lean condition opinion

[TOM SCHANNE]

I'm running stock actual Mikuni jets in my 81 XS400HS , 135 mains and 42.5 pilots. The air mixture screws are both out at three turns from seated. The bike is running good but I want to make sure I'm not running too lean and potentially hurting the engine.

Here's pictures of the plugs (right side first) and the blueing of the pipes.

 

[xschris]

Plugs look fine. Is that the stock exhaust? You could also use a IR gun to get temps of the head to see what it's running at. Make sure the exhaust doesn't have any air leaks.

 

[TOM SCHANNE]

Stock exhaust, yes

Where is the usual places for air leaks to happen and what's the best way to check other than visual?

 

[xschris]

When it’s cold start the motor and feel around the joints for air. There are weep holes under them that should have air passing. The usual places are at the head and where they meet under the bike. If the bike runs and starts fine your probably ok.