Air Box Mod... Lots of Pics.. Part 1

[crazy steve]

I've kept mine the way it was because from what I can see of the design, it will at higher throttle settings actually pull a little on the crankcase vent, helping to keep the crankcase pressure down a little. I figure this is a good thing, since there is not a common vacuum source I can use for a PCV valve system. But anything that helps scavenge the crankcase is going to help the engine last longer.

I think that you're overestimating both the importance and effectiveness of the 'spider'...

On a single-point vent system like these bikes have, air is constantly flowing both ways as the crankcase volume changes with the pistons going up and down. And rather large changes too; anybody who has ever started a bike motor with the fill plug out knows how fast they can 'paint' a wall with oil! So having that spider in place can (depending on what the crankshaft position is) mean that air could going either direction. This 'pulsing' in the intake can't be helpful for air/fuel mixture (besides the obstruction in the velocity stacks). I suspect this design was primarily chosen for emission reasons, as well as for keeping oil off the stock 'dry' filter. If you're running a K&N filter, this doesn't matter. Scott mentioned that this may cause problems with most of the 'blow-by' going into the 2 and 3 intakes, and that may be true. But from looking at several spiders, they were pretty much dry inside; the 'oil separator' at the cases seems to do it's job well, keeping the oil in the motor. I feel that if you're getting any serious amounts of oil in the airbox, you have either mechanical problems or the motor is overfilled. The guys running pods with external filters on the vent haven't been reporting oil dripping from the filters.

For this vent system to be truely effective, you would need another vent, with the airbox vacuum source pulling air through the motor instead of just pulsing it back and forth. Maybe a PVC valve mounted to the cam cover, with the valve installed so it lets filtered air into the motor, but none out. A set-up like this might actually be worth a bit of power. I know some of the racers use a similar system, with a open filtered vent on the crankcase and a venturi tube in the exhaust system, using the 'timed' exhaust pulses to draw out/lower the crankcase pressure. Not exactly 'emission friendly' though....

Actually, this gets me thinking.... Harley uses a rubber 'umbrella valve' in each rocker box to prevent the crankcase from pushing air out (this is to help keep the oil in the motor); it shouldn't be too tough to fab a plate containing a couple of these and sandwich it between the case and the vent housing, only allowing air to go out. That would minimize the 'pulsing' and increase crankcase vacuum... hmmmm....

[cywelchjr]

I think that you're overestimating both the importance and effectiveness of the 'spider'...

On a single-point vent system like these bikes have, air is constantly flowing both ways as the crankcase volume changes with the pistons going up and down. And rather large changes too; anybody who has ever started a bike motor with the fill plug out knows how fast they can 'paint' a wall with oil! :eek

Ok, this just doesn't make sense with how mechanical systems work. You have 4 pistons, which move 180 deg apart from each other in pairs. When two are going up, two are going down, at EXACTLY THE SAME TIME AND SPEED. This means there is NO change in volume of the crankcase, it just can't happen, nothing is being added to or subtracted from the crankcase. You DO have blow-by from the cylinders, and that will be in pulses from the cylinder on the compression and power stroke at the moment, but it's NOT from the volume of the crankcase changing. Sorry, but I have to call BS on this one, it's just too far wrong. The only way what you're saying could happen, would be with an asymmetrical stroke setup where you didn't have the pistons going up and down in a well coordinated manner, and that thing would shake itself apart, much like say, a Harley Davidson will, since they DO have an asymmetrical stroke pattern, and the crankcase volume on them DOES change, but not on these engines.

That said, you could be right about the effectiveness of the spider, but then you could be wrong, cause those Japanese engineers are pretty smart guys, and I'm pretty sure that they knew what they were doing with that thing. I'm pretty willing to be that if you checked, you would find that almost ALL of the air flow is outwards due to blow-by, and as such, I think *I* would prefer it going into the carb throats and getting burned rather than sitting in the bottom of the airbox and getting the air filter dirty with the oily stuff that comes out of their. The most common problem those with pods seem to complain about is the air pressure coming out of that vent.

