Topic: running so rich I'm only getting 15mpg

[lowbrow]

Bought a '71 CB500F in April. Came with a 4 to 1. I had the carbs rebuilt and synced, added Dyana coil and starter, everything is timed correctly. Can't figure out what the deal is. I'm fouling plugs like crazy, I have thick black exhaust, and my MPGs are stupid low. Jets are stock and I even removed the airbox lid to try and lean it out. Nothing changed. It's so bad that adjusting the carb screws does absolutely nothing.

 A guy who's bike I was admiring suggested upgrading to Mikunis with flat slides. Does this sound like it should do the trick?

[Bailgang]

Figure out why you're only getting 15 mpg first before even considering getting a set of Mikuni's. What condition is your air filter in?

[dave500]

have you got the choke control the right way?it is up for choke and down for running,if someone has done the carbs youd hope they looked at the filter like bailgang suggested,forget swapping the carbs,,get that idea right out of your head!!

[Rigid]

Needle shimmed up or ground down?  Plugged drain lines and leaky float needles running fuel into engine? 

[lowbrow]

Air filter is brand new. Choke is not engaged.

Needle shimmed up or ground down?  Plugged drain lines and leaky float needles running fuel into engine? 

I'll look into this.

[dave500]

floats upside down,perished o rings at the main jet.,you have d7ea plugs?

[dave500]

one thing i dont get?how do you sync carbs when its blowing thick black smoke?

[Mainerider]

Have you followed proper protocol and checked all the related specs? Valve adjustments all within spec? Compression test run? Is it consuming engine oil?  High-mileage bike? Strong spark at all 4 plugs confirmed? Etc.

Wen you say the carbs were rebuilt, what did you have done, specifically? Are you sure they stayed with stock jets? Are you sure the rebuilder was competent?

Also, are all 4 plugs fouling or just certain ones? Are they fouling at low engine speeds, highway speeds, or both? If it is at higher speeds, and if it is indeed a carb problem, it could be clogged-up emulsion tubes. One of the roles that emulsion tubes serve is to prevent the mixture from becoming too rich, due to the squaring of air pressure relative to air speed. Lots of questions to be answered before any advice is anything more than speculation or guesswork.

[2wheels]

Did you replace float valve and float valve seats?

Did you clean the gas tank?
Possible gunk in the tank got into the clean carbs and now you have gunk in the float valves.

[tlbranth]

Same thing happened to me when I restored my 750. First, the brand new Emgo air filter was junk. Replaced it with K&N with a big boost. Next I played with the floats, one of which was sticking, on account of a dimple in the tang and 2 floats were leaking. I now get about 45mpg where I was getting 27. My plugs are still a tad sooty. I've been gradually lowering the float levels. Lots of power now though.