NC30 some times tapping noise, can anyone help?

[fzrtim]

Hi all. A friend of mine has just bought an NC30 from off ebay. It was bought as a non runner as it had an intermittent noise that sounds like noisy tappets. The engine runs and ticks over nicely for a short while then almost seems asthough it is being starved of fuel and pitters out a bit. Then if you rev it a bit it ticks over at about 1500rpm then pitter out again. Sometimes the engine will pick up and rev as it should not making the noise but then it will act like its being starved of fuel again. The bike has new fuel in the tank new plugs fitted and we have cleaned all the carbs out. Does anybody know of anythings i should be checking.
Thanks Tim

[MexicanGringo]

Yeah iv got a similar sound on my 1990 nc30, only when warm though. Like a metallic slapping sound coming from the cams. You can check valve clearance, iv done mine but the sound is still there, im now thinking its tolerance in the cam gears or a damaged camshaft bearing. Shouldnt be written off as a non-runner for that tho! As for the running problem, all the usual suspects should be checked, float heights, fuel filter in fuel line&tank, air filter and general fuel flow to the carbs.Could also be ignition problem, take your plugs out and earth their rims on the frame&see if they all spark properly. If you'v cleaned the carbs make sure all fuel&air passageways are clear.Also check your choke linkage isnt stuck open. Spray cleaner through the jets but don't unscrew them unless they'r completely clogged. Is your sound&stall happening at same time & is it when warm or cold? Your mixture is most likely out as well, reset all pilot screws to 2 turns out & and see what happens when the bike is warm.

[Dynamohum]

mine does tap when really hot also. my old vfr750fs did it as well was told it was endfloat in camshafts making the noise some bikes did it some not?

[fzrtim]

It only makes the noise when it missfires. Im thinking its something to do with the fueling. Im going to have a look at the weekend to see if i can find whats wrong. Cheers for the pointers.

[MexicanGringo]

Might be pinging/premature ignition if its related to poor performance and a knocking sound, caused by too low octane fuel or heavily carbonised chambers. Mines def related to the cams cos of the repetition with tickover. It actuall sounds like a piston smacking one of the valves on the compression or exhause stroke..

[Polarbear]

any idea when the valves were last shimmed?

[Polarbear]

any idea when the valves were last shimmed?

[fzrtim]

We had a spare engine so after swapping the engine we found there was nothing wrong with the carbs. The new engine runs nice appart from a ticking noise when you rev it up or when the revs let off. Noise sounds like it is coming from the front of the engine.
After stripping the original engine we found that the original knocking noise was infact excessive endfloat in the piston (not sure if little or big ends yet as we have only took the heads of so far) and the piston was infact touching the head. Luckily it has not touched the valves.
The engine has only done 15000km so i think we will repair the engine and refit it as i dont trust the rattle in the engine currently fitted.

[Brainchild]

good job, sounds like you know what you're doing