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A stock 78 Z650 experiencing a slight hesitation between 2K-3K RPM. I did not have this issue until the valve seals were replaced, valve lash set, carb sync and replaced the stock foam air filter with a paper version.

The Air Screws are set at 1 turn out, stock 15 Pilot Jet, 102.5 Main Jet, needle clip 3rd down and the plugs look a little bit on the white side. Mainly used around 1000 foot elevation in warm weather climate (75-100 degrees). Engine is completely stock (including exhaust) except for Electronic Ignition. Is it possible the paper air filter is causing a lean condition and the pilot jet should be bumped up to 17.5 since this did not exist before?

Put your idle mixture screws out a bit and see if this helps.

Post edited by: newbikekiller, at: 2006/06/21 20:29

Thought the air screws would increase the air mixture and thus lean the condition. It seems to already run a bit lean. Should I turn the air screw out for a paper air cleaner as I thought it was less restrictive than the stock foam. Any thoughts would be appreciated.

I run my bike in similiar conditions, 15 pilot, 102.5 mains, with a oiled foam UNI filter. My air screws are out to 1.5 turns, and my clip is in the 4th notch down from the top. It runs without a miss and the plugs look tan. You may try clipping down to the 4th notch too, see if it helps.

Excellent suggestion! I'll try the 4th clip as the needle jet does indeed change the transition from pilot to main. Will also try reinstalling the foam air filter and see if the problem goes away. Just thought the paper air element may be the cause of a (minor) lean condition. Thanks again.