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Originally Posted by Kommando
If I was needing to go to a 23 premier pilot jet I would be looking for another fault.

Let me put this in perspective. Over the past 5 plus years we have sold over 3,000 AMAL Premier carburetors to dealers around the US. We are a full stocking distributor of AMAL carbs and replacement parts. We have only sold a couple hundred 622/502-19 #19 - 3 ring pilot jets.

There are many reason that a carburetor will not work as supplied. It has a lot to do with manifold vacuum. If any of the 10 odd things that affect manifold vacuum can manifest itself as carburetor issues.

If you need a #23 - (622/502-23 pilot) there is something wrong with your motorcycle!
John Healy
Coventry Spares, Ltd.

Last edited by John Healy; 03/30/21 6:36 pm. Reason: [quote error]
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Originally Posted by John Healy
Let me put this in perspective. Over the past 5 plus years we have sold over 3,000 AMAL Premier
carburetors to dealers around the US. .

How many of those would have been for Commandos, can you say ?


Originally Posted by John Healy
We have only sold a couple hundred 622/502-19 #19 - 3 ring pilot jets.

So if the #17 is demonstrably too lean, and is known to be too lean,
why wasn't the change to #19 covered under warranty ??
Or even changed over before being sent out.

I was in the computer biz, and if we didn't cover something like that under warranty,
we would have been sued to the back teeth.

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Originally Posted by Rohan
So if the #17 is demonstrably too lean, and is known to be too lean,
why wasn't the change to #19 covered under warranty ??
Or even changed over before being sent out.

They were only found to be lean on late 850 Commando's!!!

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Originally Posted by John Healy
Originally Posted by Rohan
So if the #17 is demonstrably too lean, and is known to be too lean,
why wasn't the change to #19 covered under warranty ??
Or even changed over before being sent out.

They were only found to be lean on late 850 Commando's!!!

I’m not sure I fully agree, I’m finding with further checking on different bikes that they respond better to #19 pilot jets. My own bikes are not exactly standard so I do my comparison against a set of carbs which have the Bush still fitted. But I am finding on other bikes that I have supplied carbs for that they seem to be on the lean side with the #17. The innitial remedy was to fit a richer slide thinking that with the anodised slide they could be a change in the bore to slide clearance. But this caused richness at the upper end of the range of the slide cutaway. Changed the bike to a #19 and not only could the 1.5 turns out (or there about) be achieved but the standard slide could be fitted and changed the characteristics of the bike.

The bike was rideable with the #17, and to those who just want to run the bike and be happy and accept that “it’s an old bike, they do that” they will probably just screw the pilot mixture screw in until it runs something like and doesn’t stall.

For anyone that’s bought a #19 and tried it, I think they will be happiest.

And if I’m honest, I never considered it myself until DonTr7 on the triumph forum had this same discussion last year and mentioned that it will be better with the #19.... so I tried it.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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So lets set-up somethings that we can agree on:
• With variable venturi carbs, and I am specifically referring to Mikuni VM type and AMAL, there is an accepted number of turns out of the pilot air screw from seated that that you tune to. If it isn't possible to attain that setting within a 1/2 turn in-or out that a different size pilot jet is required.
• With a Concentric and VM it has been 1 1/2 to 2 turns out from seated. If the carburetor settles in at a smoth idle between 1 1/2 to 2 turns for driveability it would be better to set the pilot air screw at 1 1/2 tuns out.
• Changing the pilot to suit a particular rider, conditions such as elevation or engines state of tune, is nothing new. If you ilve in Denver, and ride up into the Rockies you undersand this basic concept.
• Along with the #78 drill supplied by the US Triumph distributors in 1971/2 was two other drills: #77 and #76. They new that one size fits all, even within a particular model, or market area, was not something atainable. Tuning a carburetor in New Mexico, where avg. riding season temp's can reach 100°F is quite different than in Bemiji, Minnesota, where avg. can reach 70° F.
• While not useful for Concentrics used on the Triumph Daytona, provision to use a replaceable jet were retained on the 4 stroke versions.
•The performance of these carburetors is dependant on the state of tune of the engine and the strength of the vacuum signal it can provide.
It is also affected by:
• Manifold leak
• A carburetor too big for the swept volume of the cylinder
• Increasing the port diameter by porting the existing ports (which in many cases are too large to begin with for street use)
• A leaking head gasket between cylinders. Most noticed with the T140 (especially when bored oversize).
• Too much clearance in the intake guides
• Excessive back pressure in the exhaust
• Late valve timing
• Worn, or not seated, pison rings
• All sorts of problems caused by the ignition system
• Elevation
• Atmospheric pressure
• Air temperature
With the introduction of teh computer to measure all these factors and adjust for them we have lost the skill to use a vacuum gauge, or recognize the factors that are effecting our carburetor.

