43cc carb tuning - Pocket Bike Forum - Mini Bikes
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post #1 of 56 (permalink) Old 02-01-2020 Thread Starter
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Question 43cc carb tuning

I have a typical chinese pocket bike, i've been wanting to tune the carb for a bit and was wondering how to get peak performance out of it. The carb is 1 screw instead of 2 so i have no idea how to tune it.
Any suggestions? I'm looking for top end if that helps in anyway. Thanks
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post #2 of 56 (permalink) Old 02-02-2020
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Re: 43cc carb tuning

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Originally Posted by LittlebikesBigDreams View Post
I have a typical chinese pocket bike, i've been wanting to tune the carb for a bit and was wondering how to get peak performance out of it. The carb is 1 screw instead of 2 so i have no idea how to tune it.
Any suggestions? I'm looking for top end if that helps in anyway. Thanks
The carb has more than one screw....In fact it has 3...[1]Idle control,[2]LSN/HSN combo screw and [3]fuel rate adjustment screw..

Two screws can be seen with the naked eye and one that's kinda hidden...…….


Heres where the hidden one is.....Its the LSN / HSN combo screw..



Heres what it looks like disassembled from the top of the carb...………..



Heres a short video that may be able to help you...…..

Click on picture...…………...

004-3 by Dizzy Gillespie, on Flickr

Theres something to add that I left out of the video....seeings the exhaust was a bit restricted on the scooter used in the video plus to add the fact that I had to richen the LSN/HSN combo screw in the endI forgot to add that after you get the max wheel revs if you don't have to fiddle with the LSN/HSN combo screw you may need to richen the fuel rate screw about 1/8 turn outwards to compensate for rider load...…...

Good Luck

Last edited by CAM2; 02-02-2020 at 12:07 PM.
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post #3 of 56 (permalink) Old 02-02-2020 Thread Starter
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Re: 43cc carb tuning

Thanks for the video it was really helpful. I dont understand what he's saying when adjusting the high speed screw. Lift your rear tire off the ground and gun the throttle. Adjust the screw until you get the most wheel something. Mind telling me what he said? Because i cant understand it
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post #4 of 56 (permalink) Old 02-02-2020
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Re: 43cc carb tuning

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Originally Posted by LittlebikesBigDreams View Post
Thanks for the video it was really helpful. I dont understand what he's saying when adjusting the high speed screw. Lift your rear tire off the ground and gun the throttle. Adjust the screw until you get the most wheel something. Mind telling me what he said? Because i cant understand it

That was me and I said "until you get maximum wheel revs possible";-"Once you get the maximum wheel revs possible you're all good"...…….

Basically the fuel rate doubles as a highspeed screw too as its used to get max wheel revs.....

The LSN/HSN combo screw work in a balanced unisyn seeings theyre the same needle....

As the rotator rotates the rotator also lifts...That lifting action lifts the LSN/HSN combo screw up and out of the venturi tube it fits into...….


Last edited by CAM2; 02-02-2020 at 05:26 PM.
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post #5 of 56 (permalink) Old 02-02-2020 Thread Starter
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Re: 43cc carb tuning

Thanks dude. I'll tune it tomorrow when i have time.

Last edited by LittlebikesBigDreams; 02-02-2020 at 07:54 PM.
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post #6 of 56 (permalink) Old 02-02-2020 Thread Starter
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Re: 43cc carb tuning

Do you gain any power from tuning it? If not whats the point of tuning? I'm new to these small engines. Thanks for your help by the way!
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post #7 of 56 (permalink) Old 02-02-2020
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Re: 43cc carb tuning

Your dealing with a backpack engine made to run at 6,000 rpms, If you want more power you have to re-design the whole engine, and exhaust, intake and pick up 4,000 rpms plus.

