Left carb floods, Right carb dries out

[Spaceman7Spiff]

I'm experiencing a weird problem with my RD400.  Basically, it goes like this: Let's say it's been parked on the sidestand with the petcock off for 24 hours. When I go to start it, I can kick and kick and kick until I'm out of breath unless I do the following: with the petcock ON, barely pull the right side fuel line off the nipple until it just barely dribbles fuel. Then hold the throttle wide open for like 3 or 4 kicks until it fires up as in a flooded condition.  Basically, what I have surmised is that the left carb is flooding and the right is getting an air bubble in the fuel line. And yes, it does leave a spot of fuel on the ground when parked for more than like an hour.  After start and warm up, it runs excellent. No complaints at all.

I've adjusted float height several times, changed needle/seat assemblies... I guess all that is left is to look at the petcock 'packing' itself and/or maybe the left float is sinking? Still, that wouldn't explain why the right carb is getting the air bubble, would it?

You might be thinking, "are you sure the right carb is getting an air bubble?" and my answer is, yes, because it will not start unless i burp that right fuel line.

I dunno, any ideas?

[Striker1423]

That's most likely a petcock issue. Take it apart and clean it up.

[m in sc]

I agree, sounds like the petcock is done.

right float needle sounds like it is sticking. an 'air bubble' wont inhibit flow if the needle is open. since its obviously stuck shut for whatever reason that's the issue.  make sure there isnt a worn spot on the float tang thats 'catching' on the needle spring tip.   

on cold starting any of mine, itf fuel on, let site for a few seconds, they choke/kick. the cabs have to fill up.

[quocle603]

I would check the valve and the tubes to see if it's clogged up. Are you running inline filters? If so, check if those are clogged up too.

[Spaceman7Spiff]

I guess I should update since I seem to have solved it.  I went ahead and replaced the petcock with the cheapest one on Amazon and everything works perfectly now. 

I had originally intended to use OEM parts but a replacement OEM petcock is like $150 (f*ck that) and there is no internal rebuild kit. So my hope had been to buy a cheap one and just use the packing cone thing out of it but it seems that the design has been changed so that it's just a fully cast aluminum valve that is sealed on either side with o-rings which is a far better design in my opinion.  If these chinese o-rings prove to be of poor quality and short lifespan, I can just replace them with something of a higher quality.

In any case, I'm a happy camper now.  She barks to life with one kick pretty consistently now.

thanks for the help.

[m in sc]

nice . thanks for the follow up   

[SoCal250]

Congrats on solving the issue 

I had originally intended to use OEM parts but a replacement OEM petcock is like $150 (f*ck that) and there is no internal rebuild kit.

Replacement parts and kits are readily available for the RD400

These parts are all available from Yamaha:
1A0-24512-00-00  Gasket, petcock valve, $6
498-24522-00-00  Gasket, petcock bowl, $27
214-24512-00-00  Gasket, petcock base, $24
90202-05187-00  Washer, plate (petcock mounting bolt, 2 req), $1 ea.

Also:
Yamaha RD400 Petcock Rebuild Kit (all years) Made with OEM Yamaha parts, $66.95
Yamaha RD400 Petcock Rebuild Kit (all years) Made with reproduction parts, $17.50
Yamaha RD400 Fuel Petcock Reseal Kit, HVC20052, $25.00

[Spaceman7Spiff]

Congrats on solving the issue 

I had originally intended to use OEM parts but a replacement OEM petcock is like $150 (f*ck that) and there is no internal rebuild kit.

Replacement parts and kits are readily available for the RD400

These parts are all available from Yamaha:
1A0-24512-00-00  Gasket, petcock valve, $6
498-24522-00-00  Gasket, petcock bowl, $27
214-24512-00-00  Gasket, petcock base, $24
90202-05187-00  Washer, plate (petcock mounting bolt, 2 req), $1 ea.

Also:
Yamaha RD400 Petcock Rebuild Kit (all years) Made with OEM Yamaha parts, $66.95
Yamaha RD400 Petcock Rebuild Kit (all years) Made with reproduction parts, $17.50
Yamaha RD400 Fuel Petcock Reseal Kit, HVC20052, $25.00

All of the links you posted are for the O-rings and gaskets. I'm not sure if there is more than one version of petcock out there for these bikes but the one that I have has like some kind of plastic/rubber cone-shaped "packing" in it with a spring that holds it in place. I have never seen that cone thing or the spring for sale anywhere.  Water under the bridge, though because so far my lil cheapo amazon petcock is working just fine.