Motorcycle Repair: 1971 honda cb175, honda cb175, piston heads

Question
Hello, how are you?
I'm having some trouble with my bike.  I bought it last year begining of summer.  I cleaned the carbs, put new gas/plugs/oil and battery, it started right up.  After only about 30 seconds started to slow down and die.  I check the plugs and they are charcoal, soft, fluffy black.  I checked the choke was off, i even took off the air filter completely.  I cleaned the  carbs several more times, even leaving them overnight in a can of cleaner.  I dropped the needle down, turned out the mixture screw, adjusted the floats, (if you are not aware, this engine has a slant to it so the carbs are slanted down towards the engine) I even tried a hotter plug, (don't want to go too hot, from what I understand)  So i'm at a loss.  The guy I bought it from said the exhuast valve is sticking, I don't really know what that means or if that is causeing the problem.  I am curently on my second rebuild, just on the top end.  Cleaning the piston heads and cylinder head.  The bike has good compression.  

I also checked the spark, it really is not as fat as my old 350 had.  looks kind of weak.  I tried two different coils, new set of points, new condensor, and a full battery.  

Just wondering if you had any imput, i'm ready to throw the whole thing in the garbage.  

Sorry about the length.  If you have the time to get back that would be much appreciated.

Andrew

Answer
Andrew, I think you put the slides in backwards.... there are left and right sided ones. Cutaways go towards the air filters. Make sure that you cleared the passages in the carb throat. Air bleed passages for idle mix and main jet... if plugged they will cause rich running.

An exhaust valve sticking would result in low compression on that cylinder. Rarely happens unless the engine sits for many years with that valve open, then some corrosion can form on the stem, keeping it from closing. Be sure clearances are .002"  Might want to pop the valves out for inspection if you have the head off now and change the valve stem seals if it has any. I'm not sure that they did have them back then, however. Check the stem-to-guide clearances, though.

Spark is probably fine as it is. Check the spark advancer behind the point plate for sticking, however, then reset timing to the F mark.

Bill Silver
www.vintagehonda.com