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.

 

I sold this bike to a good friend a couple years ago. He wants to change up the bars and since its back in the shop i'm gonna update a few things.

First up is a fat bar conversion. I had these bars sitting from a different project and they seem like they will work here. I sand-blasted and painted them with Gunkote. The Pro-taper fatbar clamps are too modern billet looking so immediately after unboxing them threw them in 4 jaw on the lathe... trimmed a bit off, welded, put back in the lathe, grind, weld, grind...etc. They need a bit more work but now they look a lot more cast OEM. They will get the same finish as the top clamp.

Part of the reason for this bar conversion is to have a much stronger handlebar to help prevent damage in case of a crash. I have seen first hand how stout handlebars, like foot pegs, can save a bike from alot of damage in a simple lowside on the street and the track. Because of this I am pretty torn on whether or not to route the handle bar switches internally. Obviously this will weaken the bars. I dont see an elegant way to route the wires without drilling the bars.....ideas?

   

   

   

DoctoRot wrote:

Part of the reason for this bar conversion is to have a much stronger handlebar to help prevent damage in case of a crash. I have seen first hand how stout handlebars, like foot pegs, can save a bike from alot of damage in a simple lowside on the street and the track. Because of this I am pretty torn on whether or not to route the handle bar switches internally. Obviously this will weaken the bars. I dont see an elegant way to route the wires without drilling the bars.....ideas?

 

I would agree the options are limited however, it depends how far you want to go (I know you aren't shy) I am using a "D-Box" from Axel Joost which means you can significantly reduce the thickness of cables used (so a smaller hole) as the switches are only carrying approx 0.25 amps. Also if you use the optional handlebar adaptor there only needs to be around 3 thin wires exiting the bars to go back to the box (so a very small exit hole) as the adaptor uses a "single" data transfer wire to send switch signals to the box (just a suggestion )

I have seen stuff like that but probably a bit too much time/money to sink into this since the bike has a functioning electronic system that i don't really want to mess with. I considered re-soldering a much thinner gauge wire to the switches and have the them connected to relays to operate the lights etc but that sounds like a fiddly nightmare to make the wire bundle only slightly smaller. I'm gonna play around with wire routing and see if i cant make it acceptable before i decide to go deeper.

A much simpler alternative to tidy the wiring up would be to replace the factory tubing and tape on the switch looms with "heat shrink" tubing 

Waiting on some different handlebars. these were a tad wide and not enough pull back.

I never really liked the brass washer and yellow zinc fasteners I came up with for the footpegs and shock mounts so I machined some new ones out of stainless.
I don't have a rotary broach for my lathe, but I came up with a crude method of sharpening an allen key and hammering it into a properly sized hole in the stock to make an internal hex. Worked remarkably well. Finally fixed the high speed contactor on my lathe so 2000 RPM is possible. Combined with the coolant mister and stainless specific cutting inserts this is leaving a nice tool finish on these screws.(they are still oily in the pic)

I also remade my tach plug for the engine in aluminum with the same internal hex.

   
 
 

 

Looking good Doc !
Fantastic skills there.
Bill