Exhaust temp (lean), how hot is too hot?

I have a few bikes I'm looking at, all 650 maxims, and am wondering how lean one of these bikes would have to run to make the exhaust tubing discolor near the heads. It has that purplely coloration associated with heat cycles at higher temperatures. I made my downpipe on my turbo car do the same thing, but I also hit temps around 1700-1800F at the track with a relatively rich AFR of 11.7-12.5:1, it would get cherry red and it didn't worry me a bit. However the seller admitted to the bike running lean after a less than repitable shop tuned the carbs, he later had them redone and said it ran much better. My gut tells me to walk away and go with another one, even if it means a little extra cosmetic work in the end. What do you guys think?

 

I would be tempted to walk away too. These bikes come with double walled pipes so they have to get mighty hot to turn. Now if the bike doesn't have a stock exhaust and has been fitted with a 4-1 then I wouldn't worry too much. A lot also depends on how long it ran lean before he retuned the carbs.

 

Some aftermarket chrome pipes (Jardine) will "Blue" immediately after installation and the bike is fired-up. They're too thin ... not too.

If your looking at an excepitonally good deal ... you might ask to do an examination.

Look at the plugs for the very obvious signs of LEAN.
If their NEW Plugs ... take it for a ride ... then, look.

Compression.
Peek at where the Mixture screws are and judge if it's tweakable.

If you come-back after a test ride and the bike is HOT-Hot.
Walk.