Topic: challenge for machinists on this board

[Dusthawk]

Duster,

I am sure at one point or another, you have seen those crooked twisted up exhaust headers on hopped up V8s, right? Well, it just so happens I was thinking along those lines myself a few months ago and talked to a fabrication guy down in L.A. and according to him the crooked twisted idea is what is neded to balance lengths but since we have such limited room on our bikes it would be impractical to implement. He also said an off the cuff price to fab something like that for a stock 883 sportster carb would set me back a touch over a grand.

I don't know if this helps or not but its way out of my pocket. I'll stick to my keihins and pods.

Peace and Long Rides,

Jeff

[Terry in Australia]

Sorry for coming in so late, but the single carb thing for SOHC4's has already been done, well over 20 years ago. Here's a link to an Ebay I auction that I got "gazumped" on at the last moment recently, "Posa Carb" made a manifold to complement their trick flat slide carb (I've got a new one in a box somewhere) for fitment to a SOHC4, I read an old report about a US bike magazine fitting one to a CB550 and backing off with the speedo reading 125 Mph and the thing still accellerating!

Trouble with the Posa carbs is they don't have float bowls, so you have to remember to turn your fuel off whenever you shut it down, (or you'll be sorry) but everything I've read points toward it being a good period hot-up mod. Cheers, Terry.  

 http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=4633101958&sspagename=STRK%3AMEDW%3AIT

[dusterdude]

terry,thats it,damn shame i didnt see that auction.i  must say,im really surprised this thread has garnered so many responses.

[Lumbee]

...I have to wonder how well the setup did for everyday riding.  I'd think it would have been more popular if it were a good replacement to the 4 carb setup.  As I said in my other post my suspicion is its good on the track, but not so good on the street...

[ProTeal55]

i must say,im really surprised this thread has garnered so many responses.

Why would anyone want to deal with the upkeep/issues of 4 carbs when then could deal wiht just 1 ??

[dusterdude]

yea,what he said.i mean the dual mikuni setup looks like the way ill eventually go,but a single would be nicer.

[byidesign]

If it's not your daily driver, some things are done
   "just to do it"
         and some neat inventions....  working with carbs on cars,
       manufacturers jump through hoops, to get
       intake runners the same length, and without
        some of the space constraints..
       Now..   put the engine on a Quad...
            {Look Out}.....

                      Bruce

[Lumbee]

..speaking of single carb setsups...

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=4637657344&sspagename=ADME%3AB%3ASS%3AUS%3A1

[kaceyf2]

Its been done, if anyones interested, I have a magazine with an article on a SOHC4(what else?) cb750, called "going critical" the reason this bikes called "going critical" is as follows;
The guy was trying to run a turbo on the old girl, but for love nor money could not get it to run anything like cool enough, it was just way too hot..............so he ditched the turbo, and made up a manifold to run a single carb....a2and a half inch SU, if I remeber my own magazine which i have kept just for an occasion like this, I think the carb originated off an old landrover......anyways, when the bike had the turbo on it,the guys mate said it sounded like it was "going critical" !! hence the name of the bike, but, it appears that with the manifold and single SU it ran sweet, it was a chop, and it used the engine as a stressed member,the guy reckoned that this would be its last incarnation, went it went US, it was OVER!!! He had built it in different incarnations a few times allready I believe......
anyways, it can, and has been done, if anyone wants to see the mag, give us a message or email ........

[MRieck]

I remember the Posa and have seen them. They were not as good as the twin Mikuni set ups wwhich were after the Weber set ups. 4 carbs work best. I don't see 1 or 2 carb/inline injected bikes setting records or doing anything. The Posa and others were flash in the pan.

[Terry in Australia]

You're undoubtably right Mike as always, but I don't think anyone here is looking to break any records? The Posa carbs are actually much more popular with ultra-light aircraft folk, as they were very simple and reliable, and of course, the engines would run upside down (which is a good thing apparently when you're flying) with no loss of carburation.

I've no doubt that one carb per cylinder is the ideal, but that shouldn't stop anyone from trying some of the alternatives? Cheers, Terry.

[MRieck]

You're indubitably right Mike as always, but I don't think anyone here is looking to break any records? The Posa carbs are actually much more popular with ultra-light aircraft folk, as they were very simple and reliable, and of course, the engines would run upside down (which is a good thing apparently when you're flying) with no loss of carburation.

I've no doubt that one carb per cylinder is the ideal, but that shouldn't stop anyone from trying some of the alternatives? Cheers, Terry.

Absolutely my friend.....just don't expect superior performance.

[crazypj]

..speaking of single carb setsups...

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=4637657344&sspagename=ADME%3AB%3ASS%3AUS%3A1

 Well I had a look at pic and its a standard very old style 'log' manifold, not even a well designed one at that.
A much more efficient design is to have tube tapered and also on a diagonal so carb end is as far from number one intake as possible and the 'blank end is closer to the head.
(If you look at an automotive manifold you'll probably see what I mean)
You still dont get close to equal length intakes but its something of an improvement over whats shown. Fuel distribution must be awful as it wont like turning 90 degrees close to no. 1 cyl and probably 'drops' out before reaching no. 4 with the square edged 90degree 'bends' (just my opinion, but I do know a liitle about airflow)
You need to get Scientific design of Exhaust & Intake Systems by Phillip H. Smith and John C. Morrison
ISBN 0-8376-0309-9
Library of Congress number72-86569
PJ

[750duo]

While you're waiting for the single carb  ------

Cycle x-change has a 2 carb setup using 2 Mikunis
Whole kit is only $499

They say it stops the 4 carb "sucking sound" too. may be worth it for just that

Try their web site

http://www.cyclexchange.net/Carb%20System%20Comp%20Page.htm

Cheers

[Bob Wessner]

They say it stops the 4 carb "sucking sound" too.

And here I thought that sound was coming from my wallet. 

[ProTeal55]

I think for a "Pre-Fab" carb setup , the guys over at Cycle X are the winners, especially for the $$.

[Lumbee]

...quite a few guys over on the hondachop board have the setup, and of the dozens that have it i've only heard one or two who had problems with it.  in those cases there were questions about the overall health of the bike (motor/electrical) before the carbs were added.  I don't know how well the cyclex carbs work on a stock setup.  I think the manifolds/filters may have problems clearing the frame rails...

[caferacer51]

Ive got a copy of 'Back street Heros' magazine with an article on a Suzuki based chop with a very simple 4-1 carb/inlet setup, with a nice SU carb stickin out of the side! Dont know how well it works, but if you drop me a line il try and 'Scan' the article for you.