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Thread: Need help .which predator is best.

  1. #1

    Need help .which predator is best.

    My class is going to these from the harbor freight blues. We can remove gov, and any air, and exhaust, red plate. Carbs have to be stock jet change only.so what predator would be best. Hemi or non.any help is greatly needed. We are new at this.

  2. #2
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    I would run the non hemi engine. The head flows better in stock form and they can sometimes have better carbs. If above changes are all that is allowed.

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    I agree, get you a non hemi predator, a good pipe like the SEK advantage 3 or 4, good air filter adapter and a good blueprinted carb, advance the timing to 28-32* if allowed as well. .038 main jet, .028 pilot jet and tune from there

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    With a red plate get you a .880 pipe sek makes one as well as rapp. Timing 36-38 with .38-.39 main and .28-.30 low speed jet. If get a blue printed carb then get it for your build and they will jet it properly for you. I would also run a cl1I or cl2 cam if no tech on it.

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    My kart came with a brand new shop-prepared non-hemi box stock Predator which was strong from Day 1. Put aftermarket air filter and pipe/muffler on, re-jetted and it holds its own in any clone or stock appearing class. Stock rod gave up after about 5 races @ 6700 rpm but the replacement motor is hanging in there just fine. I have a hemi too and really just don't like it as much.

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    Quote Originally Posted by mike97760 View Post
    My kart came with a brand new shop-prepared non-hemi box stock Predator which was strong from Day 1. Put aftermarket air filter and pipe/muffler on, re-jetted and it holds its own in any clone or stock appearing class. Stock rod gave up after about 5 races @ 6700 rpm but the replacement motor is hanging in there just fine. I have a hemi too and really just don't like it as much.
    Put the non hemi head on your hemi Mike, and the non hemi head gasket, and you'll start to love that hemi, trust me. I don't care much for the hemi heads either honestly

  7. #7
    4 Cycle Advanced User DynoDon's Avatar
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    I doubt it was the fault of the rod that gave out after 5 races on your shop prepared engine. Something caused the rod to go and it wasn't 6700 unless the shop prepared engine wasn't done correctly. I turn my stock rod 6700 week in/week out and have never blown a rod.
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    Don when I disassembled the remains of the motor first thing I noticed was the rod bolts weren't very tight. Do they stretch?

  9. #9
    4 Cycle Advanced User DynoDon's Avatar
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    Not in 5 races. They weren't torqued properly.
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    Checking the torque on the rod after failure generally would not be accurate.

  11. #11
    4 Cycle Advanced User DynoDon's Avatar
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    Nine out of ten times when a rod breaks and the rod cap is still attached, the timing slipped at high rpm. If the rod lays in the bottom in pieces, including the rod cap, the engine was lacking oil and the rod seized on the crank creating so much heat and resistance that it disintegrates.
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  12. #12
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    Don I have never seen the timing slip in these engines cause contact that would break a rod, unless you are talking about cam timing slipping, by maybe the crank gear moving? If ignition timing slips that's not going to affect valve timing to cause piston to valve interference, or am I thinking of this wrong?

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    4 Cycle Advanced User DynoDon's Avatar
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    If someone had the flywheel off and put it back on without a key the flywheel can move if not torqued properly. Then you will break a rod and other things.
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    4 Cycle Advanced User DynoDon's Avatar
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    Now that I think about it, I guess it would be illegal to remove the key and advance the flywheel on a stock predator. Although, one could rewind the coil for an advanced timing and the only way to find it would be with a lite
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    I'm still not seeing how the flywheel slipping breaks a rod Don....ive had flywheels slip time alot and it just shuts off the engine 90% of the time, not letting it restart. The flywheel timing only controls the spark timing, at least that is how I have always looked at it. The valve timing does not change when the flywheel slips time....

  16. #16
    4 Cycle Advanced User DynoDon's Avatar
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    Fire that piston at the wrong time at high rpm and see what happens.
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    Quote Originally Posted by DynoDon View Post
    Fire that piston at the wrong time at high rpm and see what happens.
    Bingo!

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    I have had that happened but never broken a rod because of it, did not know you could break one that way so I guess I've just been lucky. I had one engine that slipped time several times in a row before I finally got to looking closer and found a burr on the flywheel taper that was causing it to not seat properly....got rid of the burr, lapped it good without the key that time and used red loctite to lock it down and never had a problem after that. Guess you learn something new everyday

  19. #19
    4 Cycle Advanced User DynoDon's Avatar
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    Most of the time a flywheel will slip at a low speed and the engine will simply shut down and nothing hurt. When damage takes place it is usually when lifting for a corner and then getting back to the throttle. This is where the wheel will slip and a big explosion will take place
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  20. #20
    I lap my flywheels and get away without using a key.
    Never had a slip but some of that could be luck and light flywheels.

  21. #21
    4 Cycle Advanced User DynoDon's Avatar
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    No luck. Just paying attention to detail
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  22. #22
    Quote Originally Posted by DynoDon View Post
    No luck. Just paying attention to detail
    Its all a game of numbers game, paying attention to detail tilts the table in your favour.
    By the numbers you should spend about as much time in checks and service as you do in actual run time.
    Something is always trying to come loose and fail.
    If these engines were designed to be reliable and produce this kind of power they would 3 times larger and spin less than half as fast.

    But agreed luck good or bad is a factor we try to mitigate with best practices.

  23. #23
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    what you mean rewind the coil

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    Quote Originally Posted by kartboy63 View Post
    what you mean rewind the coil
    You can wind /build your own coils sometime you have to look to 60yo books to find out how... making it "look stock" might be an issue... but... i have "observed" a rev limiter wired into the on/off switch I assume for those who are running a "5500 rpm" on the stand rule... I did not ask the use...

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