Messing Around with the Stock Sheng Wey PZ30 Carburetor on the Hawk

[Torgo]

As I'm coming up on 1k miles, I've kept the bike stock except for a 17T front sprocket. We've had a couple of warm days around here, > 80F, and the carb has started to act up at full throttle. Bogs and starts to stutter. If I go half-choke, it smooths out with OK power. I ended up pulling the plug, and it's white, so it's been running lean as expected. It's a little counter-intuitive since I would expect higher temperature to run richer, but I guess there's some interaction going on with the dialed-down EPA setup.

So I've been getting the idea to do the standard mod around here and get a Mikuni installed, with a jet set for around here and another one for West TX with the higher altitude, if needed. Before doing that, I figured I get some quality wrench time and see what's going on in the PZ30.

First of all, it's not actually riveted. It's actually screwed together with break-aways. Instead of drilling them out, I drilled a start hole, then crammed in some small torx bits from one of my many Harbor Freight collections into a drill and reversed them out. All 3 came out with not much effort.

http://chinariders.net/attachment.ph...1&d=1457400230

The needle is not adjustable like a Mikuni - it has one setting for the c-clip. I guess you could do the old trick of adding a washer or two under it to make it richer if you wanted to adjust it.

http://chinariders.net/attachment.ph...1&d=1457400230

The mixture screw has a black plastic plug installed preventing access. This is easily removed by making a small hole with a hand-turned drill bit and popping it out with a jeweler's screw driver . It's only backed off a single turn.

http://chinariders.net/attachment.ph...1&d=1457400230

The slow and main jets are right there and easy to find and remove. The main is a 'K 98' and the slow is a 'K40A.'

The main looks standard and looks like you can easily match it up to OEM or aftermarket versions that are available all over the place. Not so for the slow jet - it's some kind of EPA monstrosity.

The slow jet is a non-standard 28mm and has 4.4mm threads at the bottom of it. There's a threaded cylinder that looks like it was pressed into the shaft to engage the threads of the slow jet . The flare towards the top of the jet then seats at the top of the shaft. I was unable to find any standard jets that match up.

Best I can tell is that you would have to thread the shaft itself if you wanted to use more common 28mm Keihen jets. Somewhere I read that folks sent theirs in for modifications - seems like a lot of effort when it's so cheap and easy to just swap out. So if you want to adjust that, I think you'll have some difficulty.

http://chinariders.net/attachment.ph...1&d=1457400230

While I had it open, I figured I'd hack away a bit, without the effort of spending any extra money since I'll just put that towards the Mikuni if I end up doing the swap. I did two things:

1) Backed off another half turn to the mix screw.

2) Used a scriber tool with a very tapered point to pound into both sides of the main jet to increase the diameter. (My smallest drill bit on hand was 1/16", so that would have been too much.) What did this set it to? No idea, just a little bigger than '98.'

http://chinariders.net/attachment.ph...1&d=1457400230

Big difference: it idles better, jumps now, and has more power available through the full throttle range. Actually felt close to popping a wheelie and I wasn't really trying. Now, flat out, it pushed above 60mph. Still have the rear 50T. It had never gone above 55-57 previously. I'll need more time on it to get a better feel overall, but that's the initial impression.


After playing around with this, I still think going with the Mikuni and pod filter is the path of least resistance. Still, you can crack the PZ30 open without too much difficulty and fiddle with a couple of things if you want to try to squeeze a little more out of it. The mix adjustment almost seems like it should be a requirement now that I've done it, and for $5 or so, you could actually increase the main the right way. The pilot is another story - look like you're stuck with that if you run out of room with the mix screw.

[2LZ]

EXCELLENT write-up! You've answered a ton of questions for many here!

[SeerAtlas]

x2

[Adjuster]

I purchased the micro drill bits mentioned here on the forum several times. It was very easy to drill by hand straight through the brass jets. In fact I think I need to take my carb off and go a little bigger.

If I am not mistaken:

If I need to turn my idle mixture screw out two turns or more that means I need a bigger main jet. Correct?

Is there a simple similar methodology to tell if I need a bigger slow jet?


My needle is not adjustable as it has only one clip notch.



/

[Torgo]

Originally Posted by Adjuster

If I need to turn my idle mixture screw out two turns or more that means I need a bigger main jet. Correct?

Is there a simple similar methodology to tell if I need a bigger slow jet?

My needle is not adjustable as it has only one clip notch.

/

Slow/pilot jet, not main jet. Main jet is full throttle only. If you go more than 2 turns out, you should step up one size or more on the slow/pilot. The main should be adjusted for temperature/altitude.

