200GY-2B Exhaust mods

[Yster perd]

Hi - My user name is Yster Perd (or Iron Horse in Afrikaans) - a very apt name for a motorbike. I am a farmer in South Africa and have owned a Gomoto 200GY-2B for the last 4 years and love the bike as it's perfect for the farm roads. I like doing my own mods on a bike and I would like to know how to modify the standard exhaust ie how to remove baffles etc to make it a bit more powerfull as it does run out of steam at the altitude of 1,7Km above sea level where i live. Maybe Spud or some one else can help. I can fit an after market exhaust, but I would rather modify the existing one and don't want to make things worse by messing it up.

[SpudRider]

Welcome; we are glad you joined us. :hi:

I am unfamiliar with your bike. If you have time, please post photos of your bike. We love to view photos, and they also help us to identify your bike. :)

Forum member Weldangrind is expert at modifying mufflers. I'm sure he will soon stop by to help you with some advice.

[Yster perd]

Hi Spud

Its the same generic Honda clone motor, as used on your Zongshen 200GY-2, but with a balance shaft and uses the same CV carburetor. I have information, from another site, that drilling 8 x 12mm holes in the muffler's back plate is a good place to start - they call it stage 1, and I will try that this weekend. The muffler is still new and I haven't got the bucks (or inclination) to import a suitable silencer. The local guys from Powerflow exhaust can make one up for me - but that defeats the objective of DIY mods on these great little Chinese bikes.

[SpudRider]

My Zongshen 200GY-2 has a motor cloned from the currently manufactured, Yamaha TW200 motorcycle. Likewise, my Zong employs a Teikei MV28 carburetor which is virtually identical to the Teikei carburetor installed on the current TW200 bikes. My Zong also accommodates a Yamaha exhaust header. ;) That is why I am less familiar with the exhaust system options for the bikes with Honda cloned engines.

[katoranger]

You are pretty high up. I think that is about 7000ft in elevation without a calculator.

Have you rejetted the carb at all? That may be place to start.

[Weldangrind]

Welcome Yster Perd!

These bikes are usually jetted rather lean from the factory, so I wouldn't be surprised if yours is close to ideal at your elevation.

Regarding modifying the muffler, do you have access to a welder?

[Yster perd]

Hi - thanks for the reply's.Yes, I have rejetted the carb and adjusted the air screw of the MV28 carburetor for optimum performance. I believe that the stock muffler is very restrictive and would like to modify it. Yes, Weldangrind, there is a oxyacetelene torch on the farm and I do know how to braze exhaust pipes as well. What are your suggestions?

[Weldangrind]

If you choose to cut the muffler apart and weld it together again, you can create as little (or as much) restriction as you wish. What I've done in the past is simply empty the entire muffler, weld the mid pipe to the muffler and have open space through the body of the muffler. On the outlet end, I've welded in a tube that is about half the length of the muffler, and had it extend outside the muffler by about 2"/50mm. That tube is welded shut on the inlet end, and then holes are drilled into the tube. The idea is that exhaust enters the empty muffler, flows through the small holes drilled into the tube and then out the back.

If you calculate the area of the midpipe, you can then determine the number of holes that will be required to meet or exceed that area. I drill 1/4" / 6mm holes, but I can't recall how many I drilled last time or what the area of the midpipe was.

Make sense?

[Yster perd]

Hi Weldangrind

Your suggestion

empty the entire muffler, weld the mid pipe to the muffler and have open space through the body of the muffler. On the outlet end, I've welded in a tube that is about half the length of the muffler, and had it extend outside the muffler by about 2"/50mm. That tube is welded shut on the inlet end, and then holes are drilled into the tube. The idea is that exhaust enters the empty muffler, flows through the small holes drilled into the tube and then out the back.

Makes a lot of sense. I will try that this week end. The closed end of the outlet pipe ensures that it is not a straight through (noisy & fire hazardous) muffler - but better than stock! Thanks dude, you saved me lots of $$$ :)

[Yster perd]

http://chinariders.net/c:/200GY-2B Muffler mods

[Yster perd]

Made pic of mods - cannot send it :(

[Weldangrind]

You can always open a free account at photobucket.com and then link to the pic. Most of us do that.

[Yster perd]

Lets try again
http://i987.photobucket.com

[Yster perd]

Not too sure

http://i987.photobucket.com

[Yster perd]

sorry - need more help. Does the user name need to be Yster perd or what?
any way - contact me if interested as I'm not an IT expert

[katoranger]

From your photobucket account you will need to go to the image you want to use. Select "get links" and the use the image code link. Copy and paste that into your post.

That should get the image to show up here.

[SpudRider]

The following thread will tell you how to post photographs on these forums. :)

http://www.chinariders.net/showthread.php?t=8377

[Yster perd]

Thanks for the information :hi: I will post the diagram tomorrow

[Yster perd]

Hi one week later and I'm looking for an old exhaust pipe bigger than the pea shooter outlet pipe for Gomoto 200GY-2B. A balanced shaft 200cc sold in South Africa. A 250cc is available - but it's more fun hotting up a 200cc :)
Anyway - the locals blacks are always amazed with Yster Perd.
"Haw, how much you want for it as I fill up with a mere R80 or $10."
"It's not for sale. You can buy it brand new for R16 000."

