Strange performance

James Aasman /

Up till now, my QT-50 has only been doing about 22 Mph. I was driving it yesterday, and after about 30 min of driving it all of a sudden jumped up to 28 Mph, held it for about 3 seconds, and then the engine died. Now, I can't keep the engine going for more than about 10 seconds without stalling.

Any sugestions as to why this is happening? Could it have something to do with fuel flow?

Re: Strange performance

sounds like you soft seized maybe.

a great performance boost, and then bang.

is it oil injectioned?? did you run out of oil?

Re: Strange performance

Don Pflueger /

sounds like dirt in thecarb or fuel tank, or the gas cap vent is plugged.

Re: Strange performance

James Aasman /

It is oil injected, and it does have oil

Re: Strange performance

Paul ask a good question about oil injected.

Could be one of two things.

1.Even though you have oil in the oil tank you don't know if the oil pump is pumping oil unless you pull the line off and test it.

The only way the engine gets lubricated is with the oil in the gas so to do the test you have to drain the straight gas from the tank or figure out how to put enough oil in the gas tank to make it about 32:1 or about 4 ounces of 2 stroke oil to a gallon (does your tank hold a gal?)

Once you have premix in your gas tank then start the bike and keep the throtlle rev'd, to keep it from stalling if you can. Pull the oil line off where it either goes into the carb or intake manifold and see if spurts of oil are coming out every few seconds. If it is not, your oil pump is not working.

The sudden jump in your performance could be from running on straight gas if the oil pump stopped working.

2. Fuel flow problem. Either your gas fuel valve is partially clogged and /or your carb is dirty and needs cleaning.

Engines will speed up right before they run out of gas.

So check the fuel flow and clean your carb

Re: Strange performance

James Aasman /

I don't think that the carb is dirty - it was just cleaned a few weeks ago.

I took the fuel line off of the valve and opened the valve - fuel barely came out (a few drops). It didn't help to take the gas cap off.

I took the valve off of the tank, and the fuel came out pretty quick. Does this mean that the fuel valve is dirty, or should the valve slow the fuel down that much?

Re: Strange performance

Jason Luther /

your valve is dirty

Re: Strange performance

Don Pflueger /

yep, fuel should flow just as freely whether the valve is on the tank or not.

Re: Strange performance

James Aasman /

Is the valve easily cleanable, or am I better off getting a new one?

Re: Strange performance

Don Pflueger /

they are easier to clean than a carb is.

Re: Strange performance

James Aasman /

I took the valve apart and cleaned it, but it didn't seem that dirty. I tried running water through it, and it didn't seem to have any trouble.

Is there a trick to opening up the whole assembly? It only seemed to be 2 tubes going in, and the valve controls which of those 2 tubes (if any) connect to the exit which connects to the fuel line. Is there more to the assembly than that?

Re: Strange performance

Don Pflueger /

one tube is for your regular tank fuel level and the other tube is for your reserve should be longer than the other. if you have good flow with water, you may havedislodged whatever was blocking the valve. clean your tank out very thoroughly and make sure fuel can easily flow thru both tubes and each valve setting.

Re: Strange performance

I had the same problem before. The QT 50 gas tank is famous for the rust & gunk inside.

Basically, what you would need to do is, take the petcock (gas valve) off the gas tank (I am assuming this is already done)

On the petcock switch, in the center is a screw holding the switch there. Unscrew that. Take the switch off.

You will see a tiny hole in the switch and a tiny hole in the hole where the switch came off of. That is where the gas flows.

Take something thin like a good wire or MAYBE a coat hanger and poke through the holes to clear it out. (may be just right, or too thick) Don't force anything.

The petcock is alumninum I think. I know it won't rust for sure. With this in mind, it is best that maybe you can soak the whole thing in brake cleaner or carb cleaner. Either works fine. Soak it for like 10 minutes.

Then rinse it off well... And here's the important part- use an air compressor and force air through the danged thing. If you don't have an air compressor you can use your mouth, put the clean & assembled petcock to your mouth (you can keep the screw holding the switch on the petcock off at this point)

As you blow, alternate between on and off. When on, you should have air flow. If there is no air flow, then you need to redo everything and make sure you have cleaned everything completely.

It's been awhile, since I took mine apart, but I believe there is a screen between the bolt on top that hooks to the tank and the petcock. You have to remove the bolt to access it. It'd be a good idea to do this. Clean the screen.

After that, don't put the petcock on yet. This is only 50% of the problem. The other 50% is the gas tank. You can buy a gas tank cleaner kit. There is a name for it, but it doesn't come to mind at this time. (There's a mention of it on this site) It eats rust and gunk and leaves your tank shiny clean.

If you can't find this thing, buy engine brite (engine cleaner) from pepboys or autozone. Spray this stuff inside the tank and leave it there for a good hour, rinse. Then repeat this 3 or 4 times, having it soak for an hour each time and rinse out each time.

If you have a wire brush, MAKE SURE THE DANGED bristles ARE GOING TO STAY ON THE BRUSH. Otherwise, you may be stuck with brush bristles in the tank. Brush the inside of the tank the best you can. Then rinse out.

After you have rinsed the gas tank out by water, then put in about 1/2 tank worth of gas and shake the thing (at this point, the tank has to be removed from the moped) And let the gas out. Then put in a 1/2 cup of Yamalube in the tank and shake it around. Make sure it coats all the walls in there. It will help protect your tank from rust and kind of coat it.

KEEP YOUR TANK FULL as much you can. It stops rust.

Then put the whole thing back on and the petcock as well and youre all set.

If you don't really want to do the gas tank thing, you can skip it. But the petcock will keep getting stuck (if you have rust or gunk in the tank) In this case, just keep taking it off, clean it, put it back on.

Another thing I would recommend to make the QT 50 run nice and keep the carb clean- splice in a lawnmower filter. They are about 2 or 3 bucks at a local hardware store/small engine repair store.

Best of luck to you.

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