ChinaRiders Forums - View Single Post - Mikuni Carb Swap Jet Replacement Question

KirkN · 05-27-2015, 02:46 PM

Thanks for that info and the link. I hadn't seen that.

My (stock) PZ30, then, is a Kei Hin knockoff then. It has an inked 'PZ30' on the side but no other identification as to make or model, etc.

I've done a bit of jetting tuning on it using spare KeiHin jets I had already. Main jet is OK, but there was a difference in the slow (pilot) jets. The knock-off carb's slow jets did not have any extension 'below' the threads, and the 'nozzle' above the threads was twice as tall. The KeiHin jets I had had a taller extension below the threads (that is, the part that sticks down into the fuel in the bowl) and a shorter nozzle that sticks up into the air passages in the carb body.

It runs great above idle, but idle and just off idle is still not great. I don't know how much that slow jet difference contributes. But then again, I also have to check valve clearances, since I think they're too tight.

Also, the knock-off carb's throttle slide (metal) has a bit of a binding spot at about 1/2 throttle opening. Not a full bind, just a slightly tight spot.

So, long story short, I bought the Mikuni. The carb in the ebay photos definitely says "Mikuni' on the body, but the ad also says 'Made in China".

Interesting re: the Mikuni jetting. Those numbers (25 or 30 / 110) came out of Weldangrind's reply to another member re: that member's 250cc motor. We'll see...

Thanks again,

Kirk

**EDIT** just ordered the jets from Jets R Us. I got 25, 27.5 & 30 pilot jets and 110 & 112.5 main jets. Woo Hoo!

05-27-2015, 02:46 PM	#3
KirkN Join Date: Nov 2014 Posts: 50	Thanks for that info and the link. I hadn't seen that. My (stock) PZ30, then, is a Kei Hin knockoff then. It has an inked 'PZ30' on the side but no other identification as to make or model, etc. I've done a bit of jetting tuning on it using spare KeiHin jets I had already. Main jet is OK, but there was a difference in the slow (pilot) jets. The knock-off carb's slow jets did not have any extension 'below' the threads, and the 'nozzle' above the threads was twice as tall. The KeiHin jets I had had a taller extension below the threads (that is, the part that sticks down into the fuel in the bowl) and a shorter nozzle that sticks up into the air passages in the carb body. It runs great above idle, but idle and just off idle is still not great. I don't know how much that slow jet difference contributes. But then again, I also have to check valve clearances, since I think they're too tight. Also, the knock-off carb's throttle slide (metal) has a bit of a binding spot at about 1/2 throttle opening. Not a full bind, just a slightly tight spot. So, long story short, I bought the Mikuni. The carb in the ebay photos definitely says "Mikuni' on the body, but the ad also says 'Made in China". Interesting re: the Mikuni jetting. Those numbers (25 or 30 / 110) came out of Weldangrind's reply to another member re: that member's 250cc motor. We'll see... Thanks again, Kirk EDIT just ordered the jets from Jets R Us. I got 25, 27.5 & 30 pilot jets and 110 & 112.5 main jets. Woo Hoo!
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