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  1. #1

    A problem with popoff or jetting? Death at 4K

    So I've done a top end rebuild on an '01 SUV 1200, 65u non-pv. I had high hopes of finally seeing this thing running right. It was a disappointing day.

    Before the rebuild the carbs were rebuilt with mikuni kits and jetting set at Bill's recipe with pressurized mod. Pop-off pressure is around 52 with trimmed 115 springs and 1.5 n/s.

    I can maintain an idle and I can run if I jump to 1/2 throttle or more. If I try to run at 1/4 throttle, it slowly starts to drop RPM, *pop... pop pop... pop*, and will ultimately die if I held it long enough. If I run it for about 10 seconds at 1/2 throttle, I can drop down to 1/4 throttle and it will hold okay for about 4 or 5 seconds and feels like it runs out of excess gas and starts to cut out.

    I've been dealing with this symptom for quite awhile. I've already reduced pop off with a small trim of the spring. Am I just battling too small of a pilot jet? It's all so odd since Bill's carb recipe works for so many others. I'm at high altitude and the last thing I suspected was a lean condition. I talked to the power sports mechanics and they more often than not have to rejet lower here. The temp is also lower here and they said the cold water keeps the manifold pressure lower. A couple of opinions were that I was actually running rich, not lean, even though the symptoms sound lean.

    I have a video and sound recording....



    https://soundcloud.com/brad-boatrigh...in-at-3800-rpm
    Last edited by jhawker23; 09-10-2017 at 10:24 AM.


  2. #2
    boudin's Avatar
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    What are you running for the high/low adjustment screws? Checked all the jet sizes when rebuilding? What do the plugs look like? Everything is stock except the return mod? Any other mods? Compression is good?

    -Greg

  3. #3
    Quote Originally Posted by boudin View Post
    What are you running for the high/low adjustment screws? Checked all the jet sizes when rebuilding? What do the plugs look like? Everything is stock except the return mod? Any other mods? Compression is good?

    -Greg
    Thanks Greg. Here's more info...

    135 highs
    100 lows

    Low 1 1/2 out
    High 1 1/4 out

    Chokes removed
    Aftermarket F/A's
    Pre-mix 40:1

    I was having this exact issue even last year. In the process of troubleshooting this last year, I found low compression and a ring pin had banged up one of the pistons. The cylinders were just bored out with new pistons and rings with a little over an hour into the break-in. Compression is good at this elevation. They were all 95 but have been told multiple times the elevation (7,000') will reduce it by 15 - 20.

    The engine held pressure with the leakdown test. About 4 minutes from 8 to 7 and kept getting better from there.

    The plugs are pretty rich at idle, often slightly wet. I change out plugs every time I go out to test this thing so they're not fouled. On new plugs, I rode 1/2 throttle, around 5k rpms, for short bursts of 10 seconds. The plugs were white/ash and clearly lean. This is with all of the settings above and nothing adjusted.

    I am 99% positive its the elevation creating this problem. A recent suggestion was a popoff around 21 and another recommendation at 42. It's currently around 53.

    Then another question has bounced around about the 105 return mod and whether this is correctly sized because of elevation.

    Unfortunately I don't have any PWC dealers or mechanics around because this is snowmobile country. I wish I had an expert in this area to address the elevation.

  4. #4
    I'm not a carb nor Yamaha expert, but I run all my watercraft at 5000'. My waveblaster and sxr are both highly modified and running what they were set up for at sea level. My seadoo is jetted slightly leaner. We bring many watercraft up here from sea level, and they run perfectly acceptable. I would be suspect of your pop off, as well as cutting springs.

  5. #5
    Also, I have run a non pv gp1200 up here with stock jetting with no problems.

  6. #6
    Quote Originally Posted by Wire4Money View Post
    Also, I have run a non pv gp1200 up here with stock jetting with no problems.
    That's great to know! How about pop off? I've gotten different recommendations and I took it to 42 tonight.

  7. #7
    Quote Originally Posted by jhawker23 View Post
    That's great to know! How about pop off? I've gotten different recommendations and I took it to 42 tonight.
    I put a fresh top end in, pressure tested, cleaned carbs, set them to factory settings, and it was good to go. I remember being disappointed that it was only 1 mph faster than my seadoo.

  8. #8
    It had factory air box with choke. 100% stock.

  9. #9
    ncdoo's Avatar
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    When it starts to bog, try pulling the choke partially out. If it picks up speed, you're not getting enough fuel. If it continues to bog, you're getting too much fuel.

  10. #10
    boudin's Avatar
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    Aftermarket F/As should require a richer mixture. Did you change the jets to match the Oside Bill formula?

    http://www.greenhulk.net/forums/show...=1#post1951162


    -Greg

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