JS Motorsports Carbs

I see you are runniong the right angle fittings, I kept mine straight from the original type( ne w replacements) screened petcocks/taps, but drilled out the ferrules on the hose fittings to 7mm to get a real good flow.
Although mine arent perfect looking, they let me use WOT up to 5000 RPM no problem with one petcock/valve open.
Haven't changed anything on the carbs jetting wise, just pilot and idle adjustment.
Regards Mike

I got them all installed and running great! I had to drop the main jets from 160 to 150 and drop the needles all the way. I will monitor plugs to make sure the needle settings are correct.

Thank you all for your great advice!

Great to here, another happy customer.

Johnnymac said:

I got them all installed and running great! I had to drop the main jets from 160 to 150 and drop the needles all the way. I will monitor plugs to make sure the needle settings are correct.

Thank you all for your great advice!

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Worth remembering that taking plug readings if you are using Efuel, may not provide a particularly accurate idea of mixture strength, as the alcohol itself tends to affect the colour of the plugs. If you cant set the bike up on a dyno, its best to leave settings as stock and only change things if there is an obvious problem, either too rich or too lean.

well, even though my fuel line setup was good at getting me fuel, I was still getting crap in my carbs. I did flush the tank when i took it off to install the carbs, but there was still stuff in the there. So, I decided to rethink my fuel line configuration. It ended up being very simple and I am happy to report after a long test drive that they are getting enough fuel and the carbs run great.

Essentially, I used the 2 in/2 out pingel hi flow fuel filter. There are no 90 degree bends and looks pretty good. I would have preferred to use clear fuel lines throughout, but this was all I had in my garage.

Looks good, is it a fiberglass tank or is it rusty inside?

Thanks dave. It is a metal tank. The PO sealed it with some sort of epoxy. Every so often little bits come off and find their way out of the tank. I dont think that there is much I can do other then filter it. The great thing about the pingel filter is that you can easily open the filter up and clean it.

Johnnymac said:

Thanks dave. It is a metal tank. The PO sealed it with some sort of epoxy. Every so often little bits come off and find their way out of the tank. I dont think that there is much I can do other then filter it. The great thing about the pingel filter is that you can easily open the filter up and clean it.

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I think there is stuff that will take out the lining, if you end up going that route.

Unfortunately I have to send back one of my carburetors to Jim. For some reason the floats keep getting stuck on one of them and therefore fuel just pours out the vent hose. Jim has been great assistance and is going to replace it with a new carb. Rather frustrating as it is now almost 65 degrees in St. Louis and I can't take my Combat out for a ride until he gets the old carb and sends me a new one. Oh well. he is also going to shorten the air filter boot so there is more clearance from the original Air filter backing plate.

I would still recommend this setup and Jim is fantastic to work with. Top notch guy.

Hi Guys. Quick question.

What Spark plugs would you recommend for a Combat Motor running these 32mm PWK's? I have been trying the NGK BPR7ES (because that is what was on my Combat when I got it from the the PO) but from what I've been reading, these may not be the best plugs for a high compression motor.... running high performance carbs, Boyer ignition.

In the book it says to run Champion N6Y for combat engines so just get the same heat range in NGK, my Norton perferrs chamion plugs have never had any problems with them and when I run NGKs in it they seem to play up after a weeks running.

Ashley

Just wanted to compliment Jim from JS motorsports. The carbs are great. I used them instead of buying new amals as it was not too much more expensive to do so. I have received many remarks and positive compliments by others who did some work on the bike as well.
As I wrote in a previous post, my Norton fired up this week forthe first time in 31 years. What I didn't mention was that it was 25 degrees out at the time. There was zero hesitation, no burps, no farts, and it idles at a low steady purr. Coupled with the Pazon Altair, it is truly a one kick fire up.

Without this forum, I would never have heard of them or the Pazon.

I've just fitted these carbs to my 750. The easy start and solid tickover is the way ahead. Even with postage and import duty the price is favourable compared with two new Mk2 concentrics, rubber mounted manifolds, air filters and throttle cables, here in the UK. Over the last 37 years with this bike I've had twin Mk1s, single Mk1, single Mk2, SU, single Mikuni. The SU was excellent but shite to start without a brimming tank (needs a head of fuel) the Mikuni was good but runs out of puff at about 80mph. Hopefully this is the setup that will see me out. I'll let you know how it goes.

