Top Speed Rear sprocket help?

[Philandra Chambliss]

What's the estimated speed predicted for a China girl eBay classic...


Currently I have a 44 in the rear end which gives about 21mph to 23mph pedal assisted, and was debating a 38 tooth as to be inbetween 36toothfor flat ground and the 44t which is meant to do hills..

In addition looking to buy a long pipe chrome muffler or fancy muffler which is basically the stock muffler but parallel to the underbelly of the cranks from bb.com

Also expecting to drill some holes in the exterior body to free up some power approximately 3-4 as I have been told that the 66/80cc long pipe tends to overheat the motor.

Working on getting her beefed up before spring jumps out on us.

Got my old set of bars and the fenders and looking to throw those on too.

What would you recommend as well I don't want to here that "it's garbage theory" I intend on keeping it fairly stock looking to keep police out my business in addition to that I will be building a 50cc jug up for the future once my jug kicks the bucket.


Thinking ported along side with a windowed piston to match.
Seems like overthrow for a cheap engine but I'll keep it 100% chinanbanger may not be the fastest per say but I will be the best of the no names.

 

[CrazyDan]

Low 20s with the 44 tooth on a China girl sounds like issues to me. You should be well into the 30s. The 44 tooth is by no means a "hill climbing gear", there are many larger sprockets out there. 48, 56 and 60 toothed sprockets would be far superior to a 44 on hills, and I'm pretty sure even the 60 should see over 21mph without pedal assistance.
You aren't generating the power needed to push over 5k rpm or something, not sure what's wrong because I haven't ridden your bike nor have it in front of me.

 

[FurryOnTheInside]

£85 cheapest on eBay no-brand engine?
No fancy cop-magnet pipe?
Not even broken in yet or done any jetting to the stock NT carb?
Carefully built, but with no skill or prior experience with an engine of any kind, and the largest tool is a little bench grinder?
On a limited length of straightish narrow track, with a 42t on a 700c, with a 252lb rider, and two full rear panniers?
37.27mph at 8000rpm.

It's more speed than I wanted. It was meant to be a low-mid RPM motor lol.

But that's had some ham-fisted work I did to the jug and crank, and the cheap MZ R head (not so cheap once you ship it overseas)...
I think they're good to have if you're doing other stuff to make more power because they have the mass and surface area to cool the engine.

You can make the cheapest engine go fast enough, but it's mostly in the way you build it up IME. Follow the conventional wisdom. Then get scientific about it later on if you want to.
I'm sure broken in and jetted, and with a tuned pipe and 38t it's capable of high 40's.

@TheBaldKiwi said look at the intake gasket. It has a tiny hole that can be carefully cut and opened up to the size of the intake.
You'll get much better speed if you correct that. If you already did then we at least know the problem is elsewhere.

What speed would you be happy with?

 

[Philandra Chambliss]

Low 20s with the 44 tooth on a China girl sounds like issues to me. You should be well into the 30s. The 44 tooth is by no means a "hill climbing gear", there are many larger sprockets out there. 48, 56 and 60 toothed sprockets would be far superior to a 44 on hills, and I'm pretty sure even the 60 should see over 21mph without pedal assistance.
You aren't generating the power needed to push over 5k rpm or something, not sure what's wrong because I haven't ridden your bike nor have it in front of me.

Yeah she's not fully broke in yet I assume only on 3rd tank and I'm down to half on that.

Just making sure I'm not crazy.

 

[6blueoval9]

Your good after the second tank.

Get a high quality oil like Amsoil Dominator and run it at a 40:1 mix

After proper tuning and some very simple basic modifications like the intake gasket as mentioned, the 44t gear should be plenty to hit 30 plus mph.

There's a lot of threads on here showing cylinder port work and about improving your ignition system...look around and ask questions and you should be on your way closer to 40mph if that's what you want.

 

[Philandra Chambliss]

Your good after the second tank.

Get a high quality oil like Amsoil Dominator and run it at a 40:1 mix

After proper tuning and some very simple basic modifications like the intake gasket as mentioned, the 44t gear should be plenty to hit 30 plus mph.

