1980 Yamaha XS850 Special

[chicorugger]

I have recently purchased a universal muffler for instalation in the existing muffler body and have some initial questions, The delivery come with a muffler core, 12 discs and an end cap, and six screws. 3 are short, 3 are long. there is no screw to mount the core to the muffler body.

bike specs:
The air filter is a foam air filter, with the stock airbox, carbs are mikuni off a 78 or 79 xs750 (adjustable positions on the needle, more available jets). I also have the stock 850 hatachi's

1) The muffler is tapered, from 3.75in down to about 1.5in. the core is not tapered in any way. Do I need to modify the core so it has a taper that matches the mufler body?

"On V-twin, metric and cruiser bikes, start with twelve discs"

2) If I use all 12 discs the short screws engage about 4-6 threads. If I use the long screws, I end up hitting an obstruction. Which screws should I use? Are the long screws for 12+ discs?

I appreciate your help and will post a pic when done.

[bschultz]

I have recently purchased a universal muffler for instalation in the existing muffler body and have some initial questions, The delivery come with a muffler core, 12 discs and an end cap, and six screws. 3 are short, 3 are long. there is no screw to mount the core to the muffler body.

bike specs:
The air filter is a foam air filter, with the stock airbox, carbs are mikuni off a 78 or 79 xs750 (adjustable positions on the needle, more available jets). I also have the stock 850 hatachi's

1) The muffler is tapered, from 3.75in down to about 1.5in. the core is not tapered in any way. Do I need to modify the core so it has a taper that matches the mufler body?
NO, the core assembly was designed to work as manufactured.

"On V-twin, metric and cruiser bikes, start with twelve discs"

2) If I use all 12 discs the short screws engage about 4-6 threads. If I use the long screws, I end up hitting an obstruction. Which screws should I use? Are the long screws for 12+ discs?
Use the short screws and yes the longer screws are for more discs.

I appreciate your help and will post a pic when done.

........................................

[chicorugger]

This may be a thread for installation, I messed up posting, I can't wait to get on to tuning! the final delivery was:
041-7300 core assy,1.75"ODx9.875"LG,3"IBC,3-bolt

The first time I tried to test fit it I ended up pulling out the core, and leaving the fiberglass in there, so I re-wrapped the core (a couple times). given the 3in diameter the core settled about half way down the 11in cone at the end of the muffler, with the 1.75in core jammed against the left turn. there is about a 32nd or 16th of an inch gap around the core, at the widest part.

Would it be better to cut off an inch or so of the 9.875in of core so the 3in part of the core fits securely and the 1.75in end of the core isn't touching any metal?

I haven't fired it up yet, but I am wondering if it is going to rattle.

Also, I noticed your instructions say not to add disc's but to remove them. When would you use more than 12 discs?

[bschultz]

Sounds like the core is a little to short. The inlet end of the core assembly needs to "locate" or center itself to be secure and allow exhaust flow directly through the core. If it doesn't, exhaust flow will be allowed to flow directly into the packing and end up rattling.
You would use more discs if more exhaust flow was needed.

[chicorugger]

[QUOTE=bschultz;965]Sounds like the core is a little to short. QUOTE]

I took some measurements. the core is just under 10 inches long. If the core was about 6-7 inches long (4-3 inches shorter than it is) it would center itself better and be a MUCH better fit.

I could cut 3-4 inches of the core, and cut the same amount off the packing, and the thing would be 6-7 inches long and fit better and center up better, what do you think?

[bschultz]

If that will cause it to self locate at the inlet end and prevent movement of the core once secured, then yes it sounds like a sound plan.

[chicorugger]

here are some photos of before, after, and the header that is known as KERKER

Is there any sealant or liquid that hardens to a rubber like material that I could put around the core to "fill in the gaps" between the core and the muffler body?

I would weld it, but then it would be MUCH harder to replace the fiberglass insulation.

also the allen wrench for the screw that hold in the discs is 9/64ths, right?

[bschultz]

You may want to try running a bead of high heat silicone around inside of the megaphone and the outside of the core where they will be seating. Let them set up overnight before securing them together.
The allen heads on the 4" discs screws should be 5/32.

[chicorugger]

well, they are 3" discs I don't know if that uses a different allen.

as for the high heat silicone which one do you reccomend?
copper -Temp from -75°F to 700°F
black - Temp from 65ºF to 500ºF


I can't wait to get this fired up, and post a short movie of the sound

[bschultz]

You are correct, 3" allen head screw heads are 9/64's.