I didn't mean to suggest the 2 mods go together. The change to the mix screw may have required moving to a bigger slow/pilot, but I got enough of an improvement, that I left it at that. Besides, I saw no way to actually order the next size up since the slow/pilot jet does not seem to be a standard Keihin jet.

The needle could be made richer by adding a washer or two under the c-clamp. It's old school - I remember doing that for a dirt bike a LONG time ago. Similar to moving the c-clamp down on a Mikuni. If you look at the picture, there's a retention clip that holds down the c-clamp. If you remove that, the needle will slide out and you can add the washers before reinstalling the needle and retention clip. It's one direction only, richer.

[NzBrakelathes]

I think I found the slow jets!
Can anyone take some measurements? I’ll compare to mine when I’m in my shop next

[JerryHawk250]

Originally Posted by NzBrakelathes

I think I found the slow jets!
Can anyone take some measurements? I’ll compare to mine when I’m in my shop next

That sure does look like them. One of a kind. If nobody confirms the measurements today I'll open up my PZ30 carb when I get home from work tonight. I'm glad you were able to find these. I've been a member for over two and a half years and no one has been able to find them. Those will be perfect for your kit.

[NzBrakelathes]

#40 goes in the kit
And #42, #45 can be added at an extra cost
I doubt bigger is needed but there are about 8-10 sizes from 36-55 or something like that
Only CCW has the jet only #45 tho

It makes using stock carb just more and more economical and less saying “must change to mikuni” saves some $ reduced waste and I make a few $ while the customer doesn’t need to search for the bits to get things up n running well!

To be fair there are 3 ways to tune the carb with or without buying much or changing carbs.
IMO I have the better bang for buck and I suggest it will be perfectly fine for 95% of the end users

Haters will hate other will be happy

[JerryHawk250]

Originally Posted by NzBrakelathes

#40 goes in the kit
And #42, #45 can be added at an extra cost
I doubt bigger is needed but there are about 8-10 sizes from 36-55 or something like that
Only CCW has the jet only #45 tho

It makes using stock carb just more and more economical and less saying “must change to mikuni” saves some $ reduced waste and I make a few $ while the customer doesn’t need to search for the bits to get things up n running well!

To be fair there are 3 ways to tune the carb with or without buying much or changing carbs.
IMO I have the better bang for buck and I suggest it will be perfectly fine for 95% of the end users

Haters will hate other will be happy

The stock Hawk PZ30 comes with a #40. A #42 and #45 would be a good selection to add to your kit. Then there will be no need to drill the stock jet.

[NzBrakelathes]

Originally Posted by JerryHawk250

The stock Hawk PZ30 comes with a #40. A #42 and #45 would be a good selection to add to your kit. Then there will be no need to drill the stock jet.

Can you confirm it’s #40?
Others tend to be 36-38
I’ve got the kit with common keihin and the short keihin (Bashan storm?)#40 jets, it takes nothing to change the basic size in the kit as the price I pay is the same with 2 pilot jet styles - but having a size up from stock is a good starter and all 3 types I could add at an extra fee etc.

[JerryHawk250]

Originally Posted by NzBrakelathes

Can you confirm it’s #40?
Others tend to be 36-38
I’ve got the kit with common keihin and the short keihin (Bashan storm?)#40 jets, it takes nothing to change the basic size in the kit as the price I pay is the same with 2 pilot jet styles - but having a size up from stock is a good starter and all 3 types I could add at an extra fee etc.

I already confirm it's a #40 on the Hawk. A few others will tell you the same. Not sure what the Bashan Storm come with.

[NzBrakelathes]

Next would be what jet n size in the Tao Tao TBR7 and the Bashan Storm as well an Enforcer etc!
The kit is intended suitable for near all china bikes regardless OHC or push rod as long as it’s a PZ30 Keihin or Keihin clone.
Not Mikuni clones

[roundhouse]

Excuse my ignorance. I am new to mechanic-ing. So my bike once warmed up runs great but starting cold is a pain. Which jet thingy do I need to replace or modify to get that better?

[Kivi]

Here are some measures that I have.

[JerryHawk250]

Originally Posted by roundhouse

Excuse my ignorance. I am new to mechanic-ing. So my bike once warmed up runs great but starting cold is a pain. Which jet thingy do I need to replace or modify to get that better?

That has a lot to do with the pilot jet and idle mixture. If you have to turn out the idle mixture more that 2 turns that is a good sign you need a larger pilot jet. Look at the first post picture. The one marked slow is the pilot jet.