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.

Thanks!

John

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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.

Re: Yamaha QT50 Premix or Oil Pump?

Dan DiRenzo /

What did you do to keep tension on your throttle? Also what to do with the cable that used to run to the oil injector?

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Re: Yamaha QT50 Premix or Oil Pump?

I always run premix; stock oil pumps tend to be way too rich. Sure, excess carbon on head & piston and in the exhaust can be cleaned up, but who has time for that? I always have a few gallons of premix around for my bikes that didn't come with oil pumps anyway.

Re: Yamaha QT50 Premix or Oil Pump?

I kept the black junction box and just removed the oil pump cable. The throttle return gets a little weak but it works.

Re: Yamaha QT50 Premix or Oil Pump?

Dan DiRenzo /

I didn’t have a choice. My tank has a leak in the wall between the oil and gas. Can’t spot it but they’re mixing somehow.

Re: Yamaha QT50 Premix or Oil Pump?

After 40 some years, the cable gets gunked up. You can remove it and clean it by spraying carb cleaner, ever so often, in one end and moving the cable back and forth and this will help free it up. Also clean the throttle assembly on the handlebars.

Re: Yamaha QT50 Premix or Oil Pump?

Dan DiRenzo /

> Peter v. wrote:

> -------------------------------------------------------

> I kept the black junction box and just removed the oil pump cable. The

> throttle return gets a little weak but it works.

I tried this last night. Still no recoil. I wish I could get that oil injector to separate at the seam and mount it on top of my block plate but its not possible. I wonder if a new throttle cable that goes straight to the carb would help?

Re: Yamaha QT50 Premix or Oil Pump?

> Dan DiRenzo wrote:

> -------------------------------------------------------

> I wonder if a new throttle cable that goes

> straight to the carb would help?

It should. New cables are pretty much always better than 40 year old ones, and removing the splitter from the equation will result in less resistance.

Re: Yamaha QT50 Premix or Oil Pump?

If you like spending money, go for it. Clean it good and it’ll be fine, unless it’s frayed, which it doesn’t sound like it is.

Re: Yamaha QT50 Premix or Oil Pump?

If you are trying to stay as stock as possible keep the oil pump. If it’s been worked on or sat for awhile, remove the oil line from the carb side and run it with premix to make sure its working and getting oil to the carb before reconnecting. The blue QT I have is using the oil pump for years and no issues so far after breaking in the new top end. The red one currently working on I’m running a half tank of premix then reconnecting the oil pump.

Regarding oil leaking, just clean it well and see if there’s actually a leak. Put new oil lines on and clamp them down with zip ties.

If you wanted to delete the oil pump Treats sells a block off plate. Or someone mentioned in another thread you can remove the oil pump gear and keep it connected. Just cap the line at the carb and carb oil input.

Re: Yamaha QT50 Premix or Oil Pump?

Dan DiRenzo /

> S C wrote:

> -------------------------------------------------------

> If you are trying to stay as stock as possible keep the oil pump. If

> it’s been worked on or sat for awhile, remove the oil line from the carb

> side and run it with premix to make sure its working and getting oil to

> the carb before reconnecting. The blue QT I have is using the oil pump

> for years and no issues so far after breaking in the new top end. The

> red one currently working on I’m running a half tank of premix then

> reconnecting the oil pump.

>

> Regarding oil leaking, just clean it well and see if there’s actually a

> leak. Put new oil lines on and clamp them down with zip ties.

>

> If you wanted to delete the oil pump Treats sells a block off plate. Or

> someone mentioned in another thread you can remove the oil pump gear and

> keep it connected. Just cap the line at the carb and carb oil input.

Im actually really surprised at how clean/rust free I was able to get my tank. I plugged the petcock hole and shined some light inside and couldn't spot any holes/cracks but it definitely leaks somewhere. Im using clear gas line and the fuel is blue right from the petcock. Is it possible that its getting the oil up from the carb?.... Im probably going to pop the pump back in without the gear, vacuum cap the carb and run premix. All is stock except for a replacement carb (stock jets) and a MLM next level exhaust. Would you guys recommend 40:1 or 50:1? Also thinking about using some JB gas tank weld to fix the oil sensor to the tank. Its super loose.

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Re: Yamaha QT50 Premix or Oil Pump?

Yeah in your case probably best to either a) get a new tank or b) drain it out and triple rinse it. Then run premix in both oil and gas tank. Oil tank could be used as a reserve tank and tee into the other fuel line from the gas tank. Oil won’t be coming from carb to tank. It’s a very minimal amount from oil pump to carb and that doesn’t go out the fuel input on the carb.

Premix would be an easier and potentially cheaper option than a used tank. Just depends on price difference between used tank and new throttle cable direct to carb.

40:1 is what I’ve been running on this one I have for now until I hook the oil pump back up. I just bought a can of premix at Lowes to use and it works fine since I don’t plan on running premix.

Regarding loose oil sensor, some of the used tanks on ebay have them attached.

Re: Yamaha QT50 Premix or Oil Pump?

@dan - if you delete the oil pump you’ll probably also want to remove that oil sensor and plug the hole. Dash light will probably come on unless you connect those wires together from the oil sensor.

Re: Yamaha QT50 Premix or Oil Pump?

Dan DiRenzo /

> S C wrote:

> -------------------------------------------------------

> @dan - if you delete the oil pump you’ll probably also want to remove

> that oil sensor and plug the hole. Dash light will probably come on

> unless you connect those wires together from the oil sensor.

I’ve been looking for a good plug option actually. Any suggestions? I thought about a freeze plug but not sure how the rubber and metal would hold up after a while. Otherwise, I planned on disconnecting the electric and using some JB gas tank epoxy to hold the sensor in place.

Re: Yamaha QT50 Premix or Oil Pump?

Automotive freeze plug should be fine. People use those to cap off the oil pump too.

Re: Yamaha QT50 Premix or Oil Pump?

Can always pull the bulb like I did.

Re: Yamaha QT50 Premix or Oil Pump?

Late to the party but I thought a bit about your suspicion of a leak between the gas and oil tanks.

Maybe start with both empty, fill the gas tank to the very top with water/other, then either blow with your mouth, or fix up a weak vacuum in blowing mode, and blow to create pressure in the oil tank. Then look to see if the fluid in your gas tank bubbles.

If you don't see anything, and your vacuum complains loudly, you probably don't have a leak.

Jim

Re: Yamaha QT50 Premix or Oil Pump?

Dan DiRenzo /

Im just sticking with premix. I had the tank completely empty with lines set up to use the oil tank as a reserve. I filled just the gas side only with the reserve switch off and it started filling my reserve almost instantly. Now I just have a larger main tank I guess....Moving on to seals and a new stock piston and head kit this weekend. My "treats" should be arriving soon....

Re: Yamaha QT50 Premix or Oil Pump?

> Dan DiRenzo wrote:

> -------------------------------------------------------

> Im just sticking with premix. I had the tank completely empty with

> lines set up to use the oil tank as a reserve. I filled just the gas

> side only with the reserve switch off and it started filling my reserve

> almost instantly. Now I just have a larger main tank I guess....Moving

> on to seals and a new stock piston and head kit this weekend. My

> "treats" should be arriving soon....

If you ever want to return to stock configuration and usage , consider using a quality tank sealer like Caswell's or RedKote . Both will seal the holes between the tanks and last for a very long time ( maybe forever ) . ;)

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