Random carb idea/question for you.

[Blake]

Hey everyone.  After finally straightening out my carb problem,(missing idle jet), but still having a slight hesitation, i was wondering.  wouldnt life be a lot easier with just a bigger SINGLE carb?  im here flipping through the dennis kirk harley cataloge (even though i dont have a harley...but they have some intresting stuff in here for a good price that i can modify to use on my bikes)....but im here looking through the carb section, and they have single carb applications for the harley ranging in sized from 48mm, 45mm, 42mm, and even a 39mm and a 38mm carb.  now i know for a fact most harleys have a bigger displacement than the vision's 550cc, yet they use a single carb.    while bored at school today (yes, still in school..) i was doing a little math and figured that for the surface area of the opening of the visions 2 34mm carbs, you'd need a single carb that is nearly 50mm wide (i think it wa around 47.)...  yet, like i said, the harleys with their 110cubic inch engines use carbs much smaller than that.

here's a quote from one of the carbs "super E carb has 47.6mm thoar at the butterfly and a 39.6mm venturi and is recommended for use on any displacement bigtwin or sportster (sporster is 1100cc)."
then another quote "Super G car had 52.3mm throat at butterfly and 44.5mm opening at venturi and is recommended for use on 74cubic inch engines and larger where high performance modifications have been done or are planned (not recommended for smaller, lower compression engines). if you are not sure which carb to use we suddest the 39.6mm super E carb."

here..we see that the more than a liter displacement engines have a SINGLE 40mm carb.  

the reason im saying this, is that i personally think a single carb would make jetting a LOT easier, since you dont have to mess with two SEPERATE settings between the front and rear cylinders (front main 127, rear is 122.5), and plus, wouldnt it help the performance a little, since the cylinders would be getting the same amount of fuel and the same fuel/air mixture?  A guy i know did this with an yamaha xs650 (they have dual 36mm carbs).  he fabricated an intake manifold out of copper pipe, and used a large CV carb from a large dirtbike (Honda XR650L).  (http://www.650motorcycles.com/UJ.html)  the guy said its helped performance and that the bike is pretty quick now.  intresting.  from two 36mm to a single 42mm on a 650cc engine.  hmm

i just went and took a look at my parts bike.  everythings out but the engine.  without the carbs and airbox there actually is a LOT of space under the tank.  imagining it in my head, a single 38,40, or 44mm carb could either be mounted so that the manifold goes up and towards the front of the bike, then connects to the carb (like an upside down L), or maybe possibly be kicked out the right side of the bike for access to colder air (and possibly some ram air effects) (but then again it just hit me, i forgot the gastank wasnt on when i looked at the parts bike... tank may go too low for that..)  of course, a K&N is a must.

What i was hoping to get from all of you was an opinion on the performance and gains of a single larger carb.  with a single carb feeding both cylinders, would it not be a problem (what im trying to say is since the two stock carbs have different jettings, would a single carb have the two cylinders running just as good?)  i would hope to think that with the same exact jetting flowing to both cylinders, the engine would run much better, since there is no syncronizing and the same fuel/air mixture would help with equal combustion.

i found some single mikuni carbs on the net...for not that much..109 for a 38, $134 for a 40, and $149 for 44mm (http://www.pro-flo.com/proflo_mikuni_round_slide_carbs.htm) if this can replace the visions dual carb setup and help out peformance a little..i say..why not?   If you guys think this is a viable idea, i would be more than happy to try this out on my bike.  


any ideas? suggestions?


Many thanks,

Blake

[Kenny]

  Hi Blake,
    Sounds like a great idea,but a lot of work.
  I had been thinking that if I was to get rid of the carburators I would attempt to put a fuel injection setup from a wrecked bike of aproximately the same cc.
  Food for thought.
          Cheers Ken S  

[jasonm.]

I think you have your main jets backwards. The book and a Yamaha bulletin says 122.5 front and 127.5 rear. Try that before swaping to some alien carb set up. If you get some '83(black) front head pipes. You can run 127.5 in front also.

[sdinino]

Kenny,
I thought of the fuel injection too, but can't quite visualize how you'd get the electronics timed. You'd need to use the TCI pulse somehow, but it would begin and end before the spark fires. This almost deserves it's own thread... think of the time everyone here has spent twiddling away at these dang carbs. It'd be nice to toss 'em.

[Lucky]

what about using the pickup coils as a timming mechanisim?  the mounting holes could be elongated to advance the timming, then, for the coils, could be electronicly delayed. seperate leads tapped off the pickups could run to the FI control which would have it's own timming controlls.

alternatly, you could tap off the Tach lead...

