Normal?

[mike72903]

If I turn the petcock to off and the bike sits for a day or more, if I forget to open the petcock when starting, the bike will only run at idle for less than a minute before dying.  This is without choke and just holding the RPM at a few hundred RPM.  Seemed odd. So I tried leaving the fuel on and closing the petcock just before starting.  It will run for several ( 5 or so) minutes. I've repeated this a few times to confirm.  Don't think its leaking into the cylinders. Never had any kind of hydro lock even after it sat for many days between use with the petcock open. Always starts right in either case.  I never smell gasoline either. It just doesn't seem right to me.

[Itinifni]

It sure sounds like you have one or more float valves leaking.

Just because you haven't yet experienced any sort of hydrolock doesn't mean you're safe. Aside from a leaking float valve and petcock, piston and valves also need to be in the correct position at the time while fuel is leaking into the cylinder for hydrolock to occur.

To find the leaking float valve remove the intake manifolds, I think you'll find one or more wet manifolds, dripping carbs or pooled fuel on the back of an intake valve. It's an easy job and good opportunity to replace the manifold O rings if you haven't done it already.

Matt

[Firefighter]

I think the hot engine will evaporate or cause fuel to turn to vapor and vent out the carbs. and with the petcock closed there is no fuel to replace it. When petcock is open the fuel bowels are completely full so your engine runs longer.

I think you would have hydrolock or flooded condition if your petcock was leaking and you have leaking float needles.

[Harryc]

Open your bowl drains one at a time into a calibrated cylinder/container and compare the fuel volume to when you turn the bike off and prior to the first time it is started...on different days/rides of course. That will tell the tale. If one of those bowls has a reduced volume prior to a cold start, you'll know you have a leaking or stuck float valve. If not, then have a nice day.

[mike72903]

All good suggestions, thanks.  Im going to try another experiment to test Firefighters theory.  I'll leave the petcock open until the engine cools. Then close it and see what happens the next day when I start it with the petcock left off.  Easiest thing to try first.  If the gas was in a cylinder, wouldn't I see it exit the exhaust when the engine starts?

[Ricky-D]

I wouldn't get all worried and stuff about what you report. Each bike has it's own idiosyncrasies, yours not withstanding. There is nothing you report that sounds amiss and nothing also that would make me think something is wrong with your carburetors. Id suggest to use an gas additive and to also shut the gas off when the bike is turned off. There's nothing wrong there and if you start to mess with the fuel system you're likely to screw things up and then really need help.

***

[John Schmidt]

What you're describing seems normal to me. First....if you cut off the petcock before cutting the engine, you're dropping the level of gas in the bowls which means if you start without opening the petcock it won't run for long. You're simply using up the small amount of remaining fuel in the bowls before it dies. But the second thing you mention allows just the opposite. You're starting out with FULL bowls before you cut off the petcock so it will run longer before exhausting the gas already in there.

I'm with Ricky on this....I don't think you have anything abnormal going on. Give it a good dose of Berrymans(vitamin ) B-12 to keep things clean and remember to shut off the petcock at the end of each ride. This is where the old adage of "if it ain't broke, don't fix it" comes into play so at this point I'd leave the carbs alone. If, at some point down the road the starter begins to turn over and suddenly stops....YOU STOP!  Pull the spark plugs to see which cylinder is flooded with raw fuel...do it outside for safety. That's when you know you have a petcock problem.

[Gryphon Rider]

My bike usually needs choke for a cold start.  A few times I have started the bike, let it run until the choke isn't needed, then ridden a few hundred feet before the engine starts to lose power, then, without stopping, reached down and turned on the fuel.  My bike will idle a LONG time, well more than five minutes, with the fuel off before it starts to miss.

If this is something new, i.e. not an "always been there" idiosyncrasy, then it should be investigated, perhaps after seeing that a carb-cleaning fuel additive doesn't change anything.

[Blackduck]

If you leave the fuel on (petcock open) there should be no flow unless here is vacuum to the petcock under normal circumstances
BUT there is a very small orifice in the middle of the petcock that can block and lock the vacuum in,
This holds the diaphragm open.
Maybe pull the fuel line off the petcock and see if there is flow  when the engine is not running/
Have pic's some where of this.
Cheers Steve

[mike72903]

Thanks.  More good advice.  I try not to mess with things unnecessarily because as mentioned it's possible to create additional problems. I do have petcock experience on other bikes and am confident there is not a problem with my existing one.  I am not shutting off the petcock until the engine stops.  Sorry if I did not make that clear.  And no, this is not something new, so I'm not worried so much as curious. In any event I'm off on a little ride to test out Firefighters theory.

[Willow]

For what it's worth one of my Valkyries will start fine without the enricher.  The other one will run fine without if it starts on the first couple of revolutions.  If it doesn't it will need the enricher and will not idle without the enricher until it's warmed up.  It does seem to be more sensitive if it's sat for awhile.  Doesn't seem to have anything to do with the petcock.

[mike72903]

I started the bike yesterday after it sat overnight. I had waited until the engine was cold before shutting off the petcock the day before.  It ran for about 5 minutes before it became obvious it was starving for fuel. This is opposed to a one minute or less interval when I turn off the petcock with a hot engine.  Looks strongly like Firedighter is correct that engine heat is vaporizing the fuel in the bowls. I'll repeat to confirm,  curious if anyone else has noticed this with their Valk.

[Christbiker]

Probably has something to do with that guy you bought it from.  I hear he's suspect.

Blessings,

Woody

 

[mike72903]

Probably has something to do with that guy you bought it from.  I hear he's suspect.

Blessings,

Woody

 

LOL I don't think so my friend.  I'd buy another from you in a minute. Nothing but good stuff from Desdemona. 200 mile trip yesterday and zero issues since I got it.  Shortly after getting her we did an SS1000.  Ran all day and all night smooth as silk.  Added Mustang seats, MCcruise cruise control and a few lighting and safety do dads.  Briefly considered your yellow bike as a tug for a sidecar but it's just too pretty and I would have to have a hack painted to match. Same reasons I wouldn't use Desdemona.
Blessing to YOU Sir. 

[John Schmidt]

I started the bike yesterday after it sat overnight. I had waited until the engine was cold before shutting off the petcock the day before.  It ran for about 5 minutes before it became obvious it was starving for fuel. This is opposed to a one minute or less interval when I turn off the petcock with a hot engine.  Looks strongly like Firedighter is correct that engine heat is vaporizing the fuel in the bowls. I'll repeat to confirm,  curious if anyone else has noticed this with their Valk.

When the engine is hot, are you turning off the petcock while it's still running? If so, then what you've described is pretty normal. In the first scenario you're beginning with full bowls so it will run longer. In the second, you're starting with partially empty bowls so will run substantially less time.

[mike72903]

I started the bike yesterday after it sat overnight. I had waited until the engine was cold before shutting off the petcock the day before.  It ran for about 5 minutes before it became obvious it was starving for fuel. This is opposed to a one minute or less interval when I turn off the petcock with a hot engine.  Looks strongly like Firedighter is correct that engine heat is vaporizing the fuel in the bowls. I'll repeat to confirm,  curious if anyone else has noticed this with their Valk.

When the engine is hot, are you turning off the petcock while it's still running? If so, then what you've described is pretty normal. In the first scenario you're beginning with full bowls so it will run longer. In the second, you're starting with partially empty bowls so will run substantially less time.

No, petcock is turned off after engine is off.

[John Schmidt]

OK, then you'll have full bowls when you go to start next time and if you don't turn the petcock on right away when you start it, it will run for a few minutes before starving.