Any other ideas...

Danno · Dec 20, 2019

Fast Eddie said:
Another long shot... Iridium plugs with their tiny electrodes are supposed to revisit fouling. They will still foul if things are bad enough, but they do resist fouling much better.

How are your air screws? Does turning them in / out little at a time make much difference to how the motor runs or sounds? How many turns out from fully home are they?

The N4G plugs were the forerunners of Iridiums and have a similar wire center electrode made of gold rather than iridium. Same sort of resistance to fouling. I personally think the "Gold Palladiums" as they were called, are a bit better.

Lineslinger · Dec 20, 2019

I gave you guys some incorrect info. I originally removed 220 mains and replaced them with 260's for my crossover pipes.
Sorry senior moment.
I am still thinking that my riding does not make the transition from the idle circuit into the mains very often. I have been considering my riding over the end of the summer and the fall and I do a lot of sitting at stoplights and not a lot of airing it out.
Could it be as simple as a notch adjustment on the needle?

Lineslinger · Dec 20, 2019

o0norton0o said:
I've got 2 things...

1) you have 220 mains on an 850, when the recommended mains are 260... and still you are too rich. That makes Zero sense to me and is a red flag. My guess is that possibly you have the wrong slide cutaway size too, or the wrong needles and yet you've somehow adjusted the bike to run well enough until the marginally workable AF ratio eventually fouls your plug and you're toast... Norton got the carb specifications right. Slight deviation in spec's can be attributed to slide wear or needle jet wear, but non specified parts like a 220 main in an 850 sounds like you have the wrong parts in the bike.

2) You've lost magnetism in your rotor, and maybe you use a battery tender when your bike is parked. So,... you go out with a strong battery charge (and and strong spark) and as your ride along your voltage drops and your spark gets weaker and weaker. Weak spark causes poor combustion, and eventually a fouled plug.... If you had an ammeter mounted you would see the direction of flow between your alternator and your battery, which makes it easy to see when this situation appears.

That is a good thought. I do use a tender every day. Magnetism does begin to deteriorate at or around 40+ years.

Danno · Dec 20, 2019

260s may be a bit large for non-crossover pipes. Seems like the problem is lower in the range. If you bump up the advance, you may have to set the idle speed back down a smidge via the slide stops. Normal practice is to lean out the idle with the air screw until it falls on it's face and then richen it back up a hair until it stabilizes. If advancing the spark doesn't work, you could try dropping the needle, but I think power will suffer when you do.

Fast Eddie · Dec 20, 2019

Lineslinger said:
I gave you guys some incorrect info. I originally removed 220 mains and replaced them with 260's. Sorry senior moment.
I am still thinking that my riding does not make the transition from the idle circuit into the mains very often. I have been considering my riding over the end of the summer and the fall and I do a lot of sitting at stoplights and not a lot of airing it out.
Could it be as simple as a notch adjustment on the needle?

The ‘just off idle’ fuelling is primarily controlled by the slide cut away. It would help the diagnosis if you could tell us what number the slide is. You say you replaced like for like... but like for like what?

Lineslinger · Dec 20, 2019

Fast Eddie said:
The ‘just off idle’ fuelling is primarily controlled by the slide cut away. It would help the diagnosis if you could tell us what number the slide is. You say you replaced like for like... but like for like what?

The replacement slides were 3's or 3.5's.
I need to get out to the shop and look at my records but I did match the new to the old size wise.

MichaelB · Dec 20, 2019

Stock is 3.5 slide, notched spray tube with a 4 ring needle. The rings are at the very top above the clip rings.

Lineslinger · Dec 20, 2019

The slides are the hardened 3.0's.
I am going to pull the then break them down and check the needles. I usually take comprehensive photos but I didn't get any showing the circlip position on the needle.
Thank you all, gotta hit the sack, going duck hunting in the morning and have the grand rug rats the rest of the day.
I WILL follow through, take some photos and offer more detailed info on carb settings.
Thanks again.

Torontonian · Dec 20, 2019

Lineslinger said:
That is a good thought. I do use a tender every day. Magnetism does begin to deteriorate at or around 40+ years.

Buy a new rotor and fit it to the crank end. Buy a new battery and drop it into the tray. Clean up the fuse connections and any other pertinent ones to ignition. Sounds like you have done enough with refreshing the carbs.

Lineslinger · Dec 20, 2019

Torontonian said:
Buy a new rotor and fit it to the crank end. Buy a new battery and drop it into the tray. Clean up the fuse connections and any other pertinent ones to ignition. Sounds like you have done enough with refreshing the carbs.

