Vacuum hose to nowhere

[SpoogeMCMM]

Curious... IOMC = Iron Order?

 

[IOMC Hardtail]

Curious... IOMC = Iron Order?

Yup. Dirty 13 Chapter in Omaha, Ne.

 

[Christen]

When Yamaha started building these bikes they new a lot about crankcase pressures and vacuums. Two strokes won't run if these things are not right.
On the early years they had two nipples with hoses run down below and behind the engine. They were vents so the crank case would not over pressure and blow out the seal. As time went by they made changes to this breather system. They plugged one side and just ran one hose. They ran this hose through a hole in the left side engine cover so excess oil blowby would lube the chain.
They added a restrictor in the side with one hose to help slow down excess oil blowby. Along in there somewhen they dropped the oil capacity from 3000 cc's to 2500cc's. This also helped with excess oil blowby.
I don't think the hooked hoses into the carbs till around 80, when they went to the BS34 carbs. They also changed from a two nipple brearther to a single nipple breather, this smaller housing with one nipple was when they started plumbing the breather into the carbs. The nipple had a small hole to act as a restrictor.
Plumbing it this way did two things, it prevented excess oil blow by getting out and added a small vacuum to the crank case. This vacuum help slow weeping gaskets and seals. It also helps the rings seal better.
You might want to look up inside the nipples you have. I think by 78 they had one side plugged and the restrictor installed in the other side.
I have one of the later sungle nipple breathers on my 75 with a short piece of the stock hose, about two inches, run to a power brake check valve. The inlet side of the check valve is a perfect fit in the stock hose. Other do the same with the out let side pointing to one of there pod air filters. I run a 3/8's size hose off the outlet down to behind and below the engine. Some do thuis with a filter in the end of the hose. I think the filter is a wate. The lenght of hose, especially after it gets a coat of oil is plenty of filter. Any air coming out of the long hose won't be drawn back in the engine because of the one way valve.
Even with out the valve any air drawn back in won't reach the engine. The length of hose and the built in restriction won't allow it. The oily hose collects most of any dirt that might be drawn in.
Leo

Thanks for the history and suggestions on the dual nipple oil vent. Just got the pictured '75 XS650 with one hose to the chain, nothing on the other nipple and oil burned on to the top of the right carburetor. The oil capacity noted is 2500cc. I'm thinking of a "Y" fitting to one hose to the chain oiling hole in left engine housing. This bike sat for 20+ years with fresh oil and old gas. I'm still getting the gunk out but almost there.

 

[5twins]

You should plug one outlet and just run one hose from the other outlet. Running both wide open could allow too much oil and oil vapor out.

 

[Cwyck83]

Starting around 76 they routed the CCV lines to the air boxes. In 80 they changed to one line that tees to both air boxes.
76 up, the line(s) go down below the air box then back up to a "stand pipe" that has it's opening facing up across the air flow. it is a basic venturi. (Bernoulli's principle) at low RPM slow air motion lets any oil puddle in the low parts of the tubes. Note the tubes are large diameter, This allows lower velocity so the oil can drop out of the air stream. At higher RPM increased air flow across the tube mouth pulls air and any accumulated oil into the combustion process, the motor can easily burn off the oil mist at higher RPM.
This was enough to satisfy the EPA for quite a while and is a simple solution to what to do with that nasty oil mist. Probably even contributes a mite to efficiency, the oil does contain energy. Keep reminding your self that engineers did this stuff and penny pinchers were watching, excess parts and expense were constantly pared from the bike, if it's on the bike and isn't about looks, there's a reason.
I am old enough to remember when cars used a road draft tube for CCV and also how religious we bikers had to be about staying out of the area between the tire tracks at intersections. I don't mind doing my little part to keep that oil mist burned off in the engine (stock air boxes) or a similar system plumbed on after market filters.

Didn't do this to jerk your chain Leo~

I have a 77, no idea what ports were for. And my left side pulls more than the right. Is this an indication that something is wrong?

 

[gggGary]

welcome aboard Cwyck83!
I'll suggest;
Start by setting cam chain, and valves, then ignition, finally clean and synch the carbs.
Somewhere in there do a compression check.

 

[Cwyck83]

welcome aboard Cwyck83!
I'll suggest;
Start by setting cam chain, and valves, then ignition, finally clean and synch the carbs.
Somewhere in there do a compression check.

welcome aboard Cwyck83!
I'll suggest;
Start by setting cam chain, and valves, then ignition, finally clean and synch the carbs.
Somewhere in there do a compression check.

Cam and valves adjusted. Timing is a cdi box so I can’t adjust that(which kinda sucks) and my vm34’s don’t have vacuum lines and I can’t find carb holders with vacuum lines pre installed (for my size carb) so I synced them manually (which was a process) im still wondering though are the ports both supposed to have the same pressure?

 

[gggGary]

Cam and valves adjusted. Timing is a cdi box so I can’t adjust that(which kinda sucks) and my vm34’s don’t have vacuum lines and I can’t find carb holders with vacuum lines pre installed (for my size carb) so I synced them manually (which was a process) im still wondering though are the ports both supposed to have the same pressure?

Not sure what ports you mean?

 

[Cwyck83]

Not sure what ports you mean?
View attachment 193832

Sorry, referring back to the two on the top of the engine

 

[gggGary]

The crankcase vent set up varied just about yearly. Keeping the oil in while letting air flow in a 360 twin is not an easy task. Some had two ports but one was plugged (from the factory) others have two ports with drilled rubber plugs for less flow. After 75 the factory used fairly large tubing to run the vents into the airboxes. 75 they just dumped one port on the chain and called it done, LOL.

 

[HOTEL71]

New to the XS650 realm, but not new to bikes. Been looking for a project for awhile and ran across 78 Special that was already hardtailed. Couldn't pass up the deal. Anyway, it runs rough, as expected (the PO wasn't quite the wrench turner he claimed to be), but I'm working on the rough running issue. Just some carb issues that I'm working through (pods and open exhaust (plus a 145 jet in left carb and a 142.5 in the right)). So yeah, the PO had no clue what he was doing. Anyway, back to the question at hand.... Above the carbs, attached to the top of the engine, there are two ports, pointing at each carb, with a vacuum hose coming out each port. The hoses go nowhere and have air coming out of them when it's running. Does anyone know where these hoses go? I couldn't find it in the Haynes or Clymers. I've attached a pic for your viewing pleasure. The part is circled with and arrow pointing to it. Thanks. View attachment 54187

see picture
left side (one each) goes under and attaches at the bottom nipple of the breather box
right side goes to your circle in picture (top of motor)

 

[Torchard]

What size hose for those vents?

 

[5twins]

I don't know the exact size but MikesXS and YamahaXS650.com sell the perfect replacement, thin wall just like the original .....

https://yamahaxs650.com/product/breather-vent-hose/