Zx50 Build results and some questions.

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mantrans
BMX
BMX
Posts: 45
Joined: Mon Nov 30, 2015 2:06 am
Location: bethalto il

Zx50 Build results and some questions.

Post by mantrans »

I acquired a zx50 for $40 last year and messed with it a little, years of cars and atvs/dirtbikes but never messed with scooters.I installed a Malossi 70cc kit, PG long pipe, 19mm Cp carb, stage 6 intake and reeds 7:1 gears, variator,clutch the usual. Compared to my buddies Big bore 139qmb, chinese 100cc kit, mediocre head and a9 cam ect and it got him pretty good. Besides not having a temp gauge I towed him home one night and soft seized the motor.

Ok that was the past, This winter I pulled it all apart and bought the Polini Corsa kit, malossi MHR crank, not a stroker its the full circle one that boost primary compression a tad.. is that what you call ministroker?, kept the pipe and intake, went with a polini 24mm carb, ported the Case myself to match the transfers on the cylinder then cleaned up and re shaped some spots where I felt there was an obvious restriction.. oh and also using same gears as last year.

Here is my current tuning specs and the issues I am having, Could REALLY use the help and advice.
Polini evolution clutch with blue springs( tried yellow also and tried every stiffness setting ) Just incase the blue is the stiffest, around 8krpm I think and yell,ow was 6700 to 700

Red malossi center ( contra) (clutch) Spring 35% I believe and tried every other one

Malossi Variator with 8.0 gram sliders, tried 7.0 to 9gram rollers.

126 main jet needle on third clip from the top

Measured out some distances I am familiar with from the car scene so 330', 660' and the quarter mile, with a stop watch and Gps ( I understand a track would be more accurate) it ran 18.2 in the quarter at 65 mph at 9400 rpm
top speed on flat ground has made it to 70 mph a few times.

CONCERNS : Although I shouldnt be crying because I think that is pretty decent power, I cant stand how terrible the low end power is. It launches slow, sounds lean but plug is more wet than anything, watching the exhaust looks good. My friend who I meantioned above ditched his build and went with a big stroker true 92cc big ported head, big valves 15:1 compression. He murders me the first 60' then I am caught up by then and fly around him, it is at least a win by 10 bikes. He is a very talented builder also, he runs a wideband and AFR are perfect. I was suprised the zx50 was that much quicker.


I know I ramble, my question is Can I add some bottom end power to my bike without losing too much top end power? I am sure the pipe robs the low end, could I just change pipes or will it throw everything off. Thanks everyone!
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