Running rich...and float levels set too LOW?

While doing engine work on my bike recently I noticed the plugs were very black and oily thus indicating a motor that is running rich. After searching the forums here one of the possible causes that seemed to explain it was that the float levels having been set too high and allowing too much fuel in for any amount if vacuum. However, when I checked the fuel height in the bowls I was surprised to see that the fluid level was 7-10mm below the lip of the bowl which is well below spec and if anything should lead to a lean condition.

Does anyone have any ideas as to what might be causing this apparent discrepancy?

 

While float levels are important, it is not the only cause for a rich mixture. Dirty air filter, weak spark, improper carb tuning and jet size will all have a effect on fuel mixture and burning. Burning oil will also make the plugs black.
Start with a fresh set of plugs and check the air filter. Ride for awhile and check the plugs, if the problem is still there then go a little deeper. Pull the carbs and check jet sizes , float level, slides and all the other stuff. Don't forget to check the valve clearences.

 

Hmmm... well it does misfire like hell at anything below 5000 RPMs so perhaps the ignition is the source. The valves are not quite in spec but not enough to account for the poor running at lower RPMs.

 

Misfiring ignition will make your plugs black, lots of unburned fuel. Misfiring could be carbs or ignition.
I would start with the carbs and make sure they are in order. Then look at the ignition.
Out of spec valves have the most effect at lower engine speeds.

 

Burning Rich could mean a few things.
Excessively Rich narrows it down some.

Before you make any adjustments, ... try this:
You can do this without pulling the Carbs.

Pull the tank and clear the way so you can remove the Top of all the carbs.
Pull the tops and springs. Unseat the rubber diaphragms.
See if the Diaphragm Pistons are able to Rise and Fall without binding or hesitating in the slightest.

You may find a Piston stuck.
You may encounter one or more sticking.

If you do, ...
Burnish the Bores.

Use ScotchBrite Pad (Gray) - Medium. A strip 1-Inch wide. Scrub Bores.
Finish using ScotchBrite (White) - Extra Fine - Apply a finish.

Polish Bores.
Polishing Compound and a Cotton Tee-shirt.
(Or a DREMEL Tool and a Flex-wand with Polishing Kit)

 

Well I gave it a Clunk test and 3 of the 4 dropped like a World Cup soccer player who though the ref was looking. The fourth had a stripped screw that I was reluctant to spray PB blaster on because of my concern about what it might do to the diaphragm if it came in contact with it. Figured out how to solve that with the help of this forum and will check the fourth tomorrow.

It has had a partial carb rebuild done but the cold start enrichment system and the idle mixture screw were not touched.