1962 650ss Build

It is curious that the alcohol seat is stamped .125 and measures 0.140
You had better go with that seat and needle without further drilling. Surely you will have improved fuel flow that should tell you that you are onto the source of your issue. If no change, look somewhere else.

Slick

Yeah I’m not gonna mess with it any further.

Here’s an aside question. Running these carbs without the choke slides installed, would that have any bearing on its running quality?

As in, would more air be able to pass through the carb with the slides not installed? They currently are not in the bike, as they did not come with the basket of parts I got initially. Just been mulling that over.

seanalex said:

Yeah I’m not gonna mess with it any further.

Here’s an aside question. Running these carbs without the choke slides installed, would that have any bearing on its running quality?

As in, would more air be able to pass through the carb with the slides not installed? They currently are not in the bike, as they did not come with the basket of parts I got initially. Just been mulling that over.

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No running without the choke slide will have no bearing
However you do need to block off the cable hole in the cap
As an aside a high mileage mate of mine always keeps the slides in on MK1 concentrics as he believes the extra weight of the choke slide takes some the shock from the vacuum pulses from the engine running that wears the slides out
It's just one of his theories

I have the holes blocked for sure. K. Just seems running a little heavy still.

Need to investigate it a bit more.

My main jets are 270, pilot is 25, and needle is 106.

270 mains for a 650 seems large to me. Larger than what Norton put in muffled 850's

Are you getting anywhere with the carburetion?

Schwany said:

270 mains for a 650 seems large to me. Larger than what Norton put in muffled 850's

Are you getting anywhere with the carburetion?

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after you posted this I went back and read through the Dunstall manual. It seems my ADHD prevented me from reading the following correctly.

"settings for high compression 650cc engines are as for the 750cc unit but with 230 or 240 main jets where silencers are fitted, and 270 or 280 jets for megaphone equipped machines . . . "

then of course the next line, which somehow I did not even see "standard, low compression engines need 200 to 210"

beyond having incorrectly sized main jets, which I've since reordered and am awaiting fedex, I pulled the carbs back off to recheck to air screws, and to make sure everything was cleaned. In this process noted that the tops of one of the needles was bent pretty badly. I was also getting weird throttle action from the cables. New cables are on and run properly to the carbs, and the action feels much smoother and tighter, still need to balance.

The other gripe was that one of the petcocks was leaking a bit, so drained the tank, and am awaiting new Dowty washers for reassembly. Also re-ran the fuel lines, and got a better piece fitted between the two carbs. Will have a full report hopefully by Saturday.

NorLuck said:

Did you end up getting an RGM side stand? Did you have any issues with it?

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@NorLuck. I have not. Funny enough I went back looking through my emails for which stand I had fitted to which bike. Its actually the Stand from Andover AN stand that I have on the Triton, and feels quite stable.

I honestly do not think I can get a side stand on with the way the primary inner, rear sets, exhaust, yada yada, sits on the bike. If I ever do tear down the Triton, I may try fitting the AN stand and see how it goes. But at the moment unless the pound falls lower than a dollar, I don't see myself dropping $200++ just to find out.

Maybe Amals with unfiltered 3.5" velocity stacks and dual open megaphone exhaust would appreciate 270 mains. Don't know for sure, since I've never owned a Norton 650 twin engine. Would certainly be loud.

Out of curiosity I just pulled the Amal carburetors I have out of storage to check. I ran 220's in my Amal 930's on the 750 with a 2 into 1 megaphone. I think I made them work, but no longer use them to verify. I have 2 small drawers of Amal main jets. I probably tried most of them at one time or another. Although totally irrelevant for a restoration I got better no maintenance all-around street performance and top end when switching to Mikuni 34mm carburetors sometime in the 1990's. Now Keihin FCRs do the fueling work.

Schwany said:

Maybe Amals with unfiltered 3.5" velocity stacks and dual open megaphone exhaust would appreciate 270 mains. Don't know for sure, since I've never owned a Norton 650 twin engine. Would certainly be loud.

Out of curiosity I just pulled the Amal carburetors I have out of storage to check. I ran 220's in my Amal 930's on the 750 with a 2 into 1 megaphone. I think I made them work, but no longer use them to verify. I have 2 small drawers of Amal main jets. I probably tried most of them at one time or another. Although totally irrelevant for a restoration I got better no maintenance all-around street performance and top end when switching to Mikuni 34mm carburetors sometime in the 1990's. Now Keihin FCRs do the fueling work.

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Concentrics and monblocs use different jet sizes for the same bore. @seanalex is using monoblocs, so 930 jet sizes are irrelevant.

t ingermanson said:

Concentrics and monblocs use different jet sizes for the same bore. @seanalex is using monoblocs, so 930 jet sizes are irrelevant.

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So what you are saying is a 270 main jet flows a different rate of fuel in an Amal monobloc carburetor than a 270 main flows in an Amal concentric carburetor? Just want to be sure I understand that the main jet numbers don't mean the same with regard to flow rate with Amals. It wouldn't surprise me.

The mains are too large if as he said the bike is running heavy, or whatever is considered the correct terminology for too large a main jet. Unless it is happening sooner in the throttle range than close to WOT in which case it could be needle, needle jet, or clip position related. Then again it could be ignition timing related.

If you know the answer sean needs to make things right, let sean know? I'm just trying to help because I like his bike.

It is my understanding that the jet number equals the flow rate thru the jet under certain test conditions in ml/min. At least that is what is stated in Amal literature.

Whether that rate is equal in Monoblocs AND concentrics is a matter of conjecture.

Schwany said:

So what you are saying is a 270 main jet flows a different rate of fuel in an Amal monobloc carburetor than a 270 main flows in an Amal concentric carburetor? Just want to be sure I understand that the main jet numbers don't mean the same with regard to flow rate with Amals. It wouldn't surprise me.

