QT 50 Oil injector troubles

Hello all! Thanks to everyone who posts to this forum, this is probably the best place to get good moped maintenance info that I've ever found.

I have a question about the Yamaha QT-50 oil injector. I have a QT-50 that leaks oil all over the place whenever the oil tank is filled. It's done this ever since I bought it (a few weeks ago). Having gotten the engine running pretty well (using premixed gas & oil in the tank), I'm now turning my attention to fixing this little problem so I can go back to straight gas.

For one thing, I'm not entirely sure I understand how the mechanism in the oil injector works. My best guess is that it controls the amount of oil based both on throttle position and on actual engine RPMs. Is that right? Until I understand how it works a little better, I'm not terribly inclined to start taking it apart.

Second, I have no idea how to tune the oil pump. (Sadly, I have no access to a service manual) There are two screws I can see on mine which look like they may be for adjusting the oil mix. I think they're adjustment screws because they're both currently "out" several turns. Does anyone know what the function of these screws is? Or, is it possible that one (or both) of them is just a screw holding the pump together which has come loose? I'm suspicious because neither of them seems to be pressing against any kind of internal or external spring, like the idle adjustment screws on the carb.

Lastly, though the space is kind of cramped, I think I can see a screw-hole with no screw in it, at the bottom-right of the injector assembly (looking at it from the rear of the bike). If I'm missing one of the screws for the housing, I'd be willing to bet that that's the cause of my oil leak.

So... anybody got any info about the oil pump on the QT-50 that they'd like to share? Anybody got any better theories about what may be causing mine to leak?

Thanks a lot, and keep up the good work!

Re: QT 50 Oil injector troubles

the QT50 isnt a moped so you won't find much help here. go to the dealer and spend asome money for the manual. or plug it up and premix gas.

Re: QT 50 Oil injector troubles

I have to arguew with the other guy who posted... there is plenty of QT 50 help on this board... 50cc motor is a 50cc motor... and the size of the QT50 hardly qualitfies it as a motorcycle, I call mine that only because it defined that way in the State law... Well on second thought, how about we agree that its a mini bike... :)

Oil pump... Follow the throttle cable from the handle grip to the carb. Along the way you will see a 'junction box' and then a second cable running to the oil pump. in that section there should be a couple adjusting nuts. This adjusts how much oil is pumped at any given throttle position. There is one large nut, about an inch long, a smaller normal looking nut. back the end of the cable out of the large nut, and then tighten the small nut to the large one to set the position. My cable end is about 1/4" from the smaller set nut. Look at the right side (outboard) of the oil pump. You should see a phillips screw, at or near a < looking part of the ring nuts on the pump. THis phillips screw is supposed to line up at the < when the throttle is released. I set mine a litte leaned than that, with the screw about a 1/8" under the <, as I have some trouble with the motor apparently flooding out at random times. (or how it acts anyway)

hope that helps. There was some dude selling copies of the maint. manual on this board once; I got one last year try searching the board...

Re: QT 50 Oil injector troubles

david f martin /

Hi Reed,

I don't have my QT anymore, but I still have the manual...

Before you do anything else, clean your engine up with some degreaser, and then try to figure out exactly where the oil is coming from.

The manual mentions a bleeder screw, but doesn't point it out. I would guess that the bleeder screw is in the line somewhere between the oil pump and the carb.

There are several adjustments to the oil pump, one of which requires a dial indicator. If you have one of these tools, I'll give you the specs. Otherwise, don't try to make any adjustments. Best to premix until you can make repairs and adjustments properly with the right tools...

Let me know if I can help.


PS: Andrew, please don't say the QT isn't a moped. You might upset Wayne.

Re: QT 50 Oil injector troubles

Bryan and david, thanks to you both for the info!

I don't have a dial indicator, so you're probably right that I'm best to premix until I can get it tuned properly using the right tools. The inconvenience of premixing is nothing compared to the "inconvenience" of a having it seize on me!

The problem I've been having in locating the leak is that the oil just seems to emerge from underneath the bottom half of the white plastic housing that is around the injector pump. So, despite my best efforts to clean the engine up, I can't quite pinpoint the source of the leak. I'll go back and see whether I can't take the lower half of that plastic box off, to try to get a better idea of where the leak is.

Thanks again for the info, and sorry for almost starting another "what is a moped" thread! :-)

Re: QT 50 Oil injector troubles

WHat type of gear oil that goes in a cimatti mopad its has oil misture but it has a plug on top of the motor i put a scrow driver in it and pulled it out and dthe oil was thin. So What type of oil do i need to go in it.

Thank you


Re: QT 50 Oil injector troubles

Sounds like your air bleed screw may be leaking or not tight. Take half of the plastic cover off, then you'll see a panhead screw on top, that's the bleed screw. See if it's tight. You could also have two problems. First, the delivery pipe that goes from pump to carb, may be clogged, try and clean it out. Second, that whole pump assembly simply slides out once you get to it. It uses nylon gears, sometimes those wear out. But if your simply loosing oil, I would suspect it's coming from that drain screw or something is just simple loose. Tighten everything and see if you can locate the source.

Re: QT 50 Oil injector troubles

I hate to differ, but in Iowa, my 49cc (the actual displacement) QT-50 is defined as a motorized bicycle, since the displacement and the max speed (under 30 mph) meets the definition. It requires a license plate, but doesn't require a motorcycle driver's license to operate. Also, it won't hurt a thing to eliminate the oil pump and premix. It's just a bit more trouble than the stock setup.


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