tonyc
XS650 Guru
Bearcat I have thought seriously of running one 36mm VM carb for my next project. If I do Iwill build a plenum located behind the frame center post. It will have runners to the intake ports.
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2 into 1 Intake crossover
- Thread starter bearcat
- Start date
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- Tags
- carburetors
hoffman900
XS650 Addict
Tony,
A wet plenum design?
Let me know when you're ready for that. I'll run your combination through PipeMax and dig up some other information.
And Jack,
You're confident in your work. That's good. I've been reading Speedtalk since 2006. Good site - it use to be a lot better. On the other hand, I had an ex girlfriend who used the excuse of being 'honest' to cover for her really being a bitch. Anything you've offered isn't anything I've read elsewhere. It might be new here, but it's not once you get outside of this relatively small pond and into the motorsports / engine building scene. The point is, you can get the same information elsewhere without the attitude.
Cheers,
Bob
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tonyc
XS650 Guru
Thanx for the offer Hoffman.
You couldn't understand my rambling????? How do you plan to move forward in developing a suitable manifold if you can't fully grasp how the balance tube corrected the overly rich condition. All I can say is good luck to you or just purchase the Joe Wiseguy manifold and I would be honored if you named it after me
: No doubt there is a better way and I'd love to see you work on a different design.
Tony, Hoffman,,, how about a Marvel Schebler updraft mounted below that plenum?
hoffman900
XS650 Addict
Not sure. It might be okay for a bobber just cruising around. I can't really venture to say.
My thinking of a wet plenum for a XS would be to look at a tunnel ram from head on, and flip it on its side. Maybe bring in the two runners a little closer since we're not talking about a spread bore carburetor. Regardless, it might be a pain in the butt to start up cold. It's just a manner of getting the runner lengths and plenum sized correctly. I'd venture to say most XS engines are running too short of an intake tract anyway (probably needs to be somewhere in the 11-12" from the intake seat range).
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tonyc
XS650 Guru
Twomany and Hoff, I thought about updraft. I have a brand new Zenith updraft from a tractor never had gas through it. I think with a stock frame finding enough room for fitment is the problem.
Here is the result.... I finally passed emissions. Here is the minor adjustments I made. Minor valve clearance adjustment, small advance on timing, leaned out carb and adjusted the idle up a bit, fixed a small leak in the intake and replaced gaskets, and finally changed the oil. I was told if it was running rich, it could contaminate oil enough to get a bad reading? Didn't take a chance on that. Passed with flying colors. Over
Good for you Bearcat.
Free at last, free at last.
I thank the DMV I'm free at last.
Woo hoo, go ridin'
Free at last, free at last.
I thank the DMV I'm free at last.
Woo hoo, go ridin'
Congrats, bearcat. You gonna remove your mods, or leave 'em in? Does it run better with your mods?
plane_ben
XS650 Junkie
Bearcat. You in Phoenix? I'm in Tucson and we stopped emissions on bike 5 years ago.
Just finished up a home made single intake for my bike. Didn't have any of your problems. Just mistakenly went lean when my original set-up was spot on.
Just finished up a home made single intake for my bike. Didn't have any of your problems. Just mistakenly went lean when my original set-up was spot on.
TwoMany, I am leaving the current setup on my bike. I like the way it runs, and just got to be different. At some point I will attempt to make a better 2 into 1 that fits like it does now. My summer project is a rephase of my original motor with a 750 kit.
plane_ben, your carb sets just about where mine does and I like that. Yea, I'm just outside Phoenix. We finally passed the law, not requiring motorcycles to go through emissions. Only took about 8 years, must have been too busy with our border?
plane_ben, your carb sets just about where mine does and I like that. Yea, I'm just outside Phoenix. We finally passed the law, not requiring motorcycles to go through emissions. Only took about 8 years, must have been too busy with our border?
Reviving an old thread:
A few posts above Hoffman900 suggests intake tract lengths of up to 11-12" may not be too long and possibly even optimal. This would easily enable building a single carb setup with a mandrel U-bend with the carb centered on a plenum behind the frame downtube. It's all empty space on the current cafe build anyway.
Anyone built a similar intake yet? It may indeed be hard to start cold without ether...
Also, the air velocity through a single carb nominally doubles, correct? It's not necessarily more restrictive than dual carbs of the same design, or am i off base here.... plan is to try a 34mm TM flatslide.
A few posts above Hoffman900 suggests intake tract lengths of up to 11-12" may not be too long and possibly even optimal. This would easily enable building a single carb setup with a mandrel U-bend with the carb centered on a plenum behind the frame downtube. It's all empty space on the current cafe build anyway.
Anyone built a similar intake yet? It may indeed be hard to start cold without ether...
Also, the air velocity through a single carb nominally doubles, correct? It's not necessarily more restrictive than dual carbs of the same design, or am i off base here.... plan is to try a 34mm TM flatslide.
A lotta cats in this thread.
Mathematically yes, the average velocity doubles.
But not the instantaneous velocities.
Simply put, air/fuel is drawn thru the carb during the intake stroke. No draw during the other 3 strokes, the carb is dormant.
With the 2-into-1 carb, you still have the isolated draws, just twice as often.