The mains are too large if as he said the bike is running heavy, or whatever is considered the correct terminology for too large a main jet. Unless it is happening sooner in the throttle range than close to WOT in which case it could be needle, needle jet, or clip position related. Then again it could be ignition timing related.

If you know the answer sean needs to make things right, let sean know? I'm just trying to help because I like his bike.

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Slick

First things first, I need to get the petcocks back in and sealed decently. Hope this delivery comes tomorrow, then at the very least I can get it all set for testing. Then will check the float height.

Everything I can find as far as literature for settings of jet sizing is literally all over the place. It has me thinking that even the Dunstall manual is referring to Concentric's being fitted on a 650 as opposed to Monobloc's. With the main jet size being 200 -210 *using concentric carbs* that isn't stated, but I'm wondering if that was the go, given it was the "latest technology"

A few older posts I've come across on the NOC website state the correct settings for the Monoblocs are as I have them now. 106 needle, 270 main, #3.5 slide, 25 pilot.

Then there is some other postings of stock 650ss settings with a 250 main, and 30 pilot, with a #3 slide


I currently have the #3.5, and a 25 pilot. I also have 270, 260, 250, main jets. With 210's, and 220's on the way with the dowty washers. Will try everything when it arrives.

Since both carburetor types use the same main jets, I figured they would perform the same function. Larger numbers flowing more fuel, smaller numbers flowing less fuel. If a motor feels like it is running rich WOT (heavy being the term used in one of the NV manuals I have) try a smaller main. Simple, not rocket science.

Excuse the story about what I discovered in my old concentric carburetors. I did not mean to imply that 220 mains would work. I was just providing an example of a larger displacement engine that ran with leaner jetting. The 220's might not have been optimal and left in there when I decided to quit using the Amals. It was 30 years ago. A 250 was the recommended main jet size for a filtered 30mm Amal on my motor with the OEM dual exhaust. Unfiltered was 270. The 2 into 1 I was and still am using is a one off exhaust and it requires different tuning.

Good luck with your tune sean.

Where it is explained why concentric /monobloc jet size are diiferent ..........

and again same question about concentricvs monobloc

marinatlas said:

Replacing Amal Monobloc with Concentric?

I am replacing my 65 bonneville's Monobloc carbs with Concentric ones. I assume I should get the 930 replacement. My question is which main jets and needle jets should I use. The ones that come stock or should I change them out. Do the carbs come setup for single carb use? Thanks.

www.britbike.com

and again same question about concentricvs monobloc

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I agree that in theory the same bore of carb, and same motor/main/needle/slide/etc should result in the same outcome, but no recommendations for jet size are the same for monobloc vs concentric.

I also agree that recommendations seem to be a bit scattered, but monoblocs always seem to be recommended bigger jets than concentrics.

Why? No idea.

Also agree that 270 seems bananas-big for a 650cc twin carb'ed bike but that's the recommendation from several (including Burlen/Amal) and, again, don't know. Misprint leads to feedback loop?

I think the main reason is that fuel level in the float chamber compared to the bore is different. So a lower fuel level needs a bigger jet for same fuel flow.
Some other things in the design might also affect.

Many aspects in a carbs design will impact how much fuel any given jet size will pass IN THAT CARB TYPE.

There is no point in comparing jet sizes between different carb types at all IMO.

So, everything is now back onto the bike. It's running very very strong. Much better than it was before this whole process started.

I think that I can attribute the running issue to the hose that was going from banjo to banjo being too long, and most likely kinked. Another thing I noticed on disassembly was that one of the needles had a very slight bend to it. Re-reading through all the different books I have, all suggest that jetting should be 270. The "Super Tuning Amal Monoblocs" book also suggested that a bike set up with open megaphones needs to be run slightly richer if the intention is not to run only at WOT, and suggests raising the needle to the 4th notch. There is just a touch of black smoke through the exhaust when put onto revs. I think that in time, and once Ive gotten things properly up to temp I should be able to adjust this out with the pilot air screw. They are each exactly 1.5 turns out from full stop position, and it's already running super strong, so a small little adjustment should set it right.

I am just now about to take it out for a little road test, and hopefully won't get into too much trouble.

Hopefully you'll get it tuned without the not that helpful discussion about the same jet sizes in different carburetor bodies. I get it, some people have nothing better to do than twist and pick apart other's posts. Sad but it is the nature of the internet. Would be better if they actually tried to assist the individual asking for thoughts or help.

My point is and always has been simple; larger main jet numbers flow more fuel, smaller main jet numbers flow less fuel in the carburetor body the jets are installed in. Everybody knows that or at least they should? Find the right main jet and the right needle position for the needle and slide you are using and you'll be happy regardless of the carburetor body. Sounds like you think the main jet was right all along now that you have made some other corrections. You'll know once you get a load on the motor.

Schwany said:

Hopefully you'll get it tuned without the not that helpful discussion about the same jet sizes in different carburetor bodies. I get it, some people have nothing better to do than twist and pick apart other's posts. Sad but it is the nature of the internet. Would be better if they actually tried to assist the individual asking for thoughts or help.

My point is and always has been simple; larger main jet numbers flow more fuel, smaller main jet numbers flow less fuel in the carburetor body the jets are installed in. Everybody knows that or at least they should? Find the right main jet and the right needle position for the needle and slide you are using and you'll be happy regardless of the carburetor body. Sounds like you think the main jet was right all along now that you have made some other corrections. You'll know once you get a load on the motor.

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People were not picking apart another persons post AT ALL.

They were trying to prevent irrelevant comments about different carbs from muddying the waters.