CV Carb leak

[salty_monk]

If the carb is leaking (constant since it started) and coming out into the airbox (primarily on the right or Number 4 side) with some down the airbox drain & some in the breather tubes that come off the rail I assume that means that the Petcock has started letting gas by & that at least one of the float valves is leaking..... Sound about right?

Doesn't seem to be any gas in the oil. I've got the Fuel hose pinched off with some Mole grips now.

Think I'm going to bite the bullet & buy some new float valves and change them out. I'm pretty sure that the petcock was replaced a couple of years back so I'll try giving that a clean first. I've had it before where some c*ap makes it's way past the petcock filter & into the body when a bike has restarted after a long layup....

About 150 miles (ish) on her now...

Nessism kindly sent me a link to what I assume are the right valves... https://www.amazon.com/Mikuni-Needle...e&sr=1-1-fkmr0

[Steve]

Those <look> like the right valves.

If they are, that's one heck of a good price, too.
The place I get them, they are $10 each.
I might have to switch.

Your guessing makes sense to me.

Just make sure you don't leave the petcock in PRIme, you shouldn't have much of a problem unless you are riding.
But again, riding might jostle the needle a bit and re-seat it so it works just fine.

.

[Nessism]

The needle spring gets weak after four decades so replacing those valves is money in the bank for a bike that's going to be a keeper. For some reason this seems to be more of a problem with the BS carbs compared to VM's. Typically a VM needle, even an old one, will hold up the full weight of the float assembly. On BS carbs the spring typically compresses significantly with the carbs up side down. Not sure what the difference is exactly but it is something to be watched. Oh, and K&L float needle valves have weak azz springs in them so don't even think of going that route.

[salty_monk]

Ed - Yeah, planning on getting a full set of those ones on Amazon unless you have some new ones you need to get rid of... In which case I'll buy them from you. Didn't quite get your email

Steve - That price is each not a set of 4. Where do you get them for 10 bucks (Pm me if you want to protect your source )? Maybe I'll get them there instead!

Hoping I don't also have to replace the petcock. Worst thing now is that I have a brimmed tank less 30 miles so I need to drain some gas out of it...

[Nessism]

Dennis Kirk has a better price, but not sure how much they charge for shipping.

https://www.denniskirk.com/mikuni/size-2-0-needle-and-seat-for-rs34-40mm-carbs-n149-040-2-0.p170352.prd/170352.sku

[salty_monk]

That came up in a search for me earlier. Went through the process $7.99 so works out approx the same (plus only 3 in stock).

[salty_monk]

Can anyone measure one up for me? I haven't got any to hand until I pull mine apart...

Measurements to compare are on this page:

https://www.denniskirk.com/mikuni/size-2-0-needle-and-seat-for-rs34-40mm-carbs-n149-040-2-0.p170352.prd/170352.sku

[Steve]

Steve - That price is each not a set of 4.

I guess I mis-interpreted this line in the listing:

New (4) from [COLOR=#B12704 !important]$16.12[/COLOR]+ FREE Shipping

.

[Nessism]

Okay, measured a couple of old valves and they measure like those new Mikuni parts listed.

Oh, and I've got two brand new ones Dan if that would be any help.

[salty_monk]

Assume they are a "replace as a full set type item".. If you particularly want to sell them Ed I'll buy them off you, if not I'll just order some... Thanks for all the help as ever!

[londonboards]

Don't forget the O rings:

[steve murdoch]

Nice find, Richard.

[salty_monk]

Yep, the Orings are good in these. The carbs were rebuilt fully not so long ago and the bike is running fine.

[salty_monk]

So I replaced the valves in full. The new ones sealed right away.

I guess the springs were weak, the floats varied over this first 150 miles getting richer until it started to overflow (pretty sure at least one wasn't sealing, luckily the petcock was fine).

They were towards the rich end of spec when I set them & when I measured again they'd moved by about 2-3mm. Certainly the one that felt worse by hand was the main culprit for leaking (number 4). Amazing how it richened up the whole bank of carbs across the range. I need to make some carb adjustments now... (I will also sync again - bike is due for head re-torque in about 300+ miles)