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Old 09-14-2009, 05:46 AM   #1
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Default OS Speed help

I am running Mugen 30% fuel and I have a lot of carbon build up on the top of the piston. It is really black. I know that I need to change the shimming on it, but I just can't remember which way I need to go. Can someone lend a hand? I did a search and couldn't find anything. Thanks.
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Old 09-14-2009, 05:58 AM   #2
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With time, no matter what your going to get that on the top of piston. You can usually wipe it clean with cleaner/rag.
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Old 09-14-2009, 06:04 AM   #3
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With time, no matter what your going to get that on the top of piston. You can usually wipe it clean with cleaner/rag.
So technically, how should it be shimmed? I am running two copper shims on it right now.
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Old 09-14-2009, 06:10 AM   #4
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have 2 speed wnginesand I run super clean no additives cold fusion 30%. The rest of the engine looks like it is still new but on the top of the piston there is some carbon. This is wher the boom happens so there will always be some blackening. I have cleaned it off on engines before but if the engine is running well and the bearings are good I leave it alone. If I have to tear it down then I'll clean the top of the piston off otherwise it's not a prob. With 30% you want to use the extra shim. It's as simple as that.
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Old 09-14-2009, 06:16 AM   #5
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have 2 speed wnginesand I run super clean no additives cold fusion 30%. The rest of the engine looks like it is still new but on the top of the piston there is some carbon. This is wher the boom happens so there will always be some blackening. I have cleaned it off on engines before but if the engine is running well and the bearings are good I leave it alone. If I have to tear it down then I'll clean the top of the piston off otherwise it's not a prob. With 30% you want to use the extra shim. It's as simple as that.
I understand that the boom happens here. I am just saying that it has a lot of carbon build up on there. I mean a lot. The piston is completely black. I have a VZ-B and that one is nearly not as black with more fuel on it. This is why I believe that the motor is not shimmed right. I can't read my manual because it is in Japanese. But a good rule is of thumb is .1mm of shim for every 10% of fuel. (i.e. 20%=.2mm shim, 30%=.3mm shim) Someone correct me if I am wrong. I only got about 4.5 gallons out of this last piston and sleeve, so I want this new one to last.
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Old 09-14-2009, 06:37 AM   #6
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Your probably just running too rich. Clean it up and reinstall the head button with just one copper and one silver shim only and lean it out some more. You can use a smaller restrictor to limit the power if needed.
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Old 09-14-2009, 07:05 AM   #7
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You are not seeing the silver shim that is stuck to the button.. stock the engine comes shimmed for 30% with one silver 0.008 shim and one copper 0.004 shim.. the extra shim that come in the box is just an extra.. if you run 20% pull the one copper 0.004 shim out and just run the silver 0.008 shim.
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Old 09-14-2009, 07:08 AM   #8
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I run one thin and one thick shim on my speeds 30% Byrons, and Clean my engines after every race weekend
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Old 09-14-2009, 07:13 AM   #9
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You are not seeing the silver shim that is stuck to the button.. stock the engine comes shimmed for 30% with one silver 0.008 shim and one copper 0.004 shim.. the extra shim that come in the box is just an extra.. if you run 20% pull the one copper 0.004 shim out and just run the silver 0.008 shim.
Sweet. Thanks for the help. This was what I was looking for.
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Old 09-14-2009, 07:53 AM   #10
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Sweet. Thanks for the help. This was what I was looking for.
no problem!
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