Scooter Fuel Vacuum Petcock Problem and Workaround 

Thanks, I hope it works out for you!

Lol, surprise. Glad it was helpful!

Thanks for the feedback! I'm glad the video helped. I'm really glad someone left a comment on my earlier video and let me know of this issue, it has completely solved my starting problems as well.

Or a manual fuel shut off valve if its easier.

@@TheAfterWorkGarage p

Thank you for the kind words!

Thank you!

Hi Bryan, I hope your new parts fixed your problem, and thanks for the shout out to the Jayhawks!

Hi, thanks for the comment. Here's the link to the petcock I ordered: www.amazon.com/gp/product/B00XVS3FXW/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 There are others out there that will work, that's just the one I used. Hope it helps!

Glad it was helpful!

Awesome, I hope it works out for you!

Thanks for sharing. It makes sense that there would be insufficient vacuum at WOT to open the petcock.

Thanks, and I hope you got your scooter issue worked out!

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This sounds like it may be a faulty auto-enricher. It's usually used in scooters instead of a choke to let more fuel into the engine when it is cold. Covering the intake a little acts like a choke to pull more fuel out of the carb, which to me suggests that it's an enrichment issue. they are pretty easy to replace (usually just an electrical clip and a screw). I actually had to replace mine, and may have video of it somewhere.

Hi Cathy, it's hard to say, it may be coming out a vacuum hose, or it's possible the float needle in your carb that shuts off the fuel valve when the carb bowl is full is leaking and letting gas out of a breather hose. Do you know what the place where the gas is coming out of is connected to?

@@TheAfterWorkGarage its not connected to anything. Thats the weird thing. Its an open ended hose with a nice beveled edge to the hose. I sent a couple pics to your Facebook messenger.

No problem! Glad it was helpful!

Thank you!

Exaclty

Generally these are signs of a dirty cab, but since you say it's new, I would check a few things. First, make sure the new carb is adjusted and actually clean/free of water. Second make sure the booster pump is being correctly actuated by the throttle lever. I'm not sure of the specific design on that scooter, but there's often an arm or follower that actuates the accelerator pump plunger which can get bent our stick so you no longer get an extra shot of gas on quick acceleration. The second thing I would look for is your PCV system (usually a hose coming out of the valve cover) to see if it's completely full of oil. The PCV system leads back to the air box/intake and can cause weird things when it gets a bunch of oil in it. While not specific to your scooter's symptoms, it might be worth checking for things like vacuum leaks, and the electrical connection for the idle air valve (since the carb is new this may have not gotten re-connected). Good luck, and if you figure out the problem, I'd love to hear what it was.

The petcocks I used are as follows: At the tank - 16mm x 1.5mm Fuel Shut Off Valve (ASIN B00XVS3FXW) www.amazon.com/gp/product/B00XVS3FXW/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 In line shut off - 07-403 Inline Fuel Shut Off 1/4" Ball Valve (ASIN B0018U234W) www.amazon.com/gp/product/B0018U234W/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1 Hope it helps!

@@TheAfterWorkGarage That does help a lot. Thank you.

Glad it was helpful!

The original petcock was vacuum actuated, meaning that it only opens when the engine is pulling a vacuum (turning over at enough speed to create a vacuum). The new one is just a regular manual petcock that you open by turning. In theory I could have just deleted it since I have an inline petcock further down, but it was just as easy/cheap to purchase a manual petcock that was a direct fit, and leave it open all the time.

Air getting into the carb from the fuel line isn't going to cause missing, but the fact that you're getting bubbles into your fuel system could be telling of some other type of issue. Are you sure your motor has a fuel pump, or is it gravity fed from the tank like most scooters?

Once it's going, it should have enough vacuum to keep the petcock open. Make sure you check for vacuum leaks, which could cause lean running, but also cause issues sustaining vacuum pressure to the petcock. At the very least it couldn't hurt to make sure all of your vacuum lines are tight, and your connection between your carb and head isn't leaking.

@@TheAfterWorkGarage hi Andrew I have the same problem with my kymco agility 50. I need to find out where you got that manual fuel tap from.. Help 👍😜

@@grubble01 Good luck with your scooter! The manual shut off valve is here: www.amazon.com/gp/product/B0018U234W/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

That sounds like you are running rich and need to adjust the fuel air mix on the carb.

@@williamhobbs9112 also.. every scooter owner needs to adjust the valves every so often. It sounds difficult but isnt.. you need a feeler gauge, an 8mm socket to remove valve cover, a 9mm socket and small needle nose pliers. Get timing mark on line on compression stroke and set.. recommend 3-4 thousandths on intake and 4-5 on exhaust, for 4 stroke..

