How To: Choke Plunger Pad Replacement

Anytime you are rebuilding a set of motorcycle carburetors equipped with an enrichment circuit (choke plungers), do not overlook the rubber pad on the bottom of the plunger! The rubber pad on the bottom gets hard and indented over time. Shot plunger pads will not seal the port properly and the bike will run rich at all times.

Now, the easiest thing to do is to head over to Cheap Cycle Parts or Bike Bandit and order new ones. Well, I was working on a 76’ Yamaha XS360 and the choke plungers were obsolete (PN 584-14171-00-00). Time to get creative!

Below is the choke plunger assembly removed from the carburetor.

Next, I used a pick and small blade screwdriver to “dig” the old rubber from the brass plunger.

I made new pads using a ¼” punch and Buna-N rubber from McMaster, PN 8635K543, 3/32″ THK, 50 duro. Buna-N is a good material to use around gasoline. The punch shown is something I found laying around, and is typically used in steel rule dies. McMaster sells a punch you can use under PN 3424A19, and is trade size 9. You can also make one if you have access to a lathe.

The end of the plunger has a ridge that holds the pad in place nicely. For extra insurance and peace of mind, I used some adhesive (Permabond 102).

I hope you found this post useful. Please comment below if this helped you rebuilt some obsolete parts (or didn’t feel like paying ~$15 per plunger).

BTW, if you own a XS360 or XS400, make sure to check out this forum.