PZ30 trouble

[Ad642254]

Not specifically a China bike, but a China carb. And this forum seems to have the most info and best experience in the keihin clone PZ30.
I have a honda single cylinder built up with a Chinese big bore kit to 145cc. I got a keihin copy pz30. Three screws on the float bowl? It's branded keihin but may be mikuni copy? It's the common one on eBay.
I got a slow and main jet kit as well. Since this is a new engine build and carb combination I didn't know where to start for getting. I
nitially tried a 42 slow on a suggestion and it wouldn't start. Started with a 32 but ran lean. 35 and it was good at idle. Then, on a longer ride for engine break in it felt lean at 1/2-full throttle. Swapped the 120 main for a 125 and richened needle clip.

On a slightly longer ride later it started to cut out and feel lean and hot again. Let it cool then rode 2 more min and it cut out fully.

The choke plate screw had come loose and choke was fully on. Got home and fixed the choke and added a 125 main since it was kean. Now won't start at all with the same idle jets that it liked before.

In troubleshooting the new no start I confirmed spark, timing, valves and fuel.
Float level was 12mm from gasket mating surface, floats perpendicular. However, using clear tubing the fuel level was very low. I have raised the fuel level and it still won't start.
.I'm lost.

[Megadan]

Not specifically a China bike, but a China carb. And this forum seems to have the most info and best experience in the keihin clone PZ30.
I have a honda single cylinder built up with a Chinese big bore kit to 145cc. I got a keihin copy pz30. Three screws on the float bowl? It's branded keihin but may be mikuni copy? It's the common one on eBay.
I got a slow and main jet kit as well. Since this is a new engine build and carb combination I didn't know where to start for getting. I
nitially tried a 42 slow on a suggestion and it wouldn't start. Started with a 32 but ran lean. 35 and it was good at idle. Then, on a longer ride for engine break in it felt lean at 1/2-full throttle. Swapped the 120 main for a 125 and richened needle clip.

On a slightly longer ride later it started to cut out and feel lean and hot again. Let it cool then rode 2 more min and it cut out fully.

The choke plate screw had come loose and choke was fully on. Got home and fixed the choke and added a 125 main since it was kean. Now won't start at all with the same idle jets that it liked before.

In troubleshooting the new no start I confirmed spark, timing, valves and fuel.
Float level was 12mm from gasket mating surface, floats perpendicular. However, using clear tubing the fuel level was very low. I have raised the fuel level and it still won't start.
.I'm lost.


My suggestion would be to start from scratch. Forget everything about the main jet and the needle. for now, leave them as they are. I would also suggest to double check your valve lash before attempting to tune the carb. Maybe it is fine, but it is a good thing to know for sure/ Bad lash settings can make tuning a carb a real pain in the rear.

First thing I would do is inspect any seals or rubber parts for potential vacuum leaks and then take the carb apart, jets, rubber seals, and all, get your can of carb cleaner, take the straw end, and spray through every possible hole thoroughly. Then, if you have access to an air compressor, blow some air through the passages. This will ensure we are 100% clean. Sometimes these cheap carbs have junk left in them from manufacturing that can potentially make your life hell by clogging up the little passages and tiny jet holes.

Put the carb back together with the jets you had before since they were a known quantity. Set the idle mixture screw out 1 1/2 turns from lightly seated as a baseline number.

Now, forgive me if you do already know the following information, but I want to simply cover all bases. The pilot jet on these carbs still contributes fuel to the rest of the system and in cases can actually cause a change in main jet and needle positioning depending on how big of an increase there is. Think of it like a "total fueling" situation. While each jet has a main job where it does 90% of the work, they all add fuel, all the time.

