Motorcycle Repair: Clacking sound, fuel line blockages, honda cb550

Question
I have a 1978 Honda CB550. At start up cold it runs fine then as it warms up, a loud clacking noise starts and increases in noise level and speed as throttle is applied. The engine will also increase and decrease rpm on its own. It sounds almost like an air chisel hitting the block. My compression sounds ok. I checked the rocker arms for excessive play there is none. I checked the valve clearances they are at .002 and .003 respectively and the tappets are properly positioned. I checked the cam chain and the cam chain tension they are ok. I checked the cam spocket position to the timing marks, its ok. I can't isolate the noise. Any help is appreciated.
Mark Fagan.

Answer
Load related noises are usually connecting rods, wrist pins, piston slap if they are mechanical.
Engine knock can come from excessive spark timing and/or lean mixtures in the cylinders. Read the plugs and look for signs of detonation... like pepper flakes on the electrodes or signs of aluminum from serious detonation. Be sure all carbs have clean jets, correct float levels and it is getting sufficent fuel delivery under loads. Restricted petcock passages/fuel screens or fuel line blockages will cause lean conditions.

Your erratic idle sounds like either spark timing issues or a vacuum leak, perhaps. Check the spark advancer for proper function and check all intake manifolds for signs of looseness or splits in the rubber, etc.

Bill Silver