Try and tune PD1 or go for new carb?

danjferg · 09-21-2024, 06:18 PM

Hey folks. I'm looking for some carburetor advice.

I've got a PD1 on my 2005 Trailmaster 200. To get it started it takes full throttle and choke even after running for a few minutes. It barely runs at idle after a full 10 minute warmup. If I give it a little choke then it idles much better. If I blip the throttle the RMPs come down slower than I expect, but not terrible. I'm thinking these are symptoms of running a tad lean.

My past experience(which is very little) tells me to adjust the mixture screws and enrich the mixture. But I cannot find any mixture screws on the carb. Am I blind? Or does this mean I have to fiddle with the interior? Like adjust the float?

I've only toyed with carbs on weed-eaters, with not a ton of success. I'm wondering if it's worth learning and going through the process to tune the PD1? Or If I have to take it apart, should I just shell out the cash for a better carb?

Thanks for any guidance, suggestions and advice!

zero_dgz · 09-22-2024, 10:57 AM

There are never any mixture screws on these carbs other than the idle mixture screw, which from the factory on many OEM carbs will be concealed by a plug you have to drill or pry out. To change the mixture at mid or open throttle you will have to change the jets and/or needle, or adjust the needle if it is adjustable.

Changing the carb on a Chinese bike is generally not done to get a "better" one, per se, but to get one which has known compatibility with various jet kits or can be more easily disassembled (i.e. is not riveted shut like some OEM carbs).

danjferg · 09-22-2024, 07:08 PM

Thanks for the response. I looked more into it today and found this video: https://www.tiktok.com/@rabdaurepair...35435036806443

It's the same carb, but I was confused because mine had a hose attached to the adjustment screw which I though was an overflow tube. I moved the hose to the fuel bowl drain outlet.

Is that front screw the proper one to adjust?

Many of the other Sheng Wey carbs I see have an adjustment screw on on the intake side, but mine is plugged like in the picture. Is there a screw behind the plug, and is that what I should adjust instead of the one on front?

Thanks so much!

ProDigit · Yesterday, 11:42 AM

You could adjust the idle screw, but my first question would be if you're still running the stock intake and exhaust?

If you've changed the intake to a pod filter, more than likely you'll need bigger jets. Same with the exhaust.

Adjusting the AF screw might help some, but is a bad tune.

Looks like a PZ or VM carburetor, which use oko or minkuni jets. Costs $10 for a jetpack with idle and main jets.

If you have no money, use a drill and a steel (clothes pin) needle. The steel needle can widen the idle jet aperture by enough to run richer. Your main jet will also need to be richer. You can drill it out, but drilling a main jet out can often lead to uneven burn, as some of the fuel will be released as larger droplets. It's better to bump up the main jet size with one from a pack, than to drill one out.

If you have a good eye, you can compare jets by looking through them towards a light source, and comparing the aperture of the jets to the one you got.
Get one that looks slightly larger.

danjferg · Yesterday, 09:09 PM

Thanks for the response.

Intake and exhaust are still stock. For now I don't have any plans to upgrade. At least I know the path forward for making those adjustments.

While fiddling with the drain tube I also discovered the crankcase breather tube was disintegrating. So I'm replacing that as well.

I'll make all the replacements and fine adjustments on my list. If those don't work then I'll be cracking the carb open.

Thanks so much everyone!

09-21-2024, 06:18 PM	#1
danjferg Join Date: Sep 2024 Posts: 4	Try and tune PD1 or go for new carb? Hey folks. I'm looking for some carburetor advice. I've got a PD1 on my 2005 Trailmaster 200. To get it started it takes full throttle and choke even after running for a few minutes. It barely runs at idle after a full 10 minute warmup. If I give it a little choke then it idles much better. If I blip the throttle the RMPs come down slower than I expect, but not terrible. I'm thinking these are symptoms of running a tad lean. My past experience(which is very little) tells me to adjust the mixture screws and enrich the mixture. But I cannot find any mixture screws on the carb. Am I blind? Or does this mean I have to fiddle with the interior? Like adjust the float? I've only toyed with carbs on weed-eaters, with not a ton of success. I'm wondering if it's worth learning and going through the process to tune the PD1? Or If I have to take it apart, should I just shell out the cash for a better carb? Thanks for any guidance, suggestions and advice!
	0

09-22-2024, 07:08 PM	#3
danjferg Join Date: Sep 2024 Posts: 4	Thanks for the response. I looked more into it today and found this video: https://www.tiktok.com/@rabdaurepair...35435036806443 It's the same carb, but I was confused because mine had a hose attached to the adjustment screw which I though was an overflow tube. I moved the hose to the fuel bowl drain outlet. Is that front screw the proper one to adjust? Many of the other Sheng Wey carbs I see have an adjustment screw on on the intake side, but mine is plugged like in the picture. Is there a screw behind the plug, and is that what I should adjust instead of the one on front? Thanks so much! Attached Thumbnails
	0

Yesterday, 11:42 AM	#4
ProDigit Join Date: Aug 2013 Posts: 285	You could adjust the idle screw, but my first question would be if you're still running the stock intake and exhaust? If you've changed the intake to a pod filter, more than likely you'll need bigger jets. Same with the exhaust. Adjusting the AF screw might help some, but is a bad tune. Looks like a PZ or VM carburetor, which use oko or minkuni jets. Costs $10 for a jetpack with idle and main jets. If you have no money, use a drill and a steel (clothes pin) needle. The steel needle can widen the idle jet aperture by enough to run richer. Your main jet will also need to be richer. You can drill it out, but drilling a main jet out can often lead to uneven burn, as some of the fuel will be released as larger droplets. It's better to bump up the main jet size with one from a pack, than to drill one out. If you have a good eye, you can compare jets by looking through them towards a light source, and comparing the aperture of the jets to the one you got. Get one that looks slightly larger. __________________
	0

09-22-2024, 10:57 AM	#2
zero_dgz Join Date: Jan 2020 Posts: 277	There are never any mixture screws on these carbs other than the idle mixture screw, which from the factory on many OEM carbs will be concealed by a plug you have to drill or pry out. To change the mixture at mid or open throttle you will have to change the jets and/or needle, or adjust the needle if it is adjustable. Changing the carb on a Chinese bike is generally not done to get a "better" one, per se, but to get one which has known compatibility with various jet kits or can be more easily disassembled (i.e. is not riveted shut like some OEM carbs).
	1

Yesterday, 09:09 PM	#5
danjferg Join Date: Sep 2024 Posts: 4	Thanks for the response. Intake and exhaust are still stock. For now I don't have any plans to upgrade. At least I know the path forward for making those adjustments. While fiddling with the drain tube I also discovered the crankcase breather tube was disintegrating. So I'm replacing that as well. I'll make all the replacements and fine adjustments on my list. If those don't work then I'll be cracking the carb open. Thanks so much everyone!
	0