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Pookie wrote: Are you happy with how it sounds?
I'm planning on making a similar exhaust for my scrambled Z400, but going for a high level stainless steel system with both pipes on the same side.
I'm going to use 1.5" going into 2" muffler packed with exhaust wadding, so I should think the sound level will be about the same as yours.

Those tube dimensions are way too big for a 400cc engine, it will kill torque. I would think you need to be more in the 1.25 " range, match the ID of theprimary tube to the exhaust port, you can step up from there after 8 or so inches, otherwise you will have issues with reversion.

I do love the way it sounds. It's much quieter than it was at idle, and at high revs it has a very deep growl sound to it. It's somewhat typical of the straight-through type mufflers (Kerekers etc.). At low RPM the muffler has extra internal space to muffle the sound, but at higher RPMs the exhaust pressure just blasts through the mufflers to get the fumes out as fast as possible.

Like Doc says, the 400 uses pretty small header pipes. Remember, the pipes you see are not the size of the header . The real pipe is inside the visible pipe.

I'll try to measure the actual pipe if I can find that scrap piece laying around.

Yes it would be helpful to know what size the inter pipe is, as I think I may add a short length off inner tubing.

Go up in your attic....all that pink stuff is good silencer packing.

The header pipe diameters, as near as I can tell, are as follows:
Outer Pipe OD = 1-1/2"
Outer Pipe ID = 1-13/32"
Inner Pipe OD = 1-1/4"
Inner Pipe ID = 1-5/32"

It may be metric, but those are the closest inch measurements I can come up with.
The wall thickness is about 1.2 to 1.3 mm.

So at this point we really hoped we could finally start jetting these Chinese carbs. All summer we've been able to get the bike to putter every now and then, but not enough that we thought it could be ride-able, so we never added any gas to it. The previous owner had left just a little in the tank so it would flow on "on" and not need the reserve. Now we know he couldn't fill the tank, and he knew it.

After a few days of owning it, we noticed a couple bubbles in the paint forming near the back of the tank. I told my buddy to not touch it and don't pick at it. It could have just been a bad paint job where the paint was just bubbling from heat and not having been clean when painted, but I feared worse.

Well now that we might fire it up for real and tool around, we had to see what was under those paint bubbles... yup they just bondo-ed over two 1/4" holes with no attempt to fix them and then painted over the whole mess.



That was just water. We drained it and filled with water to start washing the gas out.



They can't have thought that bondo was going to keep gasoline in, so they knew it was a leak bomb. Or they were just that stupid. I think maybe a combination of both, looking at the whole bike.

The starnge thing is that the holes look intentional. Maybe they welded studs onto the tank to pull a dent? The tank is dented in there pretty badly. But they ground the metal down to paper thin. At first there were just the two 1/4" holes but after just a light cleaning with the soft wire wheel, several tiny holes opened up and you could see the metal was actually thinner than paper. THe holes were shaped like 1/4" semi-circles.







Who the F does this S?

Summer was quickly ending and I needed to get this thing running, for my own sanity, you know how it is. So I had to start hatching a plan for this tank.

It´s time to head up your big soldering iron to close the holes in the tank.
Put a copper Cent into the inside of the tank where the holes are located as a patch and fill the hole with solder.
Yust my 2 Cents

Or maybe attach a handle and use it as a watering can.

To use your tank as a watering can you Need some more holes before you attach a handle.

Because I don't know what other damage they did to the tank, like grinding it down to paper thin, I would eventually want to strip the whole tank, cut out the entire bad area, and weld in a complete new section. But we don't have the time, I'm doing all this work for free, and I hate stripping and painting and sanding, so this is going to be a fast, dirty, and temporary.

I was originally thinking the same thing as Scirocco's suggestion as I done that in the past... solder in some small round patches from inside. I even cut some steel patches... I hadn't thought of using pennies. I'll have to test-solder some pennies together to see if that works for other projects.



But because this is going to be temporary, and I want to try new things, I decided against soldering. I knew I would have to cover a large area which would require a lot of heat and the solder would contaminate the area against welding later. It's probably good that we decided against it as we found out later the area was so thin, there would have only been solder there with basically no steel.

So I cut out a larger patch to weld in.





To hold it in place I fabricated an arm that would rest against the tank inlet and would be hands-free using a bungie.

I just used a piece of tape to hold the patch to the arm. It's some weird plastic tape I found that shrinks and curls up with heat, so i'm hoping the tape curls off the patch and stays with the arm for removal.





Here, you can see through the holes that the patch is in place and the sharpie marks show the alignment.





All ready to fill with water and nothing left to do but the swearing.

I apologize I didn't get pictures of the setup and welding. This was again being done in a hurry before I left for work so I didn't have time for photos.

But it was pretty straight forward. I setup the tank so the weld area was level with the tank fill neck. Then filled with water slowly till it overflowed which told me the water level was just below the weld area. Nice and simple.

The welding was just small tacks upon tacks. When an area would blow through, as many did, I just had to weld in blobs and grind them down. Considering how thin the metal was, I was half-expecting a total failure which would require plan C... cut it all out and fab a giant patch.

But this went pretty well. I used an awl to test a bunch of area and couldn't punch through.





I'm just going to rattle some gloss black on there to protect it. Later they can wire it off and slap some bondo over it if they want.
The whole welded area is in a dented area, so bondo will cover all of it when shaped to the normal shape of the tank.