I also think that most of that oil that paints the wall comes from being slung off the clutch pack, since it's bathed in oil and right UNDER the fill plug hole, which combined with the positive pressure that exists in MOST internal combustion engines crankcases that don't have a PCV system, helps create your very oil oil painting gun, gas powered .

[mharrington]

This is whats been done for ever in the automotive world- both street and definately race cars. This kit comes with bungs you weld into your header reducers. Then you install the breathers into each valve cover. The breathers replace oem PCV valve and oem breather- both originally by emission requirements plumbed into the air cleaner. A hose goes from each new breather to the bungs welded into the header reducers. So scavenging is still strong but being placed into the exhaust and not the intake. Would be easy to do on a bike too. Obviously this degrades exhaust emissions.

[natemoen]

Steve, you need to put this on one of your running bikes and try it out!

[Pat Kelly]

Seems you're replacing velocity with volume. Still restricted by slide height and butterfly opening. Max volume cannot excede the area at the venturiis. Air velocity can be increased with a restriction (again, venturi).
Hope it works as well as you hope it does (nothing ventured, nothing gained).

[crazy steve]

Steve, you need to put this on one of your running bikes and try it out!

I wish I had a XS that was running.... The only one that did I sold...

[natemoen]

I wish I had a XS that was running.... The only one that did I sold...

Never looked super close at your sig, you need to work on that!

[motoman]

Yup, last line in sig. says it all. Have to agree with Pat on this one plus the many years of performance building myself.......a step backwards. That stock airbox WITH the snorkel WAS intentional And was specificly designed as a whole based on capable intake flows and volumes in the cyl. chamber. The necessary compact design being a motorcycle doesn't leave much metal to be removed from head or other areas for any flow improvement. Yamaha already did all the figuring for ya and designed the airbox intake around that. I'm sure the sound generated though ought to make up for any losses though.

[donebysunday]

Air box mod

was never finished. Work/NO work ?

[crazy steve]

This bike is still a pile'o parts....

[IanDMacDonald]

was never finished. Work/NO work ?

I have an airbox mod similar to Steve's on my bike, with a much bigger filter on mine, and it works well. (See my signature).

[donebysunday]

I have an airbox mod similar to Steve's on my bike, with a much bigger filter on mine, and it works well. (See my signature).

Is there a thread on removing the carbs and air box on an SF.
Just pulled my SF carbs and I don't remember my LH being that time consuming ?
I changed the intake boots on my first SF back in about 81, I remember that was a job that took way to long.

I realize you can't pull it for a photo shoot, do you have pics of yours on the bike or can you tell it's not stock ?
Thank You ! Done

[crazy steve]

Is there a thread on removing the carbs and air box on an SF.
Just pulled my SF carbs and I don't remember my LH being that time consuming ?
I changed the intake boots on my first SF back in about 81, I remember that was a job that took way to long...

Here's a video... http://www.xs11.com/forum/showthread.php?t=35349

[IanDMacDonald]

Here's my thread Done: http://www.xs11.com/forum/showthread.php?t=38459

[donebysunday]

Here's a video... http://www.xs11.com/forum/showthread.php?t=35349

Here's my thread Done: http://www.xs11.com/forum/showthread.php?t=38459

Thanks guys !
Steve I think that looks so easy, can't believe how long it took me to get them off. All hoses were used from the sound of it ?

Ian so the bottom is gone on the air box, really want it to look stock.
Ever thought of putting just the bottom sides on ?

I've five sets of carbs to clean up and sync to this bike, last I checked, before putting 20 mi. on it compression was 180 straight across. Have not checked since. I figure I can use Uni pods for testing and primary sync, must check valves and torque the head nuts.
Don't know if there was a return to the dealer for torque after 5K as some other bikes were supposed to get ?
That oil dripping from the #1 exhaust collar nut seems to be coming from along the fins under the head, can't hurt to do and maybe cure the oil seepage ?