37mm FCR experience anyone ?

Has anyone got any experience setting up 37mm FCRs on a 920 Norton? I’m just fishing for some baseline / starting point advice.

FCRs are simple to tune. i use 35s on a 650 triumph, so maybe some of that experience could be helpful to you.

will it idle decently? if so the pilot fuel jet is probably good to start with and the accellerator pumps can help off-idle. if it accepts midrange throttle without burbling or gasping the needle is probably close enough for the moment. no alternative needle jets are used in these carbs- its all done with different needle diameters. i jet the needles with roll-offs. the carbs are informative when they go rich on a 1/8 roll-off. the way i jet the mains is to start at a stupid rich setting and just jet down until the carburation is clean. on my machine the correct main is obvious within one or two sizes doing this.

on a 650 motor with C12 gasoline, i run 150 main jets. on the same motor with oxygenated Q16, i run 195s. in both cases the needles are EMS, 3rd or 4th notch up, pilots are 58 or 60.

there are additional jets and needle adjusters in these carbs that no ordinary person can take advantage of.

what needles and jets came with the 37s? they may be good, but i have generally found that fussing with the mains will yield the most benefits.

Thanks for that.

I actually already run 35s and have them set up:

Main jet 152
Pilot jet 58
Needle EMR

But the above set up was with a Maney 2:1 pipe. I noticed that with stock unbalanced pipes and peashooters it needed a richer needle setting and fitted a richer needle (EKR) with those pipes.

So I’m guessing the same settings with perhaps 1 or 2 size bigger mains would be a good starting point for 37s.

Why are you going to 37s?

gortnipper said:

Why are you going to 37s?

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Cos the ports are 36mm. And the 35s require the smaller manifold rubbers, which means I can’t use the beautiful 36mm Maney manifolds.

So I’m running carbs that are too small on DIY ‘hogged out’ manifolds.

If I want FCRs I get to choose between 37 and 39.

Gotta be worth a few BHP I reckon…

Fast Eddie said:

Cos the ports are 36mm. And the 35s require the smaller manifold rubbers, which means I can’t use the beautiful 36mm Maney manifolds.

So I’m running carbs that are too small on DIY ‘hogged out’ manifolds.

If I want FCRs I get to choose between 37 and 39.

Gotta be worth a few BHP I reckon…

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are they going to fit?

gortnipper said:

are they going to fit?

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Well, that’s part of a longer story, but, basically, yes.

i have used the same EMS needles with my two fuels, entirely because the richer needles like EMQ and EMR werent available when i needed them. the M taper worked for both standard (lean) and oxygenated (rich-burning) fuels. i have more needles now and can test the richer diameters, but the S worked fine in a 650.

all this was with separate 1-5/8 inch pipes 34 inches around the bend.

im really interested to hear what happens with the 37s. ive considered going up from 35s too but the FCRs are stupid expensive, so ive put it off. i would guess that you are right estimating just a couple of sizes larger on the mains, but the only way to know is to do it and see.

If needles are your jam get/download a Keihin FCR needle chart if you have not already. They are easy to read if you know where the addition or reduction in fuel is needed.

EMR needles worked fine with the 152 mains in my +.040 750 with a less aggressive ported stock valve size head, JS2SS cam, high CR pistons and 1.5" headers into a 2 into 1 collector with a long megaphone terminated with 21 4" Supertrapp plates. I run the EMR needle clips in the 5th position from the top, which I believe but am not certain is how they came from Sudco.

I can't imagine the 37mm FCRs would be very difficult to setup for your 920 after getting the 35mm units setup for the same motor configuration. 2mm isn't that much of a difference to workaround for a tuner.

Who did you find to assemble or sell a dual 37mm FCR set for the Norton intake centers?

Are you planning to build the set? Just curious.

Definitely should give you a small boost blending down the intake manifolds from 37mm to the 36mm holes in the head. Should be both smooth running and responsive. A Seeley frame might make the fitting part easier. Is that next on the list?

Good luck with the project.

Schwany said:

Who did you find to assemble or sell a dual 37mm FCR set for the Norton intake centers?

Are you planning to build the set? Just curious.

Definitely should give you a small boost blending down the intake manifolds from 37mm to the 36mm holes in the head. Should be both smooth running and responsive. A Seeley frame might make the fitting part easier. Is that next on the list?