Oh boy, I really don't know. If it's 3/4 full and you open the fill cap and try to run it, does it run normally again? The only thing I can think of here is that the fuel tank vent is blocked, so it's drawing a vacuum in the tank as you use fuel. Otherwise, it may be a partial blockage in the fuel lines, and the additional pressure of the fuel in the full tank is enough to force it through. If it's not a vent cap problem, I'd start by tracking down the fuel lines, and make sure there's not a blockage. Oh also check the carb float - if float isn't dropping down all the way or the needle is sticking, it could also cause a restriction.

Glad it helped! Here's the link to the fuel shut off valve I used: www.amazon.com/gp/product/B0018U234W/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Hi Wesley, to me that sounds more like a vacuum leak issue. The revs spike when you introduce more air (either through an intermittent leak or by pulling the vacuum hose off) and you lean out the mixture. This increases the revs, but also makes the engine run hotter, so you definitely want to track down where the issue might be. Good luck!

These small motors don't make a ton of vacuum to start with, so if the vacuum petcock is stiff or sticks a little, the vacuum from the motor may not be able to overcome it.

This could very likely be your issue - it's definitely work a try switching it out and seeing if it helps!

If you haven't tried it already, make sure you clean your carb out, and make sure your spark plug is clean/gapped properly. If this doesn't work, check for vacuum leaks.

Thanks for the comment, and yes, assuming the carburetor float needle is seating correctly, you shouldn't have issues with flooding. It would be recommended to turn off the gas at either the tank or line when storing for long periods however. Good luck with your scooter, it sounds like it may just be a fuel issue - hopefully it's not too much to get going!

Good luck, hope it works for you

@@TheAfterWorkGarage nope... Now, i will try to adjust the valves...

@@Fred6ERIC ugh that's frustrating. If you can narrow it down to either spark, fuel, or air as being your problem, that could save you some hunting. Check for vacuum leaks and make sure you are getting fuel in the carburetor. It might also be worth checking the auto-enricher which many scooters have in place of a traditional choke. If that's not working, then it'll be hard to start.

@@TheAfterWorkGarage i put a new carburetor, i change the petcock for a fuel tap. There's a spark. When i try with Startpilot, the motor start for 5 seconds and stop... that's why I suspect a misadjustment of the valves. What do you thing?

@@Fred6ERIC If there's a ton of miles on the scooter, then possibly. It's certainly worth checking with a feeler gauge. My first thought would be a vacuum leak letting too much air in. Will the scooter start on starting fluid? It can't hurt to double check your vacuum lines and all their connections, as well as make sure all the connections to the carb are secure. an enricher valve has an electrical connector, so don't forget that one if it's there. If it's easy to pull the timing cover, it might be worth checking that to make sure it's in time as well. Keep eliminating one thing after another and you'll get there eventually. I just like to check the easy to get to things first. Also make sure that neither of the kill switches are engaged (though if you're sure you have spark at the spark plug, they aren't). When you find the issue do share, I'm curious!

Not sure exactly which line you're looking at, but one is for crankcase ventilation, and then there is also an EGR system for emissions. Some scooters also have extra hoses that aren't vacuum related, like carb bowl drain hoses, and breather hoses.

It's worked great so far!

@@TheAfterWorkGarage Thank you very much for your reply. Good luck.

The one I used is at this link: www.amazon.com/gp/product/B00XVS3FXW/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Thanks for the comment. It sounds like this may be an issue with a dirty or restricted carburetor/fuel supply. As you add more throttle, the mixture leans out and kills the motor. Also make sure that the back wheel turns freely by hand, since a stuck on brake or problem with the final drive gears/system could be causing increased load when the centrifugal clutch engages that is killing out your motor. Hope this helps!

Hard to say from the brief description, but my only advice would be to check the obvious things like clean your carb (new carb kit etc) and check for restrictions in the fuel system.

This is the one I used at the tank is here: www.amazon.com/gp/product/B00XVS3FXW/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 Though you may need a different threading depending on your tank. The tap I used at the in line is here: www.amazon.com/gp/product/B0018U234W/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Awesome, thanks for sharing. Sounds like you did the vacuum block off right!

I got a r50 with the same issue...thank you!!!life saver!!!

Thanks!

Not 100% sure how it's set up, but most likely if you don't have it connected, it won't start. There's a chance it it's like a kill switch (closed circuit shorts out starting), then it doesn't matter, but I'm guessing it's not that simple. If you don't have yours, and it's not starting, you might try bridging across the two wires to see if it lets it start.