I have followed Don, and yourself. My bike runs better tells me nothing. Why does it run better? Is my experience the same as others enough to consider it a Global problem. Are all of the factors that determine how the carburetor deals with the conditions it faces the same for the people you are giving advice. If you remember it was from me that you set out to install a small port BSA head on your BSA. You expereinced what increasing the air velocity can do to the rideability of a motorcycle.

I recommend that you study what the computer in your car measures to adjust the amount of fuel it delivers in all of the conditions it is ging to experience. Then you will understand what you need to bring to the table when setting out to be a carburetor expert.

The axiom we have lived with for years still applies if your pilot air screw doesn't settle out at 1 1/2 t 2 turns out you might consider the size of the pilot jet. If it does, there is nothing wrong with the jet for the conditions that affect it. And conditions change almost hourly.

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Hi John, thanks for taking the time to reply.

I’m not professing to be an expert, but I have sold a good few premier carbs, most of them have been fitted to standard bikes, some restored and everything done and some on original bikes. A lot for unit singles. They all experience the same effect with the #17 pilot jet. They all need to be screwed in to within 3/4-1 full turn out to run correctly. I have also ran 928,930 and 932 on the same bike (my lightning) the same bike has had different heads (standard port, early small port and even smaller ports) and different cams (standard cam, full race and road race), big valves, to small valves, different carb intakes from filters, screw on bell mouths and velocity stacks and different exhausts from standard, modified standard, and different types of original Dunstall mega.
When I was running with my original 930’s the pilot jet with the pressed in Bush never caused a problem, it often needed cleaning and that would fix the issue each time (a #78 drill bit). It didn’t matter what I did with the bike, setup wise the pilot jet setting never went less than 1 1/4 turn from fully in.

One of the biggest issues I noticed was a rich condition to the point where the plugs were fouling. This is on my non standard Lightning and with its non standard jetting. All the symptoms pointed to needing a leaner slide cutaway. If I fitted that it ran better but wanted to cut out. If I was out on the motorway the bike would be fine and pull like a champ, but low throttle openings were not good, the motor would run rich and if I did enough “town work” the plugs would foul. The bike was running a 3 slide and the 17 pilot jet. This was using the 932, if I ran the 3.5 slide it wouldn’t take throttle very well, from 1/4 throttle up was fine, tick over was tuneable but transitioning onto 1/4 throttle felt lean, didn’t want to pull. Not having a 19 pilot jet on me
At the time I tried to make compensations through the jetting range. I got the bike working but I wasn’t happy with it. The engine wasn’t smooth any more either at lower throttle openings (at this point I had leant the bike
To Shane for the British bsa rally) I didn’t say anything but he confirmed my thoughts.
I changed back to the 928’s, ditched the velocity stacks and fitted air filters again. I felt this would give me a good basis to work from and I suspected that air flow through a 932 at low throttle openings one each 340cc cylinder could be too slow. This time I started with the 3.5 slides and went from there. Again the bike was ok, but similar symptoms. Ok it wasn’t fouling plugs, but the motor didn’t pull cleanly. I changed to the #4 slide which improved the bike a lot but again it felt lean just off the throttle, it was about this time I saw Dons post about the #19 pilot jet, I tried it and the bike is running well. Much smoother and much better throttle response at lower throttle openings. It doesn’t cut out on me 1 miles down the road when you shut off the throttle for a junction like it would do with the 17 pilot jet and leaner slide.

Another instance is my friends B44, the engine is stock, std bore new guides, je piston, everything new and standard. At the moment that’s running with a slide richer than the book setting, it came with the 17 pilot jet, it should have a 3.5 slide but we couldn’t get that thing to run. So I substituted it for a #3, the bike runs and it runs ok. The exhaust is as blue as a peacocks arse feathers and the timing is spot on and verified by 2 timing lights. The pilot air screw is screwed in much more than it aught to be also. But as it stands the bike starts and goes, there’s no comparison for this bike against another so how do you know it’s running as it should (this was my point of my original post) many owners have little to compare against. But to see an exhaust pipe blued as if the engine was too far retarded, having to change the stock slide and having to use a richer pilot air screw setting doesn’t seem right to me. I’ve suggested the change of jet and I’m waiting to see how it goes.

Another if a friends standard Lightning which I built for him but with softer compression pistons. Again it runs well, but the pilot air screws are screwed in about 1turn out.

And the list goes on. Some bikes really highlight the issue and some not as much.

