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flooded carb needs rebuild...

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Anybody leave their petcock on prime and have it cause carburetor problems?!!

I was distracted and left the petcock on prime causing the carb to flood. I drained the float bowl (via the drain screw on bottom of bowl) and the bike still had a very hard time starting. It would run okay with the throttle open but won't idle unless the petcock vacuum line is disconnected (and then petcock cycled between prime and on, so it gets fuel).

 

I removed the carb and inspected/cleaned the pilot jet, mixture screw (it likes 2.75 turns out normally) and blew out the visible air passages... everything looked clean (I run premium ethanol free gas)... problem remains!!

 

I ordered a new float needle assy, and float bowl gasket (it proved to be leaky when flooded). I also ordered an adjustable mixture screw (from TT)... 

 

Anyone have a similar experience or can offer advice?? I'm surprised that flooding the engine would cause idle problems... What am I missing?

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Anybody leave their petcock on prime and have it cause carburetor problems?!!

I was distracted and left the petcock on prime causing the carb to flood. I drained the float bowl (via the drain screw on bottom of bowl) and the bike still had a very hard time starting. It would run okay with the throttle open but won't idle unless the petcock vacuum line is disconnected (and then petcock cycled between prime and on, so it gets fuel).

 

I removed the carb and inspected/cleaned the pilot jet, mixture screw (it likes 2.75 turns out normally) and blew out the visible air passages... everything looked clean (I run premium ethanol free gas)... problem remains!!

 

I ordered a new float needle assy, and float bowl gasket (it proved to be leaky when flooded). I also ordered an adjustable mixture screw (from TT)... 

 

Anyone have a similar experience or can offer advice?? I'm surprised that flooding the engine would cause idle problems... What am I missing?

 

Leaving the petcock on prime in itself is not an concern, unless there is an issue with the needle valve ....

always best to leave it on "on"......I suggest a manual petcock but you still need to remember to turn it "off" when you shut down the engine...

Edited by Craig-o

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Crankcase vapor return line feeds gas fumes from the crankcase back into the carb. Change the oil.  Might have to do it more them once.

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It's great that you ordered a new needle valve and seat, but I'd bet that isn't the problem. At least 90% of the time it's nothing more than the little o-ring that lies under the brass seat component of the float valve. Take a look at a parts diagram and you will see it. When you take the needle valve out it will likely look just fine and when you remove the needle valve seat the o-ring will be compressed or cracked and therein lies the problem!

 

Of course I could be wrong, but you will have a little more info to work with either way.

 

Then, I would get a tank petcock that you can control....the worst that can happen is you ride off with the valve on OFF and the engine quits at the worst possible time. This is not to be ignored as it can be quite dangerous.

Change your oild immediately as it will likley be contaminated with gas

Edited by shuswap1

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Thanks for the input guys, I appreciate this website and everyone that contributes to it.

  I checked the oil once I realized the bike flooded and it doesn't seem contaminated (no smell and still synthetic red), the air box was clean and dry, no fuel puddle on ground...  I'm still gonna change the oil though, it's about due anyways.

  Shuswap1 you're right, the needle doesn't look too bad but needle / seat comes as an assembly (guess I could've tried to match just the seat o-ring but parts are scarce out here at the end of the world). The seat o-ring and the float bowl o-rings are toast... they almost look like they are made of leather! Guess I didn't switch off the "corn juice" quick enough... :o

I tried swapping out the stock petcock a couple years ago but what I received (supposed to be the Yamaha Raptor valve) didn't fit without trimming (even using the stocker's extension) and I've kinda learned to like having a reserve so I ended up going back with the stocker... my logic is that I've been using vacuum petcocks in all my four cylinder street bikes since the 80's without problems (fingers crossed).

  Hard part now is I gotta wait a week for parts to make it out to this little island in the middle of the ocean before I can find out if the SM is happy again... I appreciate living in Hawaii but it has it's drawbacks.

  Craig-o I usually leave the petcock "on" but I've found that "priming" it while I push it out of the garage leads to an instant start and idle in the warm climate that I live in (too warm for choke), my guess is that when it sits in the warm garage for a week some of the fuel evaporates from the bowl... If I don't "prime" it first then it takes a few seconds of motoring before it fires up.

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While I got an audience, can someone explain the purpose of the throttle position sensor and the idle cut-off diaphragm on the stock SM carb? I'm a bit curious about the needed complexity to this little carburetor...

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Disregard my last, found a good explanation of TPS (to vary ignition timing) and the "idle cut-off" is actually the coast down enrichment valve... I need to buy the dang manual!

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Is there a source to get the complete service manual online? I've found chapters online but I would like to download the entire manual, I prefer using the iPad to paper... it's in a lifeprooof water/grease proof case (the wife uses it as a recipe book).

I'm not looking to get a pirated copy... Is there a source?

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I understand the urge to have a reserve position on the petcock and my manual petcock does....think it came from a WR400. But if you've had good luck with the OEM, so much the better.

I was just about to order a needle/seat when a learned someone told me about the seat o-ring. So, just passing on the favor. Hawaii is a fantastic place and your roads offer terrific grip....ideal for a SM.

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