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Post by rehabkymco on Sept 12, 2020 15:22:53 GMT -5
Thinking about sticking my stock Kymco head on for this weekend and break in this cylinder. New head will be here by Tuesday or Wednesday.
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Post by rehabkymco on Sept 18, 2020 6:12:24 GMT -5
Decided to wait on breaking into 50 mm kit for the new head to come in,good thing that I did. The head come in Thursday and i got looking at it this morning. Universal Parts 47 mm chamber according to PFS website has 17 and 18 millimeter ports. Measure them this morning and got 20 mm on both intake and exhaust and it appears that the chamber volume is 8.6 Cc or so. According to a compression calculator that I'm messing with should give me 9 to 1 compression with the flat top. Not bad for Street engine may actually be able to run it on 87 octane. and with the high compression piston should be 12.5 to 1.
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Post by rehabkymco on Nov 29, 2020 7:51:11 GMT -5
It's been a minute since I posted. But I wanted to give an update. Ive opened my "rehab shop" again. Kym is running ok. Still doesn't want to start when it's below 40*F. Still not sure on that. It cranks until flooded and drained of battery. Could be jetting but not sure. At 34 pilot on a CVK 18 with a "manual choke".
When she runs it's not performing anywhere near where I want it to. Got a good idea why and that is the 47mm head and 50mm flattop don't have the compression that using a stock 39mm head does, there for I'm not making the power needed for even 50 mph.
Current setup 139qmb long case with rear disk brake 50mm flat with 47mm Universal Parts head with pretty big ports CVK 18 34/90 jets middle needle 9.367 gears (16/52 pri 17/49 sec) 120/70-12 tires 89mm vari from PFS, I think 5 gram rollers Naraku 738/18-28 belt 2k clutch springs And I think a 1k contra
I am planning on going threw everything again over this winter with this plan
11:1 stock gearing Stock 39mm Kymco head, ported and with dual valve springs installed New contra springs, 1 and 1.5k (blue and yellow) the eBay type like my 1k I've used forever Adjustable clutch and performance bell from PFS
I plan to do the head 1st actually just to see if I get the 50-55 mph top speeds back like I had with a similarly set up stock Kymco block with 10:1 gears. Might have to still go back to stock gears due to not having the torque for my goals.
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Post by rehabkymco on Dec 18, 2020 14:47:35 GMT -5
Well I've started doing the head today. Kymco 50cc head reusing the stock 64mm valves and a set of double valve springs from another junk head. Gonna port and polish the ports. I've also weighted the stock Kymco retainers and the ones from the double springs. Kymco 6.8g the China ones 7.3g. Gonna use the kymco retainers since they are also for dual springs and lighter.
Also I've messed with my carb enough to get her to start when it's at freezeing. I gotta put my hand over the intake tube at first but it starts and runs. Amd once it has some heat in it she rips. Gonna spend the money once I have it to get a pack of spark plugs and do a couple plug chops. Think I'm too lean. Currently at 34 pj 90 mj and middle on needle. Gonna try one down (#4) and see if that stops my stumble at part throttle on accel. Honestly wish a wideband wasn't $200.
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Post by rehabkymco on Dec 20, 2020 10:33:35 GMT -5
Got the kymco head finished up and put back together. Opened the ports to roughly 19mm on both intake and exhaust. Double springs with 6.78g retainers installed on the oe stock 18.5/16mm valves. I also put a new set of valve seals. My camera is messed up or id have pictures. I expect that this head will flow a bit better then my 1st head i ported. Most of my porting focused on the port floors and short side radii. Very straight and direct looking flow to the valves.
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Post by rehabkymco on Dec 30, 2020 11:58:24 GMT -5
Put the stock,now ported Kymco head on just now. And this should give me all the power I used to have on a similar build I did on the Kymco block. I didn't pull the the CVT apart but belt travel is roughly 3mm or so, and I've been using a stock contra this whole time. Looks like I may have to address that if I cant hit 50. Also may put my old "6" gram sliders back in it.
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Post by 808ministroke on Dec 31, 2020 7:04:58 GMT -5
so you did valve work to a stock head an opened up ports? i thought bout doing this for my freinds head its a big valve head but nowere near a ncy head for flow do you think gains can be achieved ? without changing the valve stems?
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Post by rehabkymco on Jan 1, 2021 6:05:45 GMT -5
so you did valve work to a stock head an opened up ports? i thought bout doing this for my freinds head its a big valve head but nowere near a ncy head for flow do you think gains can be achieved ? without changing the valve stems? If it's got tiny ports, (less then 17mm) yes it will have some gains. Most BVH I've seen have a intake port roughly the same size as the valve. I've used that same theory on my ported heads. Exhaust port can be a bit bigger then the valve size. Also keep in mind if your gonna have to match the intake spacer and manifold to your new port size. Don't want a bottle neck. Carb size, port size and valve size should all nearly match. Same for exhaust. 18mm carb, 18.5mm intake valve, 18-19mm port. Exhaust side has a smaller valve but in my case my pipe is 20/21mm id. So I've put my port at roughly 19 as to flow the best
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