" With the head breathers hooked to the exhaust, the exhaust will create a vacuum and help suck the crank case pressure out of the motor. With these tubes sticking into the ends of the pipes,it helps break up the exhaust pulses,making the bike a bit easier to tune."
Post by tomterrific on Nov 28, 2007 7:51:12 GMT -5
Yep. Running a vacuum in the crankcase has a bunch of benefits. The first most folks think of is an increase in power. I learned about the exhaust sucker type breather from articles in which Grumpy Jenkins told how his secrets worked. Both my Triumph T140 and my XS650 use power brake booster check valves in the breather hose so the pistons pump the crankcase out but the valve checks when the pistons go up. My primary concern is oil leaks from old dry gaskets. Both engines are mechanically fine but old gaskets and seals are suspect. Note that some of the top Vintage racers use teh exhaust sucker as you discribed.
PCV valves do not work in a motorcycle breather hose. The PCV system of a car is totally different in concept and the valve checks in both directions so can INCREASE pressure in the crankcase. Don't use a PCV valve in the breather hose of a bike.
Thanx Tom! I'm going to go with it. Should I also add the check valve that mikesxs has? I've also noticed a small amount of blowby on mine and I'd rather have that oil being burned up in my exhaust than making a mess on my motor.
Post by tomterrific on Nov 28, 2007 11:55:35 GMT -5
Do you have a '77? Put the important stuff about your bike in teh side bar like I have. You can get there with your Profile.
My '77 has two breather hoses that are 1/2". You can get a 'power brake booster check valve' that is cheap ($5) and perfect for the job we want from Advance Auto on the Help rack in the aisle of the store. The 1/2" nipple of the valve plugs right into the 1/2" hose running off the breather. The other nipple is 3/8" and I found vinyl hose plugged onto that nipple. You can route this to the ground or it will fit inside 1/2" hose if needed to feed into the stock air box. Remember the air needs to go out of the crankcase but not back in. Don't get the check valve backwards. You can try to make exhaust suckers but they will be allot of work and may not be a help unless racing.
So, Tom, do you have this check valve on just one hose or both (2 check valves)? I have my 2 hoses run to a brass "T", then down to a K&N breather filter. I'm thinking I could add the check valve in the single line that runs to that filter (if it's not too big). Hose size differences could be addressed by using smaller hose "sleeves" over the valve nipples so it would fit my current single hose I.D. Here's my set-up now with a 3/4" single hose to the breather filter .....
Tom. I don't know about putting the restriction in breather. I am familiar with the booster one way valve, but it will create a negative in the case when the pistons go up, is that a good thing, especially with old seals and gaskets. But you reckon it's been working on your Triumph, so can't be that bad. I would just get rid of that rubber plug that Yamaha found necessary to stick in the breather block, route the lines away from the motor. Mine run along the top frame rails and exit out back, or do as 5twins did. John.
Post by tomterrific on Nov 29, 2007 9:18:05 GMT -5
The brake booster check valve is a 90° bend which can help or hinder an installation. I'd like to find a suitable check valve the has straight nipples. The 3/8" hose sleeve to 1/2" is what I was trying to describe. You did it better. I haven't ran the Triumph long with the check valve and it is cold now but other Brit bikes run the valve with good results. The Triumph seemed like it ran freer on the highway at 70 mph but that could be the cooler weather as well. I'm not sure a breather filter is needed since the direstion of gases is only out of the breather hose.
I have in mind a more sophisticated positve ventilation system in mind that will pump air through the crankcase to vent it of moisture and combustion by-products but still keep a slight forced vacuum in the crankcase. No restriction in my '77D breather really. I use two valves and pulled the blocking pieces of hose from the breather box on the head. Remember the amount of air/gases the breather system passes is much lower with a one way valve checking the intake of air into the crankcase.
Post by Six-Five-O on Nov 29, 2007 11:03:48 GMT -5
Tom..I have installed the single outlet breather set-up on the 78-79 engine that currently resides in my 82SJ which retains the stock airboxs..I have hogged out the single outlet, plus enlarged the hole in the restrictor plate and have a single breather hose feeding a T-Fitting, that in turn, provides venting into the right and left airbox breather inlet nipples...I presume a single power brake bleeded valve would be all that is needed on a stock airbox set-up on the later XS-650s?
Great info...I think this needs a sticky!
Yamaha XS650, the past is a just a blur in the mirrors.
My base gasket leaks badly. The front of the case would get soaked and it would leave a large spot on the ground anywhere it was parked. I tried the check valve and it made a huge difference. It still leaks a bit but not bad enough to drip on the ground.
Well, is it possible that if there is a vacuum in the crankcase there would be a tendency for the oil on the cylinder walls to get "sucked" down? In other words, would the vacuum contribute to blow by and a reduction of lubrication on the all important cylinder walls and rings? Or, to put it a third way, would there be a lessening of distribution of oil on the cylinder walls during the intake stroke when the combination of vacuum in the cylinder head and pressure in the crankcase draws oil up to lube the rings?
When these types of issues come up, I always think about the 1,000 engineers who designed the XS650 and wonder if they didn't know what they were doing. I think that this situation is the reason for the design of the PCV valve. The intent was to draw unburned hydrocarbons into the intake manifold to burn them up, but not create a large vacuum in the crankcase.
Last Edit: Feb 26, 2008 12:24:08 GMT -5 by pamcopete
Isn't the PCV just a check-valve, i.e. a one-way passage? If so it seems that its purpose is to vent the crankcase under positive crankcase pressure but not allow fuel/air misture to get sucked into the crankcase on the negative pressure end of the cycle.
