Zuma 50cc carb leaks oil after bowl fills with oil

[mikulskn]

I have a 50cc 2004 Yamaha Zuma YW50S.  It sat for a few months, and after pulling it out of storage, oil was dripping from the overflow tube on the bottom of the carburetor and there was quite a big mess on the floor.  Seems oil was coming from the oil reservoir thru oil pump and into the carb/bowl, and eventually started overflowing inside the bowl continually.  After monitoring it (without starting it after storage), there would be a drips coming from the carb overflow tube on bottom.  To me, this should not happen just from the moped sitting.

I pulled the oil feed tube off the carb, and sure enough, a few drops of oil would come out of the tube after observing it for a 1/2 day or so.  Even though there is gravity pressure on the oil from the oil reservoir, I would think the oil should not come out during sitting.  There is a oil pump in between the oil reservoir and carburetor, so I thought that maybe the oil pump was bad and was thinking the oil pump should not let oil thru while sitting.  So I bought a used oil pump and just connected it to the oil supply, and sure enough, oil comes thru the pump as well after sitting for a half day.

There is no check valve between oil reservoir (like I heard about on other threads on other types of mopeds).

See attached pic of oil pump and attached part diagrams of oil pump and oil reservoir.

I am wondering what is normal operation and expectation of the oil system and carb and while sitting for this Zuma.  Should oil be expected to flow thru the oil pump and into the carb (and then carb bowl) while sitting? 

I have subsequently cleaned the carb, and yes, the bowl was completely full of oil!  I have not put everything back together nor started it because I want to understand and fix this problem before putting everything back together.

[aeroxbud]

You will sometimes get a small amount of oil leak past the pump if not used for a while. Enough to make it smoke on start-up.
But it sounds like both of your pumps are bad. New after market pumps are not very expensive. Or perhaps do away with the pump altogether, and premix.

[pinkscoot]

Some carbs have an oil check valve on them. I'm not familiar with the carbs used on these scoots so perhaps that's where you failure is.

[snaker]

Not just a mess to worry about.
Those oil pumps in general do not like to self prime.
I'm not familiar with your pump but I suspect that phillips screw in your photo is the bleeder screw(#2 in parts breakdown)

Its possible that the oil is draining all the way through from the tank.
If not, there's a chance that air is getting into the pump which could lead to oil starvation.

[mikulskn]

pinkscoot, attached is a two pics, one showing my carb and the oil inlet. I am not sure if the oil inlet piece shown is a "check valve" or is just there to act as a male fitting for the hose. It does not look like it is removable/replaceable, and it is not on the parts diagram for the carb either as shown in attached pic. So I am wondering if anyone knows if that is a check-valve piece or not in this particular carb.

If it is a check-valve piece that has been press-fit into the carb and it is the cause of the problem, I am thinking I would just have to get a new carb.

Or like aeroxbud suggested above, just get a brand new after-market oil pump and see if that works first.

I am thinking of not going to pre-mix at this point.

[aeroxbud]

If you can blow through the oil inlet, it doesn't have a check valve. You should not be able to generate enough force to push it open.

[geoffh]

My2cents,the oil pump inlet on the carb is a press fit and should be left as is,the O E feed pipe is very small and a tight fit if it,s been replaced by a spurious one it may leak because it,s just to big,post a picture of your pipe,I would take the leap to pre mix it,s not difficult and I sleep better now I pre mix.

Geoff

[snaker]

Doubtful that it has a one way check valve causing the issue.
The direction of flow for the leak is the same as the direction of normal operation.

Systems I worked with relied on constriction, the line/fittings were sized so that a drop could be forced through by the pump but couldn't easily flow by gravity or siphoning.

If everything mechanical is ok and the proper parts, then you may want to consider a higher viscosity/different brand injection oil

[mikulskn]

I just received an after-market new oil pump, and installed it on the oil feed hose from the oil tank, still with the oil pump not installed back on the moped. So after 12 hours, there was significant oil going thru the oil pump just based on gravity. See attached two pics. This the now same experimental setup I have had on three oil pumps...my original, another used oil pump, and now the brand new after-market, and all had the same results.

So to me at this point, either there is a carb issue (not enough restriction on oil feed when just sitting) or maybe I just need to have higher viscosity of oil(as suggested by snaker above). However, I am not sure what injection oil would have a higher viscosity. I currently use Amsoil synthetic 2-stroke interceptor oil, see attached pic. If someone would recommend an oil I should try, I could switch out the oil and see if I get the same results as those noted above.

Or maybe I try a new after-market carb and see if that works.

[pinkscoot]

Just get one of these and put it in: www.amazon.com/gp/product/B0085D2I40/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1. It will stop the oil until the pump demands it.

[aeroxbud]

You really need to fit the pump to do that test. You have no resistance against the drive wheel. And the positioning and extra length of the pipe leaving the pump could make a difference.

[mikulskn]

pinkscoot, maybe I can just go with the spring check valve. Do you think the check valve would easily open as the pump pulses and pumps oil to overcome the spring? And push enough oil each stroke into the carb? I am just wondering if there is a chance the fuel mix could get a little starved with oil with the introduction of the spring check valve.

[pinkscoot]

I put that one on my TGB and it worked great. I premixed until I knew they oil was going in the engine. If you look at the size of the hose feeding the pump versus the hose to the carb there is plenty of capacity. DO NOT PUT IT IN BACKWARDS. There should be an arrow on it telling you the direction of flow. It helps off all of the lines are clear so that you can see the oil moving.

[mikulskn]

Thanks for all the input and ideas, so here is where I am at...

I took the carb off again, and did a another cleaning. As part of that, I closely inspected the oil inlet on the carb. I took a piece of wire (with insulation on) and softly poked it into the oil inlet of the carb. When it hits the fat part of the inlet, I just push a little harder and then let go. It definitely bounces back and it tells me there is a spring check valve there (very similar to the add-on spring check valve recommended by pinkscoot). There is a link below to a youtube video where I show my piece of wire bouncing back.

I cleaned the check valve rigorously with carb cleaner, thinking that maybe the check valve spring/ball was plugged a bit keeping it open. I reinstalled the oil pump as shown in attached photo and going to do some testing over a long period of time with the oil pump it its correct position as aeroxbud recommended above. I will first make sure oil comes out the tube end that fits on to the carb, and you can see in the attached photo of my first test position. Once oil comes out of the tube, I will then proceed to reinstall the carb without bowl, jets, float and without throttle slide. I will then attach the oil feed tube to the carb and see what happens over a period of days. I am hoping NO oil comes into the carb proving that now the spring check valve is now working. I will update this thread with any findings.

youtu.be/TrO36hNtsz0

[pinkscoot]

Excellent deductive work. Lets all hope for the best.