1976 Z750 twin

Be SURE to use a new, correct lock washer on that engine sprocket so the problem never happens again. Ed

Hi guys,

I have some troubles here....for some time I tried to figure out why my bike in running pretty well when the tank is full, and start to run on only 1 cyl when the tank is half full. Then I took apart petcock and installed new gas tubes and it worked fine. Yesterday I reset the ignition timing with strobe light. Today I went on a ride but the engine doesn't run well. It vibrates a lot and it doesn't have the right kick when I open the throttle. I wonder if there is maybe something about ignition timing...since the instruction manual was written 40 years ago and I suppose that gasoline back then was a bit different? Does octane rating affect ignition?

Hi guys, I think I found the problem. Today I removed needle jets and one is considerably more worn than another. How much play should the needle have in the jet? Should the needle completely close the needle and prevent flow of the gasoline?

Here’s a photo of needle inside the jet.

Photo

if the needle jet or needle are worn they should be replaced. what state are the diaphragms in? Did you figure out your ignition problem? is your advancer rusty?

Is that a pic of the needle and seat or the needle jet and jet needle?
Post a pic that is 90 degrees of the one you posted.


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DoctoRot wrote: if the needle jet or needle are worn they should be replaced. what state are the diaphragms in? Did you figure out your ignition problem? is your advancer rusty?

Yes I know but I have problem finding the correct one (Z-4), but I do have machines to make new ones.
The diaphragms are in good shape, they are not torn or damaged.
The ignition works fine, breaker points and capacitor are new, advancer cleaned and lubricated.

Here’s the pic (I hope it will upload from mobile phone...)

That is the emulsion tube and jet needle. The tube looks worn, corroded and maybe the needle is worn too... I seems like it should be nearly perfectly round inside so the emulsion tube operates correctly at different manifold pressures and throttle settings.

Yes, the tube is in pretty bad shape and you can feel play of the needle inside. But does (when new) needle completely closes the hole in the tube and seals it?

is the internal bore of the needle jet worn? is the needle worn?

The needles seem ok. I measured them, they are both 2.99 mm in diameter, the inside diamter of emulsion tubes is 3.15 mm, but since the inside micrometer has 3 spindles I can't measure roundness...