I wonder if it's just the extra length on the stock intake tract that improves performance or if there's some other aerodynamic thing going on there.
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Hello from Wisconsin! 82 XS400SJ track bound...
- Thread starter beta_kevin
- Start date
Oil vapors will be drawn into the motor to be burned up during combustion.
Yep. If your motor is running proper any blow by gases will be sucked into the motor and reburnt. You want the filter to be round and long. This helps smooth out the air better. Thats another reason why short cone filters don't work well with these type carbs.
beta_kevin
XS400 Enthusiast
So basically there is no build-up of excess oil or gas as long as you have that hose connection between the engine and h-pipe? I can't currently look at the bike to see the connection...assuming there is only one. Seems hard to believe it all goes back into the engine some how. If someone can confirm this is correct, that would be greatly appreciated.
That's it.
I wouldn't say that it goes "back" into the engine, it goes into the combustion chamber, burns up, and goes out the exhaust pipes.
No buildup.
I have put almost 20k miles on sohc xs400s' in the last 17yrs and never had any oil leak out of the filters or pipe. Oils should NOT be pushed up that hose but vapors that end up in the case from the combustion process. There are baffels that keep the oil down in the motor.
Yep, the design of the breather system is actually a 'built in catch can' itself. The oil that still remains in vapor form just gets burnt. The catch can rule came about since guys just tap the crankcase and pop a filter on. This creates a mist of oil coming out of the filter, so they require a catch can to at least stop some of it from getting on your tire, the track, etc. Our system pretty much eliminates that issue from the factory. They may still want you to have one, but check first since fabricating one would be a waste of time and parts if you don't really need it.
That's exactly what it is
All about the reversion. Gotta rob Peter to pay Paul though, so intake length shifts the torque/HP curves around. Twins naturally are stout down low to begin with, so might as well focus on the top, especially on a track bike. On CV carbs, the runner length in-front of the carbs affects the action of the slides as well.
Just for some reference, this is my intake length. Think about it as the carb being fully open. So from the head to the filter opening, I'm sitting at 25mm of runner. With the filters directly on the carb, I'm at 18mm. From road testing, with the 25mm length, you can clearly feel the power start to drop off in the upper 9k-10k range. When I move the filters to the carbs, you can feel a power drop off (bike stops pulling) right around 8.5k to 9k. Dyno results would be great, and they will come.
Now keep in mind I have an aftermarket cam, so my results may be more 'pronounced' because of it, but the results will be similar on the stock cam and carbs at WOT.
So take that for what it's worth. On the stock cam and carbs, I'd try to get the runner length as close to stock as possible, to put that power band where the motor wants it.
Now keep in mind I have an aftermarket cam, so my results may be more 'pronounced' because of it, but the results will be similar on the stock cam and carbs at WOT.
So take that for what it's worth. On the stock cam and carbs, I'd try to get the runner length as close to stock as possible, to put that power band where the motor wants it.
I measured the head to the end of the H-pipe on my stock 79 and got about 23.5 cm. I also did it on my 82 that has the xs360 carbs and xs360 H-pipe which was about the same length. But the xs360 carb and H-pipes cross over tube was an inch closer to the motor than the 79 400 setup. A little more info on the xs360/400 H-pipes. There are three styles used from 76-82. The 76-77 xs360, the 77 D-78 2-E xs400 and the 78 E- 82. The cross over is different over all length and also the runner path's smoothness. See pictures below. First pic is 76-77 xs360 (left) and 77 D-78 2-E (right). Second is 77 D-78 2-E (left) and 78 E - 82 (right). Third is 76-77 xs360. fourth is 77-78 2-E. Last is 78 E - 82 sohc xs400.
Interesting. Having the crossover tube further from the carbs probably allows for slightly more laminar flow at the carb mouth where the air jets/vents are.
For no particular reason I've been doing up various designs in CAD for elliptical bellmouth velocity stacks to fit the BS34s.
Debating between matching the stock H-pipe length, approx 85mm, or something else. Probably doesn't have to be as long as stock. Even a short bellmouth will allow for smoother airflow into the carbs.
Maybe something based on the formulas used here, if applicable: http://www.mezporting.com/exhaust_length.html
Might eventually cast a set in a durable rubber to try out.
For no particular reason I've been doing up various designs in CAD for elliptical bellmouth velocity stacks to fit the BS34s.
