Yamaha QT50 Premix or Oil Pump?

This is my first moped restoration, so lots to learn. Took a QT50 out of storage. Hasn't run in at least 25 years. Have a few parts of the restoration completed so far, but I'm stuck on what to do with fuel/oil. I've seen a few posts that advocate for either using oil pump or premix, but would like to get a few more opinions about how to proceed. There was still oil in the tank but there is evidence of significant leakage on rear fender, engine, frame, etc.. I'm not sure how much repair is needed to oil pump, lines yet.

1. What are the advantages of premix or using oil pump? Threads seem to lean toward premix, which sounds simpler in some ways.

2. What do I need to do if I go premix? How do I cap off oil line, or what parts can I remove?

3. Is it worth converting oil tank into a reserve gas tank if I go with premix? I've seen a post or two on that, but not sure if the juice is worth the squeeze.




Re: Yamaha QT50 Premix or Oil Pump?

Japanese oil pumps are pretty much bulletproof.

I've been running my original FA50 oil pump for almost 12 years , without a single problem .

I like the convenience of filling my oil tank a couple of times a year , rather than having to mix oil with every tank of gas . That really seems like an added pain . Having to carry oil and a measuring cup ...

But , I guess you have to have something to do while you pump a half-gallon of gas . ;)

Re: Yamaha QT50 Premix or Oil Pump?

Jason Majernik /

Agree with PD. These pumps are very simple. There’s the huge convenience factor he mentions, and it’s there, why not use it? Sure it can fail, just like everything thing else on a 40 year old bike. I think if you’re going to push the fuel ratios (bigger carb, bigger cylinder), it might make more sense to delete, because now, you’re out of factory spec. If it’s stockish, I’d use it. They’re cool to top it all off.

Re: Yamaha QT50 Premix or Oil Pump?

The answer to your question hinges on what the end result of the noped is to be. Keeping it all stock? Keep the pump. Kitting, pipe and other performance mods or upgrades then ditch the pump.

The Japanese pumps on hondas, suzukis and yamahas are indeed bullet proof but they all err on the rich side of injecting oil (More oil than what is really needed). With more oil comes more heat and carbon deposits (not good on a modded motor). Also, a performance motor will tune better with premix being more precise.

Re: Yamaha QT50 Premix or Oil Pump?

I run premix on my QT50’s. I don’t have a lot of modifications. One is just the airbox removed. The reason I run premix is because of the improved 2-stroke oil today. It doesn’t need as much oil as back in the day. To much oil and it runs lean. For example, I have a 1985 Honda FL350 that says on the tank to mix 20:1, if I run that much oil I’m going to blow a piston and at $150 a piston, that gets expensive. I run between 35-40:1. Just my 2 cents.

Re: Yamaha QT50 Premix or Oil Pump?

I have 9+, only thing I've had go bad with the pump is it is set too high stock and if the seal leaks you have to drain the carb if it you don't run it for a while. Never had one "fail". Still have my first QT50 running the stock pump with a YT60cc jug and head, MLM exhaust. Still running and pump is still a bit too high. I got it in 1993 btw.

Re: Yamaha QT50 Premix or Oil Pump?

I would keep the pump, I have not read my service manual in a while, but I believe you can adjust the amount of oil it provides.

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