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 Stock Exhaust mod? 
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Post Stock Exhaust mod?
Sorry, I am new. I tried using the search tool but it completely throws out the word "exhaust." So idk if this has been asked before.

I just got a '98 zuma and was thinking of toying with the stock exhaust. Wth is with the 4 bolts in the rear end of the muffler? They don't seem to be doing much of anything. If I remove them nothing seems to move or come loose, even on the inside. Is this just part of assembly before it is welded?


I don't really know what to do with this setup. Would cutting out the stock rear bit, just to make a bigger hole, give me anything? Doesn't seem to be much I can do with this except gut the entire thing, which im assuming is too loud.


Suggestions?


Mon Apr 06, 2015 1:46 pm
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Post Re: Stock Exhaust mod?
There he is!
Glad you found your way here, Side, welcome to the forum!

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Mon Apr 06, 2015 3:09 pm
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Post Re: Stock Exhaust mod?
A two stroke exhaust is not a simple thing

Pulling those out at one time should have been able to pull the baffles out

But moding a stock pipe unless you read Jennings book and do the math you aren't going to gain anything other then noise

And when you read the book you will find out how hard making the math work is and realize it's not worth the hassel

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2008 zuma dual headlight mod koso mirrors liquid cooled polini corsa kit leo vince zx stage 6 variator rally kit custom red paintFUEL INJECTEDsoon to be 100cc
2008 stella olive custom ported 177 cc kit dechromed ford tear drop tail light alive and breathing and awaiting cosmtic surgery thanks to an donkey hind quater hole cager
1985 elite 150 how long can i leave it stock


Mon Apr 06, 2015 4:36 pm
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Post Re: Stock Exhaust mod?
Sorry but, honesty... I never been that optimistic of performance gains from modified OEM parts... I pretty sure that Yamaha engineers gave you the best for cost and performance the way they made it.

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Mon Apr 06, 2015 5:00 pm
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Post Re: Stock Exhaust mod?
I would think Yamaha has to find a balance between economy, performance, and noise. The average person doesn't want a loud exhaust, so performance is sacrificed a bit.


I have looked into it a little and understand that an exhaust with an expansion chamber has to be pretty specifically tuned to work, but I also looked up a couple of videos and diagrams of stock exhaust. They seem to be basic mufflers with fiberglass, baffles and pipes. If this is the case, the stock pipes wouldn't seem to be tuned in anyway, the way expansion chambers are. This being the case, I can't imagine modifying the stock exhaust would be detrimental except at the point where back-pressure would be too low.
Does that make sense?

I've cut out of a couple of stock exhaust on motorcycles before, but they were always big enough that torque didn't seem to change. They just made a bit more noise and seemed to rev a teeny bit more freely.

Anyway, I just want to get it back to stock and running first. Maybe I will save up and get an aftermarket pipe, and then be free to experiment with the stock one. Even if I found a cheap stock pipe, I'd probably buy it to experiment with. I have a little stick welder, but I haven't used it in a reaaaally long time.

So nobody even thinks cutting the little end off and making a quarter or half dollar sized hole would be beneficial? If not, I will just leave it along for now.


Tue Apr 07, 2015 1:44 pm
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Post Re: Stock Exhaust mod?
It's not really that performance is sacrificed, it's that it's designed to be a touring pipe. And it's matched to the other stock components in the scooter.

The first thing you learn about modifying a Zuma is that every change requires re-balancing somewhere else. Let's pretend you actually can make the stock pipe rev higher. That means your power band has shifted higher, so you have to change your clutch springs and lighten the rollers in your variator. And if you increase the performance, you're stressing the reeds, which means you should replace them with carbon fiber ones that don't spew shards all over your engine if they break. If it's revving too high - unlikely with a rigged stock pipe - you might be stressing the stock crank too much, making the bike dangerous to ride.

There's a lot of experience with mods on this forum, so I'd suggest continuing to do what you're doing: ask before you go off half-cocked.

Jmkjr is one of the people here worth listening to, by the way. He's cautious :) but if he's saying you're unlikely to get more performance out of a hacked-up stock exhaust, there's a very good chance he's right.

