XJ650RJ - Air leak at the choke?

I'm hunting an air leak and decided to try something new. I lightly blew some compressed air into the sync hoses while covering the intake side, with some soapy water sprayed on the manifold. Standard gas leak test procedure- look for the bubbles. The air slowly leaked out from around the choke plunger, even when I pressed it down to ensure it wasn't loose. I saw no bubbles around the manifold.

It starts fine and the idle is currently high when warm, with the mixture screw about 4.25 turns out. I just cleared the pilots with fine wire, and compressed air flows where it should when blown in the pilot jet. Everything about the way it runs and responds to mixture changes is pointing me to an air leak, but the usual culprits haven't paid off so far. I've never gotten any results from the propane trick. The manifold gaskets and bolts are fairly new.

Can lean running be caused by an air leak here at the plungers? I would think that an air leak there would enrich it, since that what opening it for starting does.

 

I think our carburettors add more fuel for cold starting rather than cutting off the air supply with the lever. There is an enrichment circuit that does that in the float bowls via the brass tube on each carburettor.

 

4.25 turns out from bottom is waa-a-y-y-y to open......it's right on the verge of coming out of its threads! There's a reason why it was set like that, perhaps to compensate for some other issue/problem (such as the internal pilot fuel passage being partially clogged, and trying to compensate for reduced pilot circuit fuel flow by setting the mixture screw "wide open").

I'm not absolutely sure of whether the choke plunger seals serve as "dust wipers" or whether they are actually air seals....even new ones are just a little bit loose on the plunger shaft (imo) to act as fluid seals, although it would make sense that significant air intrusion thru those seals would lead to a lean condition.....

 

Yes the wide open setting was to verify if the mixture screw was doing anything, since 3.25 out was still dying at idle. And what it did was act like there is an air leak and way too much pilot. So that's expected based on everything I know.

Is the true diameter of the pilot passage known? I used a .010 wire. I also tried a .016 wire but that seemed too big.

Next step is to tear down the choke plunger rack, clean and polish as necessary, and grease the plunger and seal with heavy silicone.

 

I can't remember but I think you can get at least .020 through it. Might be more.

 

I applied compressed air to the top of a plunger and got a good bit of air leaking past the brass->aluminum seal. (Be careful if you try this- it wants to push gas back out the intake side, not surprisingly.) It's weird there's not a real seal here, just the dust cap.

The plunger looks smooth but the seat looks like it could use some work. It looks like there's a burr on the inside edge of the seat. I have various blocks of rouge for lapping the seat.

 

I marked a .010" guitar string at the max depth it would go in the hole under the pilot jet. Then I marked the rest of the strings to match. The #32 string was the biggest that would go all the way. It did not feel like there was anything blocking the passage.

I cleaned and greased the plungers, and set the mixture to 3.25 turns out. It dies slowly when the throttle is closed, and bogs when opened with any load. I have to give it some RPMs and slip the clutch to get moving without bogging.