New Norton Owner; tuning questions

Good picture Lab.

Basically, unless I am mistaken (again) that choke slide only has any actual impact when protruding from the bottom of the slide like that.

I presume Maylar’s must be too, hence it does work for him.

But many folk do claim things like ‘ just a touch of choke’ etc. But we can see from the pic that is nonsense.

concours said:

The PARTIAL CHOKE (1/2 choke) position will do nothing at idle, but, as you get underway, and use more throttle, the slide reaches (and then goes higher than) the choke level, and then the mixture richening effect is very real.
So, unlike a butterfly choke, it can be used to richen the midrange (needle) and top (main) only as well.
I have used it to “acid test” suspected weak(lean) mixture.

Also, if your ever out on the road, and it turns off, say, 0F.... it will help.

As illustrated in LAB’s post, the TINYEST amount of pull back from full choke will give some variability.

Click to expand...

Also the photo is showing the cutaway side of the slide
A number 3 in this instance
If you viewed it from the engine side the slide would be almost shut at idle
I'm not disputing that the choke dosent work
I just find it hard to believe it affects idle if the choke isn't fully on
But however anyone starts their bike it's fine with me
The thing I don't like is bikes that are set up so bloody rich
I've often seen them/ smelt them at bike events usually trailer queen's that just don't run properly
Personally I've never used choke slides on any twin carb Amal equipt bikes
I have however used a choke slide on my old iron head thunder bird also a tr7 and a plunger A10 all these bikes (single carb) benifitted from the choke slide

baz said:

Also the photo is showing the cutaway side of the slide
A number 3 in this instance
If you viewed it from the engine side the slide would be almost shut at idle

Click to expand...

Yes, but when starting from cold the slides wouldn't normally be in the fully closed position as shown in my photo.

One look at LAB's picture of the choke down tells me that the choke should work at idle to richen the mixture since the vacuum is applied by the intake. Wouldn't closing off the air opening partially, naturally make the vacuum pull greater on the fuel?..

I don't use the chokes ever myself, so I don't have a personal data point of reference to form an opinion, but it seems like they should have some effect

L.A.B. said:

Yes, but when starting from cold the slides wouldn't normally be in the fully closed position as shown in my photo.

Click to expand...

The point I was making was when the bike was at idle
Not when it was being started

Not a true update with good information, but I wanted to let you guys know the current state.

I fitted the exhaust with new seals this evening and it appears there are no more leaks, so that's good. I started the bike up (no air filter, 17 pilot, 106 needle jet, 240 main) and it fired right up with the chokes DOWN. I started pulling them up and the bike ran progressively worse until it shut off. Trying my best to fix this right, I figured the only explanation was it was running particularly lean and raising the chokes basically killed any fuel flow I had and made it leaner; shutting the bike off.

So off came the carbs. Cleaned them with carb cleaner and compressed air through all passages, installed 19 pilot jet and 260 main. I also confirmed I have the half circle spray tubes, which I think is correct? I also reset the fuel level as I believe I was way too low previously. It's hitting within spec at .17-.24" from the top of the bowl (using a hose from the drain plug.) I re-installed the carbs WITH the air filter this time.

It was about 9pm so I quit for the night with hope that tomorrow brings better results.

I doubt it will effect things for you this time, but as a general rule, when you’re changing things in order to experiment it really is good practice to only change one thing at a time. Otherwise you don’t know what caused which effect and you’ll continue chasing your tail!

adunham1 said:

Not a true update with good information, but I wanted to let you guys know the current state.

I fitted the exhaust with new seals this evening and it appears there are no more leaks, so that's good. I started the bike up (no air filter, 17 pilot, 106 needle jet, 240 main) and it fired right up with the chokes DOWN. I started pulling them up and the bike ran progressively worse until it shut off. Trying my best to fix this right, I figured the only explanation was it was running particularly lean and raising the chokes basically killed any fuel flow I had and made it leaner; shutting the bike off.

So off came the carbs. Cleaned them with carb cleaner and compressed air through all passages, installed 19 pilot jet and 260 main. I also confirmed I have the half circle spray tubes, which I think is correct? I also reset the fuel level as I believe I was way too low previously. It's hitting within spec at .17-.24" from the top of the bowl (using a hose from the drain plug.) I re-installed the carbs WITH the air filter this time.

It was about 9pm so I quit for the night with hope that tomorrow brings better results.

Click to expand...

If you have the notched spray tube you must use the 4 ring needles
Incase you don't know there are rings engraved above the adjustment grooves on the needle
If your needle has two rings it's for a square top spray tube
Cheers

If I understand correctly, you said it started right up/ran OK with the enricher ('choke') slide all the way down and then, as you pulled the enricher slide up, the engine faltered/quit. If the engine was cold at the time, that would be essentially normal. Are you saying that out on the road/engine warm the same thing was happening, that the bike ran OK unless the enricher slides were down?

