Hi,

Recently, I've been noticing after leaving the bike for a few weeks that the oil level has been dropping in the oil injection pump tank. This doesn't correspond to a rise in the gearbox oil level (or a change in gearbox oil colour), so it's not the usual seal dropping on the pump drive shaft (I've fixed this already). What I have noticed is that on startup one of the cylinders smokes a lot more than the other and it takes a few seconds for both cylinders to fire. This leads me to think that oil is slowly leaking in to one of the cylinders.

Someone suggested that on old two strokes with oil injection pumps there is a check valve that can malfunction, allowing oil in to the cylinders. Could this be what is happening? I did look at the parts fiche and didn't see a check valve as such. Are there seals that are serviceable in the pump that could need replacing?

Thanks guys
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MC21 Honda NSR250. TYGA 300 conversion.

Not something I've ever personally seen on an NSR. They often smoke more on one cylinder when cold, even when in A1 condition though.

While not of any technical assistance, if the pump is properly adjusted and you are still concerned with its apparent irregular performance, I would suggest replacing it with a known good one. There are no serviceable parts in the oil pump.

Although it doesn't help your situation, I will say that while I have heard [very few] claims of dead NSR250 2T pumps, in my 25 years of NSR experience I've never personally seen one fail.
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Andy.
NSR-WORLD.COM

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Thanks for the reply. Took the fairing off today to see what I could find and it turns out it's an external leak. Probably due to old hoses and/or insufficient clamps. Found blue Castrol all over the engine under the injector pump.

Also took the front spark plug out and turned the motor over and no oil came out. That's a relief. So it appears that my fears were unfounded and the oil isn't leaking into the cylinders.

The hose from the oil tank to the oil pump is still available 55107KV3830
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Why do things simply when you can complicate them

It's one of the smaller hoses that appears to be leaking slowly/weeping. Not the main hose from the big oil tank.
55113-KV3-830 - Tube Breather vinyl. Might be the one. Not sure if I can just use some generic hose or can get the original Honda part.

That was quite hard to find the fiche for the oil tank. It's under "Real Cowl, Glove box".

Might be some of the other smaller hoses around the area leaking too...very difficult to read the fiche for some things can be quite small! Not absolutely sure I got the right part no.

You can zoom in on these images
https://www.cmsnl.com/honda-nsr250r7-1990-l-japan_model49620/partslist/0113.html#.XAeWUWB2s0M
If you know the internal diameter, any fuel/oil grade hose will be ok
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Why do things simply when you can complicate them