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Couple questions after pressure test on low hour EG295

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So long story short I have all the sudden been dealing with a handling idle / decel surge on my bike in the last 3-4 rides. It never did it last year after I bought the bike. It was a fresh build that the previous owner never got to ride so everything was new. I tried 4 different pilot jets thinking it was related to that until I started reading that it was probably an air leak. So yesterday I finally got to pressure test it and want to make sure I'm correctly diagnosing what I found. At first when I set it up with the freeze plug in the exhaust port and the gauge/ air valve setup in the reed boot, there was air coming out of the Power Valve breather hose on the left side of the bike. So I assumed that I just need to plug that up to properly test. Am I wrong about that? It didn't hold any pressure at all until I plugged that up.

Then after that was plugged up, after pumping up to 6-7 psi, it moderately dropped after just 15-20 seconds, so I pulled the power valve linkage cover off and sure enough there was air leaking from the power valve shaft seal and some oil had been seeping through, I assume from the last few rides. 

So my question is, did I properly test and find the air leak that is affecting why I have no use of the air screw adjustment with 4 different size pilot jets and is there also an air leak related to the side where the breather hose is?

Edited by Scott_72

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I've never done a pressure test. But since you got no answers, I have two ideas.

Maybe replace the base gasket and the left side crank seal. Perhaps quicker than pressure testing.  Then test ride and idle the motor and if the problem persists.

You'd have to seal both the PV left side hose and the seal on the PV shaft right side. The alum wear on the shaft right side is a weakness in the YZ250 motor. The little seal can only cope with so much free play.  Some people get a custom brass bush pressed into the alum for the steel shaft to bear on. Works great.

Just to do your test, maybe try some silicone sealant on the shaft+seal. Brake clean the oil away first. Just a thought, for your test. The sealant will break away with normal use.

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Yes, it sounds like you did the pressure test correct.  You have to plug the PV breather prior to doing the test.  One of the main causes of air leaks is the crank seal, but I would not replace those until you can determine that is another source of leak.  It sounds like you've already found a leak, and like numroe said, you can easily replace the PV shaft and oil seal and retest.  Keep us updated.

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On 5/1/2017 at 8:16 AM, Scott_72 said:

after pumping up to 6-7 psi, it moderately dropped after just 15-20 seconds

Define moderately. 1 psi? 3 psi? A bad leak doesn't let you pump to 6 psi. A bad leak quickly drops from whatever pressure you got it to, to nothing.

Put the piston at bottom and pump again to 6 psi and spray soapy water around the base gasket and reed cage. It will bubble from a leak.

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It dropped 3-4 psi in about a minute after trying a couple times. Once I pulled the PV linkage cover off I heard the air hissing out and there was oil dripping through.

Wasn't sure about the left side crank seal since I have a flywheel on this bike. Sound like i need to pull that off and spray soapy water in there as well as trying the base gasket? I already sprayed around the reed cage and base gasket but I can definitely try again after sealing up the power valve shaft seal. 

 

Does this look ok as far as the inside of the power valve housing is concerned? Going to clean it up but I think it looks ok. Second opinion appreciated.

IMG_0543.JPG

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Does this look ok as far as the inside of the power valve housing is concerned? Going to clean it up but I think it looks ok. Second opinion appreciated.


You have a screw loose.

On the right side of the secondary linkage base as you look at it.

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When I pressure tested mine I spent a ton of time getting the PV cover and linkage arm sealed in order to get a good reading on the rest of the motor. I ended up having to use a combo of gasket and Yamabond on the PV cover to get it to stop leaking.

Had a ton of leaks around the reed cage to address.

Got to the point where the only leaks I could find were in my actual pressure testing rig. I had a leak between 2 brass fittings that would not go away. Gas pipe tape didn't help stop those leaks, but the leakage was slow enough and no visible bubbling anywhere on the motor that I felt good about it.

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1 hour ago, TN Dirt Rider said:

When I pressure tested mine I spent a ton of time getting the PV cover and linkage arm sealed in order to get a good reading on the rest of the motor. I ended up having to use a combo of gasket and Yamabond on the PV cover to get it to stop leaking.

Had a ton of leaks around the reed cage to address.

Got to the point where the only leaks I could find were in my actual pressure testing rig. I had a leak between 2 brass fittings that would not go away. Gas pipe tape didn't help stop those leaks, but the leakage was slow enough and no visible bubbling anywhere on the motor that I felt good about it.

When you say PV cover do you mean the one on the front of the cylinder or the one on the side that covers the linkage arm?

The gasket setup on the right side cover is pretty lacking in my opinion so I could see how using some Yamabond would help.

9 hours ago, Kinger317 said:

 


You have a screw loose.

