Any Idea What’s Causing This Gunk?

luckydevil

XS650 Member
Messages
10
Reaction score
13
Points
3
Location
North Carolina
I’m trying to get this 1978 XS750 running and I noticed burnt oil or residue from incomplete combustion in the cylinder #2 intake port. Cylinders #1 and #3 look nice and clean. I’ve attached photos for reference.

I admittedly tried to run the bike with pretty nasty carbs before starting the rebuild, and it surely caused misfire/backfire.

Compression is consistent across all 3 cylinders, squeezing 135psi-141psi.

Thanks for the input!
 

Attachments

  • 42B89900-8C85-4092-838A-CFB4D3A96E58.jpeg
    42B89900-8C85-4092-838A-CFB4D3A96E58.jpeg
    441.3 KB · Views: 40
  • 5A623D50-610A-4254-8370-A255C09D558E.jpeg
    5A623D50-610A-4254-8370-A255C09D558E.jpeg
    324.4 KB · Views: 38
Just one port doing this?

Valve guide dripping oil from rocker box.

Sloppy guides do this if really bad, but guide to head casting due to scored insertion interface on press fit is more likely.

New guides?

cliff
 
Yeah, just one port. I put new valve shims in, but didn’t touch guides. Who knows how long it’s been causing problems. Looks like I need to go shopping.

Thanks cliff!
 
Back
Top