MexicoMike, the last running I did was BEFORE making those changes listed above. The air filter was off, 17 pilot, 240 main, etc. But otherwise, yes that is correct. The bike had only been running 4 minutes or so, so it was warm but certainly not hot. Do I need to wait longer before attempting to raise the chokes?

I am going to double check the needles this morning as Baz suggested, then attempt to start it again with the changes listed above.

FastEddie, for sure you are correct. I have been a bit of a mess with changing things, which makes me extra appreciative of everyones patience here. I have started making a log of my changes and how they affect running now.

Mine likes the chokes fully on for low speed running until it has run for quite awhile, maybe 5 minutes of running on the road at a 50-60 mph. It could be even longer if warming up at idle, I never do that, just ride off.
It will run without chokes when cold by keeping revs up, but hiccups on acceleration and won't hold an idle , you must blip the throttle. The chokes smoothen all of that out.
As soon as it is warm, I pull the chokes off completely. After that it runs and idles nicely without chokes.
Although every bike is a bit different, I consider the need to have the chokes on when running cold to be normal for this bike.
It doesn't really need the chokes for cold starting, the ticklers take care of that.
I use the chokes anyway for cold starting as they are needed immediately for cold idle and pull away.
Once the bike is warm it won't rev out with the chokes dropped.

Glen

Well... it's the... GREAT UPDATE!

Ah FINALLY the bike is running well! Chokes up and she pulls like a train, revs strong over 6k, and is a real pleasure to ride. I totally get the Norton desire versus Triumph or BSA.

After checking the needles for the 4 rings (they were correct) I rolled it outside and hooked up the external fuel tank. I left the chokes on for initial start after tickling and it started up second kick. Not bad. I let it warm up a bit and apprehensively pulled the chokes up. To my surprise, the bike picked up idle a bit. I revved it and there was no backfiring! I knew right then and there things were on the up. Popped the tank on and realized I needed some gas. Perfect time for a test ride! The station is only about 5 miles away, so I figured it was fairly safe. As soon as I took off, I knew it was running better and pulling stronger. I was behind some slow cars so that was a bit agonizing but on the way back, I found some open road and gave it a good twist. Very smooth and strong power up to about 75 mph before I chickened out. The plugs look quite lean (oddly enough!), so I'm going to put one step cooler plug in and see where it goes from there.

Anyway, I just wanted to say a HUGE thank you to everyone! I am so thrilled for the bike to be running well and you all helped me so much. What a great community.

I like happy endings.
A couple of points.
I would tune it with the correct, stock heat range plug.
Sync the carbs.
Reinstall air filter.
Fine tune air screw and idle
Ride the snot out of it.

Hm. Interestingly enough, the NGK BP7ES shows to be the equivalent to the Champion N7Y plug. The NGK is what I have fitted and it looks like the plug is brand new after taking it for a ride. Almost no signs of wear at all. I feel like it is running lean, along with the slight popping on deceleration. I was planning on going to a NGK BP8ES. I’m not sure how else I can richen the mixture up. I guess I could turn the air screw in? Is that the correct direction to richen the mixture?

This is with the following settings:
19 pilot jet
260 main jet
3.5 cutaway
106 needle jet
Notched spray tube with 4 ring needle
Air Filter installed
I believe open mufflers

adunham1 said:

Hm... I guess I could turn the air screw in? Is that the correct direction to richen the mixture?

This is with the following settings:
19 pilot jet
260 main jet
3.5 cutaway
106 needle jet
Notched spray tube with 4 ring needle
Air Filter installed
I believe open mufflers

Click to expand...

Yes, turn it in = less air = richer.
Once engine has fully warmed. Turn in 1/2 turn at a time, till stumble, then back out to reach max rpm, then 1/4 turn to fine tune. Each carb.
Readjust idle equally.

Air screw should be between 1 - 2 1/2 turns = pilot jet correct.
If less than 1 turn = need larger pilot jet.
If more than 2 1/2 = need smaller pilot.

"

I've been using NGK BP7ES plugs the entire time. Several sets; "

Well, lookon the bright side . Your not going to need any more plugs for a while , anyway .

adunham1 said:

Well... it's the... GREAT UPDATE!

Ah FINALLY the bike is running well! Chokes up and she pulls like a train, revs strong over 6k, and is a real pleasure to ride. I totally get the Norton desire versus Triumph or BSA.