On the right side of the secondary linkage base as you look at it.

 

I think that was just the fuzziness of the photo making it look like it. All the bolts in there are snug and sound after double checking.

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3 minutes ago, Scott_72 said:

When you say PV cover do you mean the one on the front of the cylinder or the one on the side that covers the linkage arm?

The gasket setup on the right side cover is pretty lacking in my opinion so I could see how using some Yamabond would help.

The front cover.  Mine would leak at multiple places around the cover and around several of the bolt heads.  The only way to get mine to seal up was Yamabond, which is a pain in the butt when you want to take it over.

On the side, all I had to do was put some heavy grease where the shaft comes out to keep that from leaking.  I doubt you could ever get that right side cover to not leak.

The good news is that none of that leaking around the PV stuff matters when the bike is running, but you do have to address it to get a good pressure test.

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So essentially even after going through the PV system I still most likely have an air leak somewhere else affecting my original hanging idle issue? Just trying to cover all the bases here before I try and ride it again.

 

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1 hour ago, Scott_72 said:

So essentially even after going through the PV system I still most likely have an air leak somewhere else affecting my original hanging idle issue? Just trying to cover all the bases here before I try and ride it again.

 

Well, the PV is vented through the vent hose on the left side of the motor, so that area is not air tight and not the source of an air leak causing your hanging idle (my opinion).

I did my pressure test after a motor rebuild, and found one leak at a cylinder stud and numerous in the reed cage/intake area.  If you look at the reed cage design, there is only one gasket that sits between the cylinder and a reed plate.  There is no gasket between the reed plate and the cage, and the cage and the carb joint.  I ended up buying an extra gasket (maybe 2...can't remember) and I put one between the reed plate and the cage.  May have put one between the cage and the carb joint but I'm not 100% on that.  Regardless, doing that eliminated the leaks around the reed cage for me.  The intake area would be the first place I would look for leaks....

That being said, you can't do any of that until you get the PV area sealed off and air tight.

Edited by TN Dirt Rider
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As TN said, none of the PV related leaks have any impact on the motor when running. Just need to be sealed to do the test.  Obvious when you think about the simple 2 stroke.   The trouble sealing things is also why I said it's probably easier to just replace the base (and reed) gaskets and left side crank seal and go ride the bike again.

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I decided to do a pressure test last night since my cab was off and it held pressure pretty good until it got to 35 or 40 psi and then it just wouldn't hold pressure at all. Now it will only go to about 10 psi max, even with the big compressor I can only get it to go up to about 15 psi. I noticed oil coming out pretty bad from the countershaft sprocket? Figured I was doing something wrong like not plugging the PV vent tube or something because I could hear a lot of air.
It's a little late for April fools but I just couldn't resist! Sorry guys it's been one of those days. I hate doing pressure tests and no I didn't just blow all the seals out of my bike! As Gary would say carry-on

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So essentially even after going through the PV system I still most likely have an air leak somewhere else affecting my original hanging idle issue? Just trying to cover all the bases here before I try and ride it again.

 

I found grease works good to seal all the PV related things like shaft seal, even gasket if need be. I would try that before I squirted yamabond all over everything. As long as you're at it follow through but I am with numeroe on this, it's a pain. I just make sure my intake is all sealed up good and replace crank seals when suspect. Two times I had a hanging idle, once I raise the needle and it straightened out. Another time it was a crank seal. Good luck

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I have some Belray waterproof grease I can try using on that seal. Waiting for a new seal to show up but I can test it again before then just to see.

I need to pull my flywheel weight and fly wheel to check if the left crank seal leaks, correct?

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Only if you were losing pressure and you can't find it anywhere else. Look at the simplest things first solve any leaks you see and hopefully you don't have to go to deep.

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I have some Belray waterproof grease I can try using on that seal. Waiting for a new seal to show up but I can test it again before then just to see.
I need to pull my flywheel weight and fly wheel to check if the left crank seal leaks, correct?


I used Belray on mine and it worked fine.

And yes, FWW and fly wheel need to come off. I would pull the stator off too since I spray soapy water to check for leaks.

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I used Belray on mine and it worked fine.

And yes, FWW and fly wheel need to come off. I would pull the stator off too since I spray soapy water to check for leaks.


Thanks for the tips.
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So I am getting air immediately out of the main power valve area. Is this normal to expect when leak testing? As soon as I pump even 2-3 psi i can hear it coming through where the valve moves. I honestly just have no clue how sealed it is supposed to be.

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Totally sealed. Else you cannot do the test. 

I wonder if you could have replaced the base and reed gaskets and the left side crank seal, in 1/10th the time you've spent trying to pressure test?

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