Get yourself a good fan ready. Start the bike, let the engine get up to temp (hot) and turn that fan on and aim it at the motor to help keep it cool while you work. Attempting to adjust idle mixture on an engine that is not up to temperature will just be a waste of time (hard lesson learned long ago lol) Adjust that idle mixture screw - this is a decent guide. https://www.thejunkmanadv.com/how-to-idle-mixture-screw-adjustment.html

Now the carb you has uses a fuel screw, so turning it out adds fuel, the opposite of what you see in that video. On a fuel screw you are aiming to achieve the best idle between 1 and 2 turns out from lightly seated. If it takes more than 2 turns out to achieve a good idle mixture, go up a jet size - possibly 2 if you find yourself at nearly 3 turns out. Then start again.

Once you find a jet that can have a stable idle between 1 and 2 turns out on the mixture screw go take it for a slow ride. With the engine at operating temp, see how it behaves at just off idle throttle. I usually can test this by going about 20-25mph in a mid range or higher gear. Basically you want that throttle just barely open ( less than 1/8th of a turn) and the engine trying to maintain RPM. If you feel any hesitations/hiccups, then the pilot is still too lean. If not, you are good to go!

One exception to the 2 turns out rule that I will make is if the bike has good low throttle steadiness like described above, but the idle is still a bit funky and maybe needs another 1/4 of a turn to be right.

Now that you have the pilot jet sorted, I would leave the needle jet as it is and then move on to the main jet. Now, how you choose to try and test if the main jet is right or not really depends on your experience with carb tuning and carbed motors as a whole.

I always air on the side of caution when tuning main jets and start with something I am fairly sure is too rich. I actually will keep increasing the main jet size until I find the upper limit and it starts to bog/cut out wide open, and then usually back off a full jet size. From there I will adjust half sizes in main jets up or down (in the case of Keihin jets, 2 sizes for a full step, 1 for half) IE, if I had a 130 that was too rich I will go to a 125, If the 125 doesn't bog I then go to a 128 or a 122 for fine tuning.

You said it ran fine with a 125, so if it were me, just to be sure, I would actually toss in a 130 main jet and see how it behaves. If you go wide open and it bogs, then we know that 130 is too rich, go back to the 125 lol.

Once you have the pilot and main jets sorted out, adjusting the needle is all that is left, and that is usually fairly straight forward. My personal preference is to usually run the needle on the "safe" lean side of things and the main jet a bit rich with these smaller engines since they tend to get worked harder more often. As long as I don't get any lean hesitation between jet transitions - like a hesitation on throttle roll off from wide open. This helps keep fuel economy from tanking too much. Your motor may be different, but for my particular engine that tends to be in the 3rd or 4th notch.

[Ad642254]

Hi, thanks for the reply.
One problem is that I cannot even get it started anymore. I have double checked the valves, timing, spark, air leaks, etc. All is well. The only thing I am struggling with is fuel level. With the float height adjusted so the floats are parallel with the gasket surface (as it was from the factory) the fuel is very low; perhaps 5 mm above the drain valve. I have adjusted it up, but I can only get it as high as about 1 cm below the gasket surface. When I try to go higher it just goes too high and overflows.

When I kick it over, it occasionally gives 1 or 2 rotations then dies.

I'm starting to wonder if the engine running lean caused some sort of damage..

[Ad642254]

I'll add that I've also cleaned and blown out all the passages very well

[NzBrakelathes]

Try run on brake clean or engine start - be sure its getting fuel of some sort
Plug wet?

[Ad642254]

Prior to the choke plate slapping shut in the middle of a ride, the plug was reading on the lean side of normal. As expected, when the choke shut, the plug was dry fouled. It has remained dry fouled throughout my troubleshooting. It does not appear wet after I've kicked it over for a while.

Can anybody comment on setting the correct float height on this carb? With the floats set as per factory, the fuel level is low. I had read that the fuel level should be about 3mm below the gasket surface. Is that correct?

I have also just noticed that the fuel has a small amount of paint in it from the tank. There are two inline filters that do not have any debris in them, all the gas draining from the carb bowl is clear, and no sediment is in the carb or passages. I have cleaned and blown out the carb several times.
Perhaps micro-dissolved paint is causing an issue with starting? I will drain and put in fresh gas and see.

