbulent flow.

Jets are cheap. Don't buy carb jets on Amazon. They're junk. If you want to use Amazon jets, buy a Amazon pin gauge set, so you can size the wonky Amazon jets....

[Captain 80s]

Close down your "machine shop" and just buy new pilot jets and be done already.

[Tobias Funke]

Jets themselves cost next to nothing.

Thanks but i can only find kits, and those cost as much as a new carburettor (albeit a different type)

[Tobias Funke]

Close down your "machine shop" and just buy new pilot jets and be done already.

Thanks but i can only find kits, and those cost as much as a new carburettor (albeit a different type)

[Tobias Funke]

If you're making jets to get something to run, usually out of desperation, go nuts.

You can't TUNE with homemade jets. The difference in jets sizes is thousandths of an inch.
What's the runout on your drill press?
After ya' figure that out: read some of this Laminar and turbulent flow.

Jets are cheap. Don't buy carb jets on Amazon. They're junk. If you want to use Amazon jets, buy a Amazon pin gauge set, so you can size the wonky Amazon jets....

Its not just save money or desperate, but i enjoy engineering challenges ! my ex was a mechanical engineer and introduced me to it

yes obv the jet bores are critical, but theyre still much bigger than EFI. also, unless the bores are very very wrong, good tuning will bring things back into the operative range

thanks for the link, i'll check it out when i get back to the computer. also i'll follow up your other tips

[Tobias Funke]

do you know if there's any way to do a full end-to-end delivery test on the workbench without special machinery ?

it would save a massive amount of time, compared to installing / uninstalling the unit each time for diagnostics ..