Amal carbs and spark plugs issues and concerns

Lineslinger said:

Your question will generate a wide variety of opinions and results from different posters, none of which is "gospel" but much of the information helpful to consider.

My first time rebuilt Amals were all over the place while trying to achieve a consistent/balanced O2/fuel mix. I was really getting frustrated with my pursuit of a reliable setting. They continued jumping from lean to rich with plug color all over the place. I have a clue about carburation having worked with Holley's and Weber's and SU's and yada yada yada.
But the Amals were a unique configuration for me.

This forum helped me figure it out, and solve the issues of getting plugs and carbs "cooperating".
My 43 year old Amals were out of round/warped and leaks/mixture were consistently inconsistent.
I checked the cost of new carbs vs. rebuilt and or sleeved. The sleeve job was appx. half the cost of a new set of Amals but that was not my deciding influence as I wanted to keep the original carbs. So I tore them down, again, and sent them out for a sleeve job.

The results were profound. The sleeve job put them back on the level of consistent "breathing" and for all practical purposes regarding this set of carbs, these rebuilds compared to new. I added the Madass synch gantry and then sat in my shop and drank a bottle of wine in celebration.
Finally I was able to realize and lock in reliable and consistent results in both mix and burn results and keep them. I really have not touched the settings on them in a couple of years now, and glad of it.

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Thomasa said:

What Greg said in the post above!

Without radio-suppression-resistors (wires or plug caps) digital electronic ignitions will create their own radio interference confusing the little computer brain. Also abide the recommended plug gap because greater gap will produce higher voltage from the coils and contribute to their own self-interference. I have run pre-digital Boyers on various bikes with and without resistance with no problems. That said I've had all sorts of problems with digital electronic ignitions of various makes on customer's bikes that weren't set up correctly.

Since you have an E-start Norton and a Boyer of unknown age DO NOT attempt to start the bike with a low battery. It may/will kick back against the starter and flip the sprags over with disastrous results if the engine catches and runs. It will spin the starter up until it explodes.

There exists a needle-jet size 0.1065 between 106 and 107. I believe LAB can come up with a part number. I found that new 106 jets are too lean (I'm at 2400 ft. altitude) and the bike must run on the chokes way too long. And the pipes are blue. These are carbs that Mike Gaylord bored and sleeved which may have an effect on mixture. It ran fine on these carbs with worn 106 needle-jets but I gained about 10MPG with the jet change. Someday when it gets to the top of my priority list I'll put the worn jets back in or order some 1065 jets.

Check the banjo screens for crud and check any other fuel filters that may be fitted. Also stale petrol or petrol with ethanol that may have separated over time can contribute to bad running. Once it separates, I'm told you can't remix it.

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arcpoint said:

My Boyer was purchased and installed in Jan 2921. Most of the restoration was done that year and early 2022 so I'm reticent to redo all recent mods. The wires and plug caps are def not resistor based so for now I will keep using R type plugs. Boring the Amals and adding a gantry seems a smart and enticing route as I am most content with their capability to thrill me as long as I can keep them synced and tuned without needing some outside party to solve my issues.

One of the things I am already enjoying tremendously about my recent Norton acquisition is this forum. I will be touting the praises of this place and all you guys for a long while as it just doesn't get any better than this.

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marshg246 said:

But, a 30+ year old Boyer is not the same as a modern Boyer and you switched to a magneto a long time ago, so you must have had an analog Boyer. The digital Boyers are different, from the Boyer website:

"Why Do I Need To Use Suppressed Plug Caps?
MKIII and MKIV do not require suppressed plug caps for operation although we recommend using supressed 5000 ohm plug caps. Micro Digital and Micro Power units must be fitted with supressed plug caps. Plug caps fitted with suppression resistors are usually fitted to prevent radio interference. Radio interference (noise) can cause more complex electronic circuits like radios and computers to malfunction."

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ashman said:

I was running a Boyar EI in my Norton for over 30+ years running non resistor caps and wire core leads without any problems at all and the standard Champion N7YC plugs (my Norton never did like running NGK plugs), but these days am running a Joe Hunt magneto for even bigger spark, I still run the Champion N7YC plugs and wire core leads, but with the JH the plugs are set with less gap at 18thu.
Don't worry about what Al writes as he has never ridden a road going Commando and it's been 50 years since he has ridden a bike on the road.
The stock Amal needles work fine, but depends on the mileage I always replace needles and jet every 3 or 4 years as vibrations through the manifolds wear the jets oval over time, Amal rebuilt kits are cheap maintenance.
As mentioned the pick-up wires that come out of the points housing can break inside the insulation and cause problems, I never had this problem, but others have.
Well set up Amals the Norton runs so well with them, they are a simple carb to work on and maintain.