[OneLeggedRider]

When you pull the fuel line off the carb does it flow freely?

[Ad642254]

Yes it flows free and clear. I don't think there is a flow restriction. The carb bowl fills well.

[JerryHawk250]

You said the choke plate screw came off. Have you checked compression yet? You probably sucked a screw in and either damaged the piston or valve.

[Ad642254]

I considered that as well. I do not have a compression tester and the nearest one is a day away. I'm working on getting one.
The screws for the choke plate could not have entered the carburetor bore, they are all external. In the chance that it did enter, I snuck a bore camera in to the spark plug hole and took a look, as well as in the valve cover. There was no obvious damage or foreign object in the cylinder or valve train. I am suspecting low compression though. It is behaving like low compression. Could an engine running hot due to being lean cause that severe of damage?

Any input on the fuel level?

[Weldangrind]

Welcome!
I'm stuck on two things; the fuel flow and the carb size.


What type of fuel filters are you using? Can you show us a pic? I like the transparent filters that are cone shaped; they flow well enough, yet offer decent filtration. Perhaps one filter would be better than two. If you choose to try a transparent cone filter, note that the inlet is the small end of the cone.


With 145cc, I'd be inclined to feed it with a PZ27 (or Mikuni equivalent). A PZ27 is certainly cheap enough to try. BTW, your existing carb is definitely a Keihin clone, given the three bowl screws.

[Ad642254]

As for fuel filters, there's a screen on the fuel petcock interior (inside the tank.)
I have a clear inline filter between the petcock and carb like this: https://i.ebayimg.com/images/g/xrcAAOxyEoFSXZTU/s-l500.jpg

I have verified that it is oriented correctly.

I have seen now that the PZ30 may be oversized. However, what confuses me is the bike was running okay before the choke slapped shut. It would start first kick and had few dead spots through the first half of the throttle. Then now it suddenly won't start? Even if the carb is oversized, it should still start.

I am still unsure on the fuel level though... I have a suspicion that when I was doing initial jetting, I had bumped the float level or fuel valve so it was running leaner. I then jetted it up in both main and slow jet. When the choke slapped shut and I took it apart, perhaps the fuel level went back to running richer and now the carb is too rich?

What fuel level and slow jet should I be trying? There's a 35 slow in it now.

[Weldangrind]

I would set the float level with the carb upside down and no pressure on the floats (other than gravity). The plastic parting line in the middle of the float should be parallel to the gasket surface.
I'm unable to guide you on slow jet selection for two reasons; I use Mikuni carbs, which have a different numbering system and a much smaller slow jet requirement, and I haven't tuned an engine of that size. Most of my experience is with 200-230. As an example, a 200cc engine using a #38 Keihin slow jet might use a #27 in a Mikuni. There is a cross reference chart to determine the equivalent jet size, but that doesn't matter; Keihin carbs use a larger slow jet, even in an apples to apples comparison.


I can strongly recommend Mikuni carbs, even if they're clones. The castings have been excellent IME and jets are easy to find. I also prefer four bowl screws to three. On top of those benefits, Mikuni jets are metric referenced. IOW, a 110 main is 1.1mm and a 30 slow is 0.3mm. It makes so much more sense to me, especially if I plan to drill jets (which I often do).

[Ad642254]

Thanks for the input. To clarify, when I set the float height as you mention, with the floats parallel and the valve just resting (not depressing the spring) the fuel level is low. A clear tube on the drain will only have fuel about 1cm above the drain, approximately 3 cm below the gasket surface...

Borrowed a compression tester but it only has 14mm or 18mm connections, I need 12mm. May be a bit before I can test compression.

[Megadan]

I almost wonder if the floats weren't installed upside down. The floats should be installed with the flat side facing down at the bowl, and the V shaped side facing up to the carb body.

The proper float height setting for a PZ26/30 carburetor would be 14mm above the flange surface to the bottm (now top since its upside down) of the float - at the far edge of the float (front of the carb), or the opposite side the needle valve is on, with the carb upside down.