Last edited by EPR; 02-02-2020 at 11:37 PM.
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post #8 of 56 (permalink) Old 02-03-2020 Thread Starter
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Re: 43cc carb tuning

I have a few more questions, If i were to upgrade the whole carburetor to say a more performance standard one. What would you recommend? The engine is pretty much bone stock. So im not sure if a better carburetor would work best with a small stock engine like this. I looked around the forums looking for mods to improve power, As ive mentioned before im not mechanically inclined.Any mods that would help power but arent to hard to do? I looked at the thread about making a cheap 2 stroke pocket bike have more power. But alot of that stuff i would be scared to try lol. Any help and sorry for my lack of knowledge in these bikes.
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post #9 of 56 (permalink) Old 02-03-2020
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Re: 43cc carb tuning

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Originally Posted by LittlebikesBigDreams View Post
I have a few more questions, If i were to upgrade the whole carburetor to say a more performance standard one. What would you recommend? The engine is pretty much bone stock. So im not sure if a better carburetor would work best with a small stock engine like this. I looked around the forums looking for mods to improve power, As ive mentioned before im not mechanically inclined.Any mods that would help power but arent to hard to do? I looked at the thread about making a cheap 2 stroke pocket bike have more power. But alot of that stuff i would be scared to try lol. Any help and sorry for my lack of knowledge in these bikes.
The WYK192 15mm carb that's on there is the best one for what you have..

As far as mods theres plenty you can do...You should start with the easier ones to start building confidence in yourself.....

Like they say if you don't take a chance you'll never know and you'll never really live either.....

First thing you need to find out is whether the engine is worth modding off the bat or whether it would benefit better from a new topend kit...….

That takes a compression tester...….Best way to know if the compression is strong enough is to fully warm the engine first with a heat gun then test the compression...…

Good Luck
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Re: 43cc carb tuning

For $40 shipped online you can get 2 pcs cyld/head kit w/ new piston, rings, rod bearing and even gaskets. If you look at engines CAM2 posted you will see Cag engines w/ a round alum alloy head and separate cyld. Believe you can still get a 40mm or 44mm kits. Remember the 49cc engine has a compression relief channel about the exhaust port, the 47cc 40mm cyld does not. The engine you has a lighter crankshaft and turns more RPMs than a 49cc-44mm. Like the alum head 49cc first 2 photos to newest version is 40mm- 47cc, 3 photos That's why CAM2 put a 40mm ported/modified cyld on this one it has a Walbro HDA223B 19mm. Your carb is already good enough.
Attached Images
File Type: jpg Cag Billet Case Engine2.jpg (466.5 KB, 3 views)
File Type: jpg First Billet Engine1.jpg (495.0 KB, 3 views)
File Type: jpg 47cc Billet Cag Eng1.jpg (277.0 KB, 3 views)
File Type: jpg 47cc Billet Cag Eng2.jpg (285.3 KB, 2 views)
File Type: jpg 47cc Billet Cag Eng3.jpg (148.5 KB, 2 views)

Last edited by EPR; 02-03-2020 at 11:31 PM.
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post #11 of 56 (permalink) Old 02-04-2020 Thread Starter
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Re: 43cc carb tuning

Thanks for the help guys. One more thing, If i would benefit more from a top end kit. Do you have any you would suggest. Appreciate your guys responses
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Re: 43cc carb tuning

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Thanks for the help guys. One more thing, If i would benefit more from a top end kit. Do you have any you would suggest. Appreciate your guys responses
For novices I suggest a regular old 40mm 1pc headkit…..44mm works too..

Those 2 pc headkits require a more advanced knowledge of 2 strokers to pull off 100% correct plus requires extra maintainance too like retorqueing and frequent checking of the cylinder head studs..

https://www.amazon.com/Cylinder-Stro...dDbGljaz10cnVl


https://www.amazon.com/Cylinder-Stro...0868266&sr=8-4


https://www.amazon.com/QAZAKY-Carbur...868207&sr=8-44
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post #13 of 56 (permalink) Old 02-04-2020 Thread Starter
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Re: 43cc carb tuning

In the big bore kit what are the wires? Would i have to change some wiring in the engine? I thought a big bore kit is just the piston and cylinder with gaskets and rings. And with the carb would i also have to change that if i were to big bore the engine? Or could i keep the same carb?
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Re: 43cc carb tuning

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In the big bore kit what are the wires? Would i have to change some wiring in the engine? I thought a big bore kit is just the piston and cylinder with gaskets and rings. And with the carb would i also have to change that if i were to big bore the engine? Or could i keep the same carb?
Its new killswitch wires for the new coil the topend kit comes with.

