Saving a 1980 750 twin.

She is a beaut! Is that a custom exhaust?

wrote:

She is a beaut! Is that a custom exhaust?
 

Thanks! yes it is a custom header. I sand bent the lower header bends myself. Pages 14-18 have header and flange fabrication and pages 26-27 for muffler fabrication.

Did a little fork tuning, the front end was a little harsh for these crappy LA roads. I'm putting these numbers here for my own future reference.

33mm sag
20mm preload
10mm stiction
fork spring # 537250 - 90
oil level - 140mm from top
Gold valves with blue springs installed - 2 turns preload

She looks great Vic.

Changed out the starter clutch this weekend. This really is a crap design from Kawasaki. I pulled out an old starter clutch that had only 1000 miles on it since full rebuild and one of the springs was already deformed. and the engagement surface already had some roller marks.

Instead of the mickey mouse crap i have been doing to hold the rotor I finally made proper rotor holder. Makes it so much easier to remove and install the rotor.

I also swapped the foot pegs out for these rubber Tarrozis, dropped a jet size on the main, and did the full break-in service including re-tightening the head studs which is always a PITA because you have to remove the blind plugs under the valve cover to get to the internal studs.

 

The straight through free flowing megaphone muffler i made is pretty loud, I was OK with that when this bike had a performance oriented engine, now that it is a very mild hop up I want to tame the exhaust sound a bit.

To try apply some science to this completely non scientific venture I bought the cheapest dB meter off ebay to measure results. I doubt it is accurate, but it is probably adequate for testing the differences between the options.

The two options I wanted to try to reduce sound are just inserts so I would not have to modify the muffler. The muffler has an 15" baffle with a 1.75" 16GA perforated tube. It is wrapped with a layer of stainless steel mesh, followed by stainless wool, and then fiberglass.

Option 1: The classic "dB killer" style inserts that i have seen for years. I used a 1.25" tube - 4" long - (20) 3/8" holes. I added some neoprene foam around the flange so i could just tape it in the exhaust and get a good seal.

Option 2: "laminar flow cone" style muffler from Flowmaster. I know the Flowmaster has engineers sciencing out all the parameters for their cone designs to get optimal results, I created mine based on the existing tube diameter, and an arbitrary length of 4.5" I used a cone calculator to draw a template on 20GA stainless perforated sheet with 1/8" holes - 50% open area. I then used a tapered punch and a hammer to form the sheet into the cone before welding the seam and adding a flange. I then riveted the cones on either end of the existing baffle pointing in.

The results were:

Existing muffler - 84 at idle 102 at 4k RPM
Db killer - 81 at idle 99 at 4k RPM
Laminar Cones - 84 at idle 100 at 4k RPM

The Db killer does make a noticeable reduction in sound, however it modifies the tone and sounds tinny and cheap.

The laminar cones also make a noticeable reduction in sound, but retain a very low tone. it actually sounds better than the straight core, more of a rumble.

Both the inserts took away the sharp percussive nature of the straight muffler so I consider that a win, however neither of them are significantly quieter. Its OK for now but i probably will return to this to see if i can quiet this down further. Unfortunately I think this means a major revision to the internals, something i was hoping to avoid, as adding them will probably mean cutting the muffler open which i really don't want to do. I cant seem to find any good info on how to design muffler baffles, so it will probably be mostly trial and error. I think i may try a stock style baffle system.