DaBinChe
One of Us

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       Posts: 983 Location: BayArea Gender:
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Post subject: Re: **OFFICIAL PC20 Tuning/Problems thread** Posted: Mon Jun 27, 2011 11:05 pm |
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racerx wrote: DaBinChe wrote: Not sure if it has been address and I'm not gonna look thru 30+ pages, but the PC20 will never work well in all conditions with a 50cc.
Two reasons: 1) 50cc is very sensitive to minute changes/irregularities. Basically the smaller the motor the more sensitive and the larger the motor the more forgiving/less sensitive.
2) PC20 has an intrinsic design flaw that can't be changed...kinda like Micheal Jackson wanting to be white but can't. The intake and venturi is just not smooth, too much turbulence. What does this mean?..is that it doesn't mix well with number 1 above.
Best thing to do is go with a PE20. This carb is SO much better. You'll be kicking yourself for why you wasted so much time with the PC. And also use a real Keihin not a chinese copy, big difference in performance too.
So what to do about your PC20? sell it to the next sucker or put in in a larger cc motor. Have you used the PE20? I actually have a chance to sell my PC20 kit to somebody who is paying me to build them a Met! I am reproducing an engine just like mine (as far as mods go) so I should be able to bolt it on his without too much additional tuning. Do you know a good supplier for a PE20 kit and do they use the same jets? BTW, I found out the hard way that everything you mentioned in #1 and #2 couldn't be more true.  Yes I love my PE20 it is almost bolt on and forget it. Used it on many different motors: 2stroke, 4stroke, scooters,mopeds, dirt bikes, up to 150cc and it worked for all of them with some tuning. I use it in conjunction with a Uni two stage filter. Battlescooter has them for $99. Also add that the PC20 could be used in a larger displacement, what it was design for, like a 150cc. Many dirt bikes use this carb and it works fine.
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racerx
Dirty Sanchez


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  Posts: 2093 Location: ATL, GA Gender:
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Post subject: Re: **OFFICIAL PC20 Tuning/Problems thread** Posted: Wed Jul 13, 2011 8:23 am |
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I took some time to ponder the situation last night and thought to myself, "Self, if it is only running when choked and continues to run when choked, then maybe the problem is not that it's not getting enough gas, maybe it's getting TOO MUCH air". So I decided to remove carb and manifold to check for a possible vacum leak. It had to be getting air from somewhere to continue running when air supply was restricted via choke. Sure enough, as I start to loosen the 2 bolts that attach the carb to manifold it becomes obvious that the threads in the carb on one bolt have come apart and I get a metal spiral from one that looks similar to a thread insert! I put a 10mm nut on the backside of both bolts, eliminating the need for the cheap ass threads in the carb and sure enough, she starts right up and with a little a/f mixture and idle adjustment, I take her for a spin! My conclusion: I should have never purchases a Sheng Way, should have went with a brand new Keihin. I have a Keihin PE20 on my Met now so at least I shouldn't have to go through this crap again.
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michikuda
Junior Mint


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 Posts: 126 Location: Shytown Gender:
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Post subject: Re: **OFFICIAL PC20 Tuning/Problems thread** Posted: Mon Aug 08, 2011 4:27 pm |
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racerx wrote: KilLtImDeAd wrote: big bore motor/ performance cam/jc flywheel sheig way 38sj/88mj two brothers exhaust polini with stock rollers
fast take off,no bogs,but the exhaust pops alot from wot to close and also some around 30mph.... will the fuel/air ratio rid the pop Not for me. I've had it under decell since installing PC20. It does it with my PE20 also. I don't know that this is correct, but I've just grown used to it. I know I don't have an exhaust leak and plug is not rich or lean. I believe the exhaust pops mean you're running rich, sir.
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michikuda
Junior Mint


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 Posts: 126 Location: Shytown Gender:
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Post subject: Re: **OFFICIAL PC20 Tuning/Problems thread** Posted: Wed Aug 10, 2011 8:22 am |
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Fiffa wrote: These carbs will always pop on decel. Completely normal as long as it's not popping during accel.  ^^Truth^^ ....okay, so I wasn't spot on. lol Found this explanation for anybody else concerned... http://forum.motorcycle-usa.com/default.aspx?f=18&m=398516....which, for the people too lazy to click on, says: "So, the popping you are hearing is not back-firing. It is a popping resonating sound generated by a lean condition on decel. When you suddenly close the throttle, the incoming air is choked off and the closed throttle also causes the bike to return to idle on the very lean idle circuit of the carb(s). However, momentum of the bike is actually "driving" the engine in a sense, and that engine is still spinning at rpm that needs far more gas than the closed throttle/carb can provide. The engine is still spinning but the incoming fuel rate is very low, until just enough builds up in the combustion chamber to "fire" on the exhaust stroke of the engine."
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