If the floats are set correctly then you should be able to see the top few mm of the pilot jet when looking at it straight on from the side.

[Ad642254]

Great thinking. I just checked, and the floats are correct.
Fuel level now checks out correct with clear tubing.
32 slow and 108 main... Nothing. I'm at a loss

[Ad642254]

Compression is 130, which on a fresh build that likely hasn't broken in yet, seems reasonable. It certainly is enough to start.
Here's my checklist:

Spark: check. Strong blue spark with every kick. New plug cap, new coil, new wire, new condensor. All wires are hooked up correctly.

Timing: ignition points are clean and statically timed as per the manual. Points gap is correct

Air: clean oiled foam air filter on the carb throat. Choke plate is open at 90 degrees, all appears well

Valves: lash is correct. Both open and close as expected. Compression is good.

Fuel: fuel flows freely from petcock, fills carb bowl, and sets about 3mm below the gasket mounting surface. PZ30 with stock jets installed (32 and 108). Spark plug gets when when kicking

What am I missing? Should I just get a new carb?

[Kivi]

Can you please post the photo of the compression tester you used to test? Have you measured with wide open throttle?

Fuel: fuel flows freely from petcock, fills carb bowl, and sets about 3mm below the gasket mounting surface.


Isn't that too high level?

[Ad642254]

Brand new compression tester (just bought it), wide open throttle, 130psi peak on 4 different tests.

Fuel level was set by setting float heights to 14mm as mentioned in a previous post. Clear tubing fuel level check was 3 mm below the gasket mating surface, as described for many different carbs online. It seems appropriate.

[Kivi]

I measured 190psi with my tester. Thats why I ask for photo, but ok.

[Megadan]

Great thinking. I just checked, and the floats are correct.
Fuel level now checks out correct with clear tubing.
32 slow and 108 main... Nothing. I'm at a loss

I literally just got done messing with my PZ30B (pumper carb) for having some odd running issues causing me to have trouble getting my jetting dialed in. It actually turned out to be my float needle had a gouge in it causing a leak past the seat. Yours might be something else, but if that fuel level in the bowl keeps changing, you may have a needle sticking to the seat and not coming open fully when the floats drop.

One other thing I would say, toss a new plug on it. I usually tune my carbs with copper plugs simply because they are cheaper, and then switch to something better once I know it is good to go.

I measured 190psi with my tester. Thats why I ask for photo, but ok.

Don't get too hung up on the PSI reading. There are many things that can change that figure, such as cam lobe overlap, etc. His new engine will have more blowby than one that has been broken in. Anything over 120psi is decently healthy in my book for a typical lower compression air cooled engine.

[Ad642254]

The manual specifies 150-185 psi for this engine. This rebuild has less than 50km on it, and I'm at 2000m elevation. I think ~130psi is certainly enough to start it.

I'm going to swap back to the old coil, since the only other thing that changed is a new coil.

[Kivi]

The reading can, on these engines, vary by 80psi depending on tester used. I wanted to see how big mistake was made. Anyway, certainly enough compression to fire up.

[Ad642254]

Fresh plug, original coil, no difference.
Since the only thing that went weird was the carburetor, I'm going to chick this up to being a bad carb. I'll tear it down once again and see what's up. I'll also order a mikuni clone pz27.

Any tips on where to start with jetting?

[Ad642254]

When a choke plate slams shut, the damage that could be done I would think would have to do with the sudden change in pressures. Any debris would get pushed or sucked into a crevice.

So, I have once again cleaned and blown out all passages. Air passes through all of them
Below is a link to an album of the carb, in case fresh eyes see something I don't.

I appreciate all the input everyone. What a good forum.
PZ30 https://imgur.com/a/eOZH4To

[Kivi]

Sure. Where is mixture jet rubber oring and metal washer? You removed them before and put them back corectly after cleaning/blowing?

[Ad642254]

Metal washer is with the spring. O-ring.... I swear I had last time I took it apart. Good eye! I've had this thing apart too many times. Maybe that's my problem!