Good luck! hopefully it's an easy fix for you. Vespas are great scooters.

for the in line stop it was: www.amazon.com/gp/product/B0018U234W/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1 The replacement at the tank was: www.amazon.com/gp/product/B00XVS3FXW/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

@@TheAfterWorkGarage thank you!

Good thought. I put one there since it was easy and relatively cheap to replace the vacuum petcock with a manual one. I also liked the idea that I could shut off the gas at the tank in the event of a leak, but with such a small tank, I think this is less of a concern. I'd be interested to see what you find if you do get a through fitting for the gas tank.

@@TheAfterWorkGarage Actually, I have been thinking there may be a way to modify the vacuum valve so the fuel will flow through as though it were just a straight pipe.

I have a 150cc scooter that just stated having problems.It only has 2k miles on the engine. My problem is that when you are going down the road it wants to bog down when you give a little gas or when you are just going.

@@michaeledwards8425 trash in the main jet of the carburetor

You could do this. I only used the manual petcock at the tank so I could replace it directly without having to modify the tank to attach a hose.

A couple of HOURS of driving? That's a long time on a scooter! Hard to say without more info, but it sounds like it could be a heat soaking problem. This usually happens when hot motors sit, however similar things can happen after extended driving, where components get hot and cause poor/inconsistent fuel mixture.

Not completely sure what you're saying here. If it is a traditional petcock (not a vacuum one) then best bet is either replacing it, or if it's truly clogged with gunk, maybe a little solvent and some compressed air. I wouldn't recommend solvents on a vacuum petcock, since it may damage the diaphragm. Either way, I would probably just recommend replacement since the parts aren't terribly expensive.

Thank you so much!

Scooters can be finicky (well all small motors). It's a Lance Cabo 50 made by SYM. You may have a vacuum petcock issue on your kymco as well - many scooter designs are quite similar. Also that's a nice scooter!

Thanks for the info - I definitely need to stock up on those little caps and plugs, there's always some use for them.

a golf tee works well or any tapered bung,.....hell even a cut down six inch nail lol

If the carb has a leak, it can slowly drain the tank and make a mess. The bigger problem is over time the fuel in the carb will evaporate, and if the fuel from the tank is not shut off, it will continue to refill and evaporate from the carb. This leads to buildup of things that don't evaporate (varnish/dirt/impurities) which will accelerate the need to for a carb cleaning. Overnight, I just leave mine open, but if it's going to sit a while, I like to have the ability to shut it off.

@@TheAfterWorkGarage okiii .. from your words i can keep it on while night as carb new and no leaks but of i will park scooter for a week or more better to off the valve

Oh and I might add you’ll be replacing less starters and probably batteries

@@johnpower8356 True story, I recently replaced the battery on this scooter (and should have far earlier).

As long as the carburetor float and needle valve are working properly, there shouldn't be problems with "flooding." The concern (and reason for the second in-line shutoff) is when the scooter sits for a while, fuel in the carb bowl evaporates out. With a continuously open fuel supply, as the fuel evaporates, more replaces it, and you get an enhanced buildup of varnish/gunk in your carb instead of having the carb bowl go empty.

It's possible that an issue with a leaky needle valve/bad float, would cause something like that while sitting, but it would also have have bad vacuum petcock (stuck open) or a manual one that is left open. Alternatively, a broken vacuum petcock diaphragm would allow fuel to leak directly form that pectock into the intake, so you might take a look at that as well. Another place to look for a collection of fuel is the PCV hose/valve (it's a breather hose for the crank case) that probably runs from the timing cover or head to the vacuum system, as that's another rout from your failure point direct to your crankcase if it's not going into the combustion chamber/past the piston rings. Good luck, and I hope all is well with your post-op recovery!

@@TheAfterWorkGarage I wish I could see exactly what you're talking about. Seems like when you need one, a video is almost impossible to find, but once you dont need one, its right there. I am not mechanically inclined. I do, however, own a service manual, which I am hoping is a repair manual. Its intimidating to tear apart something that you know practically nothing about. I'll just have to refer to manual and take my time and hopefully I dont have extra nuts and bolts leftover when I'm done. That would be bad. People on youtube make it look easy. If you find anything online like you mentioned, that may help, could you send me the links? I'll post my progress once I get started and finish. Thanks.

Thanks!

This is the one I purchased: www.amazon.com/gp/product/B0018U234W/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Hard to say without any more info. Does it start again after it sits for a while (like overnight)? After it run and then won't start, see if there is fuel in the carb bowl (loosen the carb drain bolt nut and see if fuel drains out). If it's empty, then you probably have a fuel feed problem. If the scooter has a lot of mile on it, then it could also be a valve adjustment issue. Good luck, and let me know what the issue is when you get it sorted out.

