JS Motorsports Carbs

Brooking 850 · Dec 23, 2011

Hi Ashman , fuel line set up sounds great, just what I need to do, drop some pics on forum please ,if you don't have them on photo bucket or similar, you can send direct to neptechvtu@yahoo.com.au
Regards Mike

pete.v · Dec 23, 2011

rpatton said:
pvisseriii said:

The brillance will be in the functionality at sustained WOT.

Click to expand...

Elucidate?

I had a need little setup to begin with, short, tidy and neat. Due to the restrictive nature of the direct bend down to the carbs, flow became restricted. I have since did the loop around configuration with perfect success. Works brilliantly.

Brooking 850 · Dec 23, 2011

Any pics of your set up pvisser!!!?
Regards Mike

ashman · Dec 24, 2011

Hi Brooking850

I didn't take pics at the time as I had so much going through my head at the time, but next time I take my fuel tank off i will take some pics, but the way the bike is running that mite be awhile :lol: I just got a few 1/4"brass tee peices and mounted them between the 2 fuel taps, very simple and straight run to the carbies, no kinks at all and very tidy.

Ashley

pete.v · Dec 24, 2011

Brooking 850 said:
Any pics of your set up pvisser!!!?
Regards Mike

Notice the larger line in between the 2 tee's.
This may seem a little round-a-bout but it's all about gravity and flow.

Johnnymac · Dec 24, 2011

pvisseriii said:
rpatton said:

pvisseriii said:

The brillance will be in the functionality at sustained WOT.

Click to expand...

Elucidate?

Click to expand...

I had a need little setup to begin with, short, tidy and neat. Due to the restrictive nature of the direct bend down to the carbs, flow became restricted. I have since did the loop around configuration with perfect success. Works brilliantly.

If the bend starts to Kink the line in anyway, I have a set of Stainless Steel 1/4 inch barbed elbows from Grainger. http://www.grainger.com/Grainger/THOGUS ... lbow-4HFL7
I probably won't need them, but it is a good way to avoid kinking the line.

Johnnymac · Dec 24, 2011

Sorry to keep bumping this thread.... but when you guys pulled your old airboxes to fit the JS Carbs, what did you do about the oil breather to the rear plate? Won't oil just drip out the breather hole?

jseng1 · Dec 24, 2011

Johnnymac said:
I think i have put together a very good fuel line and filter setup for my JS Motorsport carbs. This is using the Pingle 2 in/2 out in line filter. What do you think? The black fuel line is from a harley. It is preshaped with a 90 degree bend. The clear line is NOS british fuel line.

That's the cleanest plumbing job I've seen. Can you give us the part numbers etc?

Jim

Brooking 850 · Dec 24, 2011

My breather hose is still on the backing plate that I left on the bike, it only gets oil there if I overfill the tank and some times after a long extended hard run, it gets a little frothy but nothing to cause grief!!!
Regards Mike

Johnnymac · Dec 24, 2011

jseng1 said:
Johnnymac said:

I think i have put together a very good fuel line and filter setup for my JS Motorsport carbs. This is using the Pingle 2 in/2 out in line filter. What do you think? The black fuel line is from a harley. It is preshaped with a 90 degree bend. The clear line is NOS british fuel line.

Click to expand...

That's the cleanest plumbing job I've seen. Can you give us the part numbers etc?

Jim

Thanks Jim.

The black fuel lines with the 90 Degree bend are Part #: 19-0475 (S&S Cycle brand) $5.95 each X 2
Pingel 2 in 2 out filter - part #SS22P - $44.70
The rest of the parts I bought at my local cycle shop in St. Louis. (Old Norton/Triumph Dealer).
-Spring Fuel line clamps
-90 Degree Stainless Steel spigot with British Threads $9.00 each (Available also on EBAY..... I ordered a set on ebay from classicenglishmotorcycles but they never arrived so buyer beware.) Ebay was expensive too.
-British made Clear fuel line. - Very thick/hard. Very unlikely to kink, but I guess we will see.

Johnnymac · Dec 25, 2011

Well I got the carbs and installed them today. They bike started right up and idles fantastic. But it doesn't ride well. I must not have the right jets.

Another issue (which could also be the main problem) is that it just doesn't seem to be getting fuel to the carbs. When I open the petcock , I can see that there is hardly any fuel flowing through the lines. I thought that it was my fuel line configuration, (And perhaps it still is). When I disconnect the lines from the carb and open the petcock, fuel flows freely to the end of the fuel line (both sides). But when I attach it to the carb, not much. Lines are practically empty - I can see about a half inch of fuel in the line above wherer it connects to the carb. Anyone have any idea?

1up3down · Dec 25, 2011

Well, I have had my JS carbs for 20 months now, and I do not have any fuel filters in my lines.

But I do have petcocks that have the screen inside the gas tank, and that is good enough as far as I am concerned.

