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Discussion Starter · #1 ·
So this is technically a single cylinder (sorry...), but I’ve been having issues getting the thing to run. Freshly rebuilt engine, lots of carb/intake/ignition tweaks throughout the troubleshooting process. Finally I tore off the muffler/header one piece unit and fired it up. The damn thing revved so hard it nearly backed itself off the centerstand! Clearly I was choking the engine out with too much back pressure from the exhaust for whatever reason.

After examining the exhaust I noticed something really strange. Right about an inch or two below the mating flange it looks like almost the entire cross section of the pipe is obstructed by some sort of metal. It’s very sooty and hard to tell what it is, but it does appear to be firmly in place.

Is there any way that is supposed to be there? Every other header I’ve mounted/seen/played with has essentially been a hollow piece of tubing. Any and all restriction should be back at the muffler/tail pipe end, correct?!
 

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That doesn't sound like something Honda would have done.
 

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Discussion Starter · #3 ·
That was my initial thought at well. Thing is, the entire exhaust appears to be in excellent condition. No rust or obvious damage. Looking closer at the flange end of the pipe, the protrusion really looks like it’s original. It’s a complex smooth formed protrusion that blocks most of the opening but does allow flow around its outsides. I tried to get a picture but couldn’t get the lighting right to be able to see down into the pipe.

Anyone know what I’m talking about?

If that’s not causing my issue, any other ideas for how to properly clean out a one piece muffler/header so that it flows properly?
 

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Not something I've ever heard of and I worked in the industry when the CB/CL125 singles came out... pictures would help

Edit: most Hondas, if not all, have double-wall pipes to help keep the outer pipe from turning golden or blue from heat. I suppose it's possible that the inner pipe came loose from long-term rust, as often happens to the insides of exhaust pipes after they sit, and caused the obstruction somehow
 

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Discussion Starter · #5 ·
Not something I've ever heard of and I worked in the industry when the CB/CL125 singles came out... pictures would help

Edit: most Hondas, if not all, have double-wall pipes to help keep the outer pipe from turning golden or blue from heat. I suppose it's possible that the inner pipe came loose from long-term rust, as often happens to the insides of exhaust pipes after they sit, and caused the obstruction somehow
Here's a couple pictures. Hopefully they're clear enough. The neon green is the remnants of soaking the inside of the pipe with EvapoRust for a bit. Didn't seem to do much, but I only had it soak for a couple hours at most.

It seems like it could be the inner pipe (the outer pipe surface shows no deformation), but I have no idea how it deformed like that, especially how uniform and symmetric the protrusion appears.

image3.jpg image2.jpg image1.jpg
 

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I've never seen anything like it (but no decent close-up, your pictures won't zoom). If it is, in fact, the inner pipe that got somehow deformed, the only thing I can think is that it started to rust between the walls and it bubbled up that much of the inner wall... the way to tell would be to drill a hole in the bubbled area to see if lots of rust particles come out. The pipe is useless anyway, I'd be tempted to try to cut into the area in hopes it might be removed with some method of cutting it out, but knowing more about it would at least give you some knowledge of the weird situation
 

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Discussion Starter · #7 ·
I've never seen anything like it (but no decent close-up, your pictures won't zoom). If it is, in fact, the inner pipe that got somehow deformed, the only thing I can think is that it started to rust between the walls and it bubbled up that much of the inner wall... the way to tell would be to drill a hole in the bubbled area to see if lots of rust particles come out. The pipe is useless anyway, I'd be tempted to try to cut into the area in hopes it might be removed with some method of cutting it out, but knowing more about it would at least give you some knowledge of the weird situation
Ok. Good to have confirmation of my thought that this couldn't have been right. I'll attempt to drill it tomorrow and go from there. Thanks for the help
 

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Discussion Starter · #8 ·
Ok, so here's my best guess. Somehow, the inner tube wall failed (maybe some metal impurities?). Under intense heat, the failure allowed the wall to droop under gravity (that's definitely the direction of the deformity when the pipe is hanging).

I drilled through and there's absolutely no rust behind the metal. But, now I can see down far enough to see that I can't get to the second blockage caused by the tube collapsing. I've attached an image showing how I think the pipe failed. I was able to drill through the topside blockage but now I'm stuck between the inner and outer tubes with no way to drill through the lower blockage.

redlined image.jpg image3-1.jpg image2-1.jpg

It's a bummer too. The exhaust really is in excellent condition. Anyone had any luck with cutting these up and rewelding? How would the double walled construction affect that? Anyone have one sitting around they'd be willing to part with?
 
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