Whats the best performance upgrade??

Goat herder, If you had a way of doing a video of the mods you made and post that in Utube or Flickr that would be something I'd want to see. I figure in time someone will buy motors and tweek them for resale or perform these steps for others who ship the motor to their shop....plus make themselves a few bucks doing these things.

Where I live 50cc and 1 hp is all you're allowed to present when you buy a license. Thus showing up in pure stock form is best. Then the bolt ons could
take place. For that matter one could present a 50cc to get a license and later bolt on a 80cc and sell the 50cc to someone else.

I'd say the first best simple mod would be with a quality spark plug & ignition
wire and making sure it's spot on timing wise. Basically a good super tune.

After that, a bolt on expansion chamber.

Lastly gears to get the bike to perform the way you want. For speed, top end, or fuel milage but to where you are happy with fuel consumption over performance.

The only problem with a tuned pipe is most people don't know the whys and hows of setting one up so it does it's intended job.

Just slapping on a tuned pipe will not increase performance beyond opening up the exhaust flow if it's not installed/tuned right.

You have to get the header length right for your application, then re-jet richer.

When set up CORRECTLY a tuned pipe will offer a big increase in power IN A SMALL AREA OF THE POWERBAND.

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If it ain't broke, and you mess with it long enough, it will be.

I agree with most of that but feel compelled to add my 2 cents.

"The only problem with a tuned pipe is most people don't know the whys and hows of setting one up so it does it's intended job."
I couldn't agree more, I have seen many adapt pocket bike pipes with incorrect header lengths and wonder why did they waste the time.

"Just slapping on a tuned pipe will not increase performance beyond opening up the exhaust flow if it's not installed/tuned right."
Absolutely correct again.

"You have to get the header length right for your application, then re-jet richer."
Yes and probably not. Header length is the overall tuning factor for an expansion chamber, however typically adding an expansion chamber will put the engine into a rich condition due to most of the intake charge not being expelled unburnt into the exhaust pipe. Again not all engine, carbs, pipes are the same but in general you will need to go leaner "if" the pipe is tuned correctly.

"When set up CORRECTLY a tuned pipe will offer a big increase in power IN A SMALL AREA OF THE POWERBAND."
Mostly true but most of the expansion chambers on the market today are designed to provide the best power through an rpm range and not in a narrow power band. True this is not optimum for any one given condition but improves overall power and driveability.

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

Roger that!

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If it ain't broke, and you mess with it long enough, it will be.

My suggestion would have to be a larger carb. Once the intake and exhaust ports are cleaned up, the engine breathes soooo much better. I am running a 18mm carb along with a 48cc tuned pipe and have a much wider powerband, and better top end. With the stock carb the powerband would end because the engine couldnt flow anymore than the 14mm carb would allow, and it much smoother going from idle, to mid, to wot, if jetted, and set up correctly. I believe a pipe without a larger carb is not worth it.

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

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

Your statements prove what Joe and I said to be accurate. Your powerband would end because your pipe is about 12 inches longer than it was designed. Variations of 1/4 to a 1/2 inch from designed will change the powerband a couple hundred rpm so you can see how far of it is being 12 inches too long. It is mostly just serving the function of a pre-silencer and not a properly tuned expansion chamber. I will guarantee that it performs better than the stock pipe but only because it flows better and not because it is doing what it is supposed to do, which is also why going to a larger carb helped.

The stock carb will work just fine if tuned correctly with a properly tuned pipe. I agree the engine can use a little larger carb but getting the fuel/air ratio correct is more important than size.

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

I agree that the header length is important, but also believe that the length and shape of the cone dictate the header length. I believe matching the pipe to the engine displacement is just as important. Most I have seen are useing 48cc pipes on 70 cc engines, and because of that mismatch they have to jet leaner, and therefore probably arent getting the performance they got out of the stock HT pipe. As Joe said "You have to get the header length right for your application, then re-jet richer".

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

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

I had a boost bottle that never seamed to work untill I ported. I totally agree with with Ghosto ,Joe, Misteright and everybody on the tuned pipe and carb ideas. However if the motor itself isn't breathing non of the great designs will ever reach there poteintal..... all these motors were built the same way.

I got the idea from another post on this forum, but I can't remmember where?I love this simple simple mod .pull the intake off run the piston to top dead center trace a mark on the piston skirt, only trim this amount of the skirt or you will weaken the piston.Next pull the jug off now the mark you made trim just that off be sure to clean up any burs. I don't recommend removing the piston because once you remove the clips to the wrist pin it almost better to replace them.Lay lots of rags around the motor where all the inners are exposed have someone hold the piston still, take your time trim the skirt to your trace mark, that simple!!This is called advancing the timing

On the bottom of the jug study the gasket, its most likely covering half the ports. Trim it with a razzer. Look at your exaust and intake ports, trim as well. While your at it make gental slopes in the exaust pipe, and the intake, you won't be able to do alot here but it still makes a differance