Thank you so much for your kind words! Hopefully I can get my channel up and running again when I find a shop space closer to where I live!

@@TheAfterWorkGarage hey man all in good time. You take care of life and just do what you can. Too many youtubers let it take over life and thats not healthy.

Hmm, I'm not a moped expert by any stretch, but it could be a fuel feed issue. Definitely check the needle valve and fuel inlet to the carb bowl as well as the vacuum petcock assembly. Could also be a clogged fuel filter. Others may have better suggestion, but that's where I'd start.

Hi Merjim, this may fix your situation. Otherwise just keep tracking down the fuel system components to see where the blockage is. Good luck!

Hmm, hard to say without more information. It could be a vacuum petcock issue, and you are turning it over faster with a kick start than the starter is able to turn it over, and the little gas that comes through is used up/leaned out too much when you try to rev it. If this isn't the issue, I would check fuel supply, and make sure the carb is cleaned and adjusted. Again this would be because a sub optimal fuel/air mixture could allow for some running with a faster kick start (higher compression) than with the starter motor. Good luck, and let us know if you figure out the issue!

I was hoping no one would ask lol. I sucked on the vacuum line like a straw.

@@TheAfterWorkGarage lol. Time to invest in a vacuum gun. I thought about doing the straw method too!

@@daveking1470 Definitely going on the wish list - somewhere below finding a new shop space in Dallas so I can start making videos again haha!

@@TheAfterWorkGarage or you can use an air pump from the aquarium aisle in the pets department at Walmart

Good luck! I hope it is an easy fix for you. If it is, sounds like you got a good deal!

Not totally sure what you mean there, but it seems like your scooter is dying if you open the throttle? That sounds much more like a carburetor issue causing it to lean out to much and starve the motor. I would recommend a carb clean, and making sure the auto enricher (an electronic component on the side of the carb) and boost pump (part of the carb - it's a little pump that is actuated by the throttle lever) are working correctly.

Hmm, I'm not familiar with this scooter in particular, but this should be relatively easy to track down. If there is a screen in the filler hole, make sure that isn't blocked up. In addition, if this tank has a breather hose, make sure it's not clogged up as well. If you put gas in it slowly does it go in?

@@TheAfterWorkGarage it's at a while with no gas cap and the two was literally full of pine needles from the woods! thanks! cleaned it out and out works great. I did have to clean out and swab the fuel tank just in case they were contaminants that could go into the engine and screw it up.

@@Hubcaps219 That would explain it I suppose lol. I'm glad you found the problem!

If you're talking about the vacuum hose, I just blocked it off. With a manual petcock there's no need to rout vacuum to it. You just have to make sure that the old vacuum connection is closed so it doesn't become a vacuum leak.

I believe 2 strokes would have a similar setup, the vacuum line would just be between the carb and the reed block.

Try carburettor cleaner. If not pull out carbie and use cleaner and compressed air to clean out jets. Or buy a new carbie for around $25... they're super cheap. Fuel filter could be clogged restricting fuel flow. Check for air leaks, make sure vacuum hoses are connected.

I'm going to agree with Caesar here. I'd first clean your carb and check your fuel system. Then keep working through the obvious things like vacuum leaks, problems with your auto-enricher/choke (depending on what your scooter has). I'm not a professional by any stretch, but 90% of the time if it has a car, and it's not running right, it's a dirty or poorly adjusted carb.

Spot on.

Any help would be great

You may have a leak in the vacuum petcock assembly that is letting fuel into the vacuum lines. Fuel can make its way into the vacuum lines from the carburetor, but that seems less likely. I'd check the vacuum petcock and replace it first and see if that solves your problem. Good Luck!

@@TheAfterWorkGarage thx I figured it out it was the fuel petcock ok but now I have another question I have another scooter that's starts and runs good bit the only way to start it is by jumping off the solenoid I've checked everything i know none of the lights works it's like it has no power no horn turn signals etc has a good fuse but you can take the key out of the ignition and it's still stays running keep in mind it is plugged in

@@jakesatvrepairandmore1346 Hard to say with electrical problems. The first thing I'd do is check your ground connections. Often the starter motor will have a dedicated ground, and other things will rely on ground straps to the frame. The next thing I'd definitely check is the ignition (the thing you stick your key into), which could have problems with it as well. Those would be my top guesses, but I'm not a scooter expert.

Whats that do ?

@@insanechevy91 Does not let the shiver go all the way up, opening air intake entirely