Debating between matching the stock H-pipe length, approx 85mm, or something else. Probably doesn't have to be as long as stock. Even a short bellmouth will allow for smoother airflow into the carbs.
Maybe something based on the formulas used here, if applicable: http://www.mezporting.com/exhaust_length.html
Might eventually cast a set in a durable rubber to try out.
beta_kevin
XS400 Enthusiast
Wow, thanks again for all the feedback, photos and specs! No doubt the passion runs strong here and of course that's what I hoped for as I have lots to learn, appreciate it!
Between the change in exhaust and jetting of the carbs, there a few twists and turns here and so everything is still on the table and thankfully to you guys, a few more options then before. I for one would love to save the built in functionality, but at the same time I have to give the shop I'm working with the freedom to do what they think is best.
One of the concerns about not having a clearly separate and visible catch tank is that since they are common place and pretty much expected in a AHRMA vintage tech inspection, not having one could throw red flags (even if not technically needed) and might not pass tech.
I'm exciting to get all the new parts on the bike...May 18th (Blackhawk Farms) is coming up quick!
Between the change in exhaust and jetting of the carbs, there a few twists and turns here and so everything is still on the table and thankfully to you guys, a few more options then before. I for one would love to save the built in functionality, but at the same time I have to give the shop I'm working with the freedom to do what they think is best.
One of the concerns about not having a clearly separate and visible catch tank is that since they are common place and pretty much expected in a AHRMA vintage tech inspection, not having one could throw red flags (even if not technically needed) and might not pass tech.
I'm exciting to get all the new parts on the bike...May 18th (Blackhawk Farms) is coming up quick!
beta_kevin
XS400 Enthusiast
Progress report! Hope to have all major mods completed this week. Bike stripped of most unneeded items, new components added, handle bars need to be chopped down a bit, shocks tightened up, pods added, new sprocket, chain, controls. Just need to squeeze out as much power as possible, decide on catch can direction, add catch pan, make sure the carbs are running well, sort out any last leaks, finish safety wiring and add number plates...then done...right? lol! *crosses fingers*
beta_kevin
XS400 Enthusiast
Bike is running and it's pretty kick-ass! At least I think so. I have no clue how it will compare to others, but I've enjoyed sneaking in some runs out in the country! Just have to add a catch pan, finish safety wiring and add number plates. I am also ready if they give me grief trying to sneak into "novice history production" haha, got my "vintage super bike" box of parts that can be added on pretty quick...speedo, headlight shell, green/white number plates.
I really have to give it to retrospeed.net, for making this a reality (so far!). The owner (Brady) and I are both heading down to Blackhawk farms to get our AHRMA race license May 18th as part of "big bob burns" vintage track day and it's coming quick!
https://www.motovid.com/product/vintage-all-levels-track-day/
I am still extremely "green" to all this and working on bikes in general, but I hope to change that as I move forward with racing and become more confident in pulling out a wrench then my wallet.
Went with this little catch tank config. It doesn't hold 10oz., but let's just keep that between us ok
I really have to give it to retrospeed.net, for making this a reality (so far!). The owner (Brady) and I are both heading down to Blackhawk farms to get our AHRMA race license May 18th as part of "big bob burns" vintage track day and it's coming quick!
https://www.motovid.com/product/vintage-all-levels-track-day/
I am still extremely "green" to all this and working on bikes in general, but I hope to change that as I move forward with racing and become more confident in pulling out a wrench then my wallet.
Went with this little catch tank config. It doesn't hold 10oz., but let's just keep that between us ok
beta_kevin
XS400 Enthusiast
Less then a week to go before Blackhawk and race school! Think I'm pretty much ready. Snuck the bike out a few more times and it seems to be running great.
The Catch pan (cake pan) seems to want a third life as a pit grill...who knows, could happen
Safety wiring selfie....
Cheap clamp...nut wins!
Getting ready to race has also helped motivate me to lose weight...down 20 pounds since march...feelin' good.
Now I just have to fix a break light on my trailer and will be good to go!
The Catch pan (cake pan) seems to want a third life as a pit grill...who knows, could happen
Safety wiring selfie....
Cheap clamp...nut wins!
Getting ready to race has also helped motivate me to lose weight...down 20 pounds since march...feelin' good.
