Bad Mikuni anti-siphon valve = idle flooding?

[Zebra]

While starting a Mikuni SBN equipped craft, fuel literally pours out the main inner venturi, which should normally only come into use at larger throttle openings, not idle. I took the ofending carb apart and the anti-siphon valve (clear check valve) appears to be ready for replacement as it does not seal perfectly to the valve body assembly. I suspect this is the problem, but wanted to verify the symptoms with someone that had to replace one of these.
Would this be something I should be able to find locally (Dallas)? What crafts use the Mikuni SBN carbs (so I can pehaps call other dealers if need be)? Thanks.

[Zebra]

Also, would it be possible to simply fix this myself by cutting a new one from clear plastic. The Mikuni manual suggests doubling then up in some applications, so I imagine most plastic should work as long as it isn't too thick.

[Technical Support]

No definitely do NOT use your own creation - the flexibility of that valve is critical, and you cannot just guess at a material. Any 1992-1997 Yamaha or 1992-1996 Sea-Doo carb uses the SBN kit, which is what you need for new parts.

Yes a bad valve can cause that, as can too low of a pop-off pressure, leaking needle & seats, or bad vibration at idle.

Yes doubling up can work on SOME skis, but it's not needed on any Sea-Doo I'm aware of.

[Zebra]

I'll check at the local sea-doo dealer. Is the valve generally available separately? Thanks.
Chris

[Technical Support]

You will only find the valve alone from an independant shop, that does high performance skis - they will have spare carb parts to sell you. No there is no separate OEM part # for them.

I recommend you rebuild them though, if that valve is due to be changed, the rest are too.

[jandrew]

Mine is doing that exact same thing. When I first tried to start the new engine, it sputtered for about a second, then shut off. Plugs were very wet, so I shut off the gas & disconnected the inlet line. AFter cranking for 5 seconds, it started right up, smoking like crazy. Definite flooding going on. I connected everything back up, and looked at the main venturi while cranking. It was spuing gas.
I rebuilt each carb before I put the new motor in. Could that little plastic valve be bad even tho it was new???
My pop off pressure was about 40.
I'm gonna tear them apart again....any other suggestions as to what might be wrong???

[Zebra]

Maybe there is another cause for this if your parts are all new. With mine, that cylinder went from getting no fuel to being flooded out after I took it apart to check everything.

[Bill O'Neal]

That flapper valve rarely fails. When I find this type of problem, it is usually the needles and seats , the lever arm, the spring, or the diaphrams are holding the lever open.
That flapper valve is susposed to keep gas from backfeeding away from the jets, not through them. Look eleswhere for your problem.

[jandrew]

Thanks Bill....I totally agree. After I tore them apart again, I noticed that the "flapper" can only prevent flow away from the jets, not towards it.
Question...the manual says to set the spring arm flush with the structure around it. when I do that...it just doesn't look right. From what I can see...if that arm is too high, it won't let the needle valve close properly, and that would allow a continuous flow of fuel...flooding the carbs.
What do you think?
btw...that flapper valve looked perfect.

thanks...

[Bill O'Neal]

Yes, if it is too high the tit on the diaphram will hold it open. Even with the carb body is correct.

[Zebra]

That makes sense. I'll check mine as well. The lever being too high does fit the symptoms. Thanks.

[Zebra]

I seemed to have fixed my problem. The lever shaft was not tightened enough and was at an angle causing what you described. Thanks for the help.

[Bill O'Neal]

LOL!
I have a motto. Go back and refix the last thing I "fixed"......... It usually is the problem.