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Post by scoot305 on Oct 11, 2010 6:26:36 GMT -5
:banghead:
I have a XMC Expresso 49cc. It runs great. Lately I've noticed an oil leak coming from my air filter box. I opened the air box up and take out the, now saturated, air filter and I can see that the oil is coming through the carb. Any suggestions on how to stop the leakage? I currently have just under 1000 miles.
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Post by 90GTVert on Oct 11, 2010 7:25:51 GMT -5
 It sounds like your oil injection system is allowing oil to flow into the carb when it shouldn't be. The oil pump shouldn't be letting oil by when it isn't running. I'd pull the oil injection hose off of the carburetor and watch it for a bit or put it in a container to see if oil is dripping out when it isn't running. If so, you either have a bad oil pump or a bad check valve (npt all scoots have the check valve, I've never seen one myself). Just make sure you reinstall the hose before you try to start the scooter. |
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Post by tomcas on Oct 11, 2010 8:07:43 GMT -5
I'd pull the oil injection hose off of the carburetor and watch it for a bit or put it in a container to see if oil is dripping out when it isn't running. I don't think this is a valid test and I would expect oil leaking out to be perfectly normal in this instance where it is disconnected from the check valve. In fact it's the check valve's job to prevent this from happening. The check valve does more then preventing air back into the oil line. It has a cracking pressure that is greater than the pressure caused by the head (elevation difference) between the oil tank fill level and carb injection point. These check valves have been known to leak especially on cheap Chinese bikes. They can be removed, cleaned, and re-peened if done carefully. I can post instructions if needed. |
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Post by 2strokd on Oct 11, 2010 8:22:35 GMT -5
A little oil might be normal, but if it continues to leak more than say 1/2oz. or so then im with Vert on that one....
If it will free-flow into the carb it will leak into the filter or into the intake.
Nothing is in the carb to stop the oil from doing so.
EDIT: Not on any of the carbs i have seen so far anyway.
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Post by tomcas on Oct 11, 2010 8:57:17 GMT -5
Here's the check valve location.  |
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Post by 90GTVert on Oct 11, 2010 9:08:09 GMT -5
I thought the check valve was supposed to be somewhere inline. I really don't know. Please excuse my ignorance, I remove the oil injection on all of my two strokes so I really haven't messed with it much. If you have instructions, please post. We can always use more info!
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Post by 2strokd on Oct 11, 2010 9:59:27 GMT -5
Ok, I just learned something too!
Please excuse me also, i didnt know that was
a check valve in there! Thanks
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Post by scoot305 on Oct 12, 2010 6:11:49 GMT -5
tomcas: Just PM'ed You
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Post by Fox on Oct 12, 2010 10:15:25 GMT -5
Here's the check valve location. This makes no sense to me. A check valve only allows flow in one direction. In this case the direction of flow would be INTO the carb. The check valve (if there is one) would be there to keep air from getting into the line I would think. It would not stop the oil from flowing into the carb. I think what's happening is the oil pressure in the oil tank is pushing oil through the oil injector and it's flowing INTO the carb and out of the air box so I think Brent's suggested test is spot-on for determining that. Pull the oil line and leave it off for an hour and see what comes out of there. Put a glass jar or something there to catch the drippings. If oil is constantly flowing out then I would reason that the oil injector is worn out. I don't trust injectors myself. I have a perfectly good one on my scooter but I disconnected it and pre-mix the fuel/oil so I never have to worry about it failing. |
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Post by 2strokd on Oct 12, 2010 10:59:43 GMT -5
Thats true Fox and Brent. If the oil would just flow on in we wouldnt even need oil pumps huh? Now i want to go see the check valve in one of stock carburetors  . I remove the oil injection too. I still have it on my DD Kymco but i dont like it. Seems to waste allot of oil compared to premix. Big ole cloud when i take off after the first start of the day :stars: . I will remove it this winter more than likely. |
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Post by tomcas on Oct 14, 2010 19:27:47 GMT -5
Here's the check valve location. This makes no sense to me. A check valve only allows flow in one direction. In this case the direction of flow would be INTO the carb. The check valve (if there is one) would be there to keep air from getting into the line I would think. It would not stop the oil from flowing into the carb. I think what's happening is the oil pressure in the oil tank is pushing oil through the oil injector and it's flowing INTO the carb and out of the air box so I think Brent's suggested test is spot-on for determining that. Pull the oil line and leave it off for an hour and see what comes out of there. Put a glass jar or something there to catch the drippings. If oil is constantly flowing out then I would reason that the oil injector is worn out. I don't trust injectors myself. I have a perfectly good one on my scooter but I disconnected it and pre-mix the fuel/oil so I never have to worry about it failing. OK, I'll say it again. Check valves, ALL check valves, while preventing flow in one direction still have a CRACKING pressure in the normal flow direction. This means flow will not begin in the normal flow direction until the cracking pressure