Good luck with the project.

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Yamaha SRX 400/600 carb sets will fit, that’s what to look out for.

Good point ref the Seeley frame, there would indeed be no gusset plate or frame spine to worry about there…

Yeah, I knew about the SRX intake centerlines, but couldn't quickly find a 37mm FCR set for the SRX. Next closest built was 39mm. I was probably looking on the wrong site.

Have fun with it.

I found it difficult to buy a set of 37 m FCRs to fit the Norton/SRX. My usual source, SUDCO, hasn't carried them for a long time. I finally found a set in Japan and immediately bought it. It was the last one left in stock. They were assembled from Keihin parts to the SRX spacing by a shop in Japan. That's also where SUDCO was getting them, but they had to order at least the 10 set minimum to get them. The guy I talked to at SUDCO said that they didn't think there was enough demand for that size, so they weren't ordering any more. They did still carry the 35 mm and 39 mm sets at that time. I did have to turn up new adapters to match the machined Maney intake manifolds. The ones supplied for the SRX were not large enough diameter.

More details on the carbs here.


Ken

Edit: Meant the first question of this comment for Ken, but screwed up the reply.

Ken,
Do you know yet if the jetting on the 37mm FCRs for a 600 are a little off for a 920?

Anyone else:

I worked with PJ Motorsports on the 35mm SUDCO kit for my Norton but did end up having to talk to Chad Thompson at SUDCO to get the intake side adapters. They were missing from the kit. Chad took care of it and sent me a set.

Buying 10 sets of FCR carbonators for a Norton would be painful on the wallet.

It looks like the Maney intake "maneyfolds" don't have a balance tube. I've often wondered if a balance tube is necessary for the FCRs given how they are already linked together for atmosphere air. Haven't tried them without a balance tube yet. Anybody actually know if it makes a difference without the balance tube?

My guess is the balance tube will give a better idle. Not sure if it does more than that? I’ve run Triumphs with and without and never felt they were really necessary to be honest.

The carbs come with 160 mains as standard and the rest looks good so I’m hopeful they’ll be a good starting point.

Allen’s in the U.K. sourced them directly from Keihin, but it’s taken 7 months…

I think there might be a placebo effect with a balance tube.

Sounds like what you are getting from Allen's is close to ready to go for your 920. Well done making it happen.

Schwany said:

Edit: Meant the first question of this comment for Ken, but screwed up the reply.

Ken,
Do you know yet if the jetting on the 37mm FCRs for a 600 are a little off for a 920?

Anyone else:

I worked with PJ Motorsports on the 35mm SUDCO kit for my Norton but did end up having to talk to Chad Thompson at SUDCO to get the intake side adapters. They were missing from the kit. Chad took care of it and sent me a set.

Buying 10 sets of FCR carbonators for a Norton would be painful on the wallet.

It looks like the Maney intake "maneyfolds" don't have a balance tube. I've often wondered if a balance tube is necessary for the FCRs given how they are already linked together for atmosphere air. Haven't tried them without a balance tube yet. Anybody actually know if it makes a difference without the balance tube?

Click to expand...

I'm afraid I don't have an experience with the 37s yet, but should have fairly soon. I have a lot of experience with 35 mm and 39 mm FCRs on racing singles, but not on Nortons.

With the MK3, I actually managed to spin the engine over with the starter yesterday while checking out the new wiring and electrical system. Still a couple of small tasks left before firing it up, but it should be soon. After that, there are some finishing touches still to do on the bike before taking the first test ride. But it's getting really close.

Ken

lcrken said:

I'm afraid I don't have an experience with the 37s yet, but should have fairly soon. I have a lot of experience with 35 mm and 39 mm FCRs on racing singles, but not on Nortons.

With the MK3, I actually managed to spin the engine over with the starter yesterday while checking out the new wiring and electrical system. Still a couple of small tasks left before firing it up, but it should be soon. After that, there are some finishing touches still to do on the bike before taking the first test ride. But it's getting really close.

Ken

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That is good news. Your build is going to be a really nice ride.

I'm sure neither of youz guyz will have any trouble tuning the 37mm FCRs for your big Nortons.

Those Rotax 560 motors were a lot of fun in a dual sport bike with a good cam and some port work. I never tried an FCR on one. Missed that boat entirely.