I guess if I can't find my rubber o-ring I'm stuck getting a carb rebuild kit shipped to me anyways. And since a pz27 is more appropriately sized for this engine, I may as well just get that. Or is there an alternative place I can get that tiny o-ring.

Edit: o-ring is in place in the carb body.

[humanbeing]

...I guess if I can't find my rubber o-ring I'm stuck getting a carb rebuild kit...
http://www.motorfans.com.cn/forum.php?mod=viewthread&tid=89339&page=1&authorid=75082 ;)
http://attachments.chyangwa.net/day_080301/yKYgMDA0_WSIwrSABZL3W.jpg
http://attachments.chyangwa.net/day_080301/yKYgMDA3_VCzaFrkzB0yz.jpg
http://attachments.chyangwa.net/day_080301/yKYgMDA5_NlCXoFDfEgyU.jpg
http://attachments.chyangwa.net/day_080301/yKYgMDEw_V1ieXwu6lxUI.jpg
http://attachments.chyangwa.net/day_080301/yKYgMDEx_n2G6KXDG0Zj1.jpg
http://attachments.chyangwa.net/day_080301/yKYgMDA2_KXe5OFLSxEbb.jpg

[Ad642254]

It's alive!!
First off, thanks to everyone who gave input and helped me troubleshoot this. Everybody's answers were helpful.

Second, I need more help. The bike will start with the following carb settings.
Keihin PZ30
Float height 14mm, fuel level approx 1 cm below gasket mating surface.
#32 keihin slow
# 108 main.
Idle speed screw turned out 4.5 turns
Fuel mixture screw out 1 turn

At these settings it idles very high (1200 rpm or more), which makes sense given that the idle speed screw is lifting the slide a fair bit. If I turn the idle speed screw down, it will idle slower but quickly dies and will not start again in that state. The bike responds well to throttle coming off of idle without stumbles, but I'm not sure it's sitting fully in an idle state anyways.

I left the bike "idling" for ~ 1 min to try and get a reading off of the plug. The plug had previously been dry fouled so I dont think it had time to burn off that dry fouling. It came out looking leaner than it had previously, but again, I don't trust that. Will be picking up another new plug today to get a better idea.

I am comfortable with figuring out how to adjust a slow jet based on how many turns out the fuel mixture screw is, but I'm out of my depth with knowing if I'm rich or lean given that it only starts with the idle screw out 4.5 turns.
Where do I go from here?

[Megadan]

I'm out of my depth with knowing if I'm rich or lean given that it only starts with the idle screw out 4.5 turns.
Where do I go from here?

4.5 turns out on a fuel mixture screw = way too lean. Step up the pilot jet size. If it is at a 32, I would honestly jump to a 38 or a 40. A small engine with a big carb isn't going to have as strong of a draw on the jets, so you may end up with jets bigger than you would think to get the right fuel flow, and it is going to be a lot more sensitive to small fueling adjustments like the idle mixture, so you may find yourself fine tuning it down to 1/8th turns to get that idle stable.

As far as idle speed, what is recommended for that motor? Most small singles generally idle around 1400-1600rpm. Go too low on the idle, especially with a large carb for the engines displacement, and it may not want to idle at all, as you are experiencing.

[Ad642254]

Thanks, that does make sense, given that I was on a 35 pilot and 120 main prior and it was still lean.

I really should be on a pz27, shouldn't I?

[Megadan]

Your are kind of right on the border of the smallest engine size a PZ30 can run, which is generally 150cc. The PZ27 is much better matched to your 145cc engine size, and as a general rule of thumb will actually perform better across a wider power band. I think the largest I would go would be a 28mm smooth bore carb.

[Ad642254]

I've ordered a Mikuni VM22 with jet kit and will see how I fare with that.
Thanks for all the advice.

[NzBrakelathes]

Thanks, that does make sense, given that I was on a 35 pilot and 120 main prior and it was still lean.

I really should be on a pz27, shouldn't I?

