1983 XV500 Cafe Racer

I have been contemplating using a single carb on my project and came across KJS motorcycle works. They seem to have a quality product,but a bit pricy for the whole kit. I was thinking of just getting there manifold and using a FCR40 carb from a MX bike I had on my project. You could find an FCR37 carb off a 250 MX'er on ebay for a good price. I bet it would work great on that 500.
 
The KJS manifold is a nice bit of kit, I've looked at these before. The reason I am currently sticking with the original twin carbs is that good quality single carb manifolds are expensive. However I am thinking of making my out of aluminium and having it professionally tig welded.


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I thought today I'd have some time looking at a lesser job on the bike, the engine casing. The XV500 has a chromed emblem plate on the R/H casing. Unfortunately the chrome was peeling, therefore I decided to see how the 3 part casing came apart. After asking on the Virago Net forum, I could find out how the casing came apart, so today I set the casing up in the mill and decided to destroy the emblem to see how it came apart. Unfortunately I also managed to break the main casing.

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Just bought the FCR carb :D. According to the guy it's in good shape (no wear on the slide at least) but it needs a bit of cleaning. Will have it tomorrow so we'll see. With a lot of people running TM40's (that's also what you get with the KJS kit) I'm not worried it's too big. But it sure is large enough :D

I've found glue from Bison that should be resistant to chemicals, heat and vibration. It's advertised for gluing metal together in tough circumstances like on engines (http://www.bison.net/en/products/647-2-components-adhesives/product/2273-epoxy-metal/). They glue together whole airplanes these days so why not a simple manifold, right? It costs less than € 10,- so it's worth a try. As for getting it airtight, the glue is supposed to "fill gaps" and I can always use a high temp silicone to make it airtight if needed. But I will also ask someone what it would cost me to get it welded, just to see if there really is a difference. On the other hand I like to do things bit different (and I'm stubborn) and using glue on an aluminium manifold certainly qualifies as different...

Because I want the carb to sit as low as possible between the cylinders (it's a rather large carburetor so I don't want it to get in the way of the fuel tank later) I've decided not to go with the 90 degree bends but create something with a lower profile by cutting a straight piece of 42mm aluminium tube at the correct angles. The SketchUp drawing shows what it should look like when it's finished.

To test if this would work I created a little rig that helps me get the aluminium cut at the right angles. I measured the angle between the intake openings at the cylinders at 100 degrees. So cutting the aluminium at 25 degrees would make it possible to attach the manifold directly to the cylinders instead of using the original rubber adapters. Though that's still something I'm considering because it will reduce vibration and heat at the manifold and carburetor. Anyway, I tested with some 40mm pieces of PVC tube and am convinced that I can get this to work. I'll keep you updated on my progress if I make any. Same goes for the FCR40 carb installation.
 

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I'm keen to see if this works. You said about getting the carb lower, could you not use a straight pipe between the two inlets, cutting the ends to at an angle to suit? Also have you thought about using two 90 degree bends and cutting them where they meet, so the inlet path is smoother without the sharp 90 turns, similar to the KJS manifold?

As for reducing heat and vibration, you could use a rubber joint between the carb and manifold?


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Got the carb yesterday and it seems in pretty good shape indeed. The slider goes smooth and the throttle and cables all work nicely. But it's a big carb... So I can actually not get it too low as it would have to stick out to the side to avoid hitting the cylinder. So a straight line between the intake openings is not going to work for me. My PVC mockup seems about all right actually. At that height I have enough clearance at the bottom as well as the top because that's where the throttle cables have to go underneath the frame.

So today I started on making the "bends". The first few cuts seem to spot on. Very happy with the result (see picture). As far as I understood the sharp angles shouldn't have any influence on getting the air/fuel mixture to the cylinders (it should actually be "turbulent"). An equal length to both cylinders does apparently. Mine is partially inspired by the BIP manifold which also is T-shaped (http://vtcportal.com/221-thickbox_default/single-carb-manifold-for-yamaha-virago-xv500-535-550-600-and-650-with-mikuni-tm-40-carburetor.jpg).

I will use a rubber joint I think, but also make a bracket to hold the carb in place. It's not only big but quite heavy as well and I'm not sure a rubber boot with clamps is going to hold it. No fun looking for a carb in the bushes... ;)

My wife met a custom bike builder this week who happens to live only 15kms away. She told him about my new project (before this I've rebuild a BMW 1150GS into a scrambler) and he was curious what I'll make of it. I could contact him if I wanted to exchange ideas or needed advice. I'll contact him tomorrow to ask his opinion on the glue thing. I believe he can weld aluminium as well so if he advises not to use glue he might be able to help me out there. I'll let you know of any progress. To be continued...
 