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'05 Zuma 50, Athena sport 70cc (12mm piston) with Polini head (.9 squish), B9ES spark plug; timing advanced about 2˚; Yasuni C16 exhaust, Buzzetti kick stand to make room for it (and Stage6 paddock stand after dropping the freaking bike because of the kick stand); stock airbox no snorkel, 5 x 1/2" holes; Stage6 21mm racing PHBG, 45/95/W7 1 lean/40 slide; Polini/Power One 12mm HPC crank; Athena 15/50 gears (also have 14/42s pressed into a gearbox cover, just switched back and like the 15/50s so far); 107mm Malossi Delta clutch, "racing" red springs/lighter "racing" counterweights ± 6800 RPM engagement, Stage6 Kupplungsglocke (bell - the light one); Malossi 6112811 Overrange kit, red contra and 28.2G rollers; VForce 3 reeds; Michelin Bopper tires; back to the stock shock; dual headlight wiring; C3 mirrors; Trailtech TTO tachometer and temp gauge.


Tue Apr 07, 2015 2:05 pm
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Post Re: Stock Exhaust mod?
So you cut up 2 stroke motorcycle pipes or 4 stroke motorcycle pipes

there is no fiberglass in the stock zuma 2 stroke pipes it's all baffles

The big bottle neck is in the header part of the pipe and the actual exhaust port

And again even with a stock or touring pipe changing them will effect the pulse and if not done right will hurt more then help

There have been several that have cut there pipes up and only one that claimed to have any success with a cut up stock pipe

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2008 zuma dual headlight mod koso mirrors liquid cooled polini corsa kit leo vince zx stage 6 variator rally kit custom red paintFUEL INJECTEDsoon to be 100cc
2008 stella olive custom ported 177 cc kit dechromed ford tear drop tail light alive and breathing and awaiting cosmtic surgery thanks to an donkey hind quater hole cager
1985 elite 150 how long can i leave it stock


Tue Apr 07, 2015 2:39 pm
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Post Re: Stock Exhaust mod?
That is why I was wondering about cutting out the stock pipe. If the stock pipe is just baffles, they aren't accomplishing anything that an expansion chamber would, and redirecting the air that much makes me wonder if the performance is stifled some and could be improved by opening it up a little bit.


Thu Apr 09, 2015 2:35 pm
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Post Re: Stock Exhaust mod?
You're just swirling around a big pot of poo.

If you want to improve the performance, get a better exhaust and do the upgrade properly.

That's my opinion.

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'05 Zuma 50, Athena sport 70cc (12mm piston) with Polini head (.9 squish), B9ES spark plug; timing advanced about 2˚; Yasuni C16 exhaust, Buzzetti kick stand to make room for it (and Stage6 paddock stand after dropping the freaking bike because of the kick stand); stock airbox no snorkel, 5 x 1/2" holes; Stage6 21mm racing PHBG, 45/95/W7 1 lean/40 slide; Polini/Power One 12mm HPC crank; Athena 15/50 gears (also have 14/42s pressed into a gearbox cover, just switched back and like the 15/50s so far); 107mm Malossi Delta clutch, "racing" red springs/lighter "racing" counterweights ± 6800 RPM engagement, Stage6 Kupplungsglocke (bell - the light one); Malossi 6112811 Overrange kit, red contra and 28.2G rollers; VForce 3 reeds; Michelin Bopper tires; back to the stock shock; dual headlight wiring; C3 mirrors; Trailtech TTO tachometer and temp gauge.


Thu Apr 09, 2015 3:26 pm
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Post Re: Stock Exhaust mod?
sidescrollin wrote:
That is why I was wondering about cutting out the stock pipe. If the stock pipe is just baffles, they aren't accomplishing anything that an expansion chamber would, and redirecting the air that much makes me wonder if the performance is stifled some and could be improved by opening it up a little bit.


Just let us know how it works out :q:

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Malossi MHR Big Bore 77 LC, Malossi RHQ crank, Roost 86 pipe, 28mm Keihin PWK Carb, Stage6 reverse intake manifold, Custom Subframe, Stage6 Vforce3 reed valve, Polini open air Filter, Malossi 2010 Over Range, Polini 2G clutch, Dr Pulley clutch bell, Malossi yellow contra. Aerox wheels. ProTaper bars. Buzzeti side stand. Many more upgrades to come...

2008 Zuma 50
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Fri Apr 17, 2015 10:50 pm
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