You may want to consider a PZ27B pumper - just a thought and I could supply with a vast range of jets etc

[Wild Dog]

I've ordered a Mikuni VM22 with jet kit and will see how I fare with that.
Thanks for all the advice.

You went from a bit too big, to a bit too small. They will show you a picture that says "26mm" but when you actually meassure it. It's actually 25mm to 24mm. That's why most seller says "125 to 140cc"

For the CG150 the PZ27 is the ideal one, that's why it even comes stock with the cheap hondas like the xr150l, titan 150

[Megadan]

You went from a bit too big, to a bit too small. They will show you a picture that says "26mm" but when you actually meassure it. It's actually 25mm to 24mm. That's why most seller says "125 to 140cc"

For the CG150 the PZ27 is the ideal one, that's why it even comes stock with the cheap hondas like the xr150l, titan 150

I agree with this 100%. The 22 will be too small (unless that was a typo?)

A true Mikuni VM26 would also be a good carb. Not the "30mm" version like we run on our CG250 engines though, an actual 26mm VM26-606. This would require a socket style intake mount though, and the carb generally costs about $80-90. Not ideal for the budget minded, but a damn good carb if you can afford it. Also completely sales pitch free.

[Ad642254]

oops!You're right, I ordered the wrong carb. Cancelled and reordered a 22. Thank you

[Megadan]

oops!You're right, I ordered the wrong carb. Cancelled and reordered a 22. Thank you

Cancelled the 22 and reordered the 22? You feeling ok? :hehe:

[Wild Dog]

I agree with this 100%. The 22 will be too small (unless that was a typo?)

A true Mikuni VM26 would also be a good carb. Not the "30mm" version like we run on our CG250 engines though, an actual 26mm VM26-606. This would require a socket style intake mount though, and the carb generally costs about $80-90. Not ideal for the budget minded, but a damn good carb if you can afford it. Also completely sales pitch free.


The VM26 is a great carb, i have two of them. One is a "ss" version that came with a kawasaki. While i was cleaning a rekiting that carb, i got a chinese VM26. That VM26 is actually a 26mm mikuni clone a far cry from the 30mm version.
The chinese sell that carb as a "DT175 carb", which is correct, since the DT175 came from the factory with a vm26.

https://lh3.googleusercontent.com/PvjmmkKrmRIAg5c6fFfJj4iPWogbqzdnhRsjl80cm-W8ygAGgfc5Ib45_2EaV_HU8RTAWR6k-4yraFcWxzJvssNNG-ozqP9jwIvFvF8d1VMD_oa0_1e_EyzHQXAf2e2Mx90NPGnit2zh GXTt0rmV3GGRa8-CD7vulTIywCj57Tnz8XYVm_rIO-3NfsG3abI2HfwiYWsLl82j-q1UvKGbur0P2_zXgeIydAWCushZLLrp01_ugexkSHHXbciW6RR yDVTmFp0taAbpGFVCyn3CHxNjKp3ilSSjk_qjRDn6BNE1X1b7K 9aiiA7Xfau9S_hBop49VGwNnH6so6k94X2MKQTW1cQyUMkID-_wranxMnWlV_AU1eFgjoF7iui4GbYKVAShfApHiOBRltpaim07 Sk0kvKzqU8ypyE-oZ5dIeEW4nveb1UdRGDXq-DNECiTcnyqkw2owJfzBx21As6hFILp6l-j1dpO_We_8EykGscvFKce-FQNkQnI1LRLH2xRceEvjNv7UXYPc0vwuxSE9vhb6ECYWPgpdsT PQnmokem__zZfQ20u2IrTOOyxG6RON5iwwuFWvH5SRh7x_oiqJ ReUj73tIuuontIPFADWhH_3ecz8e7ybUHm0Ieky5zLXTs74mZ7 51e4Rv3xxGZHe3QfpS5LTDTkt1=w662-h937-no

Is a good clone, it was just a bit too lean for the 2t and since it was a temporary carb, i never bothered to rekit it. In the end i just took the nice looking bolts from it and put them on the real VM26.


