Page 1 of 2 1 2 LastLast
Results 1 to 10 of 14
  1. #1

    Join Date
    Jul 2010
    Location
    KC
    Posts
    478
    +1
    1

    Pop off test questions

    I am rebuilding a Yamaha SUV. I am done with the engine and are now rebuilding the carb. I did a pop off test on the three card and weird result came up. First I did the check valve test using the blow and suck test. All went well. (that's what she said)Then I did the diaphragm test. It hold more then 10 sec with 4lbs pressure. All well too.Then I did the needle valve test. It hold 10lbs of pressure for more then 30 sec. All well too.Then the problem began when I did the pop off test.The 1st one goes pop off at 72lbs...... Very high pressure....... Then after the pop off. The start leaking air though the need valve. Until the pressure go to around 50lbs.The 2nd and 3rd card also have problem. It doesn't pop off. It goes all the way up to around 70lbs then it start to leak air via the need valve. And stop around 45lbs of pressure.The spring is silver oneNow my questions. 1) I inspect the needles. Using a blade and there is no worn on the needle. What could have cause these weird results?2) i don't think the needle is worn but if it was, would 3 worn out the same time?3) if I need to get new needle valve , what size should I get? I want it to be original is it 1.5?4) What should be the pop off pressure for my type of ski? 43lbs?I want to rebuild everything to the factory stage. Please give me some advice. Thanks


  2. #2
    mudslanger's Avatar
    Join Date
    Jul 2010
    Location
    Huntsville Al
    Posts
    1,326
    +1
    49
    If no one has changed them you can find the size on the seat if you pull it out. make sure the arm on the lever is level with the carb when installed and not bent down. when you do the pop off test don't spray wd40 in the fuel line when doing the test but on the outside of the needle and seat so that the wd40 sits around the needle wile it is seated in the seat. make sure to use wd40 as it gives a good result. if you already tried it this way and still have high pop off pressure you may need to try a different gram spring.

  3. #3

    Join Date
    Aug 2006
    Location
    Indiana
    Posts
    1,274
    +1
    81
    The stock boats have a super high pop-off, and once they pop they will leak by after the pop, so you have to back the pressure clear off and start again to confirm your results. I cut 1 1/2 coils off each of the stock spring to get pop-off down to around 62 lbs. You also can "tune" the pop-off to equalize them by small adjustments to the arm.

  4. #4

    Join Date
    Jul 2010
    Location
    KC
    Posts
    478
    +1
    1
    Quote Originally Posted by LT1GMC View Post
    The stock boats have a super high pop-off, and once they pop they will leak by after the pop, so you have to back the pressure clear off and start again to confirm your results. I cut 1 1/2 coils off each of the stock spring to get pop-off down to around 62 lbs. You also can "tune" the pop-off to equalize them by small adjustments to the arm.
    I am getting more confuse now. I thought the stock pop off should be around 42lbs?. According to the chart. BTW my n/s is the stock 1.2. With I silver spring, what is the pop off pressure should be. I just want to return everything stock spec.

  5. #5
    Adam's Avatar
    Join Date
    Aug 2005
    Location
    Australia
    Posts
    276
    +1
    12
    Check the carb rebuilding post by Osidebill, he covers all these topics very well ! I have found a 1.5 needle and seat to work well as it lowers the pop off pressure a small amount . The low speed mixture can then be tuned with the low speed screws . You will find this Carb rebuild post in Old School section for Yamaha's.
    Last edited by Adam; 03-17-2012 at 03:19 AM. Reason: more information added

  6. #6

    Join Date
    Jul 2010
    Location
    KC
    Posts
    478
    +1
    1
    I read that post, what i am confuse is that why change the pop off pressure? If the stock is 62 lbs then shouldn't 62 lbs be the pressure we want to get?

  7. #7
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Location
    Madison, WI, USA
    Posts
    2,500
    +1
    55
    The Mikuni SBN manual describes pop-off pressure fairly well. Check it out here:
    http://www.mikuni.com/pdf/sbn_manual.pdf

  8. #8

    Join Date
    Jul 2010
    Location
    KC
    Posts
    478
    +1
    1
    Quote Originally Posted by Cutlass View Post
    The Mikuni SBN manual describes pop-off pressure fairly well. Check it out here:
    http://www.mikuni.com/pdf/sbn_manual.pdf
    Thanks for the PDF. So what it is saying in short is that the stock flame arresstor has restrictive air intake thus needed a high pop off. Since I am not changing the flame arresstor, I need to keep the high pop off right? It is about 62-65 lbs right now. And it doesn't pop. It just hisses and stop when the pressure drop be to 60lbs pressure. The middle one is a little lower which stop at 57 lbs.

  9. #9
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Location
    Madison, WI, USA
    Posts
    2,500
    +1
    55
    Correct. Stock flame arrestor= stock pop-off is ok. I'm not sure what the stock pop off is but as long as you use the stock NS and stock springs and all 3 are pretty close to equal (say within 3 psi...not actually sure what the acceptable range is) then you should be ok.
    My pop-off didn't line up nicely with the Mikuni NS vs. spring chart but all 3 were close to each other and it turned out ok.

  10. #10

    Join Date
    Jul 2010
    Location
    KC
    Posts
    478
    +1
    1
    Cool man thanks for the info.

Page 1 of 2 1 2 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. 99 slth 700 red engine pop off test
    By 250super in forum Polaris Open Discussion
    Replies: 0
    Last Post: 06-05-2012, 04:01 PM
  2. pop off adjustment question
    By paul c in forum Yamaha PWC Performance (2-stroke)
    Replies: 2
    Last Post: 09-12-2009, 08:55 AM
  3. Can Pop-Off test be done w/carbs still in ski?
    By mrtinker in forum Yamaha PWC Performance (2-stroke)
    Replies: 2
    Last Post: 02-26-2009, 04:19 PM
  4. pop off testing
    By sunshine_n_pc in forum Yamaha PWC Performance (2-stroke)
    Replies: 9
    Last Post: 08-20-2008, 08:30 PM
  5. Pop-off testing
    By big83bronco in forum Yamaha PWC Performance (2-stroke)
    Replies: 4
    Last Post: 08-18-2006, 10:01 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •