Mikuni Carb Swap Jet Replacement Question

[KirkN]

Hi, all,

I've just ordered a Mikuni carb off ebay to replace the PZ30 carb that came on my 250cc Baja dirt bike. (I ordered one by following Weldandgrind's link in gr8rcher's Apollo 250 thread).

So, now I want to go ahead and order a larger (#25) slow jet and larger (#110) main jet, but I don't know which Mikuni jets to buy. Jetsrus lets you search by carb manufacturer, carb type, motorcycle make/model, etc. Naturally, Baja 250 isn't listed, and I don't know what model Mikuni this is, and don't (yet) have the jets in hand to do a visual comparison.

Anyone already know, so I can order the jets now, instead of waiting 'till the carb arrives, then waiting some more for the jets to arrive?

Thanks,

Kirk

[ripcuda]

The 30mm Mikuni clone carbs use these jets:
Main: N100.604 (large round heads)
Pilot: VM28/486

See this thread for carb pictures.
http://www.chinariders.net/showthread.php?t=14347

110 main/25 pilot seems the recommendation for the 200cc engines... I wonder about your larger engine??

Cheers!

[KirkN]

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!

[ripcuda]

I've only read good things about that Mikuni-clone 30mm carb here... should work well for you. And #110/#25 should be a good starting point for jetting. Side note: the Mikuni clone carb on my son's PW50 says "Miniki" on it. haha!

I have the PZ30 carb on my Kinroad and it takes the normal Keihin pilot and round main jets. I have read that some earlier (?) versions of this carb had odd pilot jets in them. In this ebay ad for a PZ30 rebuild kit (I actually bought one)... you can see the pilot and main jets it uses.
http://www.ebay.com/itm/New-30MM-Car...8445f4&vxp=mtr

Good luck tuning your carb!

[Weldangrind]

Hey Kirk, it will depend on your elevation; the higher you go, the leaner it needs to be.

If you're anywhere near sea level, you might do better with a 112.5 or even a 115 main. You might need either a 27.5 or a 30 slow jet. The 100 that came with your carb is useless, so you can drill it out to 118 using a #56 drill bit. That's quite a jump from 112.5, but it would be interesting to try. It'll depend on the muffler and air filter that you're using.

[KirkN]

Hey, thanks for the information.

I'm in Orlando, so virtually sea level. But, in a couple weeks, I'll be taking the bike to Suches GA for some riding up there. Don't know the elevations, but it's the southern end of the Appalatians. But, that's just a weekend trip.

All stock airbox. Generic uni-filter style foam filter. Stock exhaust header. Stock muffler, but I re-wrapped its core with new fiberglass wool stuff. Core is basically straight-thru - you can see straight thru it. Stock end cap with some wire mesh stuff there as a spark arrestor.

I'll start off with the 27.5 pilot / 112.5 main and see how it runs and go from there.


On a side note, last night I checked the valve clearances - hoo boy, there was virtually none at all. Couldn't slide the 0.002" feeler in there at all. The manual calls for 0.002" intake and exhaust, but that just seemed way tight to me. So, I went with 0.003" intake and 0.004" exhaust. Slappy valves are happy valves and all that!

What a difference! Starts right up easily on first kick. Before, it did NOT want to kick-start; would only start using the electric start. So, I'm really pleased overall.

Thanks,

Kirk

[Weldangrind]

I love it when a valve adjustment makes all the difference.

Have a great time in GA; please take pics and share a ride report.