--Lucky

[gaillarry]

There is a single carb conversion available for the Yamaha Virago, expensive $450 (US).  I have one on my 85 XV1000 and there is a marked peformance increase.  

Ken, the guy that makes the kit, uses one stock carb, modified, with a special manifolds.  It could be modified to fit a Vision, but an expensive proposition.  I suggest staying with  the stock carbs on the Vision.

Here's his link:
http://kjs.hypermart.net/carb.htm

[Blake]

hey larry,

that website you gave me is exactly what i wanted to see. from looking at it.. i now see that i can make this work...for much less...  simple the price of a carb, some pipe, and MAYBE a throttle cable..

from what you said about the performance increase, that helps me out knowing it will help..

from looking at ken's pictures, is that carb a modified STOCK one?  he says its a 40mm one.  i was planning on just buying a new 40mm roundslide and just mounting that.   if it is a modified stock...then the same effect, if not a better one, can be achieved with a round slide carb instead of a cv (like in you xv1000.)

simply with the information the guy gives on his web site, i actually think a single carb would work and can be achieved for much less than his requested $450.  all it would cost is the price of a 40mm carb (im set on thats the size i need. if you can use that on your 1000cc bike, it sure as hell will work on the visions 550cc) and the few bucks for pipe for an intake manifold.

the only thing that i think would be somewhat costly is the initial jetting.  trying to find the ride slide, needle, jets for that initial jetting will be the most difficult, but easier in comparison of fine tuning 2 seperate carbs.

i have next week off for spring break, so we'll see just what ill be able to get done-take a few measurements, make a rough sketch of the setup..who knows...  

keep the ideas coming guys...  i really think if we can figure out a carb setup that will help out the visions carb situation, everyone here will benefit.


Thanks everyone for the ideas!

Blake

[gaillarry]

The KJS single carb system has two versions. The first generation used a stock Harley carb with the KJS Manifold (this is the version I have).    The 2nd generation uses the stock Yamaha carb with his manifold. The Harley version is no longer available.

When I first installed the Harley carb it took a lot of adjustments to get the jets/air screw right.  With the new stock Yamaha carb version, KJS has pre-tuned the carb.

The advantage of the single carb is easy adjustments and removal.  Removing Virago carbs is a pain in the ass, and Hitachi carb parts are no longer available.

I've talked to Ken (the owner)) at KJS and he's very helpful.  Give him a call.

You can also check out the Virago Mailing List - there's extenstive debate about the KJS system - most in favour of it.

http://archives.itg.uiuc.edu/virago/

Search the archives for info on the KJS setup.

[Blake]

Thanks again larry.



-Blake

[jasonm.]

Just remember a single throat carb can never give the same maximum performance that 2 carbs can. Meaning , top end power will suffer. Just look at what happened the the Honda Shadows when they went to a single carb. A 20% decrease in max. HP. But better low end grunt. If you want low end power then a single carb is the way. But a bike with a 10,000 rpm redline could suffer big losses on top. My '82 pulls tree stumps in all gears from 2500rpm on up. So the 2 carbs can be made to work. My '83 has more top end and almost as much low end. I don't drive from stop light to stop light. So power on the bottom is not most important. It just needs to be smooth. Which both of my V's are.

[Blake]

you certainly do raise a good point larry...

just took another look at that KJS carb conversion dyno test.

what you are saying about it loosing power on the top end does seem to corelate with the dyno readings.  on the XV1000, it shows that at 6,000rpms, the top end drops out 20lbs of torgue lower than stock....and peaks earlier.  not a good thing..

and like you said, most of my riding is above 6,000rpms.  a loss of power there wouldnt be a good thing.

could you do me a favor jason and let me know two things.
1. do you have the updated airbox?
and 2.  if you do, could you tell me your carb jet settings?  as you know by now, mines less than good performance has gotten me a little irked, and with you saying you can pull "tree stumps" (nice way of putting it) above 2500, i thought maybe i could get a few ideas from your setup.


thanks a lot,

Blake

[gaillarry]

Harley's have been using single carbs for years with no drawbacks (except for parts falling off).

Two carbs require different jetting for each carb with separate fuel feeds. The front cylinder runs cooler (wind/exposure effect) while the rear cylinder runs hotter.  

I find the KJS setup great in the city, with lots of pep and torque.  On highway driving I haven't noticed any difference in throttle response or torque.  Although fuel economy is great on the highway 50/55 mpg but poor in city driving 40/45 mpg.

The manifold has a major impact on the air/fuel flow from the carb to the cylinders. I think the design of the manifold is critical.