The dormancy between draws drops by 2/3.
The carb has to recover at the beginning of each draw, known as fuel lag. With shorter dormancy between draws, the recovery is faster. Depending on the carb's design, this may cause it to appear richer...
Mathematically yes, the average velocity doubles.
But not the instantaneous velocities.
Simply put, air/fuel is drawn thru the carb during the intake stroke. No draw during the other 3 strokes, the carb is dormant.
With the 2-into-1 carb, you still have the isolated draws, just twice as often.
The dormancy between draws drops by 2/3.
The carb has to recover at the beginning of each draw, known as fuel lag. With shorter dormancy between draws, the recovery is faster. Depending on the carb's design, this may cause it to appear richer...
Insightful as always 2M. So my intuitive grasp of the airflow is basically correct. The intake events occur so quickly that the effect seems a "continuous" draw but yes technically it's only when valves open.
The TM flatslide is as you know is a very free breathing unit and should work great if i can get it to run lean enough. Plus it's a semi downdraft design. Have the leanest needle jet @ 389 Q-0 with a 7DJ1 needle on hand... only one fatter leaner needle available as far as I can tell. Will solder and experimentally drill a main to ballpark it...
Each leg of the intake will be effectively 10-11". I'll beadblast the inside of the pipe but still may be hard to cold start. What's your thinking on that tract length?
The TM flatslide is as you know is a very free breathing unit and should work great if i can get it to run lean enough. Plus it's a semi downdraft design. Have the leanest needle jet @ 389 Q-0 with a 7DJ1 needle on hand... only one fatter leaner needle available as far as I can tell. Will solder and experimentally drill a main to ballpark it...
Each leg of the intake will be effectively 10-11". I'll beadblast the inside of the pipe but still may be hard to cold start. What's your thinking on that tract length?
Reminds me of a variation on an old poker card game "Sweat".
Imagine you're dealt 4 cards, face down. Can't look at these.
The last card is dealt face up.
Now, bet.
I suppose that if the primary goal is to get a single carb positioned behind the downtube, and performance and racing isn't in the plan, then choose any length you want.
I think of these engines as sonic machines. Our relatively long duration cams with lots of overlap are part of an overall package that tries to utilize the features of reversion and scavenging. Change one feature and the whole thing can be out of tune.
Welcome to experiment land...
Bob Kelly III
Ranch Kid from way back,.... that got Old !
I'ed like to throw in that with longer intakes you start getting throttle lag.... I put a 2' intake on my honda 90 when I was a kid just to see what it would do ( a vacuum cleaner pipe) it was a bear to get started but once it finally fired up it was silly... grabbing a handfull of throttle you could count to 3 before the engine revved up ! that is why the carbs on almost all motorcycles are really close to the head as close to the intake valve as possible ! keep that in mind if you mount the carb behind the frame down tube, because you may turn the machine into a unresponsive dog !
Personally, for normal riding a single carb is more than adequate and there will be better MPG's to be had if setup right...
I'ed like to have just a single carb on my machine for the simplicity and better gas milage but sense I have the stock 2 carbs I am not about to remove them ! they will stay on there for a long time to come ! <GRIN>
......
Bob.........
Personally, for normal riding a single carb is more than adequate and there will be better MPG's to be had if setup right...
I'ed like to have just a single carb on my machine for the simplicity and better gas milage but sense I have the stock 2 carbs I am not about to remove them ! they will stay on there for a long time to come ! <GRIN>
......
Bob.........
Main objective would be a symmetrical intake that doesn't involve cutting the frame at this build stage. The Hoffman post above (who apparently has considerable performance motor experience ) suggests longer tracts may work... I've not had an opportunity to ride a single carb XS; sellers of asymmetric intakes claim they work well. Either way, a motor is largely an air pump/acoustic machine.
The 2.5" 2-2 aluminum intakes I've built do boost performance by seat of the pants dyno. A rough childhood experiment with 2' of vacuum hose can't be compared to a carefully built TIG welded manifold but undoubtedly the tract length can be too long at some point.
At any rate it's an inexpensive experiment. Just time involved. Will look trick if it works. If it doesn't perform well I'll toss it...
The 2.5" 2-2 aluminum intakes I've built do boost performance by seat of the pants dyno. A rough childhood experiment with 2' of vacuum hose can't be compared to a carefully built TIG welded manifold but undoubtedly the tract length can be too long at some point.
At any rate it's an inexpensive experiment. Just time involved. Will look trick if it works. If it doesn't perform well I'll toss it...
Right, Bob, carb as close to the head as possible--must be why every tuner who ever set up an XS650 for the track used extended mounts, they didn't want those crazy riders going too fast out of the corners and crashing their hard work.
Barncat, a single TM34 should work just fine, but the Q-0 will be way too rich. Baseline jetting is very close to the VM34 baseline; a P-6 NJ is the richest you want to use. This thread has been an interesting read and has changed my thinking on a thing or two, looking forward to more of it.
Barncat, a single TM34 should work just fine, but the Q-0 will be way too rich. Baseline jetting is very close to the VM34 baseline; a P-6 NJ is the richest you want to use. This thread has been an interesting read and has changed my thinking on a thing or two, looking forward to more of it.