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" As far as I understood the sharp angles shouldn't have any influence on getting the air/fuel mixture to the cylinders (it should actually be "turbulent"). An equal length to both cylinders does apparently"

boy do i wish all that were true when put on a dyno or flow bench or street

i dont know how you will get into the manifold to smooth the lower corner radius it will be a major reversion point

i have had to re work the assembly of several of the manifolds i build to address this they even get some burn thru on welding so get a metal build up in there
 
@cxman: do you mean I have to smoothen (like sand or file down) the inside of the manifold where the various tube sections meet? So there's no rough "edges" or "ridges" on the inside that obstruct the flow of the air/fuel mixture? It's a 42mm aluminium tube so I would actually be able to do that because I can access these points.

On the other hand, I hear and read a lot of contradicting stories on this topic. Some say the flow should be unobstructed, while others say it should be turbulent to not de-atomize the mixture. Hard to say who or what to believe. I based my design on a proven solution (many people use these without any problems) by Bike Intake Performance. It's also T-shaped and consists of the same 90 and 50 degree angles. As you can see in the third picture they don't seem to smoothen the inside of their tubes very much.

On the other hand, this is a fun solution to fix myself at low cost, so worth a try. If the bike really runs like crap with it, I can always get two 90 degree bends welded together.

I'm not saying you are wrong by the way. What I am curious about is what effect these rough edges would have on performance? Would you only notice it on a dyno run or would it actually be noticable when riding the bike in normal traffic? Mind you I'm not creating a competition race bike here.
 

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blend all the edges you can do not finish with anything smoother than 60 grit powered or 120 by hand

if you use a spigot mount put a piece of screen between it and the manifold to break up any droplets

put out by the carb

put a heat reflector above the manifold to try to get some and hold heat in the manifold to try and stop icing on cooler damp days

and to help the fuel from condensing back out of the air stream at any low pressure points or smooth air

and by the way its easy to make power on the dyno now make it run smoothly and nice on the road

without fouling plugs or having a low end chuggle or high end rich cackle ect make it run slow or cruise at a moderate speed

that is another story WFO is easy
 
jagtmans said:
So today I started on making the "bends". The first few cuts seem to spot on. Very happy with the result (see picture). As far as I understood the sharp angles shouldn't have any influence on getting the air/fuel mixture to the cylinders (it should actually be "turbulent"). An equal length to both cylinders does apparently. Mine is partially inspired by the BIP manifold which also is T-shaped (http://vtcportal.com/221-thickbox_default/single-carb-manifold-for-yamaha-virago-xv500-535-550-600-and-650-with-mikuni-tm-40-carburetor.jpg).

I will use a rubber joint I think, but also make a bracket to hold the carb in place. It's not only big but quite heavy as well and I'm not sure a rubber boot with clamps is going to hold it. No fun looking for a carb in the bushes... ;)

My wife met a custom bike builder this week who happens to live only 15kms away. She told him about my new project (before this I've rebuild a BMW 1150GS into a scrambler) and he was curious what I'll make of it. I could contact him if I wanted to exchange ideas or needed advice. I'll contact him tomorrow to ask his opinion on the glue thing. I believe he can weld aluminium as well so if he advises not to use glue he might be able to help me out there. I'll let you know of any progress. To be continued...


Looking good, equally I like the look of the black manifold you posted a link for.
 
buy the kjs manifold. it'll work much better, and as cxman says, a lot of the better will be low speed stuff.

that black manifold looks like it would function quite poorly to me.
 
Strictly from an air flow perspective...
The airstream can't make sharp turns, so you are going to get some dead areas in the flow.
For the bottom corner that projects into the air stream you are going to have a high velocity area right on the corner and spirally inversions/dead air on the side closer to the cylinder. For the top corner you will have dead air in the corner.
The higher the velocity through the tube the more these areas will grow and the smaller the effective cross section of the tube.

This might help visualize what is happening..
https://www.youtube.com/watch?v=RL0rypO794E

I didn't actually watch that video so I have no idea what it is actually about, so just take it as a pretty picture (unless its an interesting video, then I will take credit ;))

Someone else can chime in on fuel droplets and such, I'm just the airflow guy..
 
Put some finishing touches to the top yolk. The reason it's taken so long is the need to purchase the right tool for the job, in this case a 2mm slit saw.

They say a bad workman blames his tools, very true, but you still need the right tool for the job.

