PZ27 vs PZ30 Carb Upgrade - Page 3

akvilonBrown · 08-23-2012, 01:33 PM

Well, maybe I'll consider replacing too if the things get worse in cold weather.
Is there anything I should take into account additionally?
Like measuring air intake sizes or parameters (by the way, is it worth to install free-flow filter with new carb?)?
Or is it enough to pick up the exact replica from Mikuni, meaning same parameters, for 200 cm engine with 2,6-3 liters per 100 km?

UPD: Loking for the Mikuni PZ30 and on the pictures on the first page of this topic I couldn't spot the 'boosting pump' (correct me if I wrong). You can see it on the right side of my carb with a throttle cord splitting to that pump as well. It adds up fuel during quick pulling the throttle cord. Does Mikuni PZ features the same thing? I'm happy how my carb works on warm state and how it accelerates, I'd like to retain these conditions.

Weldangrind · 08-23-2012, 10:39 PM

The 30mm Mikuni carbs I've installed do not have an accelerator pump.

akvilonBrown · 08-28-2012, 11:24 AM

There is no need to replace my carb, I conclude. I just have to adjust idling and/or pick up the right pilot. But I have to know how the stuff works. I went across dozen of sites with carb basics, but I need to clear up. And I found some posibility to pick jets for Kehlin based on their measurements.
We have here: throttle stop screw and pilot screw.
Throttle stop screw - it controls how wide throttle is open in resting position, right? And when I turn in, RPM goes higher. I presume, it shouldn't be open wide.
Pilot screw. Isn't is the same as air screw? What does it do? According to theory, when the threw is on the back (close to air intake?) it regulates the amount of air flowing through the idle circuit. If it is in front, it regulates the fuel. Well, that must be my case.
So, when I turn out pilot screw from the gentle seat position engine doesn't react. Only after 2,5 turns the engine begins to slow down and stops.
I need to understand the behavior: turning out = richer mixture? or vice versa. What pilot jet should I install - bigger or smaller?
That choke behavior - may it be something wrong with air passage on idle? Maybe bigger air jet?...

Weldangrind · 08-28-2012, 11:35 AM

I'm not as familiar with your carb and the enricher circuit (or pumper), but I get the basics.

You've got it figured out. If the pilot screw is on the engine side of the carb, it's a fuel screw, and backing it out increases fuel flow. The slow jet (or idle jet) within the bowl is responsible for idle, and you have a good grasp of how the idle screw works; it's just a screw contacting a ramp on the slider. Once you open the throttle, the pilot mixture screw creates the transition from slow jet to the main jet. The needle that seats in the main jet is directly connected to the throttle cable, and the the needle is tapered. As the throttle is opened, the taper is raised and more of the main jet is uncovered. The venturi action of air passing through the carb draws fuel up through either the slow jet or the main jet, depending upon whether the throttle is open or closed.

If you need to back out the pilot mixture screw more than two turns, your slow jet is likely too small. An increase of two sizes will likely be helpful.

Make sense?

akvilonBrown · 08-28-2012, 12:08 PM

Enricher pump - don't mind it, it doesn't tamper with other circuits, it is standalone unit. The rest is classic PZ30 carb.

You wrote:

If you need to back out the pilot mixture screw more than two turn
The point is that I don't need to back out the pilot screw, because it slows down. The highest rpm is on the maximum turning in (minus 2,5 turns - there is a plateau).
So I can suggest slow jet it is too large 8O. It can explain why choke doesn't work - mixture is to rich by itself.
But !!!
1) The engine won't start whatsoever without a throttle
2) The plug is almost pristine white.
It baffles me 8O [/b][/i]

Weldangrind · 08-28-2012, 12:22 PM

The pilot mixture screw is in the ideal spot when you can crack the throttle and not have the engine stumble. If the bike won't start without throttle, that tells me that the slow jet is too small. Your white plug confirms that it's not getting enough fuel.

akvilonBrown · 08-28-2012, 12:58 PM

Yeah, cracking the throttle may cause engine go dead, especially when not fully warm, regardless of pilot screw positions.

