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Turns out the vacuum operated fuel shutoff valve was the problem.

The shutoff valve's diaphragm broke, causing gas to get sucked down its vacuum line. I know it's bad, but I put on yet another vacuum operated fuel shutoff valve. I was able to get one for free from someone I know, so I took it. Now the engine can run at high speeds without beginning to act like it's running out of gas, so the previous shutoff valve must have been too restrictive.

The diaphragm broke at a friend's house, 17 miles away. It seemed normal when I arrived, but when I started the engine upon leaving, the engine surged way up, then stalled right afterwards. The scooter was able to crawl back home though.

The next day, I hooked a clear vacuum line to the shutoff valve and turned the engine over with the kick start lever. I watched as a lot of gas flowed into the vacuum line. Gas was even dripping off the bottom of the shutoff valve. I'm surprised it was able to run at all with that much gas being dumped into the engine.

While browsing the comment section of a video on Youtube, I saw a comment saying that the Japanese Philip screws are different and need special Philip screwdrivers to be worked on properly. Curious, I looked into it and learned that the Japanese had developed their own "JIS" (Japanese Industrial Standard) screws and screwdrivers. These screws are marked with small dimples on their heads, as shown below:


After looking these JIS Screwdrivers up on Amazon and seeing good reviews, I decided to order two of them, sizes P2 and P3.

As I waited for my new screwdrivers to come in from Japan, my Chinese scooter carburetor flooded. I never opened the float bowl on this carburetor before, but had stripped two screws on my original carburetor when opening the float bowl. Seeing that the screws on the carburetor are marked with dimples, I decided to wait and put the JIS screwdrivers to the test when they arrived.

Once the screwdrivers came, I had no problem opening the float bowl. Many people complain about soft metal screws on these Chinese scooter carburetors and the screws on mine were very tight, but I removed them all without damaging any of them. I was very satisfied with how well the screwdriver had preformed during that job.

Now here is what really impressed me about these screwdrivers. When I went to remove and clean the CVT air filter on my Yamaha Zuma, I noticed that some of the CVT cover screws were extremely over tightened. The JIS screwdrivers I bought are also impact screwdrivers, so after some good hits with a rubber mallet, I got the stuck screws out and without damaging the heads.

Once I got the CVT cover off, I just had to remove one last screw that holds the air filter in place. I tried turning it out by hand, no luck. I tried the impact feature, still won't move. I tried again but with some WD-40, still nothing was happening.

Now this screw is either coming out or getting stripped. I grabbed the screwdriver handle with both hands as tightly as I could and started turning, using wrist and upper body strength. Suddenly, I heard a crack sound and felt movement. The screw had come loose and without damage. This screw had been painted black, and not even a little bit of paint on the inside of the head had come off. The tip of the screwdriver was also totally fine.

I cannot recommend these screwdrivers enough. It seems impossible to strip a screw with them. They don't "cam-out" of the screw head even during the most extreme situations. I wish so bad I had known about these screwdrivers a long time ago. Perhaps many of you here already have heard of JIS screwdrivers, but in case not, I'd like to let you all know of them before more screws are stripped.

Links to the two JIS Screwdrivers that I purchased:
www.amazon.com/Vessel-Megadora-Impacta-P2x100-Screwdriver/dp/B003BI8HHQ/ref=sr_1_2?ie=UTF8&qid=1447116491&sr=8-2&keywords=vessel+impacta+screwdriver

www.amazon.com/Vessel-125943-P3x150-Impacta-Screwdriver/dp/B003BGTTSE/ref=sr_1_1?ie=UTF8&qid=1447116491&sr=8-1&keywords=vessel+impacta+screwdriver

That's what made it unforeseeable. For three years he didn't care if I used the garage. I'd even ask him whenever he was around if where I had parked was okay, and he would always reply, "Yeah, that there's fine".

My friend recently told me that his mother and stepdad have been having marital problems for sometime now. From what I've heard, the two of them are so irritable that they'll complain about anything and everything. I assume that's why he suddenly changed his attitude about the garage.

While preventing damage from sunlight is a concern of mine, it wasn't my only concern on that particular day. When I arrived, my friend's stepdad wasn't home, his sister wasn't home, his mother was leaving soon and the two of us were also leaving soon. No one was going to be there and that neighborhood isn't very nice. There would've been a real chance of someone throwing a rock at my scooter or stealing it, had it been left out.

Like I said in my first post, they usually leave their cars out. Twice, they had CDs and electronics stolen from their cars. They had rocks thrown through the front windows of their house several times. Years ago, I had my car in their driveway. I looked out a window from inside the house and saw a teenager approaching my car. Luckily, my friend's sister happened to be outside at the time. The teen walked off right after noticing her. I have no doubt he was about to vandalize my car in someway.

In fact, when I first started riding, my friend would advise me to keep my scooter in the garage, even while at his parent's house. I remember him saying, "you should put it inside, we don't want to take any chances". I had my $300 Chinese scooter at that time. No way would I feel comfortable leaving my $2,100 Yamaha home alone outside in that neighborhood.

Yeah, I was angry to say the least. I didn't express my emotions then. But the next day, after having looked my scooter over for any possible damage, I told my friend that his step father and his buddy are careless idiots for having moved my scooter like that. Luckily, my Zuma didn't appear to have any damage, however, they now have scrap marks on their garage floor from dragging my 269lb scooter like that.

Spandi - I checked reviews on Amazon for that half cover. Everyone seems to be happy with it. I like how it can be put on right after a ride since it doesn't hang down far enough to touch against the hot exhaust.

mftic - Does 303 need to be wiped on to apply? I've been searching for something that can be sprayed on then left to dry. Not only would it be faster than wiping every spot by hand with a cloth, but it would be much easier for doing the hard to reach places.

I was wondering, does anyone know how narrow of an opening a vacuum operated fuel shutoff valve has when suction is applied? I'm sure it varies between each shutoff valve, but do you think it's extremely small?

I'm curious about the odds of a clog occurring in one of them since debris I've seen in gas cans and gas tanks don't look much larger than grains of sand.

Alright. I'll look at some of the manual shutoff valves then.

I just did an oil change and air filter cleaning because I'm pushing 4,000 miles now. I really don't want to do work of any kind to it until the 5,000 mark, especially since my whole headlight fiasco. I've had this vacuum operated valve for about two years now, so I can live with it until then.

About two years ago, I bought a new vacuum operated fuel shutoff valve because my old one appeared to have some gas leaking into its vacuum line. My fuel filter has clear, see through plastic and is between the shutoff valve and carburetor. Before getting this new shutoff valve, I would see that the fuel filter was always full of gas after every ride. However, with this new one, the filter is always around half full after every ride.

When I turn the engine over by hand with the kick start lever, I do see drops of gas fall into the filter. I even turned it over until the filter was completely full without an air pocket inside, but it went back to being partially full after the engine started.

Is this normal for these vacuum operated fuel shutoff valves?

I think this shutoff valve is being too restrictive and not allowing gas to flow freely enough. Also, I noticed if the engine speed is high for about a minute or more, it starts to act like it's running out of gas.

These shutoff valves are cheap, so I could easily get another one. I just want to find out if this one is indeed not working normally before getting another one.