PZ27 vs PZ30 Carb Upgrade

[Weldangrind]

This is a quote from your other thread:

Okay, so over the past couple of weeks, ive had to resort in trying the bigger slow jets i ordered, as the 25 still had bad low throttle responce.

The needle jet is fully up so thats not the issue i believe. First i change the slow to the 27.5, which id make it better, but even after tweeking the air screw, it was still hesitant/rough on part throttle where you just need to run at a steady 30 mph (for example)

This week i finally decided to go for the 30 slow jet, again a minor improvement, but still a bit rough on part idle.

Ive only now notice that the bike runs worse the more you open the air jet, so ive ltteraally got it about 1/8 turn from closed. But the more you close it, the worse it idles. Can you actually run the bike with the air screw fully closed? Is that recommended? And what it the best way to be adjusting it. I know that 2 turns out means a bigger jet, but i dont actually know how to adjust it as such.

I'll ask a few questions for clarification. For starters, when you say the needle jet is fully up, do you mean that the clip in the jet needle is in the bottom position? If so, that's likely too rich. Try moving the clip up one notch and tell us if there is any improvement.

You're trying to establish a smooth transition from the idle circuit to the main circuit, so each step requires a proper A/F ratio. My guess is also that the slow jet is too big, but I recommend that you make one change at a time.

[kevshek]

yes, i have the clip at the very bottom motch, meaning the needle is in the highest position. I will try raissing the clip up one to bring it down slightly, but you are right, its the transition between the slow and main ciruit.

Can you explain how the air screw works? Ive noticed if the screw is fully closed, the bike begins to stall. ive so far got it about 1/4 turn open, anything more than that doesnt seem to make any difference, and never has done with any of the other sizes i tried.

[Weldangrind]

In your application, it's a fuel screw, not an air screw. It provides the transition from idle to main, and it is directly related to the slow jet size. IOW, if your slow jet is too small, you'll need to open the fuel screw (AKA pilot jet) more than two turns. If you hardly need to open the screw at all, the slow jet is on the large side.

Looking forward to hearing what a clip adjustment does.

[kevshek]

Mate, you've only gone and done it again! I've adjusted the clip this afternoon and my ride into work tonight was silky smooth! There is no hesitation at part throttle, the transition to the main circuit is seemless, even backing off the throttle and reapplying it during higher revs, the engine doesn't jerk about.

Can't thank you enough!

With the addition of tightening up the engine mount bolts, and replacing the one that was missing which gave the bike a horrible vibration, the bike feels great and should now be ready for winter, which is just Sewell cos today we've had the first snowfall albeit very light.

[FastDoc]

Weld knows things.

Snow is evil.

[SpudRider]

Originally Posted by FastDoc

Weld knows things.

Snow is evil.

X2 on both points, oh wise physician.

Spud

[Weldangrind]

Glad to hear it, kevshek! In the words of Doc, I'm happy to serve.

[Frog]

Hi Kevshek,

did your new carb improve performance at all?

Cheers

Frog

[akvilonBrown]

Hi everybody!
I'm glad to have found this topic.
My carburateur is PZ30.
I can't get him to warm up the engine properly because it doesn't react to choke lever.
It only stops when choke is 100% closed. Other positions nearly don't affect the engine run.
I have to partially open the main throttle in order to keep warming up.
By the way when throttle is slightly open this way, there is difference between positions of the choke.
Something wrong with idle circuit.
Engine doesn't response to pilot screw much - now it turned out on 2.5 turns.
It has however good response on idle (horizontal) screw.
In other ways it works perfectly, espesially when fully warm.
Need some advice with that dead choke how to force it work.

[Weldangrind]

Welcome akvilonBrown!

Please feel free to start a new post, so that more people will be able to read it and try to help.

My feeling is that the slow jet is either partially clogged, or it's too small. If you remove the pilot jet and tell us what size it is, we can guide you from there.

[akvilonBrown]

Originally Posted by Weldangrind

Welcome akvilonBrown!

Please feel free to start a new post, so that more people will be able to read it and try to help.

My feeling is that the slow jet is either partially clogged, or it's too small. If you remove the pilot jet and tell us what size it is, we can guide you from there.

Thank you Weldangrind, for your welcome and reply.
Maybe to early for separate post, it's just small reconnaissance. Kind a small step cause it's still warm weather and I don't have so much trouble with warming up. But afraid of the fall coming.
To be honest I'm complete newbee and require some crash course.
Can I remove the pilot jet without dismantling the carb? Is it about unscrewing the pilot screw or it wants dissasembling the carb body?

[FastDoc]

Turn off the fuel. Remove the bowl screws, 3 or 4 I forget on your carb. You may have to remove or loosen the carb body to get to the screws. Carefully slide out the pivot pin for the float and the jets will be visible to unscrew with a good fitting flat blade screwdriver. Do not lose the float needle valve.

I encourage you to look at www.dansmc.com for his on line course for more detail.

[akvilonBrown]

Originally Posted by FastDoc

Turn off the fuel. Remove the bowl screws, 3 or 4 I forget on your carb. You may have to remove or loosen the carb body to get to the screws. Carefully slide out the pivot pin for the float and the jets will be visible to unscrew with a good fitting flat blade screwdriver. Do not lose the float needle valve.

That was simple!. I haven't even lost anything.
So how could I measure those jets?
I can tell only marks on them.
Main jet: 145KB
Slow Jet: K40A

Does it make sense?

Originally Posted by FastDoc

I encourage you to look at www.dansmc.com for his on line course for more detail.

Great stuff! Your FAQ no worse too.

[FastDoc]

Those marks are the sizes I think. Weld will tell you the specifics. Dan has a good site. I've been wrenching for 35 years and I still refer there sometimes.

[Weldangrind]

I can't tell you the specifics about the Keihin (and clones), but I can guess. The slow jet number is likely to be #40, but I'm not sure how to interpret the main jet. Main jets are usually in the neighbourhood of #100.

The 30mm Mikuni is much easier to work with, because jets are easily found. Depending on the Keihin clone you have, it might be very difficult to source replacements; that's why I switched to Mikuni.

With a stock muffler and airbox, I'd likely use a #110 main and a #25 slow jet in a Mikuni.