Ashley

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baz said:

Not to long ago Al claimed that he "had" ridden a standard commando
I was quite surprised by this as he'd always said he'd never ridden one!!

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Mart UK said:

I have a 2014 Boyer. I think a mkIV? It's fine. No complaints. Battery is always on a tender in my garage.

Non-resistor Champions. If I have resister leads, they don't do much, as I have to borrow an expensive multi-meter if I want to check running voltage. My cheap meter gets too much noise for a steady reading. Bike runs well though. Also, not noticed anyone looking up from their phone because I've interrupted their Internet connection

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arcpoint said:

What about my current nearly new electronic Boyer? It seems everyone has tons of experience with the old analogue ones but not the new digital ones, I presume because you all went over to the trispark camp or the JHunt magneto realm.

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Mart UK said:

You've not mentioned if you're running a stock airbox?

First ride on mine, I forgot to turn my choke off. Plugs sooted up and died. Never got it to run right until I replaced the plugs. Now the choke goes off immediately and I hold it on the throttle.

If it were me, before big expense on the carbs, I'd stick to some cheaper basics first:
- Give the carbs another look, make sure the choke is fully off and maybe blow through the hidden passages (even though it's idling fine). Could simply be the needle is not in the right position.
- Check fuel flow from your tank. We've seen blocked breather holes and blocked petcocks / filters.
- Try N7YC plugs, instead of the 9s.
- Make sure the battery is good.
- Definitely new fuel, especially if it has any ethanol, but pure can go stale, especially if you've had any winter condensation in your tank.

Then give it another go and let us know?

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baz said:

Not to long ago Al claimed that he "had" ridden a standard commando
I was quite surprised by this as he'd always said he'd never ridden one!!

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arcpoint said:

Hi newbie Mk3 owner here. Purchased mostly reconditioned bike and have only put 50-60 miles on it. Starts and idles magnificently. Ran beautifully at 1st, strong hard pull, but weak on the top end. Then started missing on mid to upper range 2nd gear on and gurgle almost popping on rapid decel. So I cleaned and gapped the plugs. Which for some strange reason are Champion RN9YC. Not sure if PO did that because of the colder climes where he lives (Indiana). I'm in Socal.

Back when this bike was built In had my 1st real bike (aside from a Rupp minibike when I was a kid). I built out a Yamaha xs 650 to some pretty cool specs and had a lot of fun with it. Did all the basic tuning on twin 34 mm Mikunis myself with a few screwdrivers.

So my questions are this. Can I similarly adjust these rebuilt original Amals to solve my issues or do I need to take them off and go batsh*t crazy to get and keep them performing well? Secondly, since I have resistor plugs that run hot with wide gaps, what would be an optimum swap out for me here in sunny CA?

As much as the wife will be on my case of I keep spending on this girl (gotta make her my own you know) should I just throw in the towel and throw down on a couple of Keihin fllatsides so I can have some peace of mind and better top end?

Please talk to me as if a 5th grader as the NASA science equations can tend to hurt my head sometimes.

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Mart UK said:

Stock airbox, do you know if your carbs are still in standard spec, as per the manual, including which needle groove the c-clips are in?

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baz said:

Just a thought
You do know which way the choke lever works on a British bike?
IE tight cable is off
Slack cable is on

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htown16 said:

Speaking from personal experience on 3 bikes you do not need resistor plugs or wires with the common Pazon Surefire analogue system. I have no experience with the other Pazon products but I believe some resistance is required with the digital ones. On the other hand at some point I switched to the NGK BPR8 plugs because they were easier to obtain and the bikes ran just the same as with the non-resistor version of the same plug. The sky is falling mentallity about NGK stopping production of non resistor plugs reminds me of the broha about valve seats when lead was removed from gasoline. Believe me the planet is a far better place without the continued production of lead.

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arcpoint said:

Holy crimini, are you serious? Was I running with the choke on? This changes everything. Also, I think the carbs are all spec per the manual as the guy who did the resto did nearly everything to original, when and where possible, although he did include a book on tuning to Dunstall specs, so... ???

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