77 XS650 BS38 White smoke from right side after rebuild

[kohh]

Hi all, I’m new to riding and just got a Yamaha XS this summer as my first bike.

I’m having an issue with my 1977 XS650 (BS38 carbs).

I recently rebuilt the carbs using a Keyster 48-1920 kit because the bike was running very rich and the idle was unstable when I bought it.

Setup
Carb cleaned + rebuilt
Float height: 24mm
Synced and mixture adjusted
OEM airbox

The bike runs, but after 20 minutes I start getting white smoke from the right side of the engine area. It doesn’t look like it’s coming from the exhaust itself, but from the engine side. I also notice a clear temp difference between left and right cylinders.

I rechecked the carbs and reassembled everything, but the issue is still there. No obvious external oil leaks.

What should I check first?
Could this be carb/air leak related, or more likely an internal engine issue?


Any tips or similar experiences would be appreciated.

 

[Jan_P]

Please clarify

It doesn’t look like it’s coming from the exhaust itself, but from the engine side.

I don't know much about carburetors .But this spring at start I had Difficulties starting the bike BS 34
petrol was flowing over from one carburetor to the Ground

After some exercise closing the fuel flow and emptying the float bowls ..it started with the non working float valve
I had white smoke from the exhaust never seen before ... nervous of engine damage .But after a while some miles ... the White smoke was gone.
Valve not closing to much fuel probably

 

[5twins]

If you used the jets from that rebuild kit then they're way too rich. That kit comes with the jet sizes for the '78-'79 carb set (#135 main, 27.5 pilot). It's wrong but has been sold that way for years, lol. You need a much smaller 122.5 main and a #25 pilot. Also, the float level spec for your carb set is 25mm. 24mm would be a MM richer.

 

[kohh]

Thanks! I ordered new float valves and the O-rings for them.

The white smoke seems to be coming from where the exhaust header meets the cylinder head, not from the exhaust itself.

 

[kohh]

Thanks! I’ll go with the 122.5 / 25 jets and set the float to 25mm.
I’m also getting some white smoke and higher heat on the right side, so I was a bit hesitant to go smaller on the jets since I wasn’t sure what was causing it.