I am trying to bring an old 89 xr4 150hp (S/N 0C184436) back to life following a voltage regulator fire nearly a decade ago. Wasn't sure if the fire was caused by poor circulation to the regulator so I figured I would go ahead and replace all components of the cooling system which includes the poppet valve.

So I pull the poppet valve cover off and someone has definitely replaced it in the past, but also behind the smaller side of the cover there is a plastic plunger piece that has an o-ring on it which looks like it's used to block water flow completely to that port back into the block, and I can't figure out if this piece is supposed to be in there or not. I've checked parts diagrams for the motor and I can't find this piece anywhere on there so I was hoping someone can identify it and let me know if it should be put back in or not.

Including a pic of the part and circled in red is the smaller end of the poppet valve cover that it was in :

???..... I've either built, bought every model 2.0, 2.4, 2.5 production and high performance motor merc has offered since 1976 ta 2004 and have never ran across a poppet part like that!..... hope someone can answer that question?.. its really got my wheels turnin'..........

its probably got something ta do with tha water cooled regulator.. '89 was first year for that and it gave them problems from tha start until tha hose was added from tha top of tha block down to tha poppet.. that helped a little by eliminating some of tha air pocket in tha divider plate that caused tha reg to over heat.. but tha water cooled only lasted 2 years then went away...

Poppet block off

Thanks TLW, it has me stumped as well.

So if it's a poppet block off I'm assuming it's supposed to be there then Gary? Do you know off hand where the water goes in that port on the block from the poppet valve? (the one circled in red in my pic)

From what I've been able to gather, and correct me if I'm wrong, but this Poppet block off is there to prevent water from going through the small hole and instead push it to the top of the block via the line hooked up to the poppet valve cover.

I just find it odd that I can't find mention of this poppet block off piece anywhere.

that is one strange piece for sure.. jus never (myself or anyone I know) has run across it before....... and you are correct.. might be on microfiche somewhere but not on any printed parts or water flow diagrams I've seen...

" Poppet block off is there to prevent water from going through the small hole and instead push it to the top of the block via the line hooked up to the poppet valve cover "

no, ya got it backwards.. water comes from top of block "down" to tha poppet... that hose (top to poppet) was designed/added to relieve air pockets in tha divider plate to help cool tha regulator but added benefits kept tha design "after" tha water cooled stuff went away

Never seen that since those motors came out!

can't find anyone who has!!!