My guess is your fuel filter is too restrictive and gas simply cannot get sucked through it fast enough to feed your carbs.

Johnnymac · Dec 25, 2011

1up3down said:
Well, I have had my JS carbs for 20 months now, and I do not have any fuel filters in my lines.

But I do have petcocks that have the screen inside the gas tank, and that is good enough as far as I am concerned.

My guess is your fuel filter is too restrictive and gas simply cannot get sucked through it fast enough to feed your carbs.

Yeah, I pulled the filter and it is getting fuel now.... It is not the filter though... I think it is the way i have it configured. There is a lot less room than I anticipated. I will try a couple other things.

One thing is for certain, the main jets are wrong. Idles like a champ, revs great sitting still. Take her for a spin and under load it is bogged down. I will go get a handfull of jets tomorrow or monday to rejet. I'm thinking that the 160's for my Combat are way to big. What are you guys running on your 750's? Thanks so much!

pete.v · Dec 25, 2011

Start with the needle clip. Raise the needle a notch ( clip 1 notch down). These carbs will react profoundly to this adjustment.

Some ( very few I think) have had success right out of the box. They require some fiddling. This is due to the fact that no 2 Nortons breathe exactly alike. Much depends on your compression, your particular exhaust, the age of the rebuild, even if you have a standard bore or are 40 over. But I have said this many time and make no mistake about it, when they are right, they're righteous.

rpatton · Dec 25, 2011

I'm using a single VM34. When I was using straight down fittings at the petcock, the hose went down, then up, then down in a high arch. An air bubble always formed at he top of the arch like a vapor-lock. I could fix it by just pulling the hose flat then letting it go, the bubble went up into the tank. Cured it with 90deg elbows. Is there a way you could burp the lines?

Johnnymac · Dec 25, 2011

pvisseriii said:
Start with the needle clip. Raise the needle a notch ( clip 1 notch down). These carbs will react profoundly to this adjustment.

Some ( very few I think) have had success right out of the box. They require some fiddling. This is due to the fact that no 2 Nortons breathe exactly alike. Much depends on your compression, your particular exhaust, the age of the rebuild, even if you have a standard bore or are 40 over. But I have said this many time and make no mistake about it, when they are right, they're righteous.

So moving the needle up will result in a leaner or richer mix?

ashman · Dec 26, 2011

Hi Johnnymac

My 850 has a SS cam grind the same as the Combat I think, Jim set my carbs up with 160 jets and it runs fine with them all through the revs, muck around with your needle settings and see what happens, mine is set on the second from the top, at first I drop it to the top mark but I lose a bit of power and the bike was running too lean and the 3rd from the top was to rich so the second from the top works well for my bike, but I think you mite have fuel flow problems to your carbies, I only run one fuel tap when riding but I notice when I get low on fuel it will starve for fuel till I turn the reseve tap on, the same as if I do any high speed runs I will turn both fuel taps on to keep the fuel up.

When I first ran my fuel lines they hung behind the carbies as I didn't have any 90 degree tap fittings and found the carbies some time starved for fuel but since I put the 90 degree fittings on with 2 tee connectors between the taps it has a straight down run to the carbies and no more problems with fuel starvation.

Ashley

AussieCombat · Dec 26, 2011

Hey Johnny,
Needles can be confusing untill you can get it stuck in your mind......
To lift the needle, which is tapered, means you are allowing more fuel through the needle jet.
To lift the needle, you must LOWER the CLIP.
And visa versa.
If your engine revs freely while in neutral, but bogs down under load, then it is probably rich.
Do a plug chop, and have a look.
If they are black, drop the needle. (lean it off)
If they are white, lift the needle. (richen it up)
It's all good fun.
AC.

Johnnymac · Dec 26, 2011

thanks guys. I played around with it all afternoon today and still having issues. I am going to the cycle shop tomorrow to get some longer lengths of fuel line. I just can't get the fuel to flow to the carbs. (I have pulled the filter for now as well). I am hoping that if I run a longer piece of fuel line and loop it around the carb it will help siphon the gas. I also put new NGK plugs in and that made a tremdous difference, but it started to rain and I was unable to finish my installation. Hopefully I will have better luck tomorrow.

1up3down · Dec 26, 2011

I have had my JS carbs for 20 months now, and my recommendation to you is to NOT change the jetting Jim set the carbs up with.

Just the fact that you said you changed the plugs and it made a big difference tells us at this point you do not
have a jetting problem.

Petcocks: I assume they are in good shape and if you take the fuel lines off and open they up that they will flow
a strong stream into a cup. Check this and verify your petcocks are not restricted in any way.

Your petcocks should have screens built in, just my opinion but you do not need any further filtering.

These carbs should flow just fine all through the range just bolting them on without any jet changes.

Once you have them properly installed with new plugs then you can slowly check the plugs on each side and
slightly change the needle position to get them to match up in color.

JS Motorsports Carbs

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