Time to bury the Amals?

Stillreel · Sep 19, 2013

After a year of frustration revolving around fouling plugs, I'm now ready to ditch the Amals and put in the single carb PWK from JS Motorsport:

http://www.jsmotorsport.com/technical_SingleCarb.asp

As much as I would like to keep it stock, I'm hoping the PWK will resolve this irritating issue that currently persists after less than 50 miles. I replaced the jets, thoroughly cleaned out the carb and ports but still, lousy running after 50 miles and I have to stop and put clean plugs in. It starts on the 1st kick but I can't keep it running smoothly.

So, in order to preserve my sanity and extend my life, the Mikuni is going in.

But! Before I throw more cash into the bottomless vacuum that the Norton has become, is there any other explanation for plug fouling? I've got a new Boyer ignition in it. Stock cam. Could this be a mechanical timing issue? Could this be anything else but carb related?

Thanks

750 Commando 71
650 TR6P 68

BC

rvich · Sep 19, 2013

Have you considered buying new Amals?

I actually find them to be easy to work on, but maybe it is just because I have done it so much that I am reluctant to move to a different carb!

Russ

Unclviny · Sep 19, 2013

There are 2 major-things with Amals that confound folks:
1. they fight old, worn out carbs that will NEVER work properly
2. they WAY overtighten them, warping the bodies.

Vince

mikegray660 · Sep 19, 2013

the PWK is not a mikuni - small point but different carbs - havinf said that i've ran both PWK and Mikunis and they are both excellent carbs, the mikunis are just more tune'able

Stillreel · Sep 19, 2013

Yes, thanks. PMK looks like the option for me. I ope it works.

BC

worntorn · Sep 19, 2013

Dont know about PWKs but I have Mikunis on two bikes, Amal concentric on five. The one I ride the most had worn out Concentrics on it and was starting to run very poorly, down in power at all but full throttle and getting lousy fuel mileage. I put new Amal Premieres (from Jerry) on it and it is now the best runner of the bunch. I just did a round trip of 800 miles with the new carbs on, averaged 57 mpg Imperial loaded two up plus gear. Lugging power in 4th is back to what it should be.
The old carbs were fine for a long time, but once they reach a certain point in wear, things deteriorate rather quickly.

Glen

pete.v · Sep 19, 2013

You'll like the single 34 from Jim.

I got new 32 Premiers this spring. They were very very good, just not as good as the single 40mm pumper. I am getting up the courage to sell them. It's not easy to let things go but as you say, I need to be realistic.

The mag didn't pan out either. Surefire is awesome.

concours · Sep 19, 2013

pete.v said:
You'll like the single 34 from Jim.

I got new 32 Premiers this spring. They were very very good, just not as good as the single 40mm pumper. I am getting up the courage to sell them. It's not easy to let things go but as you say, I need to be realistic.

The mag didn't pan out either. Surefire is awesome.

Tell us about the magneto....

Nortiboy · Sep 19, 2013

Stillreel said:
After a year of frustration revolving around fouling plugs, I'm now ready to ditch the Amals

I have 30mm Amals on a MKV 750. You can hear the slides clacking in the bores. Worn out. It starts, idles and runs perfectly. Had similar problems to you. Swapped the old boyer for a Trispark about 7 years ago. Standard 12v coils in parallel. Never a problem since. Plugs are dry and black around town and clean after the freeway.

Amals are so easy to tune, I wonder if its something else. 1/4 of a turn on the idle mixture screw makes a lot of difference.

DogT · Sep 19, 2013

My Amals have always been fine, even when they were worn out at 13K miles, only problem then is idle, otherwise they ran fine. Got anodized slides and that fixed about 90% of the problem. I should have either had them sleeved or bought new premiere. No reason the Amals should make it foul unless jetting is wrong or worn. Just my opinion. For me it was if it ain't broke that much, why change. I always seem to have issues when going after market.

Dave
69S

Unclviny · Sep 19, 2013

The one concession I am making on this new-build is to rubber-mount the Concentrics, for 2 reasons:
1. to isolate them from vibes and
2. because Commando's seem to REALLY like added intake-length.

I found the manifold-bits sitting on a shelf and I am cutting the hanger-piece out of heavy rubber.

Vince

worntorn · Sep 19, 2013

With the longer inlet tract, is the extra power on top or thru the range? Isee the long inlet used on Norton race engines, but they often have traded away some grunt for a top end powerband. I'm familiar with one bike in England that has extremely long inlets, it takes forever and a day to make power, but eventually does.
I've always thought that the really short inlet on the Norton engine gave great throttle response and loads of midrange power,which the Commando has in bucketloads, particularly the 850.
I'm all for more power on top, but not at the expense of the rest of the range. If adding length to the inlet tract made a more powerful engine for the road, wouldn't Norton have just added a couple of inches at the factory? It would be a no cost item.

Glen

pete.v · Sep 19, 2013

concours said:
pete.v said:

You'll like the single 34 from Jim.

I got new 32 Premiers this spring. They were very very good, just not as good as the single 40mm pumper. I am getting up the courage to sell them. It's not easy to let things go but as you say, I need to be realistic.

The mag didn't pan out either. Surefire is awesome.

Click to expand...

Tell us about the magneto....

Just to reiterate so I can sneak something else in here, there was and is nothing wrong with the Premiers. It is relative to my particular machine where the carb system that i use is rather proprietary, not that it wouldn't work with others. Again, the Amals are good.

concours, I just could not get the mag to go well over 4000rpm and above. Some say it maybe the condenser but after checking it with the capacitance meter and talking with the people at Joe Hunt to get the right specs, it "appears" to check out. I will send it back to JS so he can bench test it upon his suggestion. There is too much of an emotional commitment to give up on it. Trust me, I have tried all I can think of not excluding cam timing triple check. Many different plug and point gaps from what is suggested.
Thanks all for the indulgence for the highjack. Anyone wanting more info, please PM me and I will surely respond.