Now I just have to fix a break light on my trailer and will be good to go!
beta_kevin
XS400 Enthusiast
My bike and I survived our first "track day" and passed the AHRMA licensing course! It was an over-all great experience with pretty much evey emotion experienced throughout the day. There was no time to get nervous the day of as I got to the track at 6:30am, registered at 7am, tech right after, riders meeting at 8am and on the track by 8:30am...wait, what...no hours of classroom stuff prior?...nope! A bit trial by fire, but a controlled fire I suppose. Lots of bikes on the track with our group total at 38, but my class only had four riders...so small class, which was nice. There was four 15 minute track sessions in the morning and 4 in the afternoon...with about a total of 60+ laps throughout the day....so a ton of track time.
Lots of action on the track, but never felt nervous as a result of other riders...everyone played well together. There were a few crashes in our group, so seeing those was a bit stressing, especially seeing the ambulance on the track. Nothing major as a result of the crashes I believe, just precautionary measures...still though, good reminder of the reality of track riding.
The bike held up and seemed far more competent on the track then I was. I was really paranoid about grip around the corners initially...but as I got more comfortable with shifting my weight and leaning, it became less of an issue. My biggest challenges throughout the day were smooth breaking/shifting to the corners and being in the right gear coming out of the corner. Also seemed found shifting...sometimes from 3rd to 4th and especially from 4th to 5th in the straights a bit problematic. I think I was just being too soft on shifting at the high speed and more concerned with holding on or already thinking about breaking at that point. Don't think I ever made it to 6th all day...Blackhawk farms is a smaller track (1.95 miles), so even getting to 5th didn't happen much. I was told that on my bike at higher RPM's I shouldn't need the clutch at all, just backing off the throttle a tad is enough to move up a gear. Didn't feel comfortable trying this on the track, but will on a future road test.
I did have one major mishap, but it wasn't on the track. The paddock was grass and gravel roads, like a camp site and I lost control of my bike backing it out of the grass and onto the gravel road. The bike tipped over away from me and I help onto the handle bars like a captain going down with the ship. I believe holding the handle bars saved the bike from any major damage as it kept the bikes front end from twisting. Basically the grip and the fat rubble foot pegs took the brunt of the fall. I was pretty pissed as you could image...at myself mostly for dropping the bike, but luckily there were many willing hands to help me back up. The engine was a bit flooded, but within seconds she was running and I was off...shaken, but not defeated.
Wish I would have taken more photos, but there really wasn't much time. It was a great day to be on the track...weather was perfect track was perfect, at least that's what everyone was saying
Lots of action on the track, but never felt nervous as a result of other riders...everyone played well together. There were a few crashes in our group, so seeing those was a bit stressing, especially seeing the ambulance on the track. Nothing major as a result of the crashes I believe, just precautionary measures...still though, good reminder of the reality of track riding.
The bike held up and seemed far more competent on the track then I was. I was really paranoid about grip around the corners initially...but as I got more comfortable with shifting my weight and leaning, it became less of an issue. My biggest challenges throughout the day were smooth breaking/shifting to the corners and being in the right gear coming out of the corner. Also seemed found shifting...sometimes from 3rd to 4th and especially from 4th to 5th in the straights a bit problematic. I think I was just being too soft on shifting at the high speed and more concerned with holding on or already thinking about breaking at that point. Don't think I ever made it to 6th all day...Blackhawk farms is a smaller track (1.95 miles), so even getting to 5th didn't happen much. I was told that on my bike at higher RPM's I shouldn't need the clutch at all, just backing off the throttle a tad is enough to move up a gear. Didn't feel comfortable trying this on the track, but will on a future road test.
I did have one major mishap, but it wasn't on the track. The paddock was grass and gravel roads, like a camp site and I lost control of my bike backing it out of the grass and onto the gravel road. The bike tipped over away from me and I help onto the handle bars like a captain going down with the ship. I believe holding the handle bars saved the bike from any major damage as it kept the bikes front end from twisting. Basically the grip and the fat rubble foot pegs took the brunt of the fall. I was pretty pissed as you could image...at myself mostly for dropping the bike, but luckily there were many willing hands to help me back up. The engine was a bit flooded, but within seconds she was running and I was off...shaken, but not defeated.
Wish I would have taken more photos, but there really wasn't much time. It was a great day to be on the track...weather was perfect track was perfect, at least that's what everyone was saying
Sesty
H.E. Pennypacker
killer! got a video of her running?
beta_kevin
XS400 Enthusiast
No, but I can do one for sure!
beta_kevin
XS400 Enthusiast
Here is a walk around video I just shot. Missing the catch pan as it has to be removed for trailer load clearance.