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i would put a pinch bolt for the centre stem too, that way you don't need to load the top nut to secure the yoke.
 
It's taken some time but the manifold is ready and the carb mounted on the bike. When I got the bike it would hardly start (you could say it wouldn't start) and the 2 times I got it running it died after a few seconds. I had not expected it to run with the new single carb setup, and of course it didn't... ;) Then I followed some good advice from different forums and changed the spark plugs. That actually did the trick!

I haven't changed anything to the carb yet, so I put it on as I got it, with a 45 pilot and 165 main jet. I adjusted the idle and just turned out the fuel mixture screw 1 turn because it seemed to be running a little better that way. The AP isn't working so I have to fix that because I have the "bog issue" when I open the throttle fast. But when I somewhat gently open the throttle the bike actually responds pretty well. Even though the spark plugs look OK, I do have the feeling the bike could use a little richer mixture. But that's something I have to fix by setting up the carb correctly. But at least it starts and runs idle steady, and responds to the throttle so I'm happy for now.

Like I said the manifold is glued together. The glue doesn't take temperatures over 100 degrees celsius (I tested that by heating a piece of glued aluminium with a blow torch). So using glue to attach flanges to the manifold to bolt onto the cylinders was out of the question, as the outside of the cylinders will get hotter than that. And taking cxman's comment on the too sharp edges of my first design into consideration, that made me redesign the manifold and use the stock intake boots. By turning them around they face eachother at an angle of 20 degrees. So now I only had to make "sharp" edges at an angle of 10 degrees each, which I smoothed out on the inside as best as possible. the rest of the downward angle into the cylinder is now taken care of by the boots which are rounded on the inside so should make airfow much smoother than with the sharp edges. Added bonus is that I now have a thermal insulator between the cylinder and the manifold, which prevents the manifold from getting too hot and breaking the glued connections. Besides that the rubber boots also take up some vibrations and give a little room to play in case the manifold isn't "spot on" sized. All in all this manifold has cost me less than € 30,- in materials and tools I had to buy, and it actually seems to be working. So I'm quite happy :D

Anyway, I've put up a short clip on youtube of the bike running. You can see it here:
https://youtu.be/EURuICOtIgY
And yes, I know I should have put on an air filter but I haven't got that yet and was eager to test the carb setup ;)

In the movie you also see the mounted KTM front fork, which was more or less a bolt on solution with the pyramid parts bearing replacement set (both top and bottom 48x30mm). The wheels will be replaced by spoked ones which I already have. Front will be and 18" (which is roughly the same outside diameter as this 90x90x19, so both engine and ground clearance don't seem to be issues) and rear the standard 15" for now at least. I managed to get hold of a 535 rear wheel that included the drum brake at a bargain. The only problem with that wheel is that you can't mount it in the rear fork without taking the final drive off, because it's like 0,5 cm too wide to slide it in. And mouting the drum brake when the wheel is already on the final drive doesn't work either. But that's something I'll have to figure out or learn to live with. It's not a lot of work unbolting the finl drive and I hardly ever take out the rear wheel anyway...

Here are some pics of the manifold:
 

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Good work on the manifold, certainly given me food for thought on which way to go.

I wasn't aware the 535 hub was slightly wider, I'm interested to know why it won't slide in, is it the spline drive being slightly wider or something similar? If so could it be machined down a tad?

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Mounted a steering damper as I've set the rake at 24 degrees, I thought a steering damper would be a wise move.

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Get a drop tree from Cognito moto. https://cognitomoto.com/collections/fork-conversion-parts/products/1-rise-triple-clamp-lower

That'll give you another inch.

Open the forks up and add a spacer to increase the length. You can probably add another inch this way, maybe as much as two.

Either machine some spacers to use the original wheel, or get a GSXR hub and lace up a larger front wheel with spokes (also from cognito moto). The GSXR forks on that Virago frame is going to increase trail significantly, because the offset is so much less. To counter that, you'll need to drop the front end and/or raise the rear. There's only so far you can raise the rear before the driveshaft starts binding (7 degrees deflection is the limit for reliability, you can go as high as 14 degrees but longevity of the driveshaft will be compromised)

Charles.
 
I'm not using a Virago frame, I've made my own. The wheel in the picture isn't the one that'll be used, I have an 18inch to put on. I'm happy with the 24 degrees, I designed it that way.


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Yeah, I see that now. I was replying to the first page info, and I see now that there are four pages :)

Nice looking build! I wish I had the machines you do! So jealous!

Charles.
 
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