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Post by Burns on Apr 12, 2009 20:45:37 GMT -5
while browsing for Tom T's book I ran across www.bgsoflex.com/intakeln.htmlwhich is a calculator for optomizing intake track lengths to given RPM's. Using this calculator for the operating rev range of a street 650 it looks like you need something like 22-24 inches of track (measured from intake valve to carb mouth, I presume). It does not (as far as I can tell) account for I.D. of the runner. Any thoughts? |
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Post by grizld1 on Apr 12, 2009 21:03:42 GMT -5
Thoughts? Well, yeah, Burns, but if I know you at all you've already had the same thoughts, and they're not good ones. How ya gonna keep the fuel from condensing out of the mix with a runner 2 ft. long? I've seen quite a few calculators for intake tract length, but none of 'em produced that kind of result!
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Post by Burns on Apr 13, 2009 0:17:37 GMT -5
Just can't trust them on-line calculators. I think if this one were used to calculate income taxes the IRS might be able to balance the budget.
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Post by crazypj22 on Apr 13, 2009 8:55:38 GMT -5
One Mikuni replaced two Amals on the Nortons with no performance detriment. I believe that the reason most motorcycles have multiple carbs is due to intake plumbing geometry more than anything else. It's hard to get equal length intakes. My bet is that a single carb set up with equal length intake tracts on our twin will cost nothing or next to it on the top, will run cleaner on the bottom, have better roll-on and will get better gas mileage. It will always be "in synch." Besides, we just like to tinker. after working on British bikes for many years, they are seldom 'in sync' with a single carb. BSA, Triumph, Norton et al all needed tapered spacers to get mixture even on both cylinders,(point carb a few/several degrees to lean cylinder) they used to be available 'aftermarket' as well as some 'factory' ones. With an offset carb, its going to be impossible to get mixture right on both cylinders ( bit like running a V-8 with central carb, outside 'corner' cylinders running right, center 4 run rich) Either way, it works but its not efficient. 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 BTW, 1450 HD makes all of 61bhp stock PJ |
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Post by grizld1 on Apr 13, 2009 10:21:56 GMT -5
Thanks for the clarification on intake length as total distance to atmosphere, pj. That explains a lot--in particular, why long-flange filters have worked better on my VM36 carbs.
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Post by Six-Five-O on Apr 13, 2009 10:42:55 GMT -5
While I know everyone goes to great lengths not to ever drop their XS or either side...But I'd hate to be the cathead who dropped it on the left side using this set-up. Looks pretty cool though if you're into that sort of thing!
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Post by Burns on Apr 15, 2009 14:10:08 GMT -5
PJ's comments about the single-carbed Brit bike's "out of synch" problem may have soured my desire for a single-carb set up. I've been able to ignore all the other nay-sayers, but, I know that he knows what he is talking about.
Damn! I hate it when reality screws up my projects.
I might still play with it though....
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Post by crazypj22 on Apr 20, 2009 2:09:50 GMT -5
PJ's comments about the single-carbed Brit bike's "out of synch" problem may have soured my desire for a single-carb set up. I've been able to ignore all the other nay-sayers, but, I know that he knows what he is talking about. Damn! I hate it when reality screws up my projects. I might still play with it though.... Sorry.  The only way I could see around it would be to cut out the seat tube and mount carb closer to head. That way you could angle it if necessary. It usually only needs about 5~10 degrees 'tilt' Could always fit either a single pipe or twin tubes around 'outside' where carb intakes used to be (like they do on some mountain bikes with rear shocks) PJ |
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Post by slide on Apr 20, 2009 12:13:52 GMT -5
PJ, I agree with you. If people are serious about a single carb conversion, they should modify the frame to eliminate the centre down tube. A BSA frame is a perfect example and could easily be done to the Yamaha.  |
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Post by Burns on Apr 24, 2009 16:16:30 GMT -5
Well, that's a bit much for me (cutting up the frame) looks pretty cool but I'll put that project on the back-burner until I expand ;my social circle to include those skilled in the art of welding and equipped to exercise those skills.
I have the battery box off and planned to use the area behind the down-tube for a carb and air-box (fabricating a manifold to run outside of the down-tube). It would be easy to vary the intake length and hunt for the sweet spot.
But I have no idea as to how to deal with the inherient L/R fuel-air charge inbalance that you refer to.
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panic
New Member
Posts: 49
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Post by panic on Jul 12, 2009 12:51:21 GMT -5
Two carbs can be linked to operate as one at higher rpm for a big power increase
Ah... but there's no practical way to use all the plumbing and controls on the 650.
The linkage opens a big passage from each intake runner to a large plenum and permits all cylinders to breath from each carb, and also to have the extra "storage" capacity of the plenum. This is controlled by throttle position, RPM and engine vacuum.
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Post by joewiseguy on Sept 17, 2009 18:32:01 GMT -5
we build a two into one intake and use mikuni vm36 carb. works great. simple setup and looks great. functions awesome and we have video of it. joewiseguy.com
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Post by beekay on Jan 1, 2010 10:31:33 GMT -5
This is sn old thread, but I'm just in the mood.
About intake track length: Chevy started doing it in the early 80s with their TPI smallblocks.
It produced a peak in the torque curve an around 3200-3500 rpm. The same engine with a different shorter runner intake (the '90s LT1) has a noticeably higher tq peak.
With carbs on an XS engine, intake runners that long would be impractical. If you had EFI and some long snaky tube runners... maybe... But why?
Single carb: Having one carb on a twin won't make it slow.
I used to have a single carb Triumph 650 that would beat a stock ironhead Sporty by 20 bike lengths. It had a 34 VM on it.
It would beat stock Honda 750s too from about 0 to 90.
That old bike was an absolute animal.
If frame clearance wasn't an issue, I'd put a single VM34 or a BS38 on my XS and say goodbye to synching forever.
Possibly there's enough space back there if a flatslide is used??
With time permitting, in the future I'll get serious about doing a single carb mod.. Frame mods or flatslide.. Not sure right now.
Single carbs are underrated.
There's a slight loss at the upper rpms that's all.
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Post by joewiseguy on Jan 9, 2010 14:09:54 GMT -5
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. joewiseguy@live.com that is my new email address if you have any questions or would like pictures of application or video on youtube. thanks.
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Post by eric123 on Jan 27, 2010 15:30:21 GMT -5
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. joewiseguy@live.com that is my new email address if you have any questions or would like pictures of application or video on youtube. thanks. Video please... |
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