Topic: Exhaust help needed

[mkramer1121]

Getting to finishing up my CB750K4 and I've run in to some issues with the exhaust.  The header I have is off of a '76 750F that I had the chrome stripped from and had high temp powder coated black.  This may be the beginning of my issues.  I also bought what was supposed to be a slip on Dunstall silencer for the 750F from '75-'78.  Here's my 3 issues:

1) The 4-1 750F headers seem awful tight to the frame when bolted down.  This causes the Dunstall can to hit the rear peg bracket when slipped on, no real way to mount it.  Is this normal?

2) The Dunstall can does not tighten down all the way to the header.  Did I thin the header when I had the chrome stripped?

3)  I'm starting to doubt the validity of my Dunstall can being for a CB750F.  Anyone have records?  The number on it is PD1138.

If pictures are needed, let me know, I can take them. 

I appreciate the help.

[mkramer1121]

bump, any ideas?

[eldar]

Well if the exhaust came from the same bike, it was either that tight before or got bent somehow when it was stripped. Did you replace the gaskets though? If not they might be crushed down and so the pipe is not fitting quite correct.

Then you also said the dunstal does not seal to the header. This is pretty common, especially on the K bikes. I know you have an F but the header diameter is probably not going to be the same. You would have to use a reducer OR you can put the pipe on in place and tighten it down, then put the dunstall on and position it where you want and then weld it down. Then paint the weld to blend.

[mkramer1121]

Thanks for the help.  The Dunstall can I have is a slip on for a stock 750F header.  It was NOS when I got it, so I'm probably missing the gasket.  Yes, I do have rearsets, however I left the passenger peg brackets in place as that is what the Tarozzi's use to mount.   I also did not feel like cutting the frame.  Also, the exhaust did not come from this bike.  The header that was on it was beat to hell, so I replaced it with the free 750F header I got.  More then likely, I'll heed Eldar's advice and run a short piece of exhaust pipe to mount the can to, and also have it bent out to clear the bracket.  Thanks again. 

[eldar]

That is the biggest pain with swapping exhausts. I had to do it too.

[spitfire]

Here's my 76 CB750F with standard header pipes and Dunstall Decibel Silencer, fitted fine, just had to make a bracket to stop the mainstand hitting the chain. Still have the Dunstall in the garage if you want a photo.

Cheers

Den

[S-Dog]

Here's my 76 CB750F with standard header pipes and Dunstall Decibel Silencer, fitted fine, just had to make a bracket to stop the mainstand hitting the chain. Still have the Dunstall in the garage if you want a photo.

Cheers

Den

WOW... it looks like that pic was taken in '76'

[spitfire]

It was !

[mkramer1121]

Here's my 76 CB750F with standard header pipes and Dunstall Decibel Silencer, fitted fine, just had to make a bracket to stop the mainstand hitting the chain. Still have the Dunstall in the garage if you want a photo.

Cheers

Den

Thanks for the reply.  Any chance you could get the serial number off the exhaust?  Mine is PD1138, just curious if ours match or not.  Could you perhaps measure the diameter of the can where the pipe meets the header as well?

Now I'm concerned as to what my header is from.  I'll take a pic tonight, but mine doesn't look like the pic above.  Hmmm...

[spitfire]

Well the numbers on the Dunstall match, just the header, I've attached a diagram of the F1 header and pics of my F1 Dunstall.

[mkramer1121]

Yup, found my issue.  The Dunstall can is or a '75-'76 750F header, the header is for a '77-'78 750F.  The diameters of the pipes don't match up.  So, anyone have a solid header for a '75-'76 750F that they would like to get rid of?