Cb750 what to do project...

brad black

Been Around the Block
i put two new dellorto 57 pilots in a guzzi a while ago - one had the mixture screw 3/4 turn out, the other the expected 3 turns. ran bad, etc. turns out it was a bad jet. couldn't see anything wrong with it, but another 57 fixed it. so shit can get weird at times.
 

cbrianroll

Coast to Coast
That's interesting.. never had that happen yet. Got the new jets yesterday, the new pilots are smaller so, havent got a chance to try them yet. Also got a bunch of new mains just in case.
 

cbrianroll

Coast to Coast
Thought I would try toneing the exhaust down a little. Dont know the science behind but drilled a bunch of 3/16 holes in a 1"5/8 pipe x 8in long. I.d.of exhaust is approx. 2" 7/16. Still need to enlarge the ends and weld. Thoughts on if it will suck or not? Need more holes? Enlarge existing?
20200929_183733.jpg
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
You really need a lot more holes to allow the sound to escape. That's hardly a scientific way to explain it, but it's easily understood.

You also want an inch or more of a gap between the inner tube and outer shell to pack with fiberglass to attenuate the sound.

It should be possible to buy an aftermarket baffle for that pipe. What is the outside diameter of the pipe from collector back? I know someone with a MAC muffler that has never been on a bike that might also work.
 

cbrianroll

Coast to Coast
O.d. is 2.5. Im a poor boy lol, I thought making one would allow to me tune it a bit. Start with less holes...add more to see what changes until I like it. I know nothing so this would be a starting point. Thanks for the info!
 

irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
This is how I built the baffles on my CB750 chopper, with really good results. You need the air to get into the baffle, and allow back pressure to stir the air through the baffle then exit. You want a situation where there isn't a major push of air out of the tail pipe, but also not push air back into the exhaust valve. I also tuned that bike by cutting down the tail pipe I think like 6 or 8 inches, which hugely helped the midrange. I had major gurgling going on when cruising at highway speeds and the shorter pipes eliminated that issue with the jetting I had set up on the Mikunis.

 

irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
Cool, I may have some left over from my forge...assuming its similar... I'll look into it thanks.
It's absolutely similar. Kaowool, Fiberfrax, etc are all the same just with different melting points . I'm a master kiln builder and you better believe I have used Fiberfrax in a muffler.
 

cbrianroll

Coast to Coast
Anyone have a good idea on sets mounting? Right now it just snugs under at the tank and has brackets that sit inside the frames. Be nice to have a hinge maybe and a button latch?
20201004_165915.jpg
 

Rudapo

New Member
i've a bolt moulded into the middle of the seat the have a sort of button latch. still need to check if it works as mine is also still in progress.
 

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