low rpm...won't go above 4000

I have a 1979 kz400ltd. When i first got it about 2 months ago, it ran well most of the time. Sometimes however, it would really bog down and i could not get above 30 mph. After a while, it sounded as though something was blowing clear and it would run normally again. To fix this, I pulled the carbs off and sprayed them w/ carb cleaner and reassembled. Now the bike is constant lacking power and the engine will not rev over 4000 rpm. If i leave the choke open, it will drop to about 3000 rpm. I am also getting carbon fouled spark plugs. I fairly new at all of this so i'm not really sure where i should go from here. Any advice would be greatly appreciated.

Mike
NW Colorado

Have you adjusted valve clearances (and adjusted cam chain tension)? Have you performed tune up procedures outlined in a service manual; to include ignition tune up like timing, points/condensor, new plugs, wires, caps? Have you removed the petcock to check for obstructions? Is your gas line kinked? Have you checked voltage going to your coils? Have you cleaned/lubed the mechanical ignition advance?

Provide a bit more info on what you have done to resolve this issue and we can start eliminating stuff. If this is your first bike and you haven't done much of the tuning I suggested, do that stuff before worrying about your carburetors... I know, I know, you are itching to ride the bike, but you really need to get a service manual and tune it (as well as look carefully at other safety related items like tires, brakes, fluids and the chain) as well before you will be able to have fun riding a reliable bike.

I put new plugs in as soon as I got the bike although they were fouled again after one or two rides, and I have not replaced since. Is there a specific plug I should use? I just used the autolite plugs that they autoparts store gave me. The gas line does not appeared to be kinked, and i removed the petcock and it look as though it was also good.

I have not done any of the other stuff yet. I will see if i can look at some of that this evening or this weekend and keep you updated. I appreciate the advice.

Mike

I would look at the ignition first. Maybe the ignition advance mechanism. Do you have a manual for your bike?