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Thread: rocker arms

  1. #1
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    rocker arms

    Ok, so my little Predator runs far better than expected and really likes the rpms. It zinged right up to 7500 before I could get my foot out of it and it was still pulling. I have looked at the Champion rocker assembly and wondering what people think of it.

  2. #2
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    how much abuse will the stock rockers and pushrods take when running a black mamba jr cam? is the champion rocker assembly a good idea for this or go with reinforced rockers? or is it going to be fine and just let it eat? just wanting a few opinions here.

  3. #3
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    The champion rockers work well for what you are asking, alot of people are using them in open predators as well with alot more aggressive cams than the black mamba, myself included. Much better than reinforced rockers in my opinion, just a better quality product to begin with

  4. #4
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    never thought to ask, but are the stock rockers a 1.1 ratio?

  5. #5
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    Yes very close to 1:1, have seen them on both sides of 1:1

  6. #6
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    Pulled the kart out to make a couple of laps around the yard for fun yesterday and it was running terrible. It was had to start and kept kicking back. I pulled the valve cover and checked the lash. The intake was at .008 and exhaust was at .012. I'm thinking the champion rockers are going to be required if I zing it up again. Had the lash set originally at .003 which was what it called for, so I set it back to that. Started fine and ran great again. I'm guessing that the stock rockers can't handle a Black Mamba jr at 7500. I'm guessing that with the exhaust that far out, it wasn't hitting the compression release enough to pull easy, but why was it kicking back? It even backfired through the carb a few times.

  7. #7
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    Stock rockers will hold a black mamba at 8000rpm if you wanted, but how many races they last is the question, and how much spring pressure is used. With black mamba and 26lb springs you should have no problem getting a season out of the stock rockers. Anytime you set valve lash, rotate the engine over by hand several rotations then back to top dead center on the compression stroke, and double check them. Usually you will end up having to reset the lash at least once more after setting it the first time and spinning over the engine a few times. Set your lash as tight as you can get it while still letting the pushrods turn with your fingers when you try to turn them, with the engine at top dead center. Always set lash at top dead center on the compression stroke....another easy way is to watch the exhaust valve fully open, stop there and set the intake lash, then watch the intake valve fully open and stop there to set the exhaust lash, then rotate the engine over a few times and recheck, if it stays where you put it then you're good to go. Most run as close to zero lash as possible since valve lash does open up slightly when the engine is up to temperature, so you have to set them a little tigher when cold so they will be where you want them when its hot, because we don't race or ride with cold engines. Make sense?

  8. #8
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    As far as why it was hard to start, the excessive lash will make it hard to start because you are not getting the full amount of lift like you should, and likely aren't getting on the compression release enough with that much lash. Explains why it jerked back on you and backfired

  9. #9
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    I will go back tonight and reset the lash again. What is the best plug to use in that motor? it has an Autolite 3910x

  10. #10
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    I'm a fan of the autolight ap66... Its ur standard stile plug but I always liked it more then the 3910

  11. #11
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    Quote Originally Posted by Time Bomb Tom View Post
    I will go back tonight and reset the lash again. What is the best plug to use in that motor? it has an Autolite 3910x
    There is no best plug in my opinion. But, if you look in most of the top builders' engines, you'll see the same plug you are using now, simply for the reason that it takes up more space in the chamber...less cc's in the chamber equals more compression, even though its a very small amount and likely wont be a noticeable difference honestly

  12. #12
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    Quote Originally Posted by W5R View Post
    There is no best plug in my opinion. But, if you look in most of the top builders' engines, you'll see the same plug you are using now, simply for the reason that it takes up more space in the chamber...less cc's in the chamber equals more compression, even though its a very small amount and likely wont be a noticeable difference honestly
    I remember in two cycle racing, where if they could catch (like with a sharply pointed pick) a thread of the spark plug in the combustion chamber, it was the illegal.

    I personally can't see how any decrease in CC's this practice could get you could overcome the disadvantages of having that steel thing in the combustion chamber. Seems like you'd have to run rich to overcome all that heat. I can't help but think that would mess up your CHT readings too.

    I've always found it strange how people can try to save money by using the same spark plug all the time. I've been known to go through two or three spark plugs in the same day. And not because it was given me any problems at all, it's just that it's so important, and there's only one, I wanted it to be as good as it can be. I may have gone overboard, but in the scheme of things, it's just a small increase in expense.

  13. #13
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    Al, with a 2 stroke you are running oil/fuel mixture and will foul plugs more commonly and easily than with a 4 stroke that runs on pump gas, changing the plug a couple times or more in a raceday with a 2 stroke isnt uncommon at all. But with a mostly stock 4 stroke, it just is not needed unless the engine is set up to run so rich it fouls the plugs if it is allowed to idle very long, which is a common problem people run into with the clones because most set them up so rich on low end that they will foul plugs if they idle very long, especially with the 3910X Autolite plug, so it is common to change the plug several times a race day with the clones using that plug, even though some dont realize it and never change it. You can easily foul the plug on a 2 stroke just by trying to start it the wrong way, such as having the carb setup way too rich when you fire the engine up.

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