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  1. #1

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    How much 'POP' is there in a pop off?

    I'm checking the pop off pressure on my 02 GPR's carbs.

    I'm using the 1.5 needle and seat with the 95 gram springs.

    I'm using a home built deal with a pressure regulator. I'm keeping the needle valve wet with WD40.

    My question is specifically this: As I increase the pressure, I start to hear leaking past the needle at a little over 40 psi. If I increase the pressure past that point, more air comes out but the needle never 'pops' off. I tried snipping a quarter turn at a time out the springs, and the pressure where the air starts to leak past the needle is down in the 30 psi range now.

    Is that leaking air the pop off or should the needle literally 'pop' out the seat and stay there until the pressure goes back below a certain point? If I crank the pressure up to around 60 or so psi and then touch the lever arm it'll pop off like I was expecting and then if I turn the pressure down with the regulator, at between 43 or 45 psi the needle will fully seat again and 'pop' back in it's resting position. Is the point at which it pops close my pop off pressure?


  2. #2
    Moderator OsideBill's Avatar
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    once the air started leaking you lost your seal. cutting the springs was the wrong thing to do as you lowered your gram force of the spring thus lowering the pop off pressure.
    There should be no air leaking and you get a clean pop when the valve opens. you have to open the valve and allow the wd-40 to get in behind it, there is no thing as too much wd-40

  3. #3
    Yamaha artisan Cutlass's Avatar
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    right about 35 seconds into this video is a clean POP during a pop off test. It'll spray WD40 everywhere so watch you eyes.



    And at about 14 or 15 seconds into this video


  4. #4

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    Quote Originally Posted by OsideBill View Post
    once the air started leaking you lost your seal.

    cutting the springs was the wrong thing to do as you lowered your gram force of the spring thus lowering the pop off pressure.

    There should be no air leaking and you get a clean pop when the valve opens. you have to open the valve and allow the wd-40 to get in behind it, there is no thing as too much wd-40


    Bill, I've worked on hundreds of carburetors on ATVs and motorcycles. I'm just not familiar too much with the spring/needle set-up on these carbs.

    I only cut one spring on one carb. I know enough to stop when I've FUBARed one spring and not mess with the rest 'till I got some more info. The reason I cut the spring is because several other sources did it that way, including this one: http://www.hydrotoys.com/gpr/tuners/...orAssembly.pdf

    I know to keep a needle valve wet and I have the carbs loaded with plenty of WD40. The question I needed answered in my e-mail to you the other day is the one I highlighted in my first post in this topic. My experience on other types of carbs was telling me that the leaking past the needle was not what I should have seen, I just needed someone with more knowledge with this particular type of carb to confirm it. Now I have to figure out why the needle valve's aren't popping off on their own until I crank the pressure way up to around 60 psi. I've double checked the seats and the springs and the seats are 1.5s and the springs look like they're supposed and be 95 grams springs.

  5. #5
    Moderator OsideBill's Avatar
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    The easy way to tell a 95 gram spring is they are wound the opposite direction of the other springs. So if you have the stock springs that came out look what direction they are wound the 95 will be opposite.

  6. #6
    nunnink23's Avatar
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    Quote Originally Posted by Sayre View Post
    I'm checking the pop off pressure on my 02 GPR's carbs.

    I'm using the 1.5 needle and seat with the 95 gram springs.

    I'm using a home built deal with a pressure regulator. I'm keeping the needle valve wet with WD40.

    My question is specifically this: As I increase the pressure, I start to hear leaking past the needle at a little over 40 psi. If I increase the pressure past that point, more air comes out but the needle never 'pops' off. I tried snipping a quarter turn at a time out the springs, and the pressure where the air starts to leak past the needle is down in the 30 psi range now.

    Is that leaking air the pop off or should the needle literally 'pop' out the seat and stay there until the pressure goes back below a certain point? If I crank the pressure up to around 60 or so psi and then touch the lever arm it'll pop off like I was expecting and then if I turn the pressure down with the regulator, at between 43 or 45 psi the needle will fully seat again and 'pop' back in it's resting position. Is the point at which it pops close my pop off pressure?
    Did you ever figure out your problem? It is very similar to the issue I am having getting my new n/s sealing. In fact the exact same issue. I might just let it go since others have had the same problem. After seeing this thread I really was curious if you solved it, or decided to run it.

    I know my N/S is new, clean, and wet, so there is no obvious reason as to why it wont seal properly. Sometimes it pops, sometimes it leaks. Regardless im still curious to see if you solved it.

    Hope you had good luck!

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