PZ27 vs PZ30 Carb Upgrade

[kevshek]

My bike is a 2009 Shineray XY200GY-4, 200cc 4 stroke engine. I dont know which bikes they are the same as but im sure lots of people on here will know.

The original carb fitted to the bike is a SHENG WEY PZ27. While searching around for Shineray parts on ebay, i came across a Mikuni PZ30 carb, which was comfirmed to me, was fitted to 150 to 250cc bikes/quads. So i thought id take the plung and try one out.

First off, heres some pics of the 2 carbs.
PZ27 to the Left, PZ30 to the Right.





PZ27 uses these types of jets, size 40 Slow jet, 86 Main.


PZ30 uses 20 Slow jet, 100 main (standard)


The first noticable difference is that the carb is bigger obviously, which made it a bit harder to fit. The choke levers (not all pictured) were different aswell as mine is cable operated, but the mounting points are same so it was a simple swap over.

Fitting wise, now that ive done it numerous times, this is the easiest way to get it in between the frame. Its best to leave off all the choke stuff to reduce its overall size, or you wont get it in. You can refit it once the carb is seated inside the frame.

Place it into the frame at this angle


Make sure the protruding parts on the right side are under the bracket.


Then you can ease the left side into the corner and past the frame.


Finally, its a simple case of spinning it into position. The best way to do this is to push the carb inlet into the rubber airbox tube, as this is flexable, then line up the outlet flange onto the intake manifold**.


**I have replaced the manifold studs for bolts which are easier to fit in that restricted space. I also cut a slot in the bolt head, this way i could screw them in most of the way with a long flat screwdriver, and tighten with a wrench.


Tuning notes to follow....

[kevshek]

Onto tuning. In standard form, the PZ30 came with a 20 Slow jet and 100 Main jets, but after first install and running, i could tell there was a fueling issue straight away. The bike started and idled no problem, and revved in neutral no problem, but when riding, there was low torque and low top speed.

After a quick search on the net, i found a generic carb tuning guide and set about applying its advice. This is what i understand, but please correct me if im wrong.

Top End Tuning
Basically, low top end speed at full throttle meant that my main jet was too small, and the bike was lean. So i decided to order a range of jets from 110 to 130 in steps of 5. As i had also installed a bigger rear can on the bike around this time, i decided to jump straight in and fit a 120 jet. This was a much better improvement. The bike felt stronger and pulled slightly harder then usual. Top speed is a fraction higher, but higher speed easier to get to and maintain.

Mid Range Tuning
This is done by the needle inside the slide. When revving up through the rev range, if the bike feels like its holding back, then the needle needed to be raised. In standard form, it was bang on in the centre, which was fine by all accounts, but i decided to raise it up 1 slot, so it was in slot 2 of 5, counting from the bottom up. This means when you turn the throttle and open the slide, the needle will unseat allowing more fuel, sooner.

Low Speed Tuning
This is the tricky one, and the one im still working on. This is done by the Slow jet and controls the idle and low speed mixture upto 1/4 throttle, from what i believe. Idling isnt the issue here, its part throttle and backing off the throttle. Im finding part throttle unstable and the bike stumbles a bit. There is an adjustment screw on the engine side of the carb which is supposed to adjust this, but i could have the wrong size slow jet all together. The arrox#w in the picture below points to this screw.



I started off by having this fully in and gradually backing it off 1/4 turn at a time in between rides. So far, im about 2 turns out and still working on the lumpy part throttle issue. To be honest i dont fully understand how this screw effect the engine so if any could explain it, that would be great.

I do know however, slow jets for mikuni carbs are hard to come by in the UK so until i can get some proper advice, i wont be buying any, anytime soon.

[Weldangrind]

I have some experience with that engine, in both the original Honda XR200R and the current China clones. It's MHO that the 20 slow jet is too small. I'm unable to properly tune a 200cc clone or Honda with less than a 25 slow jet. Until you change it, you're not likely to see an improvement.