https://lh3.googleusercontent.com/Ky2ezGt6R4BgmABoXKYTkJedUQBm44LF6KgHXavwARvtis5gOG uHK-_UJlpIbIYdK4JYZjdtH4DKJqRT5BbOyT4CdnUWUzFzSjHojBwO 1UmyPRL0CaVWudAfIGMXf14JkRbypVH8v0d_WYsUbDERbxCJuu YjLoUFl_beUOliRZQLwtsLwoFr5vWAYajdMyVyhcXfDJAWrAId mrbSR8OcQOv73LRmHobQ9WMM25PWuTMXz5Wnn1t2K5zXMl5I9E wZ0dBFVOq9QkfWPMzxUJMivKuYHUWEM26_8bxZwGUZWXpS3UUU 9Y7X54rdEql3N5atab9J626RLc_dRF5zBDYbvl_fT_EeYC2B23 UefI4ub9d9QKIeFm8TOrzJXofc1gkOITwdpmNAvP-0NIOjPJNglYZcgK71o-5oEAdsvigri6UrnAgrC8eeXuQJxJEVDmgsdH1_MHxf6v67WIIV mZSCp3iqed7E7BMR13bhXqsKtohU9Zt8GvwcT-XrCJTWq5kSgiwr16Bsv4T6KKvmxMctLoekm26WhbgLU6f9hsVT UgTNIbCPTzpRluurz8PcnvUbpWI_iJc-YyRRzfmjxFWDhb7J6tnoL2AzLvNH5jipMTqL9iVtSrAXEDhUFi 9mpYH08AI3MyUEG8_rZnmNWchfVi54nKxr1TsQ=w770-h937-no


Also no cable operated choke....

https://lh3.googleusercontent.com/B-g1hYPxZIkFTs6i_A8tfDb8nR87VY0vePFN5yoR1jYbETdpY5zf WGh4G_jKZIgqmhQtOeMTO59j1s5kcSejzIyL7U9jxHicoEvA-CebccmO4NbctxybV-XxdsmFrdrGgM4gPC7esFyuHeYGB3zyAoNCE2FTw02hhH00cbVR jJQC2wNRTnIYlipe7bOHuOk3ZstEZbCw-zYsUmHu0GkrgZ6LkmamfuJFK7BG-Wmq3FqZ3lZUR_NPgbbhAESSNUXo4DPNwZiACK-GOmE9zlkLE5j_Wystx7EwKh8UWHF7vOevgbfd02qg7oAX3ZUlw sn4lmST1V2Yr_LbT2l-HMPIwWQZREFi3OgpCpeKh0zXQBfYfYRZSb9WDqVrobWcvFWu8D cCMdBqVYNO8U2_n1XR_d9XC53CZ_-JdM2kU9AKH18UU-ZD4yKuuNvYZx70cwxunWpiMAeI0DuV-OUz3bjO5FqZFBp4oOMOrs_KoGCRndGtw73C0xupHxG3DncSBRo SiV1OsBi1gQYxhgHtXBDArjInX-DhwexQ_KwZrw4e9ccxFCgCElj3I97QfvyH-diAoAFrVibmLwyWxP238ZYuy5_pcywoM5ATFeK4ASjnWFoTtzB mg8rv-XPYoH42aqGHi_7OaEOX-cXsa6-GLo90qkMQvuZH3A4l=w1192-h937-no

[Ad642254]

Wow, night shifts are really getting to me!
I tried to cancel the 22 and wasn't able to.. so now I'm stuck with it. Sucks. Shouldnt order when Im tired the listing said vm22 26mm so thought it'd be good. Turns out the 26 is the opening bore. The bore at the carb slide opening is 22.
I'm going to wait for a genuine mikuni 26 to come up on eBay used and rebuild it. I'll try to get this pz30 or vm22 tuned up in the mean time. Fun project at least.

