Well, I honestly wish I had a magic formula for you and could just lay it out for you right here as a guaranteed way to set your bike up with what you already basically have for hitting that 50 mph goal you've set for yourself.
But, yeah I know.... there had to be the dreaded "But" in here somewhere right....lol
Here is the "But" and as I would say, the deal/issue.. blah blah blah....
I have never had a setup anywhere even close to what you're running on your bike, I did my 52 mph personal best top speed with a completely differnt engine setup than what you have, It's been several years since I did my top speed so as far as all the specifics of that engine, I honestly dont completely remember... lots of water under my bridge since then and I got completely away from my bikes for a few years do to two **** on earth marriages that of course we're a terrible distraction and so on.....lol
I'm sorry this message is a long in, but Im a long winded southern back woods rural Texas fella and I typically use a pile of words to get my story or point across because I can and thats just me in a nut shell....lol..!
I'll tell you here what I can remember.
Base engine lower was a PK80 40mm stroke, low pin piston that I bought from a former vendor who used to be on here named Duane and his website was thatsdax.com
At the time he had gotten in a shipment of what he called " better balances lowers" they had upgraded bolts and definitely were the smoothest running lowers I had used myself, I order a PK80 jug/cylinder off ebay that I could tell in the pick had as large of transfer ports I had seen, I deburred all ports well and polished exhaust port to as mirror of a finish as I could and raised the port height roughly 1-2 mm if I remember right, I made sure the transfer and engine case were matched as good as possible and that no gaskets interfered with any of the ports for good flow, I believe I lowered intake port the same amount as I raised exhaust port and just used a medium grit sanding drum on my dremel to make it uniform but also a little rough for better fuel atomizing.
I did some crazy work on the piston, by drilling multiple holes in the skirt in areas that would not open over any port and I also ground tapered "resecced ramps" into the piston perfectly the same width of the transfer ports and they were done so they sloped toward transfers which alowed transfers to be completely open when piston was at BDC/ all the way down in cylinder and of course that changed tranfer port timing also since they opened sooner.
I believe I put a Puch 70cc Hi Hi head on it that I bought from treatland.tv and then I had to drill the 6mm holes out to 8mm so it would work on the engine, very simple process and those little heads actually work good these HT/China Girl engines in my experience even though its been said that the squish angle isn't really the best it could be for these bicycle engines... they work good and are way better than the stock heads and in my opinion even some of the so called performance heads out there for performance and cooling when an engine has been modified for higher RPM and such.
I did not have an expansion pipe exhaust on that bike, I took a stock chrome muffler and tapered the flange inside so that the exhaust could flow into the pipe better, I cut the lower part in half and there was nothing left inside it to cause any back pressure, yes very loud, but the engine could breathe easy and that was the only way I could get the RPMs out of it that I needed to reach that top speed, I tried other exhaust that added some back pressure and couldn't get even close to the 50mph mark.
I believe I was running either the SHA Dellorto clone carb or the genuine NT speed carb. its been so long Im not sure, but Ive always got great performance out of both of them and been able to achieve the speeds I personally was wanting which are normally 40 mph give or take 2 or 3 mph on my bikes, but was able to also get 52 mph with one of them, so Ive never felt I needed a different carb. in order to do what I wanted with my bikes and theyre so freaking easy to tune and maintain and cheap also.
also no reed setup, so far I've never used a reed setup on one of these engines, never seen the need to when I can make them run just how I want without all that extra stuff. ( Not hating on reeds, just never used them myself on these little engines)
The bike I did this on is an old 26" cruiser type frame and I have heavy duty 24" wheels on it and good quality 60 TPI tires and a 30T rear sprocket which worked great on the 24" wheel.
Engine was runing on 100:1 Opti2 oil, gas mix which I used for years without a single failure due to lack of lubrication.
Also an HD Lightening CDI which was good and I still have it on the bike although I did eventually take that engine off because power fell off a little and I discovered I had busted the piston...LOL to many RPMs on that piston with all those holes drilled in it...lol I later tried a stock CDI just to see if the bike would run better or worse and still got the same top speed, couldn't honestly tell any difference in performance, But I believe the custom CDI is likely much more durable long term than at least some of the stock units.
well, this has given you some reading...lol
Thats all I can remember about that little engine and how I got it to do what it did.
I know this is a lot of gabbing and will probably get a yeah OK whatever from some in here, but thats OK Im a straight shooter and everything I said here is whar I did to it and the results I got from what I did.
Just remember that there are some good upgrades out there for these engines and there is also a pile of fluff from peiple and vendors who just want to remove fiat currency from your account to theirs...lol
I kept it simple and wanted to see what the most I could get out of an almost stock setup would be other than a modified Puch moped head and some simple plet work and a little piston modification that honestly would have held up better if I hadn't drilled all the dang holes in it..LOL
OK im done, hope this book I just pecked out will possibly help you and maybe someone else on here ar some point.
I would like to hit 50 what setup do I need to achieve that? Please elaborate map