If you just change the topend youre not doing the correct and full job..

Everytime you do a topend or piston w/rings replacement its good practice to also change the coil..

In order to buy the right one you must know what you have first...

I've improvised using a 44mm piston on the 10mm pin crank by using a 44mm piston ported engine piston..

If you buy the 10mm pin kit and you have a 12mm pin crank youll have two options,,send the kit back and get the right one or change the crank too...…

Taking a picture of what you have and posting it would be very appreciative...

Last edited by CAM2; 02-05-2020 at 02:29 PM.
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post #15 of 56 (permalink) Old 02-05-2020 Thread Starter
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Re: 43cc carb tuning

Im really considering getting a whole new engine or a whole new bike completely. to do any engine mods to this i would have to take off a plastic cover on the whole thing. But the issue is that the plastic is attached to the engine without screws, So it is a huge pain to get all of it off. Even then it still is a cheap 43cc engine, There are just so many weird things on this engine than the typical 2 stroke engine i see on pocket bikes. For example i took off the pull starter to just look at the condition of the flywheel. But when i got off the starter it wasnt your typical flywheel, It was really weird looking and ive never seen anything like it, It's just annoying how much work this engine needs to do a simple thing that should take me 10 minutes. I hate it about this bike. Do you think i should get a new engine or just a new bike in total.
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Re: 43cc carb tuning

Ok dude...Don't despair...Thanks for posting the picture...It helps clear up my many questions….

That bike is riddled with EPA strangleholds.....

You just need to debug them or you can buy an engine that's already debugged...………….

Its easy to debug the one you have and I can show you how plus make a lil power....

First things you need to do is gut the box muffler and get an adjustable carb....That carb doesn't have a fuel rate screw it just has a dummy plug that's pre-set....

Like this carb on my X-Treme XG499 scooter....



Once you get an adjustable carb and uncork the exhaust your bike will run a ton better....

A $20 carb kit like this will be killer for you...…….



Only thing I hope is you don't have the pesky plate between the cylinder and crankcase too or it will have to be removed and cylinder squish checked before resealing without the plate.......

Mine was casted-in as part of the crankcase and had to be manually removed to get rid of the restriction.

As you can see I did it with the engine still on the scooter frame...

I initially hopped-up and debugged my scooter in an hour or two then I heavily modified it after that...………….LOL


Attached Images
File Type: jpg IMG_20171021_215912692_HDR.jpg (518.4 KB, 3 views)
File Type: jpg IMG_20171021_225709152_HDR (1).jpg (525.3 KB, 3 views)
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Last edited by CAM2; 02-05-2020 at 07:57 PM.
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post #17 of 56 (permalink) Old 02-05-2020 Thread Starter
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Re: 43cc carb tuning

Thanks haha, When you say gut what do you mean by that? Like take it fully off or do something to the muffler itself.
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Re: 43cc carb tuning

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Thanks haha, When you say gut what do you mean by that? Like take it fully off or do something to the muffler itself.
Remove or aleviate all restrictions from with-in to make it nice and free-flowing..






Get this carb kit as its the cheapest...The only thing you wont use is the intake...…

https://www.amazon.com/QAZAKY-Carbur...952414&sr=8-42

Last edited by CAM2; 02-05-2020 at 07:38 PM.
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post #19 of 56 (permalink) Old 02-05-2020 Thread Starter
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Re: 43cc carb tuning

Thanks alot. Do you have any idea how i can increase rpms or would i have to do something really technical to do that
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Re: 43cc carb tuning

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Thanks alot. Do you have any idea how i can increase rpms or would i have to do something really technical to do that
Once you uncork that baztard of an engine the rpm's will increase bigtime....

You saw the pics of what I did to my scooter engine..It barely revved past 6000rpm's with the strangleholds....

After getting rid of the strangleholds and doing a lil porting I got it revving to 9100 rpm's and the lowend power was off the hook....

As you can see the engine has plenty of pep to pick my heavy azz up and ride me on the rearwheel with ease...LOL



Last edited by CAM2; 02-05-2020 at 07:47 PM.
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