has been exceeded. These particular check valves have a ball bearing and a spring. The ball makes a metal-to-metal seal and is pushed into this seal by a compression spring. The preload force of the spring pushing the ball against the effective area of the seal is such that flow will not begin until approximately 3 psi. While the oil injection pump can easily exceed this pressure in operation there by allowing oil to flow into the carb unabated, once the bike is shut off the flow ceases. This is because the only pressure remaining is the pressure caused by the weight of the oil itself. The pressure caused by the weight is called static head and is determined by the difference in vertical distance between the top surface of oil in the tank and the exit point, i.e. the check valve. Typically this is about a foot, which translates into about 2 psi based on the specific gravity of the oil. As you might imagine, the higher the oil level in the tank the greater the pressure trying to crack open the valve and the greater the propensity for bypass leakage. In other words keeping the oil tank level low MAY stop the valve from leaking but the best fix is to fix a faulty of leaky valve in the first place. |
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Post by tomcas on Oct 14, 2010 19:34:45 GMT -5
Thats true Fox and Brent. If the oil would just flow on in we wouldnt even need oil pumps huh? The injector pump CONTROLS the flow in proportion to engine speed. A gravity feed drip MIGHT crudely work but the results would be wasteful and potentially damaging. The flow would vary wildly with temperature, oil viscosity, and the level of oil in the tank. That why you have an injector pump and along with it a check valve. |
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Post by Fox on Oct 14, 2010 20:18:44 GMT -5
Thats true Fox and Brent. If the oil would just flow on in we wouldnt even need oil pumps huh? The injector pump CONTROLS the flow in proportion to engine speed. A gravity feed drip MIGHT crudely work but the results would be wasteful and potentially damaging. The flow would vary wildly with temperature, oil viscosity, and the level of oil in the tank. That why you have an injector pump and along with it a check valve. Errrm... I think 2strokd was being sarcastic. I'll say it again. Premix is better. No oil tank, oil pump, check valve, oil lines or any of that stuff to concern yourself with. Just mix the gas and oil in a can, fill the gas tank and drive it like you stole it. If you are anything like me a full tank lasts a couple of weeks sometimes.  |
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Post by tomcas on Oct 14, 2010 20:59:26 GMT -5
Scoot305 posted a PM to me with the following question: “Thanks for responding. Could you give me instructions on puling and cleaning the check valve? Also, I took it to a scooter mechanic, and he said the oil mixture was too high. He adjusted some rod that looked like a brake cable. He tightened the part so less oil will flow. I don't think that is a good think since it still leaks. “ My response was: There are two types of injector pumps, fixed and variable. The fixed pump outputs a fixed displacement of oil per engine revolution. The variable pump has a control that varies the output based on the throttle setting. Basically the throttle cable coming from the twist grip splits into two cables, one going to the carb and the other going to the oil injector pump control cam. When you increase the throttle the pump control cam is rotated which in turn effectively increases the amount of oil going into the carb. What your mechanic did was adjust the synchronization between the two. Here is an example of the procedure- tinyurl.com/oilpumpcontrolcablesettingtinyurl.com/zipoilpumpsettingAnd how it's typically verified to be correct. www.etonamerica.com/PDF/WP0024.pdfI wouldn’t second guess your mechanic and I suggest you wait and see the effect of his adjustment before pulling out your check valve since the valve may be fine and if you are not extremely careful you can damage it. If after a few days you still have problems then I suggest you remove the air cleaner from the bike so that you can see down inside the carb. Shine a light down inside the carb throat and open the throttle to raise the slide. You should be able to see the small hole on the side of the throttle bore from which the oil is injected. When you shut the bike off there will be hardly a trace of oil coming from this hole. Let the bike sit for a day of two and re-inspect for traces of oil. If you see a stream of oil leading out of the hole then your valve is leaking. That’s the only point at which I would attempt a repair. |
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Post by tomcas on Oct 14, 2010 21:07:29 GMT -5
The injector pump CONTROLS the flow in proportion to engine speed. A gravity feed drip MIGHT crudely work but the results would be wasteful and potentially damaging. The flow would vary wildly with temperature, oil viscosity, and the level of oil in the tank. That why you have an injector pump and along with it a check valve. Errrm... I think 2strokd was being sarcastic. I'll say it again. Premix is better. No oil tank, oil pump, check valve, oil lines or any of that stuff to concern yourself with. Just mix the gas and oil in a can, fill the gas tank and drive it like you stole it. If you are anything like me a full tank lasts a couple of weeks sometimes. Oops, sorry. There is absolutely nothing wrong with using premix. Hell, I've even used both premix and injection simultaneously. Using premix gives you the assurance that a failure of the injection system won't leave you with a destroyed engine. On the other hand premix can be a slight pain to use, it uses slightly more oil, and lending your bike out for a weekend could be catastrophic if the user forgets to refill with premix. In the end it all comes down to personal preference. |
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