Another success.... Easy install, other than messing with the cable connector, kicked first time and sat there banging away like she'd just come back in from a long run... Very, very pleased. Thanks Jim.

I have just completed a 817 mile (1315 km) trip to and from the NOC NZ rally and kept an accurate record of the fuel useage with my JS carbs.
Riding consisted of fast twisty country road runs, winding and hilly highways, wet and dry conditions and fast pace on country back roads.
All in all the conditions you would normally encounter here in New Zealand.
i tend to run at 3800 to 4200 rpm and rarely rev it over 5000 rpm.
i had the oppurtunity to run against at least three bikes with single Mikunis and in once case a bike with twin Mikunis. The good thing is that all bikes I ran with and compared fuel consumption are all 850's, some more trick than mine, but overall very similar.The 3 guys with the single Mikunis all have the same riding style as we all road together back in the day !!!
After one hard twisty run, the twin carb Mikunis used more than mine, the single Mikunis overall were always within points of a liter difference so for the sake of the exercise I have called their useage the same.
Total distance traveled = 817 miles or 1315 km
Total fuel used = 18 Imperial gallons or 81.13 litres ( 4.5l to Imperial gallon) In the US gallon this equals 3.8 litres
Average Fuel Consumption = 45.4 mpg or 16.20 kms per litre
I did get as much as 53 mpg on general highway use at 3600 to 3800 rpm generl highway running on three different trips over the same stretch of highway about 3 hours running return trips.
Hope this helpful to you all
Regards Mike

Hey all,
have just fitted Jims' PWK Kit.
Easy, quick installation and the bike started first kick, cold, chokes on.
Chokes off, idle up to 1500, set mixtures, idle back to 1,000, fluffy on left side,
bit more mixture play, all good, sweet idle but dark plugs, crisp revs.
Stop engine, kick and start, at idle, no worries.
Fuel lines are the problem at this stage.
The problem is that the spigot on the Carb is considerably smaller than the outlet
spigot at the tap. So what fits one doesn't fit the other.
Not to worry, some machineing on a T piece might be the answer.
Hopeing all goes well with a test ride, can't see a problem.
Total time from start to finish 1 1/2 hrs. with some playing around
with fuel lines, and including checking new carbs.
This is a welcome change.
AC.

Good to hear AC, but they seem to get better with a few miles on them, when I frist put mine on in the mornings the frist start for the day it took about 3 kicks to start but once started for the day it started frist kick every time but once you get use to starting it with these carbies it will start first time every time, I find with mine when cold is to pump the trottle a few times before the frist kick, works for me and the bike will start first kick every time, with my Joe Hunt Maggie and these new carbies they work so well together and my plugs have been the cleanest I have ever seen them in 36 yrs of owning my Norton.

Ashley

Ashley, I agree with you on the JS carb starting.

I have had mine for over a year and a half now and from a cold motor start, I pull both chokes up and turn ignition on,

and then I find that I have to open the throttle a quarter turn while giving a good kick.

This usually goes not get my motor to fire, but then it always does on the second kick with some throttle.

As soon as it is running I push the choke knobs down and hold the idle around 1200 for about a half a minute and at that point it will hold its idle with a cold motor.

These carbs do seem to need the throttle opened to insure a good flow of gas gets drawn in to start.

The great thing is that the motor pulls easily with no hesitation from cold, unlike other carbs that need either the choke left on a while longer or a longer warm up.

I was one of Jim's first customers, and I thrilled with the way these carbs start, idle, and flow all the way to red line.

I don't even use the chokes on mine, just open the throttles a few times to get the fuel going then one big swing on the kick start, it always start first kick when cold doing it this way.

Ashley

If anyone is interested.....
Sorted out a fuel line setup today, seems OK, rode the bike and it was very crisp and the plugs
were quite light, Jim had set the needle clips at second from the top, so dropped them to the centre (lifting the needles).
Hopefully better, unfortunately upon starting Ed for the rerun, the right side muffler parted company from the flange.
Here's my setup.



It is great to be able to do quick changes to the carbs with 2 screwdrivers and 1 spanner.
Seat off, tank off, tilt the carb, top off, adjust, return.
Obviously / hopefully, once they are set then it won't matter, but it is good.
To remove the carbs is simple,... Seat off, tank off, tilt carbs and remove tops, right side filter off, carb off,
left side carb and filter off together.
Got some welding to do.
AC.