PZ30 takes me to school (How do you know when have to many knockoff carbs)

China Rider 27 · 01-16-2021, 12:30 PM

Last weekend I got my PZ30 out and was gonna do some testing with it on the ported head I had completed. Last time I used it was just about a year ago. I put it on the bike got it started and seemed okay, little hard starting. Got it riding around the neighborhood up to about 30 mph. Pulled onto the major roadway 45 mph speed limit and got up through second to third and went to open up the throttle to accelerate and the motor falls on its face hard from 1/3 to to 1/2 throttle, no power, spitting. Worked great last time I used it? Pulled the plug, black soot looks rich? How could that be, ported head, should be lean if anything. Hmm. Yesterday, I decided to do the first quick obvious change I removed the 2 washers under the needle. Drove it around the neighborhood, still has 1/3 and up throttle issue. Thinking about last night, gotta get up in the morning and figure this out, but how could it be rich, something is really messed up.

Took it apart this morning, missing the 125 main jet!!!!!!! How do you know when you have to many china knockoffs? When you cannibalize one to get another to work right and then forget about it!!! Lesson here about carburetor circuits and main jets.

Biker_Andy · 01-16-2021, 01:50 PM

Lol that could happen to anyone! I seem to forget which way the choke works every spring when I bring her out of hibernation.

mtiberio · 01-16-2021, 05:20 PM

Btdt

Megadan · 01-16-2021, 06:09 PM

Sounds about right. between 1/8 and 1/4 throttle you are still mostly relying on the pilot jet and the needle jet just starts to get into the taper and let a little fuel past the emulsion tube that the main jet feeds. Even up to 1/2 throttle, the needle is still blocking a large amount of the opening of the emulsion tube (Needle Jet), so the size of the main jet doesn't even factor in at that point. Once you near 1/2 throttle though, that needle taper is there to regulate the main jet fuel flow a lot more, and with nothing there, it was basically a garden hose.

By the sheer amount of times I have to correct people here and on the Facebook groups about their jetting choices or advice, it is no surprise to me that people still don't understand just how much those jet arcs REALLY do matter.

In theory one could also do the exact opposite, if you could start a bike and just start riding it at 1/4 throttle or more, the bike could have no pilot jet or idle mixture circuit and still run perfectly.

TheChairman · 01-16-2021, 10:24 PM

This reminds me of when I removed my carb for the first time and deleted my charcoal canister.

I wasnt paying attention and hooked the fuel line back up to the vacuum inlet for the canister on the carb. It started fine, and even seemed to ride fine with plenty of power. It just fouled the plug at idle.

Turns out I didn't just jet it a little rich, I had made some sort of primitive TBI system that actually worked.

China Rider 27 · 01-16-2021, 10:26 PM

Thinking back I do believe it was more like 1/2 throttle where the issue came in. It ran fine as long as you didn't go above 1/2 throttle. Drove it around and home no problem. No doubt understanding the carburetor circuits is the key to efficient tuning effort.

China Rider 27 · 01-16-2021, 10:36 PM

Quote:

Originally Posted by TheChairman

This reminds me of when I removed my carb for the first time and deleted my charcoal canister.

I wasnt paying attention and hooked the fuel line back up to the vacuum inlet for the canister on the carb. It started fine, and even seemed to ride fine with plenty of power. It just fouled the plug at idle.

Turns out I didn't just jet it a little rich, I had made some sort of primitive TBI system that actually worked.

Amazing! I've seen on U tube, where they use a regulator and dribble propane into a carburetor for generators and such.

TxTaoRider · 01-17-2021, 08:11 AM

I've seen people that tried fixing lean idle and cruise (light throttle) by going up on the main jet and puzzled why it didn't work. You can tell them they are messing with the wrong circuit but they don't listen until they've completely given up.
In their minds there's the main jet that does everything, and everything else in a carburetor was thrown in because they had parts laying around at Mikuni. Lol

Megadan · 01-17-2021, 09:54 AM

Quote:

Originally Posted by TxTaoRider

I've seen people that tried fixing lean idle and cruise (light throttle) by going up on the main jet and puzzled why it didn't work. You can tell them they are messing with the wrong circuit but they don't listen until they've completely given up.
In their minds there's the main jet that does everything, and everything else in a carburetor was thrown in because they had parts laying around at Mikuni. Lol

It makes your brain hurt with how many of them are out there too. Especially on the facebook groups.