There's a lot of threads on here showing cylinder port work and about improving your ignition system...look around and ask questions and you should be on your way closer to 40mph if that's what you want.

How about a shot bottle of trufuel 40:1 to get some synthetic on the rings. Maybe it's me not putting enough wrist in it as for the porting going to cross that bridge soon decided on a long poo pipe with the stock style muffler end.


Are the a80 heads interchangeable with the A50 engine.

 

[TheBaldKiwi]

What's the estimated speed predicted for a China girl eBay classic...


Currently I have a 44 in the rear end which gives about 21mph to 23mph pedal assisted, and was debating a 38 tooth as to be inbetween 36toothfor flat ground and the 44t which is meant to do hills..

In addition looking to buy a long pipe chrome muffler or fancy muffler which is basically the stock muffler but parallel to the underbelly of the cranks from bb.com

Also expecting to drill some holes in the exterior body to free up some power approximately 3-4 as I have been told that the 66/80cc long pipe tends to overheat the motor.

Working on getting her beefed up before spring jumps out on us.

Got my old set of bars and the fenders and looking to throw those on too.

What would you recommend as well I don't want to here that "it's garbage theory" I intend on keeping it fairly stock looking to keep police out my business in addition to that I will be building a 50cc jug up for the future once my jug kicks the bucket.


Thinking ported along side with a windowed piston to match.
Seems like overthrow for a cheap engine but I'll keep it 100% chinanbanger may not be the fastest per say but I will be the best of the no names.

Don't window your piston unless you are going to run reeds with it. The best non-reed piston mod is to trim the skirt to clear the intake port. This brings up your intake timing to a reasonable number and really helps the bike run better. You should try removing the end cap on your stock exhaust. This really helps the engine run a lot better (at the expense of it being quite a bit louder). A youtuber by the name of "2stroke stuffing" ran a motorized bike on a dyno and got an impressive .4hp gain by removing the exhaust cap! Link to video:

 

[6blueoval9]

How about a shot bottle of trufuel 40:1 to get some synthetic on the rings. Maybe it's me not putting enough wrist in it as for the porting going to cross that bridge soon decided on a long poo pipe with the stock style muffler end.


Are the a80 heads interchangeable with the A50 engine.

I'm not sure on the a80 head.

So it's a 50cc motor you have then?

 

[Street Ryderz]

How about a shot bottle of trufuel 40:1 to get some synthetic on the rings. Maybe it's me not putting enough wrist in it as for the porting going to cross that bridge soon decided on a long poo pipe with the stock style muffler end.


Are the a80 heads interchangeable with the A50 engine.

87 octane at 32:1 is the best bang for the buck IMO even with a good synthetic oil it helps to create a microscopic film layer that protects all the moving parts and helps to seal better for compression.The use of less oil means there is more fuel washing the parts leaving less of the needed protection layer and less of a seal. The long poo poo pipe is just that,It has no tunned affect and just holds oil in the overly long header tube.The head for a 48cc witch is what you have not a 50cc unless YOU changed the rod witch you didn't has a different stud spacing than the 66-69cc engine's and there is only ONE aftermarket head available for it the R.S.E. head That's it unless you mod a scooter engines head to fit it your choices are ONE.

 

[6blueoval9]

Don't window your piston unless you are going to run reeds with it. The best non-reed piston mod is to trim the skirt to clear the intake port. This brings up your intake timing to a reasonable number and really helps the bike run better. Instead of drilling holes in your stock exhaust, just remove the end-cap instead. This really helps the engine run a lot better (at the expense of it being quite a bit louder). A youtuber by the name of "2stroke stuffing" ran a motorized bike on a dyno and got an impressive .4hp gain by removing the exhaust cap! Link to video:

The gain was most likely due to a lean condition thats caused when you remove the end cap....you want some restrictiveness to the exhaust.

I've been told by someone highly respected as a builder to remove all the discs and cut the pipe off inside the canister then add a second stinger (both about 3 inches in length) to the end cap for maximum results....re-jetting richer will be a must.