Unclviny · Sep 19, 2013

worntorn said:
With the longer inlet tract, is the extra power on top or thru the range? Isee the long inlet used on Norton race engines, but they often have traded away some grunt for a top end powerband. I'm familiar with one bike in England that has extremely long inlets, it takes forever and a day to make power, but eventually does.
I've always thought that the really short inlet on the Norton engine gave great throttle response and loads of midrange power,which the Commando has in bucketloads, particularly the 850.
I'm all for more power on top, but not at the expense of the rest of the range. If adding length to the inlet tract made a more powerful engine for the road, wouldn't Norton have just added a couple of inches at the factory? It would be a no cost item.

Glen

It's top-end power at the expense of a little low-end but I think the Commando can spare it, no problem.
Adding intake length would have cost a fortune in redesigning or relocating the "ham can", the battery and/or the oil tank.

Vince

ML · Sep 19, 2013

Stillreel said:
After a year of frustration revolving around fouling plugs, I'm now ready to ditch the Amals and put in the single carb PWK from JS Motorsport:

I replaced the jets, thoroughly cleaned out the carb and ports but still, lousy running after 50 miles and I have to stop and put clean plugs in. It starts on the 1st kick but I can't keep it running smoothly.

Could this be anything else but carb related?
BC

Looks like the needle and needle jet is worn and the float levels way to high or float needle / seat leaking. The new Premiers are a very nice carb.

X-file · Sep 19, 2013

Unclviny said:
It's top-end power at the expense of a little low-end but I think the Commando can spare it, no problem.
Adding intake length would have cost a fortune in redesigning or relocating the "ham can", the battery and/or the oil tank.

If I wanted stump-pulling torque at 3000 rpm,I'd use a 30" intake (from valve to bell-mouth).Longer is always better at low rpm.
I've used 14" on a Bonneville,and it pulled OK to 7,800 rpm in top.Later on,I went to 16" to make it a little more torquey in the mid-range.
Some interesting reading http://www.emeraldm3d.com/articles/emr-adj-length-intake/

beng · Sep 19, 2013

My 850 Commando had 30K on it with the original concentrics. They were beat to hell, the screws would back out and I even had a float bowl fall off on a long ride and dump all my gas on the ground. I was always able to put the screws back in and adjust them to run just fine.

My old 61' Manxman is still running fine for it's new owner too, on it's original Amals also with tens of thousands of miles on them.

Some people ride vintage bikes because they are actually interested in them and their history, and they will have fun preserving that history.

These days it seems most people are not interested in what they can do for a vintage bike, but what it can do for them. They really don't want a vintage bike, they want the vintage name and look, but they don't want the vintage experience like the riders had back in the 50s-70s having to have some mechanical ability and having to work on the bike an hour for every two they ride it.

When you pose with your British bike that has been "fixed" with modern carbs and computerized ignition and whatever else it might be interesting to other posers, but I will be talking to the guy that has the brains and skill to keep that old bike going with it's original spec parts, the one who is getting a real vintage riding experience and cares about and has preserved a bit of history in more than one way.

JimC · Sep 19, 2013

beng said:
My 850 Commando had 30K on it with the original concentrics. They were beat to hell, the screws would back out and I even had a float bowl fall off on a long ride and dump all my gas on the ground. I was always able to put the screws back in and adjust them to run just fine.

My old 61' Manxman is still running fine for it's new owner too, on it's original Amals also with tens of thousands of miles on them.

Some people ride vintage bikes because they are actually interested in them and their history, and they will have fun preserving that history.

These days it seems most people are not interested in what they can do for a vintage bike, but what it can do for them. They really don't want a vintage bike, they want the vintage name and look, but they don't want the vintage experience like the riders had back in the 50s-70s having to have some mechanical ability and having to work on the bike an hour for every two they ride it.

When you pose with your British bike that has been "fixed" with modern carbs and computerized ignition and whatever else it might be interesting to other posers, but I will be talking to the guy that has the brains and skill to keep that old bike going with it's original spec parts, the one who is getting a real vintage riding experience and cares about and has preserved a bit of history in more than one way.

I, too, like the vintage aspect. It just isn't too practical for some Norton owners. For more than a few, their Commandos are daily riders. Ethanol spiked gas has rendered the fiberglass tank useless. The original front disc brake on the 72 and up Commandos was very poor, to be generous. The sizing of the master cylinder bore was way off the mark. Pogoing off a dropped brake pedal wasn't fun. Two piece rear axles should have never been made. The many upgrades and fixes discussed here are pretty desirable if you want to turn your Commando into a reliable, safe, daily rider.

Stock vintage bikes remind me of the old joke about Harleys: 98% of the Harleys sold are still on the road, the other 2% made it home.

Mark F · Sep 20, 2013

What sort of air cleaners are you running? You might not be getting enough air.
Are they clean?

mikie3117 · Sep 20, 2013

I am one of those who enjoy making the Commando the bike that should have been. The upgrades are all functional and keep the bike on the pavement with wheels turning vice sitting on the side of the road.i have more memories of pushing my 1972 combat roadster than riding it back in the day. Wiring up a new system with Modern electronics is nice and a layshaft roller bearing replace mandatory in my shop.i wish that more of the "mods" would have been available in 1972 but as an E-2 in the USN, I could never have afforder them.
Mike

Time to bury the Amals?

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