Author Topic: carb thought...  (Read 1046 times)


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carb thought...
« on: May 02, 2002, 01:59:45 PM »
hey everyone..

in a little down time at school today (yup..still in it) i was messing around with autocad and came up with a little intake for the vision, so that two 36mm mikuni round slide carbs could be used.

when i got home, i did it all to specs (pipe sizes, available clearances, etc.)   so its a pretty good picture of what i was thinking

i couldnt figure out how to export a picture with the surfaces on so all i could do is just the wire frame.

ok..all tubing is copper pipe. i measured. intake manifold opening is 1-5/8"

   red part is right above the front intake, yellow part is right atop the rear.
  the white tube is a 1-5/8" pipe going into the intake manifold. raises up 1" above
  then, the red and yellow parts are 1-5/8" pipe at 90* angle 45 degrees apart.
  so at this stage, both the front and rear have 45* pipes going to both the left and the right of the bike.
   from those bends (yellow and red) it transitions to a 1-1/4" pipe, where both of those pipes meet up to a 1-5/8" pipe which then goes straight out the side of the bike, to the carb. (surface area of the two 1-1/4" pipe openings was determined to be slightly bigger than that of the 1-5/8" pipe.  so no restriction.)
    all together.. from the center line between the two intake manifolds and where the carb would be connected, its less than 4" straight to the side (total distance through the pipes i dont know..didnt measure)

um....i know before i was asking everyone about a single carb setup, and we determined that that wouldnt work.   and now that im writing this now, it suddenly hit me that this might not be much different.  my reasoning for this setup was that the carb would be right under the edge of the gas tank and the airfilter (k&N of course) would be sticking out into the open, receiving nice cold air, and possible could add a little forced air at higher rpm's.  then also, i was thinking that with the dual carb setup that would go to the communal intake, jetting would be A LOT easier to work out, since it would be the same for both cylinders and both carbs, since both cylinders get the same amount of fuel/air mixture.  but what i forgot to think of (that just hit me) was the problem of the impulses in the flow of the air/fuel mixture when the valves oepn and close.  hmm....

but..BUT..what if i were to modify this instead of both carbs going to each side, i instead have one intake going to one side, and the other intake to the other side? (front intake routed to right, rear to left) so that each cylinder has its own carb?.  

another question that comes to mind.  will the distance the carb will be from the engine be THAT much of a problem for instant throttle response???   like i said before, with a little more designing i can get the carb pretty close to the original position.  hmm..

and my last question..will the angles of the pipes be a big problem.  right above the intake is a 90* bend.  that'll be the worse one.  the 45* ones i know wont be a problem because airflow wont be re-routed that much.

as you all are probably wondering by now, "why does he want to do this?"  as we all know, the vision carb situation has to be resolved.  and my main reasoning for trying to figure out some setup using horizontal flow carbs instead of downdrafts is that 36mm mikuni roundslides can easily be attained (and comparably cheaply too..each carb will be about $120 US compared to 200+ for downdrafts). not set on any specific setup, just something that will work, be easier to tune that our vision carbs, and that can be reproduced fairly easily.  just my 2 cents.

so what do you all think?  

Blake...determined to find a solution to the carb problems...
"At first it's like a new pair of underware... Frustrating and constrictive.  But then, it kind of grows on you..."


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Re: carb thought...
« Reply #1 on: May 02, 2002, 02:02:32 PM »
oops...just checked

to take a look at the up a new window and copy and paste the link....angelfire has some protection against just clicking on a link to it.

"At first it's like a new pair of underware... Frustrating and constrictive.  But then, it kind of grows on you..."


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Re: carb thought...
« Reply #2 on: May 02, 2002, 05:41:50 PM »
My $.02 (worth less probably)
I think seperating the intakes would be a good idea. with both carbs feeding both cylinders i think the fuel would have a tendency to be "hanging around" waiting for a valve to open. the problem here wouldn't be so much one of mixture so much as one of fuel condensation. smaller pipes will keep fuel velocity high. seperating the cylinders will help here.

on a related note the 90 degree bends will significantly contribute to the chances of fuel condensing on the pipe walls. any means of reducing the radius of the turns would be better, also any way you could reduce the intake diameter would also help.

my other thought on this is that you should move the carbs as close as possable to the cylinders. you could easily mount some pipe between the carbs and the filters to take advantage of "ram air" (think velocity stacks)

I have never designed or built an intake system, i'm only going on what i have learned as a wrench over years.  there could be serious flaws with my reasoning... anyway, there you are :)
1982/3 XZ550 Touring Vison, Gold on Black


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Re: carb thought...
« Reply #3 on: May 02, 2002, 06:28:14 PM »
hey lucky,

i see your point...right now im working on a seperated version of the intake... a friend of mine helped me build an intake for my riding lawnmower so i could mount a keihn carb on it (hehe..dont ask) once i get a general idea of what i want, i know he can help with the rest (not to mention a plumbing supply store is RIGHT across the street from him...more than once he sent me over there to find parts that i needed).

but with the seperated version, the one thing thats going to be a trouble to get rid of is that initial 90* bend right out of the intake manifold (lack of space). but i have that rotateed roughly 30* off the center line then theres what looks like a 60* ben to get it going straight out the side.  this part right here is giving me a little trouble right now because im trying to keep the distance at a minimum (to keep the carb as close as possible), so trying to get the pipe at the right angle is important.

and decreasing the intake diameter would help too you say?  i can see why.. you want to increase air velocity so you get a good suction through the carbs.  i looked on some copper industy web site and for pipe with a 1-5/8" (1.625) O.D, you can eitehr have a 1.481 or 1.505 I.D.   guess ill opt for the 1.481.  however, the next size down after that is a 1.375 O.D pipe with either 1.265 or 1.245 I.D...when comparing the bore surface goes from 1.720 at the small 1-5/8" diamter pipe to the large 1.375" pipe with a bore diameter of 1.260.


36mm carb bore = 1.41732" I.D / 1.69291 O.D. / 1.577 sq/in bore.

SO...if i use the 1-5/8" pipe..that would INCREASE the bore...hmm..not good...

next size down is the pipe with 1.375 o.d / 1.265 I.D / 1.260 bore.  that should be good.. you got me going to have to go find an intake boot and measure not the part where the carb would sit..but the part thats further down, the thicker part. and find that I.D.  

oh in no rush..i have plenty of time.  but im liking this seperate intake manifold idea.  and your idea of the pipe at the carb intake sounds good..have is at a slight bend barely sticking out of the side of the bike, with velocity stacks on it then you really WOULD have ram air..  hehehe (evil laugh)...  now the ideas are coming...

as i type this im downloading pro-engineer.  a REALLY good 3d autocad program. hopefully i can make a better picture for you all to see so it'll be easier to understand (since i KNOW all my rambling on doesnt make much sense as you can see...also as you can see...i like numbers)

thanks for the help!

"At first it's like a new pair of underware... Frustrating and constrictive.  But then, it kind of grows on you..."


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Re: carb thought...
« Reply #4 on: May 03, 2002, 09:32:54 AM »
Blake; one day you'll look back and be amazed at how much you learned from your Vision.  Cheers.


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