After checking the needles for the 4 rings (they were correct) I rolled it outside and hooked up the external fuel tank. I left the chokes on for initial start after tickling and it started up second kick. Not bad. I let it warm up a bit and apprehensively pulled the chokes up. To my surprise, the bike picked up idle a bit. I revved it and there was no backfiring! I knew right then and there things were on the up. Popped the tank on and realized I needed some gas. Perfect time for a test ride! The station is only about 5 miles away, so I figured it was fairly safe. As soon as I took off, I knew it was running better and pulling stronger. I was behind some slow cars so that was a bit agonizing but on the way back, I found some open road and gave it a good twist. Very smooth and strong power up to about 75 mph before I chickened out. The plugs look quite lean (oddly enough!), so I'm going to put one step cooler plug in and see where it goes from there.

Anyway, I just wanted to say a HUGE thank you to everyone! I am so thrilled for the bike to be running well and you all helped me so much. What a great community.

Click to expand...

Brilliant news
I'd stick with the bp7es if I were you and spend a bit of time syncing the carbs,a vacuum gage is good here also cable tie the carburettor junction box to the frame
Get the carbs balanced at idle
And then throughout the rev range paying particular attention to the balance of the throttle slides as they lift off of the idle adjustment screws
The commando is a better riders bike than the equivalent triumph or BSA twin if set up properly and easily holds its own in modern traffic
75mph isn't fast enough btw
Enjoy your your bike

As Baz said, "Stick with the recommended plugs and settings". Norton got that right. Unless you've increased the compression, you don't need a cooler plug. Don't over think it. If the recommended settings were wrong for a stock bike, believe me, this crowd would let you know....

As for richening the mixture, The idle enrichment screw doesn't do that! It only enriches the idle circuit which has a changing effect that diminishes as you raise the throttle. The thing adjusting the idle mixture screw does is change the A/F ratio of the idle circuit... (if you needed a richer mixture across the range you would be changing needle height, or needle jet size or cutaway size, and main jet size... a lot of stuff)

SO,... IF your idle screw has a 3/4 turn range where the bike idles OK. When you go too far in it stumbles, and you go too far out it stumbles, but everywhere in the middle of those 2 positions the bike idles pretty similarly... What your adjustment should NOT be, is to just place the screw in the mid point between the stumbling points and leave it... and here's why.

Once you find those stumbling points at idle, you've determined the rich and lean limits of the bike's idle circuit. If there was no other factors to add to that, then the mid point would be the optimum A/F ratio, but there is another factor. When you lift the slides to accelerate, a new element is added to the A/F ratio, which is the cutaway size of the inner body, the needle and the needle jet. IF the new element, has a tendency to temporarily pull the A/F ratio in one direction, then you want to counter that effect slightly with the idle air screw setting to try to keep the A/F ratio from getting too close to the "too lean" or "too rich" stumbling points. That might be hard to understand so read it again...

The technique is to find that center of the stumbling points at idle, then gently lift and lower the throttle from idle to 2000 rpms, adjusting each idle air screw to try and smooth out the transition to 2000. Once you get it set, you're bike will never cough and die as you take off at a traffic light with people behind you.... (one of the worst things on a kickstart bike)

Anyway, hopefully it makes sense to you what I'm saying here. Which is that the idle screw adjustment range is wide at idle, and the tuning to the idle circuit is done to it to make the A/F ratio optimized during the transition from the idle circuit alone to the next element of the carburation combining with it.

Thanks guys, very good information here as always. Baz, you're right. I will stick with the BP7ES plugs and try to sort out the mixture. Kinda silly to mask any issue rather than just fix it. I've had the seat, tank, and carbs off a hundred times now... what's another fifty?! I got the carbs sync'd fairly well by ear with the slides, but obviously that's a far cry from a good vacuum balance. I'll try that tomorrow; it should be pretty straight forward. I've got a Motion Pro tool.

oOnortonOo (that took me a bit to figure out how to type it correctly!) Thank you for such a detailed response and walk through the process. I had been finding the rich limit and backing off just a bit and leaving it there. Do you recommend pulling the plug wire on the side you're NOT working on, to help make things easier? I assume you're looking for a very linear throttle response from idle to 2,000?

Also, IIRC when I checked the compression (cold) I got around 170. This seems higher than usual... is it?

Currently I'm planning to sync the carbs and see how the plugs turn out. If still lean, I'll get one size larger pilot and a 2.5 slide. Looks like the next size pilot is 21.

Well, I've replaced the plugs with some Autolite AP64's and the bike runs better. The idle is very, very nice. I could fall asleep to such a nice sound. I still believe it is running lean as the exhaust is still popping a good amount. Here are a few photos of the AP64's.