Vacuum hose to nowhere

[IOMC Hardtail]

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.

 

[tonyc]

They originally terminated to the air-box. Some use a small breather filter on them and some use a brake check-valve.

 

[5twins]

They're not vacuum hoses, they're your engine breather hoses. They let excess pressure out of the crankcase.

 

[IOMC Hardtail]

Got it. Thanks for the help. And this is the reason I didn't want to buy someone elses project. You never know what you're gonna get. Guess it's time to put some small breathers on them. Now, on to the crazy ass carb crap the PO rigged together.

 

[weekendrider]

You can replace that with a single outlet breather from an '80 up if you want to clean up that area.

 

[IOMC Hardtail]

You can replace that with a single outlet breather from an '80 up if you want to clean up that area.

Thanks for the heads up on that. I like that idea better than two little baby breathers hanging out above the carbs.

 

[figure8]

Post pics of the bike!

 

[gggGary]

You can also just plug one of the ports.

 

[IOMC Hardtail]

Post pics of the bike!

I'm at work right now. I'll post up some pics tomorrow. Might as well start a build photo history. I'm just gonna get it runnin good and ride it till winter and then start the tear down. Still got my Street Glide to ride during the winter.

 

[weekendrider]

IOMC is that your motor in the picture? If so the PO maybe couldn't wrench but he/she were hell bent with spit and polish. Nice looking.

 

[IOMC Hardtail]

You can also just plug one of the ports.

Yeah, true. Was thinking of running both hoses to a T-connector and then put a breather on the single.

 

[XSLeo]

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

 

[IOMC Hardtail]

IOMC is that your motor in the picture? If so the PO maybe couldn't wrench but he/she were hell bent with spit and polish. Nice looking.

Shit no. Wish that was mine in the pic. I just grabbed one from the interwebs that showed the part I was talking about. I have no plans to shine up the engine. I am gonna paint it though. Whole bike is gonna be white and black.

 

[weekendrider]

IOMC sum times ya hafta twist his arm but gggGary IS the go to guy for used parts.
And welcome to the site.

 

[IOMC Hardtail]

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

Leo, thanks for the info. I'm a Jeep and Harley guy so these Yamahammers are something new to me. There's a crap load of guys, like yourself, that have a shit load of knowledge. I'll definitely be asking some questions soon. Especially if I can't get this thing running right. Appreciate it!!!

 

[weekendrider]

Well I don't think they ever hooked the crankcase breathers to the carbs.
And those funny looking tubes on my stock 77 air boxes must be for decoration.
Can you say EPA.

 

[chizler62]

Heres what I do.

Drill a hole in your exhaust, where gets complicated, but typically under the crank.
Weld a nut on it.
Thread a fitting as a hose attached won't melt...
Run a hose to that breather spout.

Simply the exhaust pulls the internal pressure out of the motor helping reduce pressure on the seals and such, but also helping the valve train and inners run freer (the piston goes down easier with less crankcase pressure) With the exhaust vacuum signal reducing the pressure your pistons(among other things) will go down easier than a truck stop lizard. On some motors, not XS650 but GSXR, etc, I have actually seen them rev faster.....etc.....on the dyno.

Look at the bikes on the showroom floor.

 

[gggGary]

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~

 

[XSLeo]

Ok, I stand corrected on the year they started hooking the breather into the airboxes. I haven't had a 76 to 79 bike to compare to.
On my 75 they had one hose into the hole in the left engine cover. On my 81 it has the hose into the air box.
Leo

 

[chizler62]

By the late 80s early 90s any good service department at setup while uncrating took that hose to the airbox and rerouted it up under the tank. Then plugging the airbox spout. Especially Yamaha singles XTs and ATVs in particular.
Some units like FZR's and Viragos all that was done was take a razor blade and slit the hose here or there. Then later those models came with the slits from the factory. Pretty certain it ended up being a bulletin for the manufacturers.

If they didn't have that mod done it was a 90% chance the unit would be back with issues within 6 months.......namely a good 1" of oil in the bottom of the air box.

Interesting to think why Yamaha doesn't suggest oiling a XS650 OEM air filter? LOL You know that yellow filter made from the exact same material Honda uses and sells Yamaha. That material Honda suggests to oil where it used on their units? TRX's etc that DOESN'T run a solid hose and have slits in them

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