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I have a 2001 Xplorer 4x4 (250cc) that is normally very reliable but one day wouldn't start after sitting for a couple months. As it turned out, two stroke oil had leaked into the float bowl and displaced all the gasoline. I drained the oil from the bowl, turned the gas on, and it fired right up.

The service manual references a check valve in the oil line, but this one doesn't have a check valve. In fact, I can't even find a check valve in the parts diagrams. Is that oil check valve for the 400 only? What is supposed to keep the oil from leaking into the carb when it sits?

Thanks,
Phillip
 

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I just found a bit of information...apparently the 2000 model injected the oil into the intake port on the cylinder and that was where the check valve was supposed to go. My 2001 injects the oil into a nipple on the carb, so no check valve is used in this design. I haven't looked to see where the oil port on the carb goes, but would it go directly into the float bowl and mix there? What is supposed to stop the flow of oil?

Thanks,
Phillip
 

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It's not all that uncommon - I'm working on a 2009 Q-Link two stroke scooter that had the same problem.

There is a check valve either in the nipple on the carb or on the outlet of the oil pump - it is not serviceable or replaceable - it is there to prevent oil being pushed backwards in the system due to backfire or other positive pressure in the intake - It will bleed oil from the tank to the intake during periods of disuse especially if the oil in the tank is not injector approved oil or it is stored in a very warm location - the only way to prevent it from happening is to pinch the oil line off when in storage or run it regularly.
 

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Thanks for that @latebird . @Kentuckydiesel - I have the exact same ATV with the exact same problem. In fact, if it sits for one week, I have a tough time starting it, and it blows a ton of blue smoke for the first 30 minutes of riding. Good to know about that check valve... I could never find mine either and thought someone had removed it at some point. I use Polaris Blue oil, and still have this problem... so unfortunately no help there. The only thing I have been able to do to solve it is during long periods on non-use I pull that tube off of the nipple on the carb, slide it into another plastic tube, and pull it up to where it is higher than the tank and very obviously sticking out from under the seat. I had considered installing a little in-line valve, but decided it was a bit too dangerous. I will forget to turn it on or oil will get globbed up in there or something. One more note... Anecdotally, it seems to happen less if I leave the fuel to the carb turned on, rather than shutting it off. I dont know the mechanics of why that would be the case, but it just feels like it is a little easier to start when I do that.

Please post if you ever find a better solution - this is a great little ATV, and that is the one super-annoying thing about it.
 

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I had an idea today as I tried to sart my darned Xplorer... BTW I think the float bowl is full again after sitting for 2 weeks. :(.

What if you put in a longer tube from the discharge of the pump, and ran it up and over the gas tank, then down to the little nipple on the carb. Would that stop the flow, or just create a siphon that would ultimately cause the same problem? Another thought... If there were a check valve on the input of the little nipple on the carb, would the cracking pressure be enough to stop the flow of oil?
 

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It's an unknown to me - I have never had to investigate this issue after a two week lull in operation - I've only seen it in units that set unused for a year or more. It might be a new phenomena caused by a change in the nations fuel supply that I am not aware of?
 

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Ok - well that’s a bummer... I think I am going to try to stick a little spring actuated check valve in there with a 1-2 kpa cracking pressure. That should be about right if I think of the elevation of the oil Vs the elevation of the carb.

I have a couple of questions, though.

1) Is there anything special about an oil line check valve that I need to watch for? I am thinking this is a good choice: https://www.amazon.com/gp/aw/d/B072NZ7FBD/ref=ox_sc_act_image_1?smid=ADXDBR18SJ0FV&psc=1

2) how do I know if it is working? Can I run the thing with that oil line disconnected for a few minutes to see if oil actually makes it through the check valve?

Thanks again for your help @latebird - your expertise is incredible.
 

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I'm not sure it will work - the oil line from the pump to the carb is only about 2mm ID, but to answer #2, yes you can run the engine with the line disconnected for several minutes with no ill effect - the trick is to hold the pump wide open while the engine idles about every 3 to 5 seconds there will be a blurb of oil pumped out the line.
 

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Fixed! I cant believe I lived with that for 7 years before putting a $11 check valve in line.

Prior to fixing it, I pulled the tube off of the carb and stuck it in a little spray can lid. Here is how much I got in 24 hours:

140940



140941




So all I did was pull the line off of the carb, stick this little check valve in line, and add a 3" piece of tube to the output to connect it back to the carb. I let it sit for two days and zero oil drained through the newly installed check valve, so the cracking pressure seems to be enough to hold back the oil. Then I used your advice @latebird and held the oil pump valve wide open while it idled. The nice thing is that the tube I used is translucent, so I could see the oil pumping through the line. It took about 3 minutes of idling before it filled the entire line. Took it for a little ride down the street and it seems to be OK. Plenty of white smoke coming out of the tailpipe, and thankfully, the engine did not seize.

This is the check valve that I used:

And this is the finished product:

140942



Hope this helps!
 

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Congratulations (y)

The check valve on the carb is not a common problem - they are only damaged or fail due to improper carb service. I saw a novice mechanic do this; he didn't know the brass nipple was a check valve and proceeded to 'unclog' it only to find out oil would continue to flow when the engine was not running. He didn't know the oil pump was not positive and oil could seep through it when it was not running - he ended up replacing the carb as the check valve was not available separately and carbs were still available at the time. Kind of an expensive lesson, but one he would never forget.
 

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Facinating... I never knew the nipple was actually a check valve, and that explains a lot. Intiresting note - A few years ago, I was pulling that little tube off of the nipple in an attempt to keep the bowl from filling up while the machine sat, and the nipple fell off. I could never find the nipple again, so I bought a new (used) carb on Ebay. Thinking back on this, I think the problem may have gotten worse after I replaced he carb.
 

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I had one the nipple broke off of and the spring and bb fell out - I plugged the hole, removed the oil pump and premixed after that.

My first experience with the check valve in the oil injection system was on 1960's Kawasaki's - their check valve was a banjo fitting that the line attached to. I found out it was a check valve on a lG5 100cc - I had the line off - it was a banjo fitting on both ends and a soft piece of tubing going from one to another - the fittings were the same except one had a red band on it and the hose nipple was a little longer - I installed it backwards (red banded banjo on the oil pump instead of the engine) and it would not pump oil through the line (not clear, but translucent) - I took the line off and the pump pumped just fine - I then consulted the service manual and it prescribed the red banded check valve be installed on the engine. That was when I learned there was a check valve in the oil injection system.

Almost all oil injection systems have a check valve where the line attaches to the engine, cylinder, carburetor or carb holder. Some check valves are in the fitting and some are in the bolt holding the fitting.
 
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