Engine Breather Vents - Rubber Inserts

[YL82]

Upon replacing the old petrified breather vent hose, I came across short sections of rubber tubing inserted in each vent.

On this bike, I am sticking with the factory airboxes, so the hoses will run into the boxes.

Do I need to keep these rubber pieces installed in the vents?

As far as the DORMAN Power Brake Booster Check Valves, I understand that I do NOT need these since Im routing the vent hoses into the airboxes.

Air Filters: K&N OE Replacement Filters YA-1152's.

 

[jd750ace]

YL, My bike's airbox (79 Special) is 100% stock. I have the dual outlet breather and did not find anything like what you are looking at. Perhaps someone thought restriction was a good idea, or that oil would collect behind those and run back down, VS soaking the airbox.
Regardless, mine did not have those, and my airbox is not taking on oil. Proper oil level is said to be the medicine for oil in the airbox, and It seems to be working on mine.

 

[5twins]

Yes, keep the reducers. If removed, excess oil vapor can escape from the motor. This was one of Yamaha's "fixes" for complaints from owners of excess oil and oil mist being emitted from the breathers. They also reduced the amount of oil in the crankcase by about 500cc. If you look at an early set of crankcases, you'll see "3000cc" stamped on them as the oil capacity. Look at your '76 cases and you're going to see "2500cc" on there. Before introducing the reducers, Yamaha plugged one hose completely and only ran the other single hose for a few years. About 1980, they re-designed the breather box so it had only one hose fitting with a much reduced opening size .....

A reducer in the hose was no longer required because it was "built in".

 

[YL82]

I'll clean em' and stick em' back in. I'm thinking that on my other 650 that one hole was plugged, but I don't remember for sure.

Thanks, 5twins, for the historical perspective. Interesting stuff.... I know I've got it bad for thinking so......

 

[jd750ace]

Great, so now I'm "reducerless" lol! YL, what size is the center hole, so I can fab a set to go in mine?

 

[YL82]

jd, will get back to you shortly...

 

[YL82]

Center holes on my reducers are 4.0 mm in diameter as measured with a digital caliper.

An M4 screw will fit in the center hole, albeit very snugly.

Reducer length: 25 mm

 

[jd750ace]

Sweet. Thanks bud.

 

[YL82]

You're welcome. One should not be reducerless going into the new year.

 

[5twins]

If you've got the sickness bad then that must make me a terminal case, lol.

 

[hard_y_rd]

Great, so now I'm "reducerless" lol! YL, what size is the center hole, so I can fab a set to go in mine?

Did you end up making reducers? What did you use?

 

[hard_y_rd]

I'm assuming a piece of rubber drilled out to 4mm. I know it's not rocket science. Anybody?

 

[5twins]

I'm sure that would be fine. Better yet is swapping an '80 or newer single outlet housing on there. It's a direct swap. Start watching eBay.

 

[XS650DL]

Yes, keep the reducers. If removed, excess oil vapor can escape from the motor. This was one of Yamaha's "fixes" for complaints from owners of excess oil and oil mist being emitted from the breathers. They also reduced the amount of oil in the crankcase by about 500cc. If you look at an early set of crankcases, you'll see "3000cc" stamped on them as the oil capacity. Look at your '76 cases and you're going to see "2500cc" on there. Before introducing the reducers, Yamaha plugged one hose completely and only ran the other single hose for a few years. About 1980, they re-designed the breather box so it had only one hose fitting with a much reduced opening size .....

A reducer in the hose was no longer required because it was "built in".

Interesting history, 5twins. My '77 had the "reducers" but I removed them more than 30 years ago with no bad results.
I figured the crankcase should breathe easier. I have K&N filters and a home made crankcase breather that I put cotton
balls in to absorb the oil mist (which really is minimal) Of course, as you mentioned, my model also has the lower oil level.
I bought my 650 new 36 years ago March 14th. Still love it!

 

[5twins]

Not every 650 will act in this manner. Some are just fine with the oil up to the full mark and the reducers removed. But, there were enough owner complaints that Yamaha saw fit to change things. If yours has been fine since new, I wouldn't change your routine.

But ..... I would scrap the K&Ns. It really hurts me to bad mouth them because I've used them on everything for years, but I found them to not work well on the 650 with the CV carbs. Work yes, well no. Of course, I am speaking about pods. The K&N air box replacements are a different story. They should be just fine.

 

[XS650DL]

Not every 650 will act in this manner. Some are just fine with the oil up to the full mark and the reducers removed. But, there were enough owner complaints that Yamaha saw fit to change things. If yours has been fine since new, I wouldn't change your routine.

But ..... I would scrap the K&Ns. It really hurts me to bad mouth them because I've used them on everything for years, but I found them to not work well on the 650 with the CV carbs. Work yes, well no. Of course, I am speaking about pods. The K&N air box replacements are a different story. They should be just fine.

I have vm 34 round slides on mine. They're a little rich right now.
I'm running a 2 into 1 Jardine muffler which I think is somewhat restrictive.
I intend to go back to 2 into 2 and address the rich jetting then.

 

[5twins]

K&Ns are fine on round slides.

 

[fredintoon]

Interesting history, 5twins. My '77 had the "reducers" but I removed them more than 30 years ago with no bad results.
I figured the crankcase should breathe easier. I have K&N filters and a home made crankcase breather that I put cotton
balls in to absorb the oil mist (which really is minimal) Of course, as you mentioned, my model also has the lower oil level.
I bought my 650 new 36 years ago March 14th. Still love it!

Hi DL,
years back I was advised to "let the poor bitch breathe easier" so I did the recommended mod of drilling a bigger hole in the inner steel baffle plate and through the outer hose connection.
No observable change in oil consumption or leakage for years after that.
Then, coincident with swapping the sidecar onto a larger bike, the XS650 started leaking oil like it was a pre-war Velocette.
After that the XS650 languished in the back shed for some years until my son shamed me into dragging it out of there to get it running again.
Took my Eric 5 minutes to find the problem.
The modified breather connection was held on by only 3 of it's 4 bolts and the tightest one of those was 5 turns loose.
Lesson here is, too much breathing is worse than too little.

 

[NONclow]

They also reduced the amount of oil in the crankcase by about 500cc. If you look at an early set of crankcases, you'll see "3000cc" stamped on them as the oil capacity. Look at your '76 cases and you're going to see "2500cc" on there.

I agree on the misting issue 5T, but I think the main reason for the decreased capacity was due to the inclusion of an electric starter

 

[XS650DL]

I agree on the misting issue 5T, but I think the main reason for the decreased capacity was due to the inclusion of an electric starter

That's interesting information. I feel educated. Thanks NONclow