01-16-2021, 12:30 PM	#1
China Rider 27 Join Date: Dec 2018 Location: PNW Posts: 982	PZ30 takes me to school (How do you know when have to many knockoff carbs) Last weekend I got my PZ30 out and was gonna do some testing with it on the ported head I had completed. Last time I used it was just about a year ago. I put it on the bike got it started and seemed okay, little hard starting. Got it riding around the neighborhood up to about 30 mph. Pulled onto the major roadway 45 mph speed limit and got up through second to third and went to open up the throttle to accelerate and the motor falls on its face hard from 1/3 to to 1/2 throttle, no power, spitting. Worked great last time I used it? Pulled the plug, black soot looks rich? How could that be, ported head, should be lean if anything. Hmm. Yesterday, I decided to do the first quick obvious change I removed the 2 washers under the needle. Drove it around the neighborhood, still has 1/3 and up throttle issue. Thinking about last night, gotta get up in the morning and figure this out, but how could it be rich, something is really messed up. Took it apart this morning, missing the 125 main jet!!!!!!! How do you know when you have to many china knockoffs? When you cannibalize one to get another to work right and then forget about it!!! Lesson here about carburetor circuits and main jets.
	0

01-16-2021, 01:50 PM	#2
Biker_Andy Join Date: Oct 2016 Posts: 347	Lol that could happen to anyone! I seem to forget which way the choke works every spring when I bring her out of hibernation. __________________ Electrician & Electronics Tech 2014 Honda CB500XA 2016 CSC TT250 1976 Honda CJ360T 2022 Honda Navi
	0

01-16-2021, 05:20 PM	#3
mtiberio Join Date: Jun 2016 Location: Arlington, VA Posts: 258	Btdt __________________ 4 time WERA SuperVintage Roadracing National Champion, SCTA Land Speed Record Holder, 3rd AMA Motorcycle GP of Miami
	0

01-16-2021, 06:09 PM	#4
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,053	Sounds about right. between 1/8 and 1/4 throttle you are still mostly relying on the pilot jet and the needle jet just starts to get into the taper and let a little fuel past the emulsion tube that the main jet feeds. Even up to 1/2 throttle, the needle is still blocking a large amount of the opening of the emulsion tube (Needle Jet), so the size of the main jet doesn't even factor in at that point. Once you near 1/2 throttle though, that needle taper is there to regulate the main jet fuel flow a lot more, and with nothing there, it was basically a garden hose. By the sheer amount of times I have to correct people here and on the Facebook groups about their jetting choices or advice, it is no surprise to me that people still don't understand just how much those jet arcs REALLY do matter. In theory one could also do the exact opposite, if you could start a bike and just start riding it at 1/4 throttle or more, the bike could have no pilot jet or idle mixture circuit and still run perfectly. __________________ Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124
	2

01-17-2021, 08:11 AM	#8
TxTaoRider Join Date: Oct 2020 Location: Flower Mound Texas Posts: 904	I've seen people that tried fixing lean idle and cruise (light throttle) by going up on the main jet and puzzled why it didn't work. You can tell them they are messing with the wrong circuit but they don't listen until they've completely given up. In their minds there's the main jet that does everything, and everything else in a carburetor was thrown in because they had parts laying around at Mikuni. Lol __________________ 2021 Tao Tbr7 - "Lucille" Mods so far- Brozz swingarm, 21" front rim (Bridgestone Tw302 rear/Dunlop D606 front tires), Digital gauge cluster, pz30b pumper carb, after market hand guards, aftermarket brake and clutch levers, round fold away mirrors, Fly handlebars shortened slightly, 13t front sprocket 2009 Q-link Legacy 250 1982 Suzuki GS1100ES - "Jolene"
	1

01-16-2021, 10:24 PM	#5
TheChairman Join Date: May 2020 Location: Philadelphia Posts: 115	This reminds me of when I removed my carb for the first time and deleted my charcoal canister. I wasnt paying attention and hooked the fuel line back up to the vacuum inlet for the canister on the carb. It started fine, and even seemed to ride fine with plenty of power. It just fouled the plug at idle. Turns out I didn't just jet it a little rich, I had made some sort of primitive TBI system that actually worked.
	1

01-16-2021, 10:26 PM	#6
China Rider 27 Join Date: Dec 2018 Location: PNW Posts: 982	Thinking back I do believe it was more like 1/2 throttle where the issue came in. It ran fine as long as you didn't go above 1/2 throttle. Drove it around and home no problem. No doubt understanding the carburetor circuits is the key to efficient tuning effort.
	0