Need some new carbs

18 months now with my JSMotorsport 32mm flat slide carbs

no tickling required just pull up a choke lever on a cold start with one kick

idles like a rock

jetted perfectly

came with everything, and I mean everything from manifolds to air filters to fuel line

and they flow, they flow strong all the way to red line

no fiddling after initial install, perfect plug colors

I now have three other Commando friends who have switched to these carbs, all very happy

1up3down said:

18 months now with my JSMotorsport 32mm flat slide carbs

no tickling required just pull up a choke lever on a cold start with one kick

idles like a rock

jetted perfectly

came with everything, and I mean everything from manifolds to air filters to fuel line

and they flow, they flow strong all the way to red line

no fiddling after initial install, perfect plug colors

I now have three other Commando friends who have switched to these carbs, all very happy

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I am a happy jsmotosports carb owner as well. I have the dual flatslide kit and it went in easy. I played with them a bit but my issues were electrical. I had the bike up to 95 today and it pulled strong all the way up. Idles nice too, I can idle at very low levels if I want but I set it around 1000rpm. Lots more power and a better sound than the Single Amal I had before.

The kit comes with all the stuff and instructions printed out as well as reminders on the carb boxes. So add another vote in on the js setup. I am happy with them, good bang for the buck.

I am a happy JS Motorsport carb owner too. It took some time tinkering with it to get the jetting correct but once you get them dialled in, they are sweet.

I couldn't get my Amals aor a single Mikuni to idle consistently. Update ignition to a Pazon and idles steady. Seems poor electrics can cause low idle issue!

My buddy has the single Mikuni on his 74 Roadster, and says it works great. Not hearing much love for them on here though.? What's the diff btwn Kehein & JS? Heard Keheins were a little noisy at idle.

bmwbob said:

I couldn't get my Amals aor a single Mikuni to idle consistently. Update ignition to a Pazon and idles steady. Seems poor electrics can cause low idle issue!

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Mine idles just fine... starts on first kick & I still have the old points that haven't been touched in years. I was going to upgrade to a trispark.... but if it ain't broke, don't fix it.

Ive got the trispark fitted,I replaced a old Boyer system

I would go with the JS ones as the reviews are all so positive,if the price was similar to AMals.Or if Amal hadnt brought out the premiers.
But when you factor in the import duties and shipping the price is a big factor.I know iam not selling the bike anyhow so should buy the best available but I cant afford the js ones really.
Ive been to a couple of classic shows in the last 3 weekends,seen 3 commandos and every one ive seen has had a single carb conversion of some sort on it .

MATTT said:

Dad decided for me , I said i might be buying some non standard carbs and he simply said "why do you want to put modern carbs on it when you can still buy the proper ones for the bike?"

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Thank you Dad. Exactly.

Dad decided for me , I said i might be buying some non standard carbs and he simply said "why do you want to put modern carbs on it when you can still buy the proper ones for the bike?"

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That needs a whole new thread to itself

Hands up all those who agree who have got electronic ignition on their bike(s)

I sort of agree. I've got electronic ignition. It was on when I bought the bike. I haven't put back the points.

I ran a single 34mm Mikuni for 15 years on my 850.

Started first or second kick, idled like a rock, was absolutely no fiddling reliable.

So why did I switch to the JSmotorspork twin carbs?

Because they do everything the single Mikuni does, and in addition they unleash more horsepower above 4500rpm

a twin carb set up just breaths, flows, more air, especially so from midrange to redline

However, my experience with single carbs has been limited to a max size of 36mm, so I can buy the argument that a single is better in terms of sheer simplicity, providing you can find one that flows equally as well as a good twin carb

and I am not aware that such a single carb set up exists that can do this, dyno tested proven

What's the difference btwn the JS and the Keheins? Other than a lot of $.

the JSmotorsport carbs say "PKW" stamped on them

PWK is a series of carbs under the Keihin unbrella

from the web site:

The PWK series has a semi-elliptical section valve with a great flow attitude.
The chromed valve has less wearing than other surfaces and the D shape allows the right turbulence to the noozle.
The PWK gives more revs on top and doesn't let the engine go flat

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1up3down said:

the JSmotorsport carbs say "PKW" stamped on them
PWK is a series of carbs under the Keihin unbrella

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JS PWK is a series of carbs under the Keihin umbrella?? What about a replica (OKO Taiwan) of the genuine Keihin PWK. Genuine Keihin PWK is at least twice the price of an OKO replica. Don't know about quality?

You don't know about the quality of the PWK carb bodies?

You mean what kind or quality of metals were used in their manufacture?

Not being in that business I don't know.

What I do know is that I have had mine for over two years now and they are are staying on my bike forever.

1up3down said:

You don't know about the quality of the PWK carb bodies?

You mean what kind or quality of metals were used in their manufacture?

Not being in that business I don't know.

What I do know is that I have had mine for over two years now and they are are staying on my bike forever.

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Yes I read all good criticism about JS PWK. What I meant was I don't know the difference in quality of the genuine Keihin PWK and the replica OKO PWK ?

Some posters asked whats the diff with JS carbs. First of all, some of these carb types are not rubber mounted - rubber mounting is best to avoid heat & vibration.

Here's what I put into JS motorsport flatlsides that makes them different than what others supply.

Every jet is changed to suit Nortons. Needles are replaced with needles I designed specifcally for Nortons. The needle jets (spray tubes) are replaced with custom made spray tubes that I size myself with a special custom size reamer because this works best. The carbs are completely dissassembled and all orfices checked. The mixture screws are painted with ink to check how they seat against the orfice when bottomed out. The slides are drilled to insure against needle binding because the needles are a special size. Thicker Alcohol proof rubber boots tat won't crack are provided now. The float level and clearance is checked. The float bowl brass tube vents are modified to aid assembly/disassembly. Idle speed screw springs are modified to give more tension and prevent loosening from Norton vibration. Flow to the float bowl is checked. Air cleaners are shortened so they fit. The manifolds need to be cleaned up. I test & develop everything myself.

There's is a list I go through and it takes a lot of time but thats what Ido to put out a quality product.

Jim

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Thanx for the info Jim.

I am the importer of JRC engineering carbs into the UK and there is a conversion kit which includes a manifold for single carb models, the 750 uses a 32mm carb and the 850 uses a 34 mm carb this has proved a good conversion and several members of a local bike club of which i am a member have done this and are very happy, if any one wants help or parts i do keep a good range of bits in stock, you can visit the web site for info http://www.brillbikeparts.co.uk cost for the carb and manifold is approx £180 + post

MATTT said:

need some new carbs,the amals never give reliable tick over week to week,and yesterday one jammed open on full throttle,leaving me with a 2 mile walk home up a very steep hill !!

Ive basically decided to either get a set of JS flatslides or a set of AMal premiers
Being in the Uk the amals are going to be quicker to get and cheaper,as the US shipping is $60,making the cost $525 for the flatsides
Also I read on a post about having to pay £72 import duty?,Ive not looked into this yet?
The amal premiers are £271

Although I do run a completely stock 750 and I do want to put twin carbs on ( I almost ordered a single last night when I eventually got home ! ) Im not too worried about it being either stock amals of JS ones with the k,n filters

Sorry long ramble over , does anyone know if the JS ones have a UK importer? and do I have to pay import duty ?

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So what did you get and how did they work?

In the end I bought a pair of new amal premiers
As a relative of mine runs a bike repair garage he got them at trade for me
I also sold the old set on eBay ,listing the problem with one of them sticking.
It worked out much cheaper the amals were something like £140 and the old ones sold for £45 or something
It runs fine now