Author Topic: Carb upgrade ( PZ30 to Mikuni VM3* )  (Read 6515 times)

Syanur

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Carb upgrade ( PZ30 to Mikuni VM3* )
« on: October 16, 2012, 02:12:26 PM »

Hi,

I have a Shineray XY250GY-2 SuperMoto. It comes with PZ30 carb which is very common in chinese bikes. I want to put a mikuni VM carburator. But I couldn't decide VM30, 32 or 34mm.

I think PZ30 has 100 main and 20 pilot(slow) jets (or close).

For Mikunies;

VM30:  250 main, 40 pilot
VM32:  200 main, 35 pilot
VM34:  260 main, 35 pilot jets...

Take a look;
http://www.motorcyclecarbs.com/About_Mikuni_VM_Carburetors_W143.cfm

I am confused with these numbers. I know carb. setting is not so simple but main jets are the biggest factor in performance. So in here, don't the main jets seem a little bit inconsistent ??

And another thing, when I checked the link above, VM32 has largest volume(acrd. to dimensions). It should be better for good fuel/air mixture IMO. Isn't it??

I can get a VM32 but not sure for jets...Do you have any suggestion for a jet combination? (There are jet kits for VM carbs.)
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Zuma

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Re: Carb upgrade ( PZ30 to Mikuni VM3* )
« Reply #1 on: October 25, 2012, 09:53:12 PM »

By converting to the TK MV30 CV carburetor as used on the Shineray XY250GY-2 MX in Australia, a modest 10% increase in power and a noticeable increase in throttle response is achieved. This conversion requires the replacement of the inlet manifold to enable the slip on TK brand carb to fit.

With this inlet manifold you can also choose THE Mikuni VM34mm carb which will increase peak power at high RPM but at the cost of power down low in the RPM range.

Your question in relation to jet sizes and power in carburetors. Bigger jets don't mean more power; jet size is determined by volume and speed of air an engine draws in and then finding the appropriate size jet to achieve the correct air/fuel ratio of 14.7:1 or close to it.

Michael Onrust
Managing/Director  ZUMA MOTORCYCLES / SHINERAY X2 IMPORTER AUSTRALIA

« Last Edit: October 25, 2012, 10:18:08 PM by Zuma »
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