Kitted NCZ50 Motocompo - tuning issues

Toby B /
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Hello guys,

Copy&pasting from my build thread:,4132964,page=1

I'm having an issue at WOT, as the power just falls on it's face at anything above 80% throttle, and i'm not sure hwta my next step should be. A summary of my setup as follows;

* 70cc Polini kit

* OEM custom cut head to 46mm. Basically this:

* Dual stage Boyessen reeds with slightly enlarged reed windows

* Malossi intake manifold

* Malossi air filter with metal screen

* Standard BP5HS plug

* Custom expansion chamber

* Dellorto PHBG 21mm carb kit:

As delivered settings on carb as follows;

* 90 main jet, 50 idle jet, W7 needle with clip on leanest setting, AU262 atomizer

Now. First thing I did was upjet to a 98 and change the needle setting to the 2nd richest. However, this setup just ran super boggy and struggled to manage any speed beyond half throttle, with heavy 4 stroking. I could not get a crisp 1/8 throttle either, so downjetted the idle to a 45, and dropped the main right down to a 92.

With the 45 idle, it was definitely better on the 1/8 throttle, however, I think my plug was just fouled when i was testing the 50. Either way, i'm pretty happy that the 45 is suitable.

Now, with the 92 main, I was still struggling to get that last 20% of the throttle before it started chugging again.

Against my own better judgement, I then fitted the 90 main which came with the carb, but my WOT problems remained. At 80% throttle it rides nicely, but if you ramp up the throttle too fast or go from 80% throttle to 100%, it just chugs and drops speed. I did a plug chop, and to me, it looks lean. Image below.


I then reverted back to the 92 main, and changed the needle setting one notch higher (now 3rd from the bottom), but to be honest, didn't notice much difference, with the top end still being inaccessible, but riding nicely at about 80% throttle. I did another plug chop, with it looking a little darker, but still on the lean side of an ideal looking plug (in my opinion).


So.... what next? I'm thinking I should check for air leaks, but to be honest, it seems to idle fine and work smoothly at 0-80% throttle, so not sure if that's the problem. I feel it is just the tuning that is not right. Should I work my way back up and try a 94 jet? Should I try a colder plug? I have 6's and 7's here, but just haven't tried one yet. I am also thinking of putting my un-dremeled reed block in with the standard window sizes, in case it's getting too much air... if that's even possible?

Also, my engine temp escalates way too quickly. I was seeing 430F after 5 minutes of riding, so I will be slotting some holes in the Puch gigantor head and fitting that ASAP.

I welcome any and all input!

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