The Ongoing Search for Maximum Power... except its a 48cc

I mentioned my project bike in another thread and some people showed interest in an update as I make slow but steady progress on modifications such as porting, planeing, jetting etc. (maybe Sturmey Archer trans upgrade?). This thread is where I will make those updates.

Little background: bought a 50cc kit off amazon for about $120. Replaced all the hardware with good stuff from the hardware store. Upgraded to a CNS carb and a little banana expansion chamber with a muffler, as well as a 50 tooth. There is more on the bike itself if your interested in this thread Off Road Bike Builds. Been a good little motor for me but the lack of displacement is leaving more to be desired. And the reason I don't just buy a Zeda or PK80, I guess enjoy the thought of squeezing as much power out of this thing as possible.

So, if no one really cares let me know and I won't bother to update, but I'd be happy to keep this thread alive if you guys want to see what I'm working on.

Thanks
 
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Schmidty Boy said:
Oh and as far as my plans to plane the head a little, the stock PW50 has about .065 of clearance between the chamber and the piston
and according to some sources online, if you planed that down to .035-.030 then that would be some good performance gain. So we checked the clearance at TDC and sure enough it was .065. If you can see the photo of the bottom of the head there is a raised surface so I might start with that.
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Just a recommendation. Definitely do a little work to the head to level the sealing surface, but set your squish gap by decking the jug. That ring on the head is what adds a better seal around the chamber, so I am not a fan of removing it like some people do. Same concept behind high boost turbo engines doing copper O-ring sealing. Either way, do both surfaces to at least 400 grit to get a more polished surface. This really helps with sealing metal head gaskets.

As far as the squish gap, yes the balanced "ideal"/safe squish gap for most performance builds is .8 to .9mm (.03-.035")
 
Make sure you get it all the way in on the manifold, you might have a small leak.

Does the carb have a little spring thing above the bowl on the left side? A tickler?
ImpulseRocket said:
Just a recommendation. Definitely do a little work to the head to level the sealing surface, but set your squish gap by decking the jug. That ring on the head is what adds a better seal around the chamber, so I am not a fan of removing it like some people do. Same concept behind high boost turbo engines doing copper O-ring sealing. Either way, do both surfaces to at least 400 grit to get a more polished surface. This really helps with sealing metal head gaskets.

As far as the squish gap, yes the balanced "ideal"/safe squish gap for most performance builds is .8 to .9mm (.03-.035")
Click to expand...
The little 48 head doesn't have a squish band. He has to polish the sealing surfaces, head & cylinder, then cut a little squish band with an old piston. Then use a nice copper gasket to establish the squish gap. The squish band is only going to be 5 or 6 mm wide if he's lucky, but it will be enough to get the charge turning in the bore.
 
Chainlube said:
Make sure you get it all the way in on the manifold, you might have a small leak.

Does the carb have a little spring thing above the bowl on the left side? A tickler?

The little 48 head doesn't have a squish band. He has to polish the sealing surfaces, head & cylinder, then cut a little squish band with an old piston. Then use a nice copper gasket to establish the squish gap. The squish band is only going to be 5 or 6 mm wide if he's lucky, but it will be enough to get the charge turning in the bore.
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It's on the manifold all the way, as far as a spring on the left side above the bowl, I don't think it has one. It's a CNS carb.

The squish gap is .065".
 
Can you post a picture of your carb? I don't recall seeing a carb with that name, but I could have tore one apart in the past.
 
Chainlube said:
How did you measure it?
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piece of soft solder on the top outside edge of the piston and then put the head back on and rotated the piston to TDC and then measured the thickness of the smashed solder.

I'm not by the bike currently here is the picture off bicycle-engines.com
1730996731583.png
1730996752318.png
1730996772313.png
 
Schmidty Boy said:
piece of soft solder on the top outside edge of the piston and then put the head back on and rotated the piston to TDC and then measured the thickness of the smashed solder.

I'm not by the bike currently here is the picture off bicycle-engines.com
View attachment 221437View attachment 221438View attachment 221439
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Yea, that's the way to do it. I use modeling clay, not as hard on my old hands. Put. A thin coat of oil on it, if you use it though.

If you get a 1 mm thick copper head gasket, then you can take .01 mm from the head and jug to give you a .8 squish. Of course it will be less once it's all sealed up, apx .75.

Did you completely disassemble the carb? Looks like it could have a couple of spots for an air leak. Try doing it again, be very gentle with the parts. I've struggled with a carb in the past just being heavy handed.
 
Chainlube said:
Yea, that's the way to do it. I use modeling clay, not as hard on my old hands. Put. A thin coat of oil on it, if you use it though.

If you get a 1 mm thick copper head gasket, then you can take .01 mm from the head and jug to give you a .8 squish. Of course it will be less once it's all sealed up, apx .75.

Did you completely disassemble the carb? Looks like it could have a couple of spots for an air leak. Try doing it again, be very gentle with the parts. I've struggled with a carb in the past just being heavy handed.
Click to expand...
I completely disassembled it. I went for a ride today with my friend and the bike ran great (including idling) so I don't know what changed but if it happens again ill have to do a deeper dive.

As far as an air leak on the carb, if your referring to the bronze tubes sticking out of the bowl and on the top by the filter I have those capped off.
 

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