So playing with various slow jets seems most practical idea. From now it will take long time to figure out how to ship jets, but eventually I will post the results.
Thank you, Weldangrind, for quick response.

saboor73 · 03-05-2016, 02:57 PM

Sorry guys for bring up old thread but in need of serious help can any one tell me if this is correct needle for miken pz27 if not can anyone please share a pic of correct carb needle

saboor73 · 03-06-2016, 03:49 PM

Quote:

Originally Posted by saboor73

Sorry guys for bring up old thread but in need of serious help can any one tell me if this is correct needle for miken pz27 if not can anyone please share a pic of correct carb needle

Any one

08-23-2012, 10:39 PM	#32
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	The 30mm Mikuni carbs I've installed do not have an accelerator pump. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	0

08-28-2012, 11:35 AM	#34
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	I'm not as familiar with your carb and the enricher circuit (or pumper), but I get the basics. You've got it figured out. If the pilot screw is on the engine side of the carb, it's a fuel screw, and backing it out increases fuel flow. The slow jet (or idle jet) within the bowl is responsible for idle, and you have a good grasp of how the idle screw works; it's just a screw contacting a ramp on the slider. Once you open the throttle, the pilot mixture screw creates the transition from slow jet to the main jet. The needle that seats in the main jet is directly connected to the throttle cable, and the the needle is tapered. As the throttle is opened, the taper is raised and more of the main jet is uncovered. The venturi action of air passing through the carb draws fuel up through either the slow jet or the main jet, depending upon whether the throttle is open or closed. If you need to back out the pilot mixture screw more than two turns, your slow jet is likely too small. An increase of two sizes will likely be helpful. Make sense? __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	0

08-28-2012, 12:22 PM	#36
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	The pilot mixture screw is in the ideal spot when you can crack the throttle and not have the engine stumble. If the bike won't start without throttle, that tells me that the slow jet is too small. Your white plug confirms that it's not getting enough fuel. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	0

03-05-2016, 02:57 PM	#38
saboor73 Join Date: Mar 2016 Posts: 5	carb neddle Sorry guys for bring up old thread but in need of serious help can any one tell me if this is correct needle for miken pz27 if not can anyone please share a pic of correct carb needle
	0

08-23-2012, 01:33 PM	#31
akvilonBrown Join Date: Aug 2012 Location: Ukraine Posts: 7	Well, maybe I'll consider replacing too if the things get worse in cold weather. Is there anything I should take into account additionally? Like measuring air intake sizes or parameters (by the way, is it worth to install free-flow filter with new carb?)? Or is it enough to pick up the exact replica from Mikuni, meaning same parameters, for 200 cm engine with 2,6-3 liters per 100 km? UPD: Loking for the Mikuni PZ30 and on the pictures on the first page of this topic I couldn't spot the 'boosting pump' (correct me if I wrong). You can see it on the right side of my carb with a throttle cord splitting to that pump as well. It adds up fuel during quick pulling the throttle cord. Does Mikuni PZ features the same thing? I'm happy how my carb works on warm state and how it accelerates, I'd like to retain these conditions.
	0

08-28-2012, 11:24 AM	#33
akvilonBrown Join Date: Aug 2012 Location: Ukraine Posts: 7	There is no need to replace my carb, I conclude. I just have to adjust idling and/or pick up the right pilot. But I have to know how the stuff works. I went across dozen of sites with carb basics, but I need to clear up. And I found some posibility to pick jets for Kehlin based on their measurements. We have here: throttle stop screw and pilot screw. Throttle stop screw - it controls how wide throttle is open in resting position, right? And when I turn in, RPM goes higher. I presume, it shouldn't be open wide. Pilot screw. Isn't is the same as air screw? What does it do? According to theory, when the threw is on the back (close to air intake?) it regulates the amount of air flowing through the idle circuit. If it is in front, it regulates the fuel. Well, that must be my case. So, when I turn out pilot screw from the gentle seat position engine doesn't react. Only after 2,5 turns the engine begins to slow down and stops. I need to understand the behavior: turning out = richer mixture? or vice versa. What pilot jet should I install - bigger or smaller? That choke behavior - may it be something wrong with air passage on idle? Maybe bigger air jet?...
	0

08-28-2012, 12:08 PM	#35
akvilonBrown Join Date: Aug 2012 Location: Ukraine Posts: 7	Enricher pump - don't mind it, it doesn't tamper with other circuits, it is standalone unit. The rest is classic PZ30 carb. You wrote: If you need to back out the pilot mixture screw more than two turn The point is that I don't need to back out the pilot screw, because it slows down. The highest rpm is on the maximum turning in (minus 2,5 turns - there is a plateau). So I can suggest slow jet it is too large 8O. It can explain why choke doesn't work - mixture is to rich by itself. But !!! 1) The engine won't start whatsoever without a throttle 2) The plug is almost pristine white. It baffles me 8O [/b][/i]
	0

08-28-2012, 12:58 PM	#37
akvilonBrown Join Date: Aug 2012 Location: Ukraine Posts: 7	Yeah, cracking the throttle may cause engine go dead, especially when not fully warm, regardless of pilot screw positions. So playing with various slow jets seems most practical idea. From now it will take long time to figure out how to ship jets, but eventually I will post the results. Thank you, Weldangrind, for quick response.
	0