Pilot adjustment screw plugs - air leak source?

swest wrote: 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

Before going any further, I'd press-seal small pieces of masking tape over the tops, and see if that affects how the engine runs. It may also reveal a leak, which would be fun to watch as the suction tries to pull the tape down the hole. :laugh:

Had they switched to CV carbs by 1980? If so, I'm thinking there's a hole in a diaphragm.

Had they switched to CV carbs by 1980? If so, I'm thinking there's a hole in a diaphragm.

Not on the Z1-R. Slide carbs with an accelerator pump. .

Carbs are designed without those caps. The air screw should have an oring, or a design where the air getting past the screw threads is inconsequential. The caps are a modification for the U.S. emissions laws (EDIT: as tamper prevention, like strum says, below.)

I see no reason to cover those caps. they were not put there to prevent air flow just to prevent tampering with .
if your leak is from there its a bad oring or even a bad air screw.
you still may be jetted lean or somthing eles such as float hight, blocked passeage(s) ect you may be chasing the wrong thing here. JMHO

I always thought the plug's sole purpose was anti-tamper to comply with US emissions laws as well. I know years ago I drilled them out on my brand new 81 GPz 550 and had no issues running without them. However, looking at the parts diagrams for the same year/model, the non-plugged Canadian models have an o-ring on the adjustment screw. The plugged US models do not. The FSM also says to use a dab of sealant when installing the plugs. This is what caused me to start thinking the plug must act as an air seal as well. I'll seal them somehow this weekend and see if it makes a difference.

MDZ1rider wrote: I always thought the plug's sole purpose was anti-tamper to comply with US emissions laws as well. I know years ago I drilled them out on my brand new 81 GPz 550 and had no issues running without them. However, looking at the parts diagrams for the same year/model, the non-plugged Canadian models have an o-ring on the adjustment screw. The plugged US models do not. The FSM also says to use a dab of sealant when installing the plugs. This is what caused me to start thinking the plug must act as an air seal as well. I'll seal them somehow this weekend and see if it makes a difference.

That is very interesting. They are tricky bastards. If the U.S. models don't have a place for an oring on the screw, then I guess you need caps, or Canadian screws. Do the rebuild kits come with screws? That's where they usually slip in the non-emission-compliant parts for U.S. customers.

Just a follow-up to close the discussion. I compared the rebuild kit airscrews installed with the originals. There was a noticeable difference, I installed the originals and idle settled down significantly. My guess is the kit included the non-US o-ring version and because the originals did not have O-rings, I didn't use them. I may try the kit screws with O-rings at a later date. I;m just happy to be making progress.
I guess to summarize, air leaks may be possible around the air screws, but it's probably self-inflicted.

If not already done -- and assuming fitment of stock vacuum operated petcock -- would inspect and verify integrity of the vacuum hose from carb (or carb holder) to the petcock, and snug hose attachments to the vacuum nipples at the carb and petcock.

May rule out possibility of an internal petcock air leak by disconnecting the vac hose at carb, cap/plug the carb nipple, set the petcock to PRIme, and test run.

Would double-check that there are no open vac nipples anywhere, and that all vac caps/plugs are snug and un-cracked, including the vac nipples left open and unused after the clean-air system was removed.

Good Fortune!

Perhaps I've overlooked it, but there's no indication of having performed the usual spray testing for air leak at idle.
Would do so if the racing idle issue persists.

Good Fortune!