Whats the best performance upgrade??

I believe Joe stated that he stood corrected and that unless you have tried it both ways you are not in a position to make that statement. I on the other hand have years of experience tuning 2 strokes and understand how expansion chambers work and how to correctly tune them. The only difference in tuning a pipe made for a 50cc engine on a 70cc engine, although the chamber shape may not be ideal, is to lengthen the header about an inch and this is only due to the fact that 50cc pocket bike engines run at a higher rpm. So to properly tune for a 70cc that uses a lower rpm power band it should be slightly longer. If you care to disagree that is fine but I just want accurate information out there so that others can do it correctly.

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Design is easy, execution the hard part.
www.sickbikeparts.com

I'am not trying to put anyone down here. I totaly love you guys and all the great Ideas here. I have yet to try a tuned port. and would love to in the future to get one from S.B.C. I will be getting your jack shaft soon

I agree totally herder, none of these mods are worth a damn if you don't do the basics like matching intake and exhaust ports. That should be step number one before even installing the motor in my opinion.

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Design is easy, execution the hard part.
www.sickbikeparts.com

Well we will have to agree to disagree Ghost. I also grew up with 2 strokes, jetting and tuning, and I have never put an expansion chamber on a bike and rejetted lower, to me that shows the pipe is not "scavenging" properly, and therefore not performing properly. I do agree that the ports on these engines should be looked at and cleaned up, and polished. There is casting left over that blocks the the ports.

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"No such thing as a stupid question, just a stupid answer"

48cc Grubee Starfire Round Head......

Can't we all just get along

We all get along fine. There is nothing wrong with giving an opinion or even arguing a point as long as we can all go riding together later.

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Design is easy, execution the hard part.
www.sickbikeparts.com

I like the the porting, I don't even run them any more. I measure down 1.1" for the top of the exhaust, and extend the intake port down 1/4" to increase the intake timing. I poke the .040" hole in the carb, cut the tube off the inside of the muffler and they run like my old 55cc Yamaha. I make my own 39 tooth sprockets and it will pull off any stop without any assist. I weigh 180 so that's not bad. Have fun, Dave

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Chuck - The monkey has the spark plug again!

Hello. I have the Chinese 80cc (the motor says 65.9cc, but the seller swears they just say that because of some EPA regulations and it's really 80cc's. but somewhere else i read... THERE IS NO 80cc BIKE ENGINE! he told me to check the forums, sp what do you guys think?) but anyway... I'm Very new to this and i wanted to thank all of you for being here and for helping me without even knowing you have, yet. :-P

i haven't even mounted my engine and i i alreayd looked inside my intake manifold to find that horrible blockage from where the two diff pices of that pipe are casted together. thank you SOOOO much for the heads up! I'm sure i've freed up at least twice the flow! I very tediously scored around that seem until it was mostly smooth. it took a long time working with what i had, but i LOVE the outcome! and i owe it all to you guys! never would have even thought about it! ^_^.

here's a laugh for you... i used the none sharpenned sides of a pair of titanium coated scissors, lol. it has a curved edge, so as not to score, too bad, and works alot better than you'd think, since it's so hard against just aluminum and makes 2 pretty hard 90° edges) and then finished off be running a steel wool pad through it and around it. so basically, DIY ported and polished! ^_^ i could have worked on the polished portion of it longer, but i was tired of messing with it, lol!
if anyone wants pic of my scissor ported (smoothed out and widened the openings) and steel wool polished intake.

i've also already got the NGK plug (modded to be shorter to clear my frame. PM me if you're interested in how that turns out) and a brand new plug wire, terminal, and plug wire elbow style boot.

ok, so to cut to the chase... I'm a speed demon. But i'm also doing this for mpg and i want it to last me! keeping that in mind... i'm VERY interested in some sort of exhaust upgrade. but i don't want to sacrifice the longevity of my engine, or much fuel consumption. so would this mod do this... or is it more or less, free power, like exhaust upgrades on a car... more power without sacrifice of mpg (except maybe for the cases where maybe low end torque, if you have a very low restrictive [low backpressure] set-up).

Also... if i did this, i would want somehting like kinda like this... new exhaust WOW!!!
or like this one custom one i saw on a schwinn stingray. it was low and long, and gradually got wider, like a real motorcycle.

Any suggestions? what about any other worth while performance mods that won't sacrifice fuel economy too much? and i'll bet a pocket bike NOS setup would probably REALLY shorten the engine life, wouldn't it?

To recap: Tuned pipes, ported and polished engine. High end bearings from Germany/Japan might not hurt either. I wish I knew how to do this, but I will learn. I want to upgrade all of my engines before putting them on bikes. I WANT TO BE CHRIS HILL!!!!

OKC, you have to remember if you tune your engine up for HP and use it you will see a loss of MPG. One of the things about this engine is that it is made to meet the 2 HP limit for a lot of countries and cities in this country. I is hard to restrict a engine and still give the best MPG. If you tune the engine for best overall performance you will get also better MPG but not if you use the throttle in a wide open position. The engines I build run so efficiently now that they need very little little throttle to cruse along at around 23 MPH, I mean just off of idle, so I have noticed that the fuel mileage has increased allot. I suspect that if I did a lot of hot passes it would not be that good. Have fun, Dave

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Chuck - The monkey has the spark plug again!