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I probably need to replace my cylinder head, and if I'm going to do that amount of work I might as well install a big bore kit. And my thinking is that I don't want to lose any top end at all. I can hit 81mph at 10,000 rpm in 6th with my current gearing and tire choice, and that makes cruising at 75mph possible. 70 is the sweet spot with power left for passing. I don't want that to change, unless it's for the better.
I'd go straight to the 84mm 300cc kit if I knew there was a fuel controller capable of compensating for the leaned-out top end. I already toasted my valves once, I don't want a lean-ass mixture causing problems on down the line. I'm even considering a carb conversion. Charles. |
Gentlemen, I found on youtube a video in which a Russian guy installed 298cc cylinder with 84mm piston and 17mm pin, because he did not check with the seller whether the pin is 16mm and did it with bushings in the piston The Russian guy claims that the power at the bottom increased, but at the top decreased and the max speeddecressed too, what do you think about it I attach the video.https://www.youtube.com/watch?v=NCzlAf6fRFE&t=758s
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LZX200GY-2 ZS200GY zongshen 200cc dirt bike
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looking for gas fuel tank for my bike anyone help me
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There are other tuning options, I just hooked ECU hacker to my bike to read a code, looks like you can tune with that, although I haven't tried anything yet
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Is there a walkthrough somewhere for doing the big bore install? Specifically, I'm concerned with how to set the valve timing when putting the head back on. With no service manual there's just no information available anywhere. Charles. |
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There is an NC250 manual in Spudriders post here: http://www.chinariders.net/showthrea...t=nc250+manual The hardest part is getting the rings and wrist-pin in; I did it the hard way the first time and tried to push the cylinder down onto the piston assembled. It is much easier to put the rings on and push piston into the cylinder first. Then drop it over over the connecting rod end and put in the wrist-pin. The timing marks are easy to line up and the cam sprocket is marked well so it's just a matter of lining everything up. |
Perfect. That's great to know.
What are your thoughts on buying a new head from CSC and installing valves in it myself, vs buying one from AliExpress with the valves already installed? Charles. |
Since the motor is a Zongshen exclusive, I would imagine China is protecting the intellectual property of a Chinese company within their borders... I've not heard of these being ripped off, but if you want to have recourse if there's a problem, it would be better to go through CSC. I've had problems with aliexpress customer service after the fact, and depending on the price difference, it might not be worth the gamble of something damaged in transit, for example.
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China...intellectual property...LOL!!!
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They protect what they perceive as their own, even if they don't care about anyone else's.
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I know, I've seen a case of them going after the ORIGINATOR because they thought the Chinese ripoff should be protected. He brought manufacturing back to the US pretty quickly.
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What's wrong with the current head? I've bought the AliExpress head and it seems like the same quality. (YMMV!) |
The exhaust valves won't stay adjusted for even 500 miles now. Either bad metallurgy in the existing head or valves, or I burned the valves and potentially damaged the valve seats when my bike went lean when my injector clogged up while the valves were too tight.
I could just replace the valves and hope for the best, but if I'd rather only take it apart once. Charles. |
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