TOPIC:

19976 kz 900 with 29mm smooth bores starts fine but wont idle and blows white smoke. Seems to not fire all cyclinders at low RPM. Please help, spent many hours cleaning up and getting back to spec.

Pic of plugs?
Steve

djbragg wrote: 19976 kz 900 with 29mm smooth bores starts fine but wont idle and blows white smoke. Seems to not fire all cyclinders at low RPM. Please help, spent many hours cleaning up and getting back to spec.

Could start by assuring valve clearances are within specs, and performing a leak down test.


A leak-down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor-man's leak-down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air. Or just use a portable compressed air tank.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).


Good Fortune!

djbragg wrote: 19976 kz 900 with 29mm smooth bores starts fine but wont idle and blows white smoke. Seems to not fire all cyclinders at low RPM. Please help, spent many hours cleaning up and getting back to spec.

Would do sniff-test on the crankcase oil and examine it to determine whether there's gasoline intrusion into the crankcase, which can easily happen with smoothbores because they don't have an overflow circuit and might have leaking float valve(s) for whatever reason.

Also change oil and filter. And assure that the crankcase vent isn't clogged.

Assure ignition timing is correct, and that the advancer is clean, lubed and properly functioning (not stuck or hanging).

Good fully charged battery and fat blue spark on all plugs.

Fine tuning via the carb pilot pilot screws is the last thing to be addressed.

Good Fortune!