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

 

[DAMIEN1307]

I'm watching...lol.

 

[Schmidty Boy]

So...
did some work today
Took apart the top end to get some measurements on the combustion chamber and the piston and made some crazy discoveries
this motor although it may be from amazon, (correct me if I'm wrong) seems to be based off the Yamaha PW50 engine, the bore and chamber clearance is the same as those on a PW and the piston has the same dimensions as well. Coincidence? I hope not this is kinda sweet. Also these 48ccs seem to get some crap for bad build quality, but idk about this one, the transfer ports look pretty well cast and are nearly burr free and the ports in general look alright. But yeah today was just to take some measurements.

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.

 

[Sidewinder Jerry]

Even though a thread may be closed, I've often used them to answer a current thread.

 

[Schmidty Boy]

pardon my all thread head studs, sheared 2 of the originals torquing them with the incorrect spec given by the manual. This was a while ago when I had recently installed the kit

 

[Schmidty Boy]

I should also mention that @Isvilla08 and I are working on this together so its as much his bike as it is mine.

 

[Chainlube]

Do you have an old piston for it kicking around? If you don't, buy a new one and use your existing piston to make an adjustment to the head with it. If you're interested in tuning it I'll let you know. Putting a small bevel all the way around your ports is also a good idea.

 

[Gordy]

Port matching and polishing the exhaust port is a good place to start

 

[Schmidty Boy]

Do you have an old piston for it kicking around? If you don't, buy a new one and use your existing piston to make an adjustment to the head with it. If you're interested in tuning it I'll let you know. Putting a small bevel all the way around your ports is also a good idea.

Don't have one that's some solid advice ill get that taken care of

 

[Schmidty Boy]

Hey I was adjusting the idle mixture today and I was trying some different needle positions so when I decided to revert back to how I had it set at the start (I have notes on clip position, jet size, and idle mixture screw position) the bike wouldn't idle where I had the needle and screw position at merely 10 min ago, so I turned the idle speed up so I could at least keep the bike alive and work from there, therefore the speed would be high but it would slowly taper off until it stalled so that led me to think that the carb was dirty so I did a thorough cleaning job but it didn't make a difference. Any idea what could be going on? keep in mind the engine idled and ran fine before I started making changes to the needle position.
thanks