On my Virago with the harley carb I used a stock Harley air filter and this also required modification to fit on the Yamaha.

If you plan to do a conversion use a stock Harley carb, they are cheap ($50 used on Ebay) and parts are readily available.
When I installed the Harley carb on my bike I bought a dozen different size jets for $25 at my local Harley dealer.  

When I first got the KJS manifold I installed a stock Harley carb jetted for a 1200 Evo engine.  My bike ran ok, but a little on the lean side.  This is where I used the different jets and air screw settings.  The Virago mailing list archive has a complete history of the jet sizes and adjustments four of us played with.  Adjusting the air screw and changing jets on the Harley carb is simple.  It takes me 5 mins to change a jet.


A single carb could work on the Vision but I think would require a lot of jetting combinations and manifold design
to make it function properly.  A good project for someone? If you succeed you could make a few bucks from the rest of us!!

[mac_p300]

I thought of this too.
I fitted a single SU Carberettor to my Norton Commando many years ago and it impacted the performance very little. It did however give much smoother running, easier starting and fantastic fuel economy (60mpg) thats over 300 miles on a tankful!!!

[Blake]

alright..so i took the bike out today..


well..first of all..i didnt want to say this...but last weekend..i tore my carbs apart..to clean them up..hoping that was the problem...went to rear carb...take jets out..get to pilot jet...whats that ITS NOT THERE!?!?  i was running it without a pilot jet...grr..so yeah..

i found the stupid thing on the floor..i seriously thought i put it in when i rebuilt them before...anyway..went for a ride day before yesterday..it was RUNNING..but..still..REAL BAD rich spots all over..but anyway.. THANKS JASON!!  i switched my main jets.. the thing runs like a beaut!  took it out today..definately pulling tree stumps!



but anyway...long story short..im on the highway doing about 70...theres a redlight ahead..i hit the brakes..not HARd but moderate...and i head a WACK...brake pedal jerks..and then its frozen solid..wont budge...so i pull over..im looking around..cant see anything..then i see it...holy crap...the stabilzing bar that connects to the right side rear wheel cover (that the brake pads are connected to..but that stabilizing bar was hanging down...and the right side rear wheel cover...the brake lever on it...was nearly above the swingarm.  so it was turned so what was ones at the back of the bike, was now on top. (circle rotated 90degrees clockwise)

and to top it off..the brake lever on that cover..well the shaft its attached to that seperates the brake pads, the shaft is obviously bent.. now im thinking "why the hell is it bent..?"  i look down...whats this i see?  my brake rod WRAPPED AROUND MY AXLE!?!??  not lightly wrapped around..like i could do with a hammer..i mean this thing is TIGHT.like it had a LOT of force..almost professional bend.  its bent so tight..the spring that put tension on the brake lever on the wheel cover, cant be pulled off...its wrapped that tight..  therse nothing i can do 20 miles away from my house..so i go bck home..slowly..with only a front brake...so my job for tomorrow..take pictures of the brake situation and fix it...



just thought i'd share that story with you all

Blake

[jasonm.]

Blake, Glad to hear it's running as it should. ;D Sorry to hear you had such misfortune on the ride.  :'(Need parts? let me know.

[Lucky]

so what your saying ai the stabilizer bar came loose, bolt broke or came out, and the drum assembly rotated wrapping the rod around the axel, correct? convinces me, i'll replace those 2 bolts on mine. 20 year old bolts...
--Lucky

[sdinino]

Glad you're OK. Coulda been ugly...

[Lucky]

I guess there's no way of knowing if the bolt snapped or came loose huh?  some pics of your coiled actuating rod would be neat to see, glad your ok.
--Lucky

[Blake]

Within the next few days a friend of mine will be lending me his digital camera (so i can take pictures of visions parts ill be selling), so while im at it i'll most definately take a few pictures of the actuating rod.. like i said. it has to be seen to be believed.  and to think i was THINKING of fixing the bike today..but then looked around for a normal camera, and when i couldnt find one, decided that since its cold anyways i might as well wait so i can take a few pictures.  I guess you right, i cant really tell if the bolt snapped or came loose, all i know is that when i started, it was there. and when i ended, it wasnt.  oh well.. its doesnt look liike it'll be too hard to fix (hopefully..but looks can be deciving)  ill just use the extra actuating rod from my parts bike, brake shaft (seperated brakes and makes them work) and whatever else i might need to replace.  


Thanks all for the concen,

Blake

[jasonm.]

What may have happened is the bolt at the drum may have been loose. And when the brake was applied again and again over time. The bolt just got sheared. That bolt needs to be tight. And some Loctite applied to it.