Vacuum petcock on scooter, how long should it hold pressure?

Got my scooter running last week, super oddball, '99 Hyosung sense, 50cc two stroke oil injected beast. Thing fucking rips, with a bit of time I can see 45...up to 40 quick, and registers as a moped! Yay! The bad, after sitting only a few hrs it takes a lot of cranking to get fuel to the carb running the batt low to the point it is hard to start, may not as starter turns too slow. Now if you start it within an hr of shutting down it fires up immediately, so fast you can't let go of the starter button fast enough to avoid minor drag, so me thinks the diaphragm in the petcock has degraded? Or is this normal? Stupid ethanol. If I can get this licked it will never have ethanol fuel in it again, I have a line on a place in AZ that had the petcock, but obviously can't call until tomorrow. Wish they had stuck with gravity feed! :) Guess the trade off is it has a plastic tank, so will never rust! I had to pull the kick start out of it so I need to address this so I don't get stranded. Idea's? I figured out how to ride this without it attempting to kill me, it has foot pegs for a passenger, but this thing must have been made for Hobbits, as there is no way two people could ride on it, but if I use those instead of putting feet on floorboards it's actually quite stabil.

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Re: Vacuum petcock on scooter, how long should it hold pressure?

The vacuum line is directly hook to the intake usually. Once you shut off the engine the vacuum drops immediately and closes the petcock. If you have a hole you would never start or run.

If it starts easy hot but does not cold 2 issues...

#1 Fuel drains from the carburetor? The engine starts with the remaining fuel after you turn it off. Once the engine starts the vacuum is there and opens the petcock for fuel. You are off and running.

#2 the Auto Choke is a very odd option on these scooters. It is electrical and when cold it chokes the engine to start easy the first time and then after a little time it goes back to normal. You need to check that this part on the carb is working right for the cold start.

Never turn the engine over without a spark plug in place you could ruin the CDI Box.

I hope this helps. It has been a long time since I worked on a scooter but this is what I remembered from the one I did repair.

Re: Vacuum petcock on scooter, how long should it hold pressure?

Thanks, it does have an auto choke, and I remember it working last november when I bought this thing, it would actually rev high for like 20 seconds and slow down after that, not noticed that this year but it was 80 plus out...maybe that is bad, like an autobystander on a Honda. My thoughts on the petcock is yes, when you shut down, the vac drops on the intake side, but is not supposed to behind the petcock, in a short time anyway, so only a few revolutions of the engine are required to bring the fuel to carb? So if diaphragm is bad fuel goes further back than intended? Thanks for the tip on not cranking the engine without plug, but I totally have spark. :) It is "cold" now so will test it out at lower temps when it stops raining. Thanks for the input, I appreciate it. Where would the fuel go if draining from the carb? It does not smoke or anything, and when hot pops right off, so I doubt plug is fouled. (edited)

Re: Vacuum petcock on scooter, how long should it hold pressure?

How many positions does your petcock have if any? If there is a RES this by passes the vacuum stop.

Still if there is fuel in the carb the bike will start and run for some time without fuel till it drains the bowl. I am sure you know this as I have read so many of your posts. This amount of time is WAY more than is needed to get the vacuum to the petcock and allow fuel to the bike.

I would replace all the hoses... the Chinese hoses are junk and will fail quickly. I have read this many times and have experienced it for myself.

Still check the auto choke. That is my best guess.

Re: Vacuum petcock on scooter, how long should it hold pressure?

There is no petcock lever like on a moped, no off or reserve, I wish there was, the way I understand these is that when engine stops the vac is gone and the valve closes, no input by rider (as the motorbike gods intended) ;) when starter is activated the draw from intake opens the valve, and you are off. Valve remains in the "run" position as long as engine is running, closes when vac is removed, engine off. It is Korean, so better quality than China bikes, but it is no Honda, engine is a Suzuki clone, and seems very robust, even has a catalyst in the pipe!

Re: Vacuum petcock on scooter, how long should it hold pressure?

I agree though that some fuel should remain in the bowl after shut down? I can't imagine where it would go, no leaks under the machine. I will look at the thermo-choke thing, I hope it is ok, as god knows where I can come up on another?

Re: Vacuum petcock on scooter, how long should it hold pressure?

You are 100% correct. But as stated there is plenty enough fuel in the carb for the initial start to get everything going.

I have a bad memory... I am trying to remember how I checked the auto choke... I think I removed it and hooked jumpers to it from a 12v source. I think I also checked for voltage when starting to see if the auto choke was being given the signal.

