TOPIC:

I've been chasing a misfire at idle and slow return to idle on a 80 KZ100D3 (Z1R) for 2 weeks now. This was a complete rebuild. It starts easy on chock and runs smooth at higher RPM's. It has all the symptoms of a lean condition caused by an air leak. I can't find it and I'm getting desperate. I've installed new carb holders and air box hoses. I've removed the clean air system with caps on the intake ports and a cross hose between the reed valve ports. No change. Which brings me to my question / theory.
The 80 Z1R came with cover plugs over the pilot adjustment screw . They were "preset" at the factory and "non-adjustable" to meet emissions requirements of the time. I remember drilling/popping them out was a common practice back then. The carb rebuild kits came with replacement plugs, but I didn't plan to install them.
Looking at the parts diagrams, the 78 and 80 Canadian model Z1R carbs, they use a different part # pilot adjustment screw with a rubber o-ring seal. The US model does not have an o-ring on the pilot screw. Could the plugs be needed to seal air from leaking around the non-o-ring pilot adjustment screw on the US model? I know even a small leak can cause big adjustment issues.

I'm no expert but if you've spent all this time chasing it down and you have the plugs in hand I'd say pop them in and try it!

I'm hesitant to install the plugs because they are almost impossible to remove. They're a tapered side with a smooth flat head. They have to be drilled out, ruining the plug. The FSM says to set the screws at 1 1/8 turns out and plug them. I'm not a carb tuning wizard, but every set of carbs I've ever worked on gained some improvement by tweaking from the FSM base setting. The idle is not stable enough to do a good pilot screw adjustment as is. However, if I install the plugs, I'm stuck with the FSM settings.

I got ya, I suppose you could spray carb cleaner into the recess for the screw while the bike is running to see if there's any change in idle speed or pack some thick grease in there that can be easily flushed out.

On my old munged up screws I used silicon on the threads. It worked long enough to buy a couple new ones. I wish I had bought all four.

jetsrus.com/individual_parts/002_677_su.html
I did buy four O rings.
jetsrus.com/individual_parts/002_676_su.html
You can look here for the screws you need.
Steve
jetsrus.com/carburetor/a_carburetor_parts_selection.html

You could put a little dab of axle grease on top instead of the plug. That should seal a leak if you use the ones without the o-ring. After all these years they probably are not at peak setting anymore.

Does the bike at hand have a vacuum operated petcock?

Good Fortune!

I removed these caps a long time ago and never liked leaving them open even though the carbs function fine. I'm going to cap them off with a hot glue gun which should be easy to pop out if needed at a later tuning session.
Regards,
art

aek wrote: I removed these caps a long time ago and never liked leaving them open even though the carbs function fine. I'm going to cap them off with a hot glue gun which should be easy to pop out if needed at a later tuning session.
Regards,
art

IMO, you may have a gooey/screwy mess the next time you want to adjust them.

The stuff sets up fine. A small amount at the top of the bore without filling it entirely should be no problem.

Does the bike at hand have a vacuum operated petcock?

No. Manual Petcock.
I'm going to stop by the hardware store and see if I can find some tapered rubber plugs. If not I may try some RVT. Worst case I'll order the Canadian model pilot screws with o-ring. I just hope I'm not chasing my tail and the problem lies elsewhere. Thanks for all the suggestions. I'll follow-up with the final solution regardless.

I'd try some grease on the threads before I spent any money on the screws. If the issue is solved then the screws and O rings would be worth the money.
Steve