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Saving a 1980 750 twin. 17 May 2021 01:05 #848575

  • kzstreetfighter71
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She is a beaut! Is that a custom exhaust?
06 Gsf 1200 bandit, 08 Triumph tiger 1010
05 Yam xv1700 , 02 Hon shadow 1100
1975 Z1 (currently working on)
1977 Z1000 ( running and in storage)
1978 Z1000 (currently working on)
1978 Z1r "skinny tank" (currently working on)
1978 Z1r "fat tank (gathering parts)
1979 z1000st (currently working on)
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Saving a 1980 750 twin. 17 May 2021 13:20 #848618

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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.

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Saving a 1980 750 twin. 21 May 2021 18:44 #848840

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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

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Saving a 1980 750 twin. 22 May 2021 18:01 #848884

  • rstnick
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She looks great Vic.
Rob
CANADA

Need a key for your Kawasaki? PM me

1978 KZ650 C2, 130K kms, Delkevic ex, EI, CVK32, PMC easy clutch, ATK fork brace, steering damper, braced swingarm, 18" Z1R front wheel.
2000 ZRX1100
2011 Ninja 250R
2005 z750s
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Saving a 1980 750 twin. 24 May 2021 11:12 #848949

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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.

 
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Saving a 1980 750 twin. 06 Oct 2021 16:12 #856281

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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.

 
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