JS Motorsports Carbs

I'm another satisfied JSMotorsports customer.

I use the enrichener lever on the left carb only as it is difficult to get to the right carb's lever. Starts fine, here in mild temps of California.

The supplied air cleaners do not touch the back panel of the original airbox of my '73 750. I would like to be able to use the original airbox with them and it had not ocurred to me to find a thinner air filter element - great idea. We'd also have to find a part number for rubber or neoprene bellows to connect the front plate to the carbs. That would raise the "sleeper" aspect of these carbs. Even now, almost no one notices that I don't have the original twin carb Amals; they see the carb where it is supposed to be, that is not a single carb, and their eyes move on.

Yep

I have had the flat slides for 18 months now and I think the supplied green foam air filters look great, really good.

They flow plenty of air.

I see no reason to change those filters for anything else, just me.

Hi John, i am in the process of uploading pics to photo bucket and will post what I did to the supplied filter boots so the filters didn't rub on the backing plate.
in my thread I mentioned that I had over tightened the front boot between carb and manifold, even though this did distort the square O ring, it didn't make the fliter touch the housing, Jim wrote to me about a change in the alloy manifold.
I have already trimmed the perforated grating of the original air cleaner and did a mock fit up with the original(my new ones) Amal to filter rubber boots, and it all works. Just need to find the right depth filter element
I will post pics once I have uploaded
Regards Mike

I'm just waiting for my JS motorsport carbs to arrive, can anybody tell me if they have tappings in the manifold to fit a set of vacuum gauges for setup? Temperatures here in UK are dropping towards zero and the council have started rock salting the roads. Not good for naked polished alloy. Might be sometime before I get to road test them.

hi gripper, the answer is no but there is plenty of room to fit something and use a balnce tube to blank them off when not testing
Regards mike

pics of fit up

SCHCS Didn't Fit

Drilled to fit

Distoter square O ring from over tightening

Different length idle screws,long one is original, different thread pitch on new one on right

Cut down filter boot and narrower clamp

Brooking, I certainly hope your experience is the exception to the rule.... I am looking for a bolt on solution and don't want to mess with have to customize my "Custom" carb solution.

http://www.knfilters.com/search/product ... od=NO-0100
The K&N Norton replacement is an 8.125" diameter round element, it's 2.875" tall.

This one looks good. You get 1.125" clearance. It's a little smaller in diameter, but I don't think it matters.
http://www.knfilters.com/search/product ... rod=E-9054

You need to trim the perforated surround to a height so that it's going to come within the folded border of the plates but doesn't bottom against the vertical surface the plates. All it has to do is is shape the filter.

It gets a little complicated when you get to the boots. The stock ones were the easiest way to do it but the carb needed a little machining to get a lip for it to fit to. The boots happen to fit the VM34 just right with the mod. Maybe the PWK32 could be threaded for the stock collar or the threads turned down so it could be a be a press fit on the carb.

I have a stupid question after reading all this. With the exception of mounting the ignition switch on the plate, why else would it be necessary to have it if you are not running the stock ham can filter any way? Am I missing something?

The totally different idle screws kill it for me right there. WTF?

It is good to keep the back of the air cleaner there so when the next guy goes back to stock he doesn't have to buy a new one. It hides the battery and the ugly Mikes XS breathers people are using too.

Grumpy

Also, I hate to say it...but that manifold that you had to drill out looks like it's very poor quality (soft metal that looks like it was textured with a wire bristle).... Anyone care to comment on theirs? Why were the idle screws so different? different lengths..... different threads? The more that I learn about these the more hesitant I am getting about putting them on my bike.... I am now more inclined to either stick with my frustrating Amals or wait and save for the CNW Keihins.

I removed all the stock air cleaner stuff including the back plate the ignition switch mount when I switched over to my flat slides.

I will not go back to amal or a single mikuni and will never sell my Commando. Blasphemy!

I did cut a simple bracket that holds my ignition switch and mounted in on the two threaded holes the back of the stock air box bolted to, using the same bolts.

My ignition mount bracket has a hole I put in it for the ignition switch and it faces for and aft, and is positioned
coming out to the left side and bit below the level of where the stock location would be.

Works, and look great. Sorry, I am photo illiterate.