[Ad642254]

When I look in the Mikuni VM tuning manual, an engine putting out the hp of my 145cc (~12hp), mikuni recommends a 22mm carb aperture at most.

I'm quite excited to see how the engine responds to these two carbs

[Megadan]

When I look in the Mikuni VM tuning manual, an engine putting out the hp of my 145cc (~12hp), mikuni recommends a 22mm carb aperture at most.

I'm quite excited to see how the engine responds to these two carbs

Yeah, for 12hp a VM22 might actually do just fine. It will definitely have a nice strong power curve with the smaller carb. A 26/27mm carb will breathe a lot better up top though. I would love to read your experiences between the two.

[Ad642254]

I'm quite curious as well. The bike as it was working before was pretty grunty in the low end and anemic in the high end, likely since it was running lean. The oversized carb should have been better in the higher RPMs. With a smaller carb I'm excited to see how the low end feels. It's a small bike for commuting around town and riding some trails so the low end is what I'm wanting. I'll update once the carb gets here. In the meantime, trying a 130 main and 38 slow

[Ad642254]

I'm having trouble finding recommended, or "stock" idle speed screw settings. Recommended dle mixture screw settings are easy to find, 1-3 turns from bottomed out (or 0.5-2.5, depending.)
The idle speed screw raises the slide as it is turned in. Is it similar recommended setting for this screw? I think the reason I was having problems with the bike before was because I had the idle speed screw about 4 turns out, with the idle mixture screw about 2 turns out.
Now I have a 35 slow and 125 main and can still only get it to start with the mixture screw 3 turns out and speed screw 4 turns out. Then it runs at a very high speed, not really an idle; maybe 2000 rpm. I can turn the speed screw out once it's running and bring the idle down, but then it won't kick start. Also, when it's running the mixture screw still does nothing. I tried a 38 slow and could not get it running at all. I can troubleshoot the slow jet better if I know where abouts I should have the speed screw set.

[Kivi]

The VM26 is a great carb,]

Sry for OFF, but I do not see these images. I dont know how others sees then.

[Wild Dog]

Now I have a 35 slow and 125 main
Both jets are too big for the 150cc. Just to give you an idea, Honda uses a 110 main for CG 150 and the CB 150.
Trust me on this, if your jetting is not the right one for the engine, is going to be a nightmare to make it idle right and run right. You are going to waste fuel and get very very frustated.
You should try a 25 slow and 110 main

[Ad642254]

I hear you, but with the oversized carb having such low flow velocity I would think it would need a larger jet to get the same fuel delivery.
I've had it with a 30 slow and it was very very lean at idle. I think Honda used a pz27 sized carb on that.
However, I'll give it a try with a 25 and 110 and see where I'm at. I don't trust anything the bike was doing before since I think the floats were way off

[Wild Dog]

I hear you, but with the oversized carb having such low flow velocity I would think it would need a larger jet to get the same fuel delivery.
I've had it with a 30 slow and it was very very lean at idle. I think Honda used a pz27 sized carb on that.
However, I'll give it a try with a 25 and 110 and see where I'm at. I don't trust anything the bike was doing before since I think the floats were way off

Just wait for the vm22 and mimick the jetting that honda uses on their cg150.
If you can, get a few spark plugs and test the engine a few times and read the plugs to see if it's running rich or lean.

[Ad642254]

Thanks.
One thing I still can't find are settings for the idle speed screw. As the screw turns in it raises the slide. It seems to me there's no need.to have it screwed in raising the slide at all. But I was also told that 4 turns out indicates my slow jet is too lean. However, even with a 25 slow it will only idle with the idle speed screw almost all the way out so that the slide isn't raised at all.

It seems to me that on a CV carb, if.youre setting slow jets with the idle speed screw only out two turns or so, you've got unmetered air coming in. You're then not really setting idle mix accurately.

Edit: a tuning manual for a Holley CV carb says that the idle speed screw is set until it just touched the slide, then a half turn in. That's much different than I've been doing. I've been at about 2 turns out. This is about 5 turns out.