As I say I don’t profess to being any expert but I have had a lot of time on my hands in the past. When I first took your advice on the small ports I turned a well running bike into something different, something with a lot more grunt, more tractable, faster at top end and more economical on fuel. You gave me a lot of inspiration to try and find where I could go with what I had as regards a bike. I’m thankful for all the help and information that you gave me, I see your postings and help given as mentorship and consider in a way as a friend as you have been kind enough to give that time and advice. You have also taught me to question what I have learned (I think this was once one of your signatures or a meme?), I don’t do this to be ignorant but to try and further my understanding. I have a hell of a load to learn and I do want to learn it.


We’re lucky in many respects in the UK, I doubt anywhere that I could take a bike is above 3000 feet elevation. Barometric pressure is corrected to sea level on all the equations for pump gasoline (or any petroleum based product) that you buy, that’s 101.3kpa, in the uk we see usually around 96-103kpa min and max, mostly between 99.7 and 102.6kpa, air humidity is never at any extreme sometimes 45%, sometimes 65% but I doubt seldom exceeds those figures.

I ain’t ever going to gain the 50+ (Maybe 60) years of experience that you have had, to be a fly on the wall would have been one hell of a trip I’m sure. I’ve been working on them like a religion for 15-20 years and I doubt I have a 1/8 of what you know and that would be wishful thinking on my part. So the best I offer is what I have tried and experienced. Certain things worked for me... a premier pilot jet costs what? 10 bucks a piece? It’s simple enough to change and the change is reversible.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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So, are the carb sets for 'late' 850 Commandos now supplied with #19 pilot jets. ?


Originally Posted by John Healy
They were only found to be lean on late 850 Commando's!!!

Originally Posted by Rohan
So if the #17 is demonstrably too lean, and is known to be too lean,
why wasn't the change to #19 covered under warranty ??
Or even changed over before being sent out.

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Originally Posted by Rohan
So, are the carb sets for 'late' 850 Commandos now supplied with #19 pilot jets. ?

As far as I'm aware it's all 850. Perhaps JH meant late (thus 850) Commandos.

http://amalcarb.co.uk/news/cat/news_amal/

"We are now fitting size 19 Premier pilot jets as standard to 850cc Norton Commando carburettors as this has been found to perform better than the size 17 fitted to earlier versions of the carburettor."

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Quote
So, are the carb sets for 'late' 850 Commandos now supplied with #19 pilot jets. ?

Yes, carburtors built specifically for the 850 Commando have been for quite a while. Burlen has been very pro-active on this.

This is not to be confused with the standard 932 which are generic, and not built for the Commando. These still come with the #17. We offer the dealer at no additional charge to modify the jetting for which ever application required. So all of this is not an issue with our dealers.

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Originally Posted by John Healy
Originally Posted by Kommando
If I was needing to go to a 23 premier pilot jet I would be looking for another fault.

Let me put this in perspective. Over the past 5 plus years we have sold over 3,000 AMAL Premier carburetors to dealers around the US. We are a full stocking distributor of AMAL carbs and replacement parts. We have only sold a couple hundred 622/502-19 #19 - 3 ring pilot jets.

There are many reason that a carburetor will not work as supplied. It has a lot to do with manifold vacuum. If any of the 10 odd things that affect manifold vacuum can manifest itself as carburetor issues.

If you need a #23 - (622/502-23 pilot) there is something wrong with your motorcycle!
John Healy
Coventry Spares, Ltd.



I should have perhaps mentioned that the two premier carbs (626/17) were fitted to two separate BSA Bantams. One ended up on a 23 pilot and the other on a 21. They both run very well in the mid range and top end, but the one using a 23 pilot is still running weak at the bottom end.

As well as the big pilot, I am also using a number 3 slide to richen it further for pulling away, and the air screw is turned in by 1/4 as well, but it's still not quite there. I still have to rev it too much to pull away without stalling. If I give it a little choke it helps.

The carb has been apart for thorough cleaning on a number of occassions, but it always appears to be totally clean. The 2 tiny holes in the carb body always spray through nicely with the carb cleaner.

I tend to agree with Kommando and John that there could be something wrong with the engine, but I'm at a loss to what that might be.

By the way, the bike had a similar problem with the original carb, so that might well point at an engine issue as well.

A friend now has the bike that is using the 21 pilot, so as a test I am borrowing his carb tomorrow to see if that helps the bottom end. After that, I have another barrell and piston (working pair) that I can fit as another test.

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An issue that can affect 2 strokes - but not 4 strokes in the slightest - is leaky crank seals.

If they can suck/draw any air into the crankcase on the upstroke, as you imagine this might and can weaken the mixture,