The key (that I learned from Waynev on this forum) is the amount that the pilot screw is backed out. If you need to back the screw out more than two turns, the slow jet is definitely too small. I installed a slow jet on a buddy's scooter that was on the large side, and I hardly backed out the pilot screw at all.

The pilot screw essentially adds fuel to the stream during the transition from the idle circuit to the main circuit.

[kevshek]

thats what i needed to hear, thanks, again!
ive backed it out 2 turns and more, and there hasnt been any difference. So on the hondas, what size jet were they running? This way i can buy a couple of size from that point on.

[Weldangrind]

I don't know that specifically, because the old Hondas used Keihin carbs with a slightly different numbering system. What I mean to say is that I've used Mikunis on old Hondas as well as new clones.

Several of us on this forum have 200cc Honda clone ATV engines that aren't happy until they're fed with a 110 main and 25 slow. That seems to be the best combo with a free-flowing air filter and muffler.

I prefer the 30mm Mikuni clone to the 30mm Keihin clone. The Mikuni has a better casting, and jets are much easier to find. Will www.jetsrus.com not ship to you?

[kevshek]

Hmmm, seems a bit of a hassle, no direct shipping (see below), but im sure i can find some on ebay, i just need to identify the correct fitment. Ill get a 25 and 30 to be safe.

"To protect your low prices the following method is used for international orders. We apologize in advance to our many honest customers for this inconvenience:

1) Best method - have the item purchased by us credit card holder and mailed to someone in the USA.

2) We accept Money Orders and Certified Checks (funds must be in US dollars). We DO NOT accept personal checks.

3) We accept USA Dollars, however realize that there is a risk sending cash and we are not responsible if the cash is lost or stolen in the mail. If the decision is made to ship the cash it would be advisable for the sender to insure the package for the amount of cash in it."

[kevshek]

found this
http://www.pjmotorsports.com/index.html
Mikuni VM28/486 Pilot Jet
28.1mm in length with a 5mm Head
Believe this is the one i need.

[kevshek]

Just ordered some from http://www.allensperformance.co.uk/
here in the UK, should be with me on monday, i ordered 3 jets, totaling £13 inc postage, not bad.

[Weldangrind]

That's less than a three hour ride. Get on your bike!

Glad to hear you've found jets locally. I bet that the 25 will be the ticket, unless the weather becomes very cold.

[kevshek]

yeah I think you're right, I've bought 25, 27.5 & 30 just incase.

I can sense your itching to tell and wanting me to ask, so I will, lol
Are you an ex-pat? Cos you know the UK.

I do have another bike, a ER6f which was put away for the winter, but due to the shineray being out of action, I'm using it. Plus the weather is dry, cold but not freezing, so it could have been a possibility. However I am the bike how tomorrow, well traveling down there tomorrow for Saturday.

[Weldangrind]

Nope, I'm a Canadian, but I have roots in the UK. I've been to Gloucester and London, but the rest is just general awareness, particularly about Newcastle Brown. I'd love to visit again.

I was kidding about the three hour ride; one thing I observed while in the UK was that people rarely strayed that far from home. It's a notable cultural difference, since we drive 12 hours to visit my parents.

For the price, I think it's a good idea to have the three slow jets you selected. You'll likely need a jet on the fatter side if the weather is cold.

[kevshek]

Found the thread!
So this PZ30 i have is a copy? even though it has the Mikuni name and uses their just?

Ive tried the 25 pilot jet, then onto the 27.5 and now im on the 30 jet trying to get rid of the lumpy part throttle when cruising. Surely it cant need a bigger jet again can it?

[Weldangrind]

I'm glad you found this thread; the pics provide some clarification. I wouldn't refer to your new carb as a PZ30, but rather a 30mm Mikuni. That's where I became confused.

Your carb is definitely a Mikuni (vs a Keihin), and you can tell that by three bowl screws instead of four.

[Weldangrind]

I can't imagine that you need anything bigger than a 30 slow jet. In fact, I'm surprised that it will run with a 30; I presume that a 25 would be better for a 200cc. I'm going to read your other thread and review the symptoms.

[kevshek]

thanks for the efforts, i await your advice.