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November 7th, 2020, 01:50 AM   #11
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I'm afraid that that graph is wrong Steve.

I can go from a 175 to 160MJ and need to alter the pilot screw a lot, almost enough to need to change the PJ. So the main jet has an influence down to idle.

the jet needle diameter is just total bollocks. Just go out to your bike and put an * * M in and start it, it will blubber. then thange to a * * S and you'll have glowing headers, it'll pop and bang. So the JND is totally wrong and should hit the side wall at the same height as the PS/PJ. that should come down and they should start together.

the slow air jet is wrong. it is the slow air jet that carries the fuel from the pilot. a bit like you getting in my wheelbarrow Steve and I give you a lift. as long as I keep lifting, you keep delivering so the Pilot air should stoip when the pilot jet does.

the jet needle taper fades away much earlier, it's nearly useless at half throttle.

I'm not sure how you would draw the needle clip as it is a moving part. maybe it should have been done as a band of grey? anyway, put a needle on C1 and start it and then put it on C7 and start it. the bike might not even start! yet apparently the needle clip has no influence at idle?

the whole thing is bollocks Steve and if you believe it your going to hell in a handcart.

I don't mind telling you Steve because I know you but guys like - others - never admit they lose/wrong (DJT) and just lurk, and lurk and lurk and at the end the last thing they do is say; "oh fair do's, you taught me something" they just wait to cause shit a mile down the road.

actually I might use a DJT. its fat, has a late start, finishes halfway, has a lot of papping and banging, makes an awful racket and wants throwing away as soon as possible.

Taffy

Last edited by Taffy; November 7th, 2020 at 02:44 AM.
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November 7th, 2020, 12:15 PM   #12
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Its a guide Taffy, put out by Keihin, the designers and makers of the carb. I may not have the tuning experience that you do, but I've played with enough FCRs, and in recent years, with an O2 sensor and wideband AFR meter to have a decent feel for them. People who ride my FCR'd bikes reckon they work better than theirs.

Look at the graph again, everything overlaps at some point, the challenge is getting the balance right, and in my experience, the needle is critical to that end. No one needle fits all FCR applications, else there wouldn't be the 100 + that's available.

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November 7th, 2020, 12:17 PM   #13
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I should add that I agree that a too big main can influence idle, that's why you have to start with the main first. Once that's right, its influence lower down is as per the graph. The graph assumes the jetting is close to right.
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November 8th, 2020, 02:09 AM   #14
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Originally Posted by steve View Post
Its a guide Taffy, put out by Keihin, the designers and makers of the carb. I may not have the tuning experience that you do, but I've played with enough FCRs, and in recent years, with an O2 sensor and wideband AFR meter to have a decent feel for them. People who ride my FCR'd bikes reckon they work better than theirs.

Look at the graph again, everything overlaps at some point, the challenge is getting the balance right, and in my experience, the needle is critical to that end. No one needle fits all FCR applications, else there wouldn't be the 100 + that's available.

well, if we're going to talk about people riding bikes I've got over 600 on mine now. so let's stop there.

My needles have a 4 angle change now plus straight so you might call that 5-angles (4 changes). i've so much experience now, I just ask for the needle straight width and try and work ther PJ down to join it. the question then becomes either/or;

lots past the needle and small PJ
even them up
minimum past the needle and the rest in with the PJ

with the 4 angle taper you can't go wrong, all you need is the needle straight to be right. if someone is stuck on a 42PJ then cut some slack on the straight and they can try a 40 or 38, or 35.

the latest needle I have made meant that my Yanky chum got down to a 35PJ/60PA and it took him so long to get the 50PAJ to go with the 32.5 I sent him that the Autumn had come. But I think he'll hold a 35 all Winter. I will ask...

I'm convinced that the needle is the sponge and the PJ is the cream, jam and icing....just that little add-on = the sponge is the filling = the PJ you can control. yet if you look at that chart the needle is doing nothing low down.

If people don't think the needle is working at idle; block it off and see what happens!

That chart isn't right Steve and you didn't jet your bikes following it. If what you said was true (about Keihin) , why did all the early Yams come with the "maximum" MJ at like 175 or even a 180, PJ at 48, 5 second squirt, and the needles were rich too. how come, two years later a KTM had the same jetting? (still rich). They also did totally the opposite with their air jets and put the "maximum" in as well (which = "opposite affect") when everyone got a 100PAJ and a 200MAJ. They are on 115 nowadays, some difference.... and on exactly the same bikes - whacko!

I suggest that far from testing them, the factories took Keihin's first settings and then worked gently and safely to as far as they dare (which wasn't far!).

think and draw a 4-angle needle on paper with the first being a C. It can't go wrong really, it cuts out mistakes.

why in the end do the manufacturers make their own needles and their own jets? the smallest PAJ for the later OEM/Proddie carbs is an #80 so Yamaha and Honda had to go out and have smaller PAJs made in #50, #60 and #70. and what about needles? Keihin never made a 'C' needle so Honda and Yamaha had to have them made......

So what to make of Keihin? That chart you put up just confuses people but you are covered "....because keihin did it". But it's not helpful though is it.

It was me that first put up the PA to PJ ratios in 2001 and I might have to be the one that draws....cake!

that "DJT" got chucked out yesterday - while on the golf course. what a great day for the world, hopefully it's never coming back.

regards

Taffy

Last edited by Taffy; November 9th, 2020 at 12:04 AM. Reason: elocution
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November 8th, 2020, 09:24 AM   #15
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That graph is neither right nor wrong. It gives an idea of ​​what to modify based on the position of the accelerator. Since the driver circuit and the main circuit are two distinct circuits, I believe it is more appropriate to have 2 graphs, one for each circuit. And also a third graph for the pilot screw which is located beyond the vacuum valve and which is fed by the idle circuit but also has a "screw regulator", a tap. However yes, if I change needle diameter 1 size I have to change the PJ 1 size
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November 16th, 2020, 08:22 AM   #16
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The last time "Daddy" had someone draw him a picture was how long ago Steve???o

or should it be; as it was at the time!

Just for you....

Taffy
Attached Thumbnails
Dyno Chart for '99 FE501 with FCR41-ratio-fuelling-2.jpg  
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November 16th, 2020, 01:02 PM   #17
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Not sure of your point Taffy, graph looks similar, not identical, but close enough to guide tuning along similar lines.
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November 16th, 2020, 01:20 PM   #18
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All these graphs, just put a wideband 02 in the exhaust with datalogging and get on with it..otherwise you are just pissing in the wind
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November 16th, 2020, 02:06 PM   #19
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Agreed, but the graphs guide you as to what to change to improve the AFR readings.
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November 16th, 2020, 02:55 PM   #20
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No doubt, considered that after I posted...getting to used to typing numbers into a laptop to change a/f
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