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Thread: 4150 idle and hard starting problem.

  1. #11

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    The shafts touch the stops and I did replace the original the metering block because the previous owner had screwed in the power valve at an angle and messed up the threads. So last night I took the original metering block and cleaned up the threads and screwed in a new 6.5 power valve and put in a size 69 jets. It still starts hard and runs a little rough when cold. When warmed up I adjusted the idle screws at 1.5 turns out and vacuum is 17 at 800 RPM and 20 at 1400 RPM and the needle is steady and the idle returns and doesn't hang. It does backfire a little when revved up and diesels when I shut off the engine. I did replace the vacuum advance a while ago.

  2. #12
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    Jan 2010
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    Brisbane, Australia
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    You're a bit closer, but some further tuning is necessary.
    I think you'll need an anti-diesel solenoid to give a more reliable engine shutoff.
    Are you using the choke for cold start?
    What pump cam on the primary, and hole position?
    What pump nozzle? Gary
    Last edited by Gaz64; 07-29-2020 at 11:26 PM.
    Regards, Gary

  3. #13

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    I am using the choke. The cam is pink and I'm using the #1 hole position and the nozzle is a size 35.

  4. #14
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    Jan 2010
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    Have you stepped it up to 35?
    Pink cams are slow high volume cams.
    I'd buy a set of accelerator pump cams and try one that has a bit more early lift, in the first 40°.
    Even a baby 18cc white cam has more in the first 1/4 of throttle travel.
    You might find an orange or green more suitable. Gary
    Regards, Gary

  5. #15

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    I did step up to 35s and tried the orange & green cams and still same thing; slow acceleration is fine, but quick acceleration it bogs & backfires.

  6. #16
    Join Date
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    A bog is a lean condition, more common will double pumper. A backfire is a lean condition and possibly ignition system related, timing, crossfire, etc.
    I have an 850 on smaller engine than yours. You need to invest in the right carb for your engine and driving style.
    If you have an automatic transmission, your carb has to be sized accordingly against the convertor stall speed. Gary
    Last edited by Gaz64; 08-02-2020 at 07:59 PM.
    Regards, Gary

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