i have been building two into one intakes for the last three years now. setup with a single mikuni 36mm vm carb they are great. my customers have all reported performance gains better then they had initially expected. i have sold a bunch over the last few years. never had anyone complain about performance. instead unanimously i hear the motor has great response, ease of application, no carbs to sync, great torque, etc. perhaps the best way to know about a thing is to do the thing and try it out. anyone can and will arm chair discuss why a thing will or wont work but it is the doing that is proves. so we discussed, designed, built, modified, modified some more, and built a unit with equal runners and great performance. joe. email@example.com that is my new email address if you have any questions or would like pictures of application or video on youtube. thanks.
Fortunately for me, I like working on bikes nearly as much as I like riding...
I've chewed on this for a long time and have decided to make my own 2 into one. It will be essentially not much more than a U tube bent to match up to the stock carb mounts and long enough to clear the back-bone.
All the discussion about having the carbs close to the intake ports is, I think, misinformed, at least for a street-bike application.
A racer might want all the juice he can get and want it way up close to where the valves are about to float, but a street rider needs roll-on. That means putting the torque peak at the RPM where you actually live.
The length of an intake tract is measured from the intake valve to atmosphere. The shorter that tract the higher RPM to reach maximum torque. Since HP is a fuction of torque and RPM, shorter means more HP - if your motor will spin quick enough.
XS's don't spin.
There is a point of diminishing returns in shortening their intake tracts.
26" gives max torque at around 6K rpm. Anthing much shorter than that on an XS is going to put your torque peak over your normal driving curve.
If you are not riding a miler.
Just eye-balling, it looks to me like stockers get aound 26" using an air box.
Getting that 26" is very do-able with a 2 into 1 meeting behind the back-bone (the carb and airbox/cleaner adding the rest of the length). The airbox/cleaner can easily be shaped as a velocity stack.
Of course it will be simple to fine tune that length by an inch or two to dial it in and optomize the torque peak to rider preference.
Joe Wiseguy, I believe, has proven that a 2 into 1 can work just fine on an XS, though I don't care much for where the carb ended-up in his set-up (Oklahoma).
Well, if you can't beat it don't dis it. So, Joe, congrats on your proof of concept. Maybe we'll do a dyno comparo in the great XS-hereafter.
'cause I'm gonna do a Sinatra.
Yes, I'll do it My Way.
p.s. carb choice is a Solex 38 off a TX. Those CV's are forgiving on jetting and stingy with the fuel.
Post by joewiseguy on Apr 11, 2010 22:53:35 GMT -5
i use mikuni vm 36mm carbs with a 25 pilot and 200 main. this has worked in the us, canada and europe. a couple of guys have had to step up the pilot to 27.5 and the main to 210.
sorry i dont get here very often so i dont keep up regular. i have sold 40 to date on the intakes. i have 2 left now and will have to set up to make some more. the collector tubing and machined flanges are costly so i only make a dozen at a time.
the 38mm mikuni from the early model xs will work as well and not cost you the extra for the roundslides. you will probably have to jet up a few but one customer of mine said he used the old 38 and just had to bump up the main a little. sorry i didnt get any jetting numbers from him. firstname.lastname@example.org
Joe-Wiseguy, working metal gets me sweatier than a two dollar whore on dollar off night.
The 22"~26" intake tract is about right, it's measured in total though, so includes airbox , etc on stock motor. (filters and baffles are there for a reason other than quieting things down) I'm pretty sure stock airbox set up measures about 23" total to atmosphere (if you plug 23" into intake calculator you'll see where the power peaks are, close to right?) You can mount carb relatively close to head and add piping to other end to get length right (but it does look stupid, I tried it once) 'Stock' carbs are about 9"~10" from valve head to intake, pods add about 3/4"~1" which is 'correct' length for 12,000 rpm motor
As I understand it, and please correct me if I'm wrong, the calculations you see are for a more traditional intake manifold where there is a runner and a plenum.
When the intake valve closes, the moving air piles up behind it creating a pocket of high pressure. That high pressure bounces off the intake valve and travels back up the runner then bounces off the high pressure in the plenum (atmosphere) and back to the intake valve. The length of the runner determines how long it takes for the high pressure to get back to the valve and therfore what rpm it will make the most power.
You said that the stock setup is "close to right" because it has aditional runner length on the airbox side of the carb. I can see where that may be true at full throttle but anything under full throttle there is a slide right in the middle of the runner. Wouldn't the reflection happen at the slide since at that point there is a higher pressure on the air cleaner side of the slide, not to mention a big chunk of metal for it to bounce off of? That would mean that at lower speeds, where you would want the longest runner, it's runner length is effectively cut in half.
Post by weaselbeak on Apr 17, 2011 22:52:36 GMT -5
My particular project is a trike, and HP is of no real concern to me. Torque is what I want, and driveability. I am under the impression that the increased air speed from smaller venturi will enhance my torque while costing me HP in the upper ranges. Since I'll probably never see more than 4500 RPM, I'm thinking about trying a 32mm CV Keihin I have lying around. Someone told me, tho I haven't researched it yet, that the Triumphs with the single carbs used a small venturi.
Post by tomterrific on Apr 18, 2011 7:20:09 GMT -5
Triumph's use a single 30mm Amal carb which flows more air than a BS38 CV carb. You do not want a 32mm CV carb on an XS650. A BS38 should be extremely tractable as a single carb yet still have enough for the highway.
It's a normal slide type, not a CV. Size vs. flow isn't the same for the 2 types. It takes a larger sized CV to flow the same amount as a smaller sized normal slide type. This is probably because the CV carb has both a slide and a butterfly obstructing the main bore. A slide carb only has the slide.
Post by dahondaboy on Oct 17, 2011 23:26:13 GMT -5
I have built a few 2-1 intakes as well. i have found a couple of problems that made me go back to duals. 1 is that the farther the fuel has to travel to get to to the cumbustion chamber the more chance for fuel pooling in the runner under idle and 1/4 throttle or coasting. this is increased with larger carbs. the key is to make the intake runners or tubes as short and as smooth as possible. give no rough edges for the fuel to catch on. at first i thought if it had 2 32mm i need like a 44 mm to compensate but that was dead wrong, only functioned well at full throttle or there was instant flooding. i found a single 28 pwk to work the best. smooth idle crisp response and good top end. however climbing a hill gobbles up alot of fuel and the tiny bowl ran dry fast. i even ran a fuel pump but still needed more cfm. so now i am going back to duals with fbg lectrons. just thought i would share my experiences.
Post by weaselbeak on May 26, 2012 22:32:45 GMT -5
I need direction, after reading this entire thread. Joe Wiseguy can make me a 2 into 1 manifold for my trike project, that would be equal length because I have split the backbone. To buy a new carb, it seems my best choices are roundslides. Would I be best served with 30, or 32, or maybe 34 mm? Ultimate HP is not my goal. I have a pair of stock 38s I got off ebay, and they are missing floats, mains, etc. Would I be better off with one of these with a new float and needle kit?
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