But, to follow your 1000 engineers train of thought, it seems unlikely that they all would have overlooked any positive benefit of venting crankcase pressure to the exhaust. Multiply that times all of the other 4 stroke engine applications engineers who seem to have overlooked this benefit for what, a 100 years?
I gotta see some dyno numbers on this one before it comes out of the "Garage Legends" file for me.
Well, I did the deed. I installed the brake check valves on my breather hoses and positioned them over my pods so any vapor will just get sucked into the carbs .....
I also re-installed the rubber restrictor plugs in the breather outlet nipples. My bike has always used some oil. When I rebuilt the top end last year, I was hoping this situation would improve but it hasn't. I pulled the restrictor plugs when I first got the bike running. Everyone said it was OK to do so. Well, I'm not so sure anymore. I think my motor was breathing too well without them, blowing out more oil vapor than it should. While the breather filter I had installed never actually dripped oil, it was always wet looking.
There's a page over at 650Motorcycles.com that promotes opening up the smaller one outlet breather on the later motors. I guess that removing the rubber restrictor plugs on the older 2 hose breathers is sort of doing the same thing. Now this may be fine and maybe even necessary when racing but I'm starting to think we don't need this on our street motors. 650Central just put up a bunch of articles by Farrell Hope, a long time 650 enthusiast. He has one on excessive oil blow-by and it's worth a read. He feels as I'm starting to that opening your breather more will do nothing but blow too much oil out.
r80rt: :)This is a splendid write up, THANK YOU!!!!
Dec 26, 2015 16:54:05 GMT -5
mashermoto: What the what is this shoutbox for? Or should I shout, WHAT THE WHAT IS THIS SHOUTBOX FOR!
May 12, 2016 22:22:21 GMT -5
motormike: Good Day ...just a FYI.. Wild Cat is this Labor Day weekend. Still go'n on. A few 650's still make the scene. Various rides at different skill levels each day.. awards dinner sunday eve. BS in the park'n lot after dinner.
Aug 23, 2016 7:57:01 GMT -5
lsettle: First post in over 6 years!
Aug 28, 2016 19:45:17 GMT -5
kardon: Wow quiet here, where did they all go.
Oct 7, 2016 2:18:13 GMT -5
gggGary: XS650.com LOL
Feb 16, 2017 20:49:02 GMT -5
buell88: Anybody have any idea who built the xs650 tracker used in the Draggin Jeans Ad on Pipeburn?
May 16, 2017 16:24:09 GMT -5
joshua: The regulator/rectifier unit I got from Mikes PMA has closer hole spacing than original. Are we supposed to mill the holes to fit?
Jun 7, 2017 19:25:58 GMT -5
joshua: My bad. I found the bracket they supplied to mount the rectifier/regulator... Uh oh. How is this meant to work? Which way is it meant to mount? Looks like I have to use some spacers or something. Good instructions would be nice.
Jun 7, 2017 22:09:52 GMT -5
craig8johnson: Not sure if this is the right spot or not but oh well...
Jul 11, 2017 18:04:15 GMT -5
craig8johnson: I'm checking the charging system. I'm afraid I might have fried the last battery. With the solid state regulator (after market) what should it be charging at. The book says, I think, 15 volts. I'm hitting 17 when revved. Is that too high?
Jul 11, 2017 18:06:19 GMT -5
gggGary: Yes 17 volts is too high, about 14 volts is max, sounds like you don't have the right regulator or it's wired wrong.
Jul 13, 2017 6:54:33 GMT -5
dean: Just saying Hello, new member who is going to fix up a 79 XS650 that has seen its better days. I will definitely have lots of questions coming up.
Jun 23, 2018 16:45:32 GMT -5
tt650: Trying to breathe life into a 1980 that's been stored (indoors) for 25 yrs. Air filters are dry rotted. Have cleaned carbs but she only runs briefly on choke then stops. Need jet setting info and other ideas that might help her idle and rev.
Jul 3, 2018 19:15:19 GMT -5
trix13: Hey everyone! New to the forum and am fighting those gremlins!! New charging system, ignition switch, coil and fuse box. Resistance is higher than normal on the ignition pick up so I'm trying to find one. No such luck yet.
Aug 16, 2018 8:50:48 GMT -5
trix13: Also, even though all of my connections are clean, I cannot seem to find out why , when at higher rpms, I hit the signals and the rpms pulse with the signals...hahah. same with the brake light. I appreciate all input!!
Aug 16, 2018 8:55:08 GMT -5
bob99: how do I post a question. I am new to the forum
Jun 6, 2019 10:52:10 GMT -5
adlpc: Hello all! Been enjoying your edifying posts and discussions - and as a fan of the XS650 since my early teenage years happy that I now own a 1980 Special which I plan to turn into a vintage half faired racer. Thank you all for being here!
Oct 1, 2019 0:58:56 GMT -5
jimothyj: Hello everyone, I just joined & wish would have known about this site in 2014 when I brought my 1974 TX650A back from the grave. I have spent a good deal of $$ and alot of time on it. Just painted it and working on electrical, I will post pics soon,
Apr 10, 2021 2:14:13 GMT -5
louisvan: trix13 - I had a problem with my 1975 SX650. When I got to highway speeds, the engine lost power. The problem was in the connectors. At a certain vibration and the wind pushing on the wiring loom, the connector lost continuity. A bad crimp to the wire.
May 20, 2021 1:19:09 GMT -5