2-Stroke Oil in airbox ???

[antonyp]

Ok guys this will be a long one cause I'm trying to explain the problem in detail: My mean machine '94 KDX250 is giving me strange problems lately... Recently the engine started bogging a lot losing performance throughout the powerband until I noticed that the small intake tube which connects the carb with the reeds was severely cracked. That possibly meant that there was loss of pressure because it was sucking air from the cracks. Right ? At least that's how I would explain it! Well anyway, I took out the carb, the tube and the reeds, and I noticed a drop of 2-stroke oil near the air screw (inside the carb's mouth). I thought that was strange and then I checked the large-mouthed sort of tube piece that connects the carb with the lower side of the airbox and I noticed a paddle of 2-stroke oil UNDILUTED! No smell of petrol, just thick 2-stroke oil as if it was just poured there! I thought it was strange but then again I suspected the faulty intake tube was somehow at fault for this! Notice that my bike uses a separate 2-stroke oil tank so I thought that when the oil pump was sending oil in the tube which has a hole on the top for that, some oil could have been kicked back from the carb's mouth in the lower side of the airbox. I then repaired the intake tube with a thin layer of 3M epoxy for plastics and rubber and on top of that a nice thick layer of some special black rubbery glue which is used for installing the windshields on cars. The bike worked nowhere far from perfect for a couple of days and then it started giving me a similar problem, only smaller: Engine works fine at very low RPM from idle to just above idle and then when RMP get a little bit higher but still very far far from midrange the engine starts to bog again so I either have to change to a higher gear and ride like grandma to keep it running smooth or I have to rev it until it reaches a point where bogging kinda fades ... I check the airbox again and what do I see? Again the puddle of oil is there. I'm almost sure that is what is causing the bog. But my big question is, what is causing the puddle? :think:
Please help !

 

[23jayhawk]

If the bogging is from an air leak b/t carb and reed box, you may want to be careful of a lean seizure. You indicated the problem sorta went away for a few days, then came back. Perhaps the intake boot is again ventilated. :|

 

[2001yz250]

It's untelling what kind of garbage got sucked into your cylinder. :eek: I would be pulling it checking for damage.

 

[canyncarvr]

So it's understood you have an injected bike, right? And the injection nozzle is on the manifold that attaches to the cylinder, right?

For one I can give you some anecdotal input. I rode R5s and RDs for decades. They are injected street 2-strokes. It was not uncommon to see undiluted 2-stroke oil sitting in the intake throat of the carb.

So then, how does it get there?

Although it's iffy when you get to the thought process of, '..the only thing it can be is...' well, here 'ya go:

The oil isn't going to come from anyplace other than the injection nozzle. That means it has to be traveling BACKWARDS to get to the carb bell. Something's gotta be pushing it, and that would be the piston..past the reeds.

The reason for the puddling is that the oil is heavier than the 'other stuff' it's mixed with..air and fuel, so it tends to drop out.

Yeah, would be a good idea to check your top end for damage. An excellent chance of damage due to dirt and/or a lean condition.

Bet it's time to replace your reeds, too.

 

[23jayhawk]

carver, RD's were piston port, right? Was oil blow-back a sign of ring wear in those bikes?

Nothing like the sound of an RD350/400 with Denco chambers at full chat. :aj:

 

[Boot]

Sounds like you've got any airleaks well covered. If I were you I'd try to disconnect the oil pump and temporarily run a tank of premix (say, 32:1) to see if the problem goes away. Perhaps your oil pump has gone out of calibration or something.

I'm not surprised that you find the puddle upstream of the carby. There's all sorts of funky pressure waves that get going in an intake tract, even reverse airflows, and the heavy oil would be very likely to settle at the first low-velocity place it finds. Maybe it pools in front of the small airways in the carby bell mouth and interferes with the aeration and atomisation of the fuel.

My SR model has had the oil pump and tank removed. I don't know how this was done, but the hole into the clutch housing is blocked off. I run premix instead. I wish I could give you a hint on disconnecting the pump, but maybe if you search this forum you might find some previous posts on the subject.

Of course, the easiest test route would be to just run your oil pump dry, without oil in the reservoir, but I don't know if this would harm the pump (not unlikely).

Good luck.

 

[antonyp]

I don't think there is any problem with the top end cause I have recently rebuilt the KIPS which had a broken valve (a month or so ago) and when I checked the piston and cylinder they seemed to be ok! Ok, the piston needs replacing cause the bike is 8 years old and I don't think the Japanese guy who had it in Japan replaced it before it was imported here neither the guy who had it here before I got it. But anyway the bike was only used for street riding so it hasn't been run under harsh conditions. Also my reed valves seemed to be ok when I checked them so I am quite puzzled. Maybe I should check everything again but first I will clean the air boot from the oil puddle and let you guys know if the bog clears after that... Thank you all for your comments, stay tuned for the results... :silly:

 

[antonyp]

Ok guys! I've been working on the bike today. Took out the exhaust and had a quick look through the exhaust port at the piston and cylinder (partial look) they look as intact as they were a a month ago when I changed my broken exhaust valve. I started the bike without the exhaust on and checked if the exhaust valves were working properly and they are. Then I converted my KDX to a premix fuel bike by taking the oil tank out of the way, sealing the oil injection hole on top of the intake manifold with a screw and some rubber compound and finally connectin the injection tube to the oil-pump's intake tube thus forcing the oil pump to recycle the oil that is contained in the tube through itself in an endless loop so that it doesn't get damaged... After all that I just cleaned the puddle of oil in the air boot and while I was at it I also cleaned the filter and spark plug. (It is a BR9ES by the way. Isn't that too hot?)
Now I am running a premix of about 25:1 and I think for now the air screw is 1 and 1/2 turns out. The bog is gone now and the bike seems to be working ok but I am not sure its 100% yet. I have to take it off-road and do some power slides to see how it behaves. Thats when I notice any problems right away!
Another thing I have noticed today is that I might have a small leak of tranny oil in the magneto. I opened the cover and I found some oil on it. Not too much but I don't know how much that could affect the bike if it actually draws hot air from the magneto. How will I be sure if the engine really DOES suck hot air from there?
I took some pictures of the magneto cover, the traces of oil in the carb, the goo I had from the exhaust port from the excess oil that was going in the engine and also of the spark plug and oil-pump conversion. How can I post these online for you guys to have a look?
Anyways any other suggestions and/or help will be much appreciated...

 

[Rockey5000]

Originally posted by antonyp
After all that I just cleaned the puddle of oil in the air boot and while I was at it I also cleaned the filter and spark plug. (It is a BR9ES by the way. Isn't that too hot?)

Another thing I have noticed today is that I might have a small leak of tranny oil in the magneto. I opened the cover and I found some oil on it. Not too much but I don't know how much that could affect the bike if it actually draws hot air from the magneto. How will I be sure if the engine really DOES suck hot air from there?

A BR9ES should be fine
Spray starting fluid behind the magnento while the engine is running and if the engine revs up, you have a leak.
Good Luck

 

[Jaybird]

I'm kinda lazy and didn't read this whole thing, but I want to add this.
Many many times folks will have this "puddle" of oil in their airbox and wonder how it got there.....99 times out of 100 it is filter oil that has drained from an overly oiled filter. Overoiled filters can casue bad running as well. Just a thought that you may want to check on before you think of drastic airflow corrections.
When you oil your filter and think it is dry and ready to ride with, hang it over top of a peice of plastic overnight and see how much drains out. ;)