Looking hard at the new rotor, great timing, right at Xmas.

comnoz · Dec 20, 2019

Lineslinger said:
I know, its driving me nuts!
I run 93 Octane fuel and yes it is Ethanol.
First step switch back to NGK's. Next step drop the needles down a notch and see what that produces.
Then on to the jets if results dictate....

As rich as it looks I might guess you need to go a step smaller on the needle jet. IE, drop from a 106 to a 105. That is going to have the largest effect on the normal riding range.

The main jet is only going to make a difference over 3/4 throttle and it sounds like your idle and off idle are probably OK.

So work on the needle and needle jet. One notch on the needle position is not going to be a large enough change. Jim

PS, I take it the needle jet has been renewed. They wear out quickly.
8000 miles will make a 105 into a 106.

MexicoMike · Dec 21, 2019

Is it possible your enrichers (if you have them in the carbs) are not fully withdrawn in normal operation?

I had an overly rich mixture that I couldn't seem to get rid of which went completely away when I installed velocity stacks on the carbs/no filters. I am not suggesting you do that but look closely at the filtering to be sure it is not causing this. That's why I suggested running without the air filter for some miles to see how the plugs look.

As others have noted, the main jets have virtually nothing to do with the problem in the speed/load ranges you have mentioned. The slide could be related since the 3 is richer than the OEM 3.5.

The reality is that the bike SHOULD run correctly with the stock carb setup - needle jets/needles/idle screw settings, etc. Sure, it can be tweaked as each engine is slightly different but the stock setup is the place to start.

dave M · Dec 21, 2019

Buy a pair of new Amal Premiers, the carb bodies wear particularly badly on Commandos because of the amount the engine moves in the isolastics. Even though you’ve replaced all the wearing parts your carb body will still have wear and likely not meter the mixture accurately.

acadian · Dec 21, 2019

Needle jets are the most overlooked and wearable item in the carb, Amal sells both 105 and 104.5 sizes, as Mexico mentioned, check the filter condition as well.

Lineslinger · Dec 21, 2019

comnoz said:
As rich as it looks I might guess you need to go a step smaller on the needle jet. IE, drop from a 106 to a 105. That is going to have the largest effect on the normal riding range.

The main jet is only going to make a difference over 3/4 throttle and it sounds like your idle and off idle are probably OK.

So work on the needle and needle jet. One notch on the needle position is not going to be a large enough change. Jim

PS, I take it the needle jet has been renewed. They wear out quickly.
8000 miles will make a 105 into a 106.

New needles and needle jets installed in late August of 2019...thats where I am going first to reset the circlip, new needle are 4 groove, along with a new rotor, even though the existing one passed the screwdriver test.
Thanks for the advice on the needle groove change and its influence.

Lineslinger · Dec 21, 2019

MexicoMike said:
Is it possible your enrichers (if you have them in the carbs) are not fully withdrawn in normal operation?

I had an overly rich mixture that I couldn't seem to get rid of which went completely away when I installed velocity stacks on the carbs/no filters. I am not suggesting you do that but look closely at the filtering to be sure it is not causing this. That's why I suggested running without the air filter for some miles to see how the plugs look.

As others have noted, the main jets have virtually nothing to do with the problem in the speed/load ranges you have mentioned. The slide could be related since the 3 is richer than the OEM 3.5.

The reality is that the bike SHOULD run correctly with the stock carb setup - needle jets/needles/idle screw settings, etc. Sure, it can be tweaked as each engine is slightly different but the stock setup is the place to start.

Thanks Mike. I'll give it an a try.

maylar · Dec 21, 2019

If a lot of your riding is at low throttle, the slide cutaway has the most influence there.

o0norton0o · Dec 21, 2019

How about you stop placing the bike on the battery tender and see if the plugs foul out faster, or the bike doesn't start easily without topping off the battery. Buying a new rotor might be a waste of money if the battery is just old and sulfated, or has a bad cell.

Also add an extra ground from the engine to the frame. Isolastically mounted engines need a good ground, so 2 good grounds makes sure of that. (which helps give a good spark)

maylar · Dec 22, 2019

From http://commons.princeton.edu/63-tiger-cub/wp-content/uploads/sites/81/2018/08/amalbritbike.pdf

Your #3 slide is too rich.

ludwig · Dec 23, 2019

Try a lower float level.

Any other ideas...

Danno

Lineslinger

Lineslinger

Danno

Fast Eddie

Lineslinger

MichaelB

"Sons of Arthritus"

Lineslinger

Torontonian

Lineslinger

comnoz

MexicoMike

dave M

acadian

Lineslinger

Lineslinger

maylar

o0norton0o

maylar

ludwig

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