Colorado

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Apr 2, 2005
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I bought my daughter an '82 XT125 Yamaha as a logical move up from her XR100R. I'm a 2-stroke guy, but the MX175 I tried to put her on first scared her because of the bigger size and quicker power both at the same time. The XT is kind of heavy, but doesn't seem like a bad little bike. It does have an issue with the exhaust though --- the muffler part of the stock exhaust starts right under the front of the seat, and makes for a VERY hot inner right thigh!

I rode a '77 TT500 for a little while, but it had a modified exhaust --- an older Supertrapp that was mostly behind the seat. Is something like that the way to go with the XT? Can I just add more round pipe, making the 'header' longer, then stick a supertrapp on the back? Are there tuning issues I need to consider?

Thanks!
 

Colorado

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Apr 2, 2005
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RePost! Please respond? exhaust question

#1 07-14-2006, 03:09 PM


Colorado

Registered
Bike(s): KDX175 '80, IT400 '78, MX400B '75, Join Date: Apr 2005
Location: I don't know.


Member #: 60368

Thumper exhaust question

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I bought my daughter an '82 XT125 Yamaha as a logical move up from her XR100R. I'm a 2-stroke guy, but the MX175 I tried to put her on first scared her because of the bigger size and quicker power both at the same time. The XT is kind of heavy, but doesn't seem like a bad little bike. It does have an issue with the exhaust though --- the 'muffler' (silencer/spark arrestor) part of the stock exhaust starts right under the front of the seat, and makes for a VERY hot inner right thigh!

I rode a '77 TT500 for a little while, but it had a modified exhaust --- an older Supertrapp that was mostly behind the seat, so it was only round tubing that ran under the leg there (for that matter, her XR100 was set up like that too).

Is something like that the way to go with the XT? Can I just cut the stock pipe and add more round tubing, making the 'header' longer, then stick a supertrapp or some other spark arrestor on the back? Are there tuning issues I need to consider? I'm not trying to make this into a race bike --- just her next one to get used to a more full size ride.

Thanks!
 

Ol'89r

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Jan 27, 2000
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Colorado Is something like that the way to go with the XT? Can I just cut the stock pipe and add more round tubing said:
Colorado.

I don't see why you couldn't add to the pipe and run a SuperTrapp muffler. It may affect the performance but, since the bike is just a play bike for your daughter, it shouldn't matter. If you can't tuck the pipe in further maybe you could make a pipe shield by using a larger diameter pipe and cutting it in half longways to form a shield. Weld a couple of nuts to the original pipe and mount the shield with a couple of bolts and spacers to the nuts.

Just a thought.
 

Colorado

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Apr 2, 2005
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Ol'89r said:
Colorado.

I don't see why you couldn't add to the pipe and run a SuperTrapp muffler. It may affect the performance but, since the bike is just a play bike for your daughter, it shouldn't matter. If you can't tuck the pipe in further maybe you could make a pipe shield by using a larger diameter pipe and cutting it in half longways to form a shield. Weld a couple of nuts to the original pipe and mount the shield with a couple of bolts and spacers to the nuts.

Just a thought.

Thanks 89r,

The bike has kind of a shield, I guess. It's a thin metal cover that the side plastic (if I had it) would mount over. That metal gets very hot too though! I was thinking about drilling it full of holes so it would dissipate heat better --- after reducing the bulk behind it by doing the other mod.

Any thoughts on a new silencer/spark arrestor? The new thumpers all seem to use very model specific ones, but I was hoping to just see what I could find in the yard of my neighborhood motorcycle salvage place. SuperTrapps have tuning discs to dial the bike in, but it almost seems you'd need a dyno to really use them.
 

Ol'89r

LIFETIME SPONSOR
Jan 27, 2000
6,961
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Colorado said:
SuperTrapps have tuning discs to dial the bike in, but it almost seems you'd need a dyno to really use them.

A stock SuperTrapp should work on a bike that small. If there are issues with the way it runs, just add more discs. They are pretty quiet and are approved spark arrestors also.

Also, could you mount a shield off of the frame under the seat? Such as a small piece of aluminum between the pipe and her leg.
 

Colorado

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Apr 2, 2005
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Ol'89r said:
Also, could you mount a shield off of the frame under the seat? Such as a small piece of aluminum between the pipe and her leg.


That's really what the thin steel one is like. I'd rather not take it off until I do a little more looking for the side plastics. I think the right plastic has to mount to it. If I had the plastic, it might even add the little bit extra heat insulation needed --- but I don't think a lot of XT125's were sold. At least they haven't ended up in the salvage yards here. Now that I think about it, adding a vintage type number plate there might help while I look for the plastic.

I've been pretty busy since I got the bike three weeks ago, so haven't even really done more than a cursory examination of it all. My daughter's softball tournaments have consumed our weekends, so stuff around the yard and house has filled the other time. I have Friday off, so might take her riding then, but the wife says she shouldn't risk getting hurt before their last tournament on Saturday and letting her team down. In that case, Friday can be my day to figure out the best plan of action.

What principles guide 4-stroke exhaust design? It seems like streeters sometimes run bobbed pipes and are more worried about reducing back preasure than anything else. One of the first old bikes I picked up when I got back into riding was a '75 Honda XR250 (pacage deal with an IT400). I was surprised to see that the owner manual (still under the seat) had cautions about modifying the exhaust.

This XT has a VERY quiet system! It's a lot quieter than the XR100 with the SuperTrapp was, and I have to suspect that that much sound control is robbing a little power. I'm not of the old 'pull the baffles' school, and want to keep it reasonably quiet, but it seems like adding a little more header length and a SuperTrapp is more likely to help performance than hurt it --- unless I'm missing some design principle involved.

Thanks again for your help.
 

Ol'89r

LIFETIME SPONSOR
Jan 27, 2000
6,961
45
Colorado said:
What principles guide 4-stroke exhaust design? It seems like streeters sometimes run bobbed pipes and are more worried about reducing back preasure than anything else.


I have to suspect that that much sound control is robbing a little power. I'm not of the old 'pull the baffles' school, and want to keep it reasonably quiet,

but it seems like adding a little more header length and a SuperTrapp is more likely to help performance than hurt it --- unless I'm missing some design principle involved.
.

The 'streeters' with their bobbed pipes are more interested in being noticed than how good their bikes run. IMO.

Adding the Super Trapp may help performance but, modifying the pipe length may not. The factories know a lot more about performance than people give them credit for and pipe length is critical to the way an engine will perform. Any changes in pipe length should be done on a dyno.

Another thing you could try is thermal wrap. It is available at most speed shops and many auto parts stores. It is an insulated wrap that can be wrapped around the pipe in critical areas. Works very good. Do a search for it on the forum. Many thumper riders use it on their head pipes.

We are losing riding areas at a rapid pace due to excessive noise. If you could keep the exhaust system stock with the original muffler, we would all be better off. Just my opinion.

Ol'89r
 

wetrat

Member
Jul 22, 2006
14
0
header tape

you can insulate the pipe with some header tape
available at most auto parts stores and about every muffler shop
wrap the pipe at least once with the tape overlaping it self about 1/2 use some stainles wire to keep the tape from unraveling
once you are happy with the insulation put some good quality hose clamps at each end of the pipe (ie engine and muffler)
ps start at the engine end of the pipe
 

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