Is the exhaustport restricted?

[zumakid15fromAR]

I took my stock muffler off b/c was curiouse of how loud it is without, i got extremely bored, as i looked @ the exhaustport on the cylinder head i noticed its not a circle more of an egg shape is it restricted ore what? If you get what im saying and have an answer plz tell me wondering if i can shave it and get more out of my zuma! Thx!

[Axton]

Yep, all zumas are that way. A drimel will buzz it out. Just make sure you dont grind in all the way to the cylinder walls where the piston rubs. It is a restriction by design.

[str8dum]

problem is that the exhaust port was designed around the transfer and boost ports of the motor. people have ground out the exhaust ports, but no one has come back with :ohh wow that was worth the time and effort". Thats becuase the design of the stock motor itself is restricting. teh time and money spent opening the exhaust port could be used to work an addtional hour to afford a 70cc motor thats ported properly to begin with.

[StepVino]

$140/hour? Sign me up!

[Axton]

problem is that the exhaust port was designed around the transfer and boost ports of the motor. people have ground out the exhaust ports, but no one has come back with :ohh wow that was worth the time and effort". Thats becuase the design of the stock motor itself is restricting. teh time and money spent opening the exhaust port could be used to work an addtional hour to afford a 70cc motor thats ported properly to begin with.


Where do you work to get that much? I only live down the road from you. Got an application for me?

[StepVino]

Just kidding with you str8, you are so serious all the time :)

[zumakid15fromAR]

oh ok well thx guys wud it be smart to dremel it out if id get a bigger carb?

[StepVino]

There's a post somewhere metioning better performance
with it mostly ground out. Apparently it's not necessary to
make it completely round.

Try a search with the words "half moon".

[zumakid15fromAR]

allright will do thx

[str8dum]

lol, i know. but figure you dotn have a dremel or the cutting bits, you are easily 1/2 way to the 70cc kit. Grinding cast iron is no easy task.


Just kidding with you str8, you are so serious all the time :)

[zumakid15fromAR]

yeah well i wish i cud get a 70cc im broke n trying to get faster without spending money

[str8dum]

a good cutting bit will run ya 10-20$ and if you dont have a nice powerful dremel, that will run ya 90$.

assuming that you have that stuff already, no reason not to grind it out. nothing lost except some free time.

Good luck! :)

[StepVino]

yeah well i wish i cud get a 70cc im broke n trying to get faster without spending money

Then it's sort of a catch 22. Yes, you can make it a lot faster
with very little money (especially after a pipe), but it's risky to
do if you are also doing it for the first time, with low funds to
fix possible mistakes. Plus the added pressure of risking an
"I told you so", from your father.

Maube that's where the first mod should be! Try to change his
mind :)

[meshrider]

okey here is my spare cylinder, im so bored and nothing to do so what i did is get this fella ported and have some fun of it. and here is the result.

[StepVino]

Cool, now you really need a pipe!

Make sure you clean it well before trying it, and keep
us posted.

[meshrider]

ill keep you guys updated about this thing, ill post some more pics of the ported intake chambers. now i cant decide which pipe should i get :dance: planning to get a doppler s3r 50cc pipe.

[on2wheels52]

I tend to think if there was an easy hp or two to be gained by enlarging the exhaust port the factory wonks would already have done it.
Easier to remove metal than to put it back in.
Jim

[OldGuy1]

I tend to think if there was an easy hp or two to be gained by enlarging the exhaust port the factory wonks would already have done it.
Easier to remove metal than to put it back in.
Jim

First statement: Not true. Changing the exhaust flow will move the power band up in the RPM range affecting rideability. The factory never meant to produce maximum power.

Second statement: You got that right.

[mikal]

I'm sure that Yamaha had to make these things to specs that were suitable for state laws. Too much horsepower and cc's turns scooters into motorcycles.

[Axton]

In NC, ALL scoots are restricted to 30mph. People like me, hop them up, and dont really care. The cops dont bother me.

[PsychedelicZuma]

They're supposed to be limited to 30, but my stock Zuma can go 36-37... And after some modifications, even faster than that. The throttle mod is number one on my list, going to do that today (hopefully).