Divvy Carb woes.

[Tdibs]

Hello gents,

Having a bit of a running issue on my 99 divvy 600.

Symptoms are rough sounding idle, hanging revs at idle when warm - sticks at 2-3k at traffic lights for 10 seconds, then drops back down to 1.3k idle.

Putting on sync gauge, no2 cylinder is stuck pulling huge vaccum, all other cylinders respond to adjustment, no 2 shoots up and will not move.
https://puu.sh/HnkqI.jpg

Also noted, putting my finger over these holes on 1,3,4 carbs kills the mixture, covering these holes on no2 (problem carb) makes no difference.
https://puu.sh/HnkqF.jpeg

Any smoking guns to check first? Ive had a check of the jets, needle and diaphragm all clean and in order so far.

Cheers!
____________________
Previous : 09 Vanvan 125| 02' Sv650s || Current: 1999 Xj600n | 1992 DR650 RSE | 2005 Fazer 1000

[Easy-X]

I'd compare the heat coming from the problem cylinder's exhaust to the others and see if it's actually firing. I'll bet on either low compression or no spark
____________________
Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[stinkwheel]

Those holes are jets. From your experiment, it seems like they are blocked on #2. The air that would normally be drawn through those is probably being drawn under the throttle valve, hence the higher vacuum.

Air gets drawn through the jets at certain parts of the rev range to enrichen the mixture without involving the throttle valve. They will most likely connect to the inside of the carb via a small "pinhole" in the bottom of the venturi tube. They are sometimes referred to as "power jets".

If you hold the throttle valve open and squirt carb cleaner down one that's not blocked, you'll see where it comes out. I bet it doesn't on #2.

They are very difficult to clean if blocked because they are nearly impossible to remove. Carb cleaner and compressed air but I have resorted to a bit of nylon fishing line before today, not recommended though.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Tdibs]

[Pete.]

That's the air feed for the idle circuit. I tshouldn't cause the revs to hang unless the jet has fallen out in the bowl cauing the fuel to be un-metred.

Here is a quick overview of the idle circuit.

Air goes in through the air idle jet.

https://www.bikechatforums.com/files/idle1.jpg

Flows along the passage shown by the screwdriver and across the orifice of the fuel jet causing fuel to be drawn up the tube

https://www.bikechatforums.com/files/idle2.jpg

The fuel-air mixture carries on to the idle air adjuster which meters the amount of air/fuel coming through that circuit. When this is combined with whatever little is coming past the butterfly it gives you your idle mixture.

https://www.bikechatforums.com/files/idle3.jpg

And if you want to know what's under that brass plug here it is - three liitle drillings that get un-covered by the butterfly and add fuel/air in stages at low throttle openings. These are Bandit carbs and (the machined one) Fazer carbs by the way but they all work the same more or less.

https://www.bikechatforums.com/files/drillings04.jpg

So if your carb is not responding to covering that hole, chances are the air idle screw is gummed up or perhaps the low speed fuel jet has fallen out into the float bowl causing over-fuelling at idle.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Fizzer Thou]

I would be looking for split 'O' rings between the inlet manifolds and the cylinder head.Countless times I have read about peoples bike problems that are down to these shrinking.snapping and causing all sorts of running problems.

Part number 4 on the fiche

https://www.cmsnl.com/yamaha-xj600n-1999-4kea-england-294ke-300e1_model40157/partslist/0010.html#.YEbTxG-nzIU
____________________
Just talk bikes.What else is there?

Always have a 'Plan B'

[Tdibs]

Cheers for all the replies lads,

To follow up, I could blow air through it, but was still having the same issue. After working the thinnest strand of copper wire through it with some carb cleaner it fully unblocked it. Ally synced up and going perfect now
____________________
Previous : 09 Vanvan 125| 02' Sv650s || Current: 1999 Xj600n | 1992 DR650 RSE | 2005 Fazer 1000