If you still think it is the petcock... plug the port where the hose goes into the manifold. Pull a suck on the tube and try to start. If you still have the same issue check the choke. Or you can open the drain for the float bowl, the bike I repaired had this... let it drain till it stops... with the drain still open pull a suck on the vacuum hose to see if you get the carb to drain again. I am sure it will. Then drain the carb again... hook the hose up as it should be for running... hit the started and see how long it takes to get the fuel to drain. It will take a little to drain as there is a lot of distance for it to travel.. So hit the starter for a bit and wait for the fuel.

I hope this helps to trouble shoot it.

Re: Vacuum petcock on scooter, how long should it hold pressure?

You can get a full carb for dirt cheap on ebay. It is what I had to do since the guy that had the scooter before me took the carb apart and lost the diaphragm spring. LOL!

Re: Vacuum petcock on scooter, how long should it hold pressure?

Ha! This is an odd ball bike no gy6, going to try and work it through, maybe since it was so hot the fuel evaporated? Vapor lock? Hmmm....ah the fun of the unicorn. Thanks for all the help! Highs in the 60's next few days, yeah 83 Sunday, 55 today, MN for ya. I will see if it starts faster tomorrow if I get up in enough time before work. I wish enough people knew what a choke was so we could still have manual ones, and manual petcocks! They work great, if one knows what they are! :) Thanks again for chiming in, I really appreciate it. I hope to make this reliable, as it is so much more comfortable than mopeds on my old bones! :)

Re: Vacuum petcock on scooter, how long should it hold pressure?

Those use a Suzuki/Morini based engine, similar to Derbi and TGB. Harder to make go fast than a Minarelli or Piggy engine, but stuffs out there.

Re: Vacuum petcock on scooter, how long should it hold pressure?

Thanks! I bet with a pipe/jetting and open air filter it would scream! The pipe going to the muffler is HUGE and the muffler contains a catalytic converter, so yeah...it's stifled a bit, exit pipe is tiny, but bigger than moped ones...once running it actually runs quite well, idles smooth, and pulls hard, seems to be well tuned from the factory. I really don't need more speed, maybe some clutch tuning...not worried about it for now, just want it to start quick when cold starting. My best so far is about 45, per speedo, and seat of pants/ no gps as I'm keeping both hands on bars with such tiny wheels, YES looking at mph vs kph...lol, blue wire (rev limiter for cdi has been cut) over about 37 you can hear the intake and exhaust "mesh" up and she pulls hard and the engine just sings. A joy to ride. No 4 stroking at all. (edited)

Re: Vacuum petcock on scooter, how long should it hold pressure?

When you turn the scooter off pull the vaccuum line off the petcock and see if you have fuel in it...i have had the petcock diaphram go bad and cause a problem like you are having

Re: Vacuum petcock on scooter, how long should it hold pressure?

That's what I'm thinking as well. I just wish it was not such a pain to pull all the plastic off, going to try a cold start this week and see if the choke works as well, 45 degrees this morning! Brrr!

Re: Vacuum petcock on scooter, how long should it hold pressure?

If you've got a catalytic exhaust you'll see a big improvement from swapping that out.

Re: Vacuum petcock on scooter, how long should it hold pressure?

I agree, but then I would have to rejet I assume? Just trying to get it easy starting 100% then maybe look into more speed, but it honestly seems tuned very well, 40-45, is really all I need. Not found much in performance parts listed for this model, or should I be searching for just the engine?

Re: Vacuum petcock on scooter, how long should it hold pressure?

i use a syringe to put a vac on the petcock for testing purposes.

you can also take them apart and ditch the guts and just make them 'always on' which i have done in the past, but then you have no fuel shutoff.

by the sounds of it, i'm guessing its that choke. auto chokes on scooters are always the problem, haha.

Re: Vacuum petcock on scooter, how long should it hold pressure?

Graham might be right but the last few i have worked on with simular problems ended up leaking fuel into the vaccum line ..simple test of all..start it up and let it run a few minutes then pull the vacuum line and see if it is wet with fuel. . (edited)

Re: Vacuum petcock on scooter, how long should it hold pressure?

I have had a lot of people come to me with broken scooters and i'd say at least half were just a vacuum petcock issue. Like 1st thing I check. pull off the covers, get the vac line unplugged from the intake and disconnect the fuel line from the carb (or open the drain screw on bottom) then just suck on the vac line real quick and see if gas comes out.

When it doesn't it's usually a crack or hole in the vacuum line not a petcock issue, and you can feel it. replace the line and bike's back in action.

I saved some old guy once on the side of the road with this issue, nice newer model vespa too. he was an old Italian guy who made sausages and cheese and sold em locally, every time I saw him at the local farmers market after that he'd hook me up with some great snacks. karma? maybe it was beyond worth it to see how happy he was not to need a trailer in the moment, but snacks definitely help haha!

