Home Forums Shifter Karts CR125 checking for air leaks…

This topic contains 5 replies, has 4 voices, and was last updated by  Brad Alan 8 months, 3 weeks ago.

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    Brad Alan


    I’m looking for a bit of advice regarding testing for air leaks on a CR125.  First, I plugged the intake boot and exhaust manifold.  I put a spark plug in it, move it to TDC, then pumped about 4.5 lbs of pressure in the engine via the pulse line port for the fuel pump (I hope that’s an appropriate way to pressurize the motor).  All I had was the pump I use to set the pop-off pressure in our yamaha carbs… I thought that it would work just fine to pressurize the CR125 via the pulse line port.

    Two questions:

    1. Is that the appropriate way (or an appropriate way to check for leaks)?

    2. I found a leak: it’s between the exhaust manifold and engine…  I’ve noticed that some people use this orange substance between the manifold and engine… I presume that this will fix the leak.  My question is, what is that orange substance?

    Thanks for your help.



    Glenn L Riggs

    The orange stuff is Hi temp rtv or silicone available at your auto parts store. and it gets over everything.



    James McMahon

    A leak at the exhaust manifold, while its not optimal, is not considered an air leak in the traditional sense. It will throw your test off though.
    How much is the pressure dropping after five mins?

    • This reply was modified 8 months, 4 weeks ago by  James McMahon.

    Brad Alan

    Thanks for the replies. I will get the silicone today at the auto parts store and retest.

    Since it was leaking when I did the test I can’t tell you how much it dropped off.  I will let you know when I do the test again.


    Sanford Mitz

    From what is sounds like, you are blocking the air at the pipe. Pull the pipe and put a plug in the exhaust manifold. You can get one at the hardware store. I use the rubber plug with a wing nut on it. Put it in the manifold and tighten it up. A stethoscope is good or a length of tubing for checking. You can also spray simple green on critical areas and look for bubbles. Check around the powervalve plugs. Those o rings are easily damaged when sliding the plugs in. Crank it up a little higher and then log the drop per minute.  You are definitely on the right track.


    Brad Alan

    Alright – So I got the high-temp silicone and put it b/t the manifold and cylinder and plug in the manifold again, and pressurized the engine up to 5.5psi.  I let it sit for 5 mins, came back.  Still at 5.5psi.  Looks like its all good!


    Thanks for all of your help.

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