Choke plungers

I pulled a plunger this morning and the only difference I found was the larger shaft diameter where it goes through the dust seal.  The 4.47 and 4.98 is slightly larger. This is the diagram for the Niche vm29, etc plungers, right?

Rode it today after a year and black plugs after 10 minutes, same as last year.  Just went through the carbs again, cleaning, set floats, only part I didnt (never) changed was those plungers.  Im going to pull them again and see if I can test the seal on the plungers with air or vacuum.
 
 

Kidkawie wrote:

I pulled a plunger this morning and the only difference I found was the larger shaft diameter where it goes through the dust seal.  The 4.47 and 4.98 is slightly larger. This is the diagram for the Niche vm29, etc plungers, right?

Rode it today after a year and black plugs after 10 minutes, same as last year.  Just went through the carbs again, cleaning, set floats, only part I didnt (never) changed was those plungers.  Im going to pull them again and see if I can test the seal on the plungers with air or vacuum.


 

The smoothbore plungers are slightly thicker in those areas but i don't know why they did that and it makes no difference.
The dust caps that the smoothbores use is exactly the same part as the normal VM's.
As for mucking about trying to test your seals with Vac or pressure , I wouldn't bother.
If your seals are original they ARE leaking.
It's just a matter of how bad they are.
 

My bike ran perfect in the US.  Moved to eastern Europe and its run like s*** since. 

Kidkawie post=925278 userid=5306I pulled a plunger this morning and the only difference I found was the larger shaft diameter where it goes through the dust seal.  The 4.47 and 4.98 is slightly larger. This is the diagram for the Niche vm29, etc plungers, right?

Rode it today after a year and black plugs after 10 minutes, same as last year.  Just went through the carbs again, cleaning, set floats, only part I didnt (never) changed was those plungers.  Im going to pull them again and see if I can test the seal on the plungers with air or vacuum.
 

 

   We have the Niche plungers in one of our Z1-B's.  As you mention, the shaft is 0.5mm larger on the Niche plungers than the OEM Z1 plungers.  All other dimensions match.

   The larger shaft dia. can cause just enough stiction where the shaft passes through the dust cap that the internal spring on the plunger doesn't seat the plunger completely when the choke is OFF; the plunger can lack just a few thou of seating firmly.  A gentle finger press will reveal if seating is an issue when the carb is off the rack.  We turned down the plunger shafts by 0.5mm to compensate, but a stronger internal plunger spring would accomplish the same thing & be simpler.  The top closing (pusher) tabs on the lifters could be formed* to increase pressure / travel, but there's too much flex and imprecision in that whole crude choke shaft / lifter / pusher design that we wouldn't trust doing so for the long term.

   The OEM Z1 dust cap is PN# 16039-015.   Someone mentioned some months ago that the Mikuni (smoothbore?) dust cap PN# is VM20-455.  If the ID of the VM20-455 dust cap where the plunger passes through is 0.05 larger that the OEM Z1 dust caps, that could ba a solution also when using the Niche plungers.  We don't have new dust caps of either PN# to measure the ID.

   * A good Tech never 'bends' anything; it is formed.

Good Ridin'
slmjim & Z1BEBE

  , installed, in early carbs, with later spools, and arms from a 75, work well, no issues and #4 is not wet now, was iust messing around to see if it worked , have a nice day

Perhaps coincidence Jim but actually ran across an issue with the choke plungers on this earlier set of the ramp style SC's. Wasn't what i'd initially thought, sticky plunger to bore hanging issue. It was the design of lifter (less opening perimeter) and set screw to lifter shaft was putting a side bind between lifter and choke plunger shaft above rubber dust seal. Couldn't bend the lifter enough, without making it goofy, to clearance shaft for smooth operation. I shimmed the lift lever outboard and all is fine now. Jwfels your're correct and looks fine. Note though, if you can "push" down choke plunger further after choke shaft is fully closed then You will always have a half seated/flowing access of un-needed fuel getting sucked from the bowl. Note the differences between the openings of early and later Z1-Z1B/KZ900 Lifters. Z1B (squared-off) and KZ900/1000 had a bigger opening to pull the choke plunger up. All this crap makes a difference between running and running right.          

jwfels wrote:

 

Hi jwfels, just wondered if you have seen the PM I sent you ?

As a last resort, I tried modifying the stop tab on the lever, got extra clearance there, then lengthened the slot in the lever so it wouldnt bottom out on that pinch screw.  The linkage was able to push down on the plungers but it didnt work.

Hey Kawie, maybe you should try them, and Wookie workin on a reply

I've used Clay's o-ring superglued to the plunger seal method and it works fine. (make sure to use a viton o-ring)