Re: Vacuum petcock on scooter, how long should it hold pressure?

If the lines were bad wouldn't it leak? Mine does not. I'm back to work this week so have to wait a while to mess with this. I suspect diaphragm, it is 21 yrs old of ethanol sitting in it.

Re: Vacuum petcock on scooter, how long should it hold pressure?

Still easiest test of petcock is start it and after running a few minutes shut it off and pull the vacuum line to see if it is damp from fuel...very simple and quick...

Re: Vacuum petcock on scooter, how long should it hold pressure?

That's where I'm going to start. In reading the service manual it says if it does not start right away to open the throttle 1/8 and try cranking it, I assume that is if you flooded it, the translation from Korean leaves a bit to be desired, but when the fuel is right there it starts instantly, so I assume it would be easy to flood if your plug was fouled or something.

Re: Vacuum petcock on scooter, how long should it hold pressure?

no the vac line doesn't have gas in it, nothin to leak but air. its a petal valve, there is like a little diaphragm, sometimes its a pumper but usually just allows flow only when the vacuum pulses from the cylinder draw it open, you can bypass it by sucking on the line, youre sucking under the diaphragm on the dry side to draw it "open" and check that it lets gas flow any cracks and it loses vacuum and doesn't draw it open

Re: Vacuum petcock on scooter, how long should it hold pressure?

Thanks, I think this will make much more sense once I get into it and can "see" what I'm reading, but appreciate the help, hoping to get some more rides in this year, this thing is a blast now that I have figured a way to balance it! :) Headlight is worthless, and I don't think you can aim it, but whatever.

Re: Vacuum petcock on scooter, how long should it hold pressure?

> Born to be WillD Wrote:

> -------------------------------------------------------

> no the vac line doesn't have gas in it, nothin to leak but air. its a

> petal valve, there is like a little diaphragm, sometimes its a pumper

> but usually just allows flow only when the vacuum pulses from the

> cylinder draw it open, you can bypass it by sucking on the line, youre

> sucking under the diaphragm on the dry side to draw it "open" and check

> that it lets gas flow any cracks and it loses vacuum and doesn't draw it

> open

This is about as wrong as wrong can get..the petcock will let gas.into the vacuum line...not.my first rodeo on this or googled up second hand knowlledge

Re: Vacuum petcock on scooter, how long should it hold pressure?

> Stephen Keller Wrote:

> -------------------------------------------------------

> Thanks, I think this will make much more sense once I get into it and

> can "see" what I'm reading, but appreciate the help, hoping to get some

> more rides in this year, this thing is a blast now that I have figured a

> way to balance it! :) Headlight is worthless, and I don't think you can

> aim it, but whatever.

You probably can but it's most likely a total pain in the ass. Usually modern scooters have the headlight attached to the body plastics with the adjustors on the back. So you have to pull the plastics, adjust the lamp, reinstall, check aim, try again.

Re: Vacuum petcock on scooter, how long should it hold pressure?

^ Oh joy...lol! :) The light is in the upper handlebar section and in the plastic, seems bright enough, but does not really throw the beam on the ground, maybe I can put one of those silverstar bulbs in it...

Re: Vacuum petcock on scooter, how long should it hold pressure?

> Pops Peds Wrote:

> -------------------------------------------------------

> > Born to be WillD Wrote:

>

> > -------------------------------------------------------

>

> > no the vac line doesn't have gas in it, nothin to leak but air. its a

>

> > petal valve, there is like a little diaphragm, sometimes its a pumper

>

> > but usually just allows flow only when the vacuum pulses from the

>

> > cylinder draw it open, you can bypass it by sucking on the line, youre

>

> > sucking under the diaphragm on the dry side to draw it "open" and

> check

>

> > that it lets gas flow any cracks and it loses vacuum and doesn't draw

> it

>

> > open

>

> This is about as wrong as wrong can get..the petcock will let gas.into

> the vacuum line...not.my first rodeo on this or googled up second hand

> knowlledge

Will was talking about the fact that there shouldnt be gas in a vacuum line candy ass. I have seen one design that kept the gas from entering the vacuum circuit when the diaphragm failed. You wouldnt be able to afford it though, much less work on it with your sticks and stones.

Re: Vacuum petcock on scooter, how long should it hold pressure?

Pinnochio..the way his post reads is there is no way for the gas to get in the vaccum line..very very untrue..

Re: Vacuum petcock on scooter, how long should it hold pressure?

Ordered new petcock assembly on case it is not just a line, never hurts to have spares, plus it gave me a chance to try out my new pay pal account....such a hassle, last time I ordered from this place a person answered the phone and we just did the transaction like that, so much more personal, had confidence order was placed, now all I have is an email receipt. Oh well, we will see what happens.

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