Chinese bikes are cool - especially how I am starting to Hot Rod mine - first strip off all those ugly recycled shopping bags they call fairings. Underneath you will find a cool plastic matt black fuel tank - no rusting problems! and place your favourite sport team decals on the tank. Mine is a Shark bike and we won the Currie Cup rugby final.

Second at my altitude 1,7km above sea level jet it to 150 - a 1.5mm drill bit does the trick and ensure that here are no rough bits by gently chamfering the rough edges of the hole with a 3mm drill bit. Instead "Hot" jet for nothing.

Now trim the mixture screw of the 28mm CV carb - I needed 3 1/4 turns.
OK seat bum test up a mountain pass near my farm. Pulls like a train in low revs - reaching the summit in first gear to the top on muddy roads.

Fuel consumption is excellent - But, no top end - runs out of steam - bur 100 km/h is not too shabby.

Now for the muffler mods. Drill out the pop rivets on the chrome end cover and retain it - and then hunt for an exhaust pipe with about the same diameter as the hole of the chrome end cover. Or water pipe whatever.

[Yster perd]

I got a great idea. I will use a copper water pipe for the outlet pipe and braze the end cap on and drill it full of holes (as weldengrind said).
I will cut out the old outlet and then braze the new one in. The larger copper pipe, jutting out slightly) will look very cool in contrast with the standard chrome end cap.
I will do that this weekend in the farm's workshop.

[Weldangrind]

Not a bad idea, as long as the brazing holds up to the exhaust temperatures. I suspect that it will be fine. Please take pics.

[Yster perd]

The weekend is finally here. I went to the local hardware store and bought a 500mm length of Class 2 copper water pipe and an end cap new for +/- $10 and some brazing rods.

The new pipe has an OD of 23mm and ID of 20mm - compared to the Gomoto standard of 17mm ID. That's an area increase (do the maths!) of 74% and copper doesn't rust either!

Well time to start - will post pictures of the $10 mod of the standard muffler

[Weldangrind]

I'm looking forward to this.

[Yster perd]

Hi Weldangrind

First I took the stock muffler off (pics will follow) and removed the chrome end cap.
I tried to drill through the end plate and gave up, after breaking too many drill bits.
Got the angle grinder out and cut off the end plate - muffler's outer casing is very thick! No wonder it's so heavy.

If you DIY petrol heads try this with a hack saw as it is about 5mm thick (including the fiber glass) and it will take you a month of Sundays, will take measurements, but the inner pipe is far thicker than the outlet - typical 2 stroke technology.

I saved the end cap and will braze it on later, as I want to shorten the muffler and smooth down the end cap this weekend.

[Weldangrind]

Looking forward to pics. Here's a muffler I built for an old Honda: http://www.chinariders.net/showthread.php?t=10096&highlight=xl250s

[Yster perd]

Thanks Weldengrind

for the link. I did the mods as per your pic ( I will post them later),and did the following this week:

First, using an angle grinder, cut the muffler down, about 1cm, from the end plate.
Then, discard the end plate - these Chinese mufflers use two stroke technology with venturies, etc, to speed up the exhaust gases, then cut off the old outlet pipe, with a hack saw.
You will find the main inlet pipe with an adjacent extra pipe with the inlet pipe narrowing down to the 17mm pipe and then back to about 25mm.
Then, grind the muffler smooth to accept about a 2mm thick new end plate.
Discard the old end plate and solder the 20mm copper water pipe into place with the new one, - ensuring that it almost touches the end of the expansion chamber.
Next, push in the end cap of the pipe and braze the outlet pipe assembly, onto the new end plate.
Then drill an offset array of 5mm holes through the pipe and end cap.
Now, arc weld the end cap assembly into place and then seal the holes with "Gun Gum" or another exhaust sealer.
Slip on the chrome end cap and voila!

Instant starting, with a smooth linear response to approx 3/4 throttle (with the lean mixture setting)

And the sound!, absolute smooth baritone which is surprisingly quiet. Absolutely no back fires upon close of throttle, even down hill - Actually too quiet. So need to drill out the end cap.

Result, a smooth OE Honda sound with absolutely linear throttle response through the available throttle range.

A 10$ mod - worth it.s weight in gold - but not quite there yet.

I will keep you updated, with pics.

[Weldangrind]

Cool! A little jetting, and you'll have it nailed.

[zingshoen]

interesting thread! pics would be good. i ve got the original zong muffler lying around for practice... :-)

[Yster perd]

There is enough information on my post - I am too upset to post pictures on this forum since Mandela died.

[Weldangrind]

There is enough information on my post - I am too upset to post pictures on this forum since Mandela died.

He will be missed, but his impact will live on for generations.

[Yster perd]

Absolutely - but his spirit, as a non racialistic ruler will remain in this great country of ours

[Yster perd]

Any way, I have not completed the mods on my Gomoto. I am going to convert him to a Sharkie bike - after a rugby team here in KZN. I got a tin of black and white spray paint and will spray the plastic tank after breakfast tomorrow. Then I will send the pics after I get my new "Thumper" a Royal Enfield 500 Classic

[Weldangrind]

Excellent! Please start a new thread on your RE.