The idle speed screws are different because the right side carb has had the idle speed screw switched from left to right and a custom screw with different length and thread is used for that purpose - its supposed to be that way. The square O ring is fine as long as you don't overtighten the clamps - there is no need to overtighten them. Or you can just leave out the O rings They are there just to fill an empty space and are not essential. I don't know of anyone else other than one customer (Brooking) who has had the air cleaners push too tightly against the backing cover. You can always remove the backing cover if you want but I don't know of anyone who has had to. The quality of the manifolds is fine and they are the best ones available - they were made by the Quaife gearbox people, they just aren't polished smooth on the outside. I have gone through my box of 50 manifolds and not one of the bolt holes are too tight for the bolts, they all measure greater than 5/16". Either Brooking had oversize bolts or he was very unlucky. The only other 32mm manifold available is a very poor quality product and needs to be reworked inside and outside. The Quaife and the foreign made low quality manifolds turn out to be the same length. If someone knows of a better quality 32mm manifold - let me know because I will have to resort to the low quality manifolds when the Quaife supply runs out.

Brooking

What is the diameter of your bolts?

See installation below with backing plate retained (seems to fit nicely):

Why not get some manifolds cast using the good ones you have as patterns? Alternatively maybe Amal are making "Premier" manifolds which might be fit for purpose?

I have the JS carbs, not installed yet. As far as the manifolds not being of good finish, I have a solution that works for me. I'm having my frame and other bits powder coated a silver/grey. I used anti-powder coat tape to mask both sides of the manifolds and a bit of tape to allow for fitment for the rubber part so the diameter of the manifold will not be too large for the rubber part. All you will see is a nice powder coat finish on the two manifolds. Not an easy solution, but practical if you want a clean look. I'll post pix when I get them back.

Sky

I drilled the bosses, pressed in tubes to utilize a balance tube. They say it isn't needed but I like it. It gives an extra smoothness to the idle and a little more tunability. What ever tube you have that has a 1/8 th hole will be good. I wouldn't want to go bigger.

This is where you could hook up your tool.

rpatton said:

http://www.knfilters.com/search/product.aspx?Prod=NO-0100
The K&N Norton replacement is an 8.125" diameter round element, it's 2.875" tall.

This one looks good. You get 1.125" clearance. It's a little smaller in diameter, but I don't think it matters.
http://www.knfilters.com/search/product ... rod=E-9054

You need to trim the perforated surround to a height so that it's going to come within the folded border of the plates but doesn't bottom against the vertical surface the plates. All it has to do is is shape the filter.

Click to expand...

Thanks Bob. There ought to be some boots out there, from Japanese bike applications. I'll hit the local MC junkyard . . . . to see what I can find.

I agree, Ludwig, the Concentrics carburete very well, particularly with the velocity stacks of your type, where the ID is the same as that of the carburetor. IMO, the JSMotorsports carbs would benefit from a similar stack with a 32mm ID.

I don't know what it is but there is something about the design guidelines (the ratios of jet area, bowl area, vent size, emulsion tube design, and the like) that Amal engineers followed that gave their carburetors a broader altitude range, great low end response, and good mid and upper end transitions. Those engineers did their R&D in an era when it paid to do that R&D and they knew their stuff.

But for corporate penny pinchers, the zinc on zinc, we wouldn't even be talking about other carbs for our Nortons.

Hi guys, thanks for all the feed back and as Jim says, I might have been just unlucky with my bolt holes on the inlet manifolds. All four were the same and a gentle tap with a small hammer may have seen them go through, I ran a metric drill through and it was a very small amount I had to relieve. In fact if you loook at the pic I posted the SHCS actually goes through the hole but hangs up at the bottom side, so none of the four holes had to be drilled all the way through, just partially.
As for a plug and play, yes they are and run sweet.
My Amals had sloppy slides in them, and even they still worked they are not a patch on the Keihins.
As for the manifolds looking of poor qaulity, not so, as Jim says , the outside is not polished, and they fit onto the head perfect.
In answer to Jims query about my SHCS being oversize, no, they are stock items.
As for the backing plate issue, well all that is stock on mine and as I plan to put the original air cleaner back on with a narrower element and perforated surround, cutting 5 mm off the filter boot and using a narrower clamp was very easy to do, I marked it out , cut it with workshop scissors, checked that they were square, and fitted them , 20 min job!!!!
Thanks Jim , they are great. I like the idea of a balance tube for vac testing, what are your thoughts on that?
REgards Mike

I don't have experience with the balance tube but if it works then why not? Personally I don't use the balance tube. I also like the allen screws that "pvisseriii " installed on his carb tops - nice touch and good to see someone making improvements. As for the tight fit of the aircleaners against the backing plate I'd like to know if anyone else has had this problem - so chime in. By coincidence I just received some narrow clamps today and I'm thinking about shortening the air cleaners as sperheaded by "Brooking 850".

And Brooking 850 - I still need to know the diameter of those bolts because all my manifold bolt holes measure at about .317" and 5/16" bolts commonly measure at .304" so what is going on here?