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  1. #1
    gone fishing sucks2bu's Avatar
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    185 psi what octane ? ? ?

    Fresh build,
    1100 bored to 84.5mm
    billet o-ringed head
    compression is 185 psi.
    squish (no clue).
    ported engine
    stock exhaust



    I had 3/4 tank of 93 with 40:1 premix already in ski.
    Today on way to lake I stopped to put gas and topped of the tank with 87 octane

    I was cruising at 3500 and doing throttle chops to tune my carbs , (without seat on). As soon as I would go over 3500 I would start to hear the pinging start. I put my head as close as I could to engine while still looking at my tiny tach. Just a hair over 3500 it would begin. I took plugs out several times at partial throttle and saw no sign of peppering on the ceramic of plug.

    I decided to leave full throttle tuning off till I figure out this
    Issue.

    Do u think I could get away with straight 93 or should I start using 100?


  2. #2
    What do your plugs read? Don't use 87. 185psi is high. Can you thicken the head gasket a bit for now? Post your carb configuration also.
    Last edited by ZeroClient; 12-30-2013 at 07:18 AM.

  3. #3
    gone fishing sucks2bu's Avatar
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    Plugs at 3500 rpm throttle chops are chocolate brown, no contamination of any kind on the porcelain.

    Triple 44mm mikunis with ocean pro fa

    I can't thicken head gasket as the head is o-ringed and uses no conventional gasket.

  4. #4
    gone fishing sucks2bu's Avatar
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    As for not using 87, yeahhhhh i kinda f'd up and brain farted on that one.

    think I'm going to just add some 100 or 110 octane to compensate for the 87 and tune for top end once I burn through that tank full.

  5. #5
    Did you add in premix when you added the 87 octane? You only indicated a top-off of fuel in your first post. Always add oil when you add fuel no matter the octane. I cant tell you if you need 100 octane but you've gotta be close to needing it.

    Put the stock airbox back in place of the F/As while you are locating the troubles.

    What low jets are you running? Post your carb configuration.

  6. #6
    Does it ping if you are at 75% or 100% choke?

  7. #7
    gone fishing sucks2bu's Avatar
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    Yes I added oil to the mix. If I remember correctly it was roughly 6 gallons of fuel so I put in 18 ounces yamalube. That should roughly be 40:1

    I don't remember the jet sizes or pop off at the moment. But carbs were re jetted and running perfect on 93 and 185psi before i went bigger. It's not running lean just pinging.

  8. #8
    But carbs were re jetted and running perfect on 93 and 185psi before i went bigger.

    Went bigger?? What do you mean

  9. #9
    gone fishing sucks2bu's Avatar
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    Ok let me try n fix what I wrote.. engine was running perfect at 165psi and 82mm bore. Carbs were re jetted bigger for that combo. Ran great on 93 octane, hit 68mph on phone gps. Front bearing on rod number one took a dump and bearing material went through engine. Had to go bigger. Bore cleaned up nice once 84.5mm was reached.

    Now I'm starting to re tune it and am hearing pinging at 3500 rpm. It had 93 octane from before but I topped it off with 6 gallons of 87. Stupid me.

    There is no choke on this engine. It's running primers.

  10. #10
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    When you went that much bigger on the bore I am sure you needed your heads re machined to match. Adding that much to the bore without re cutting your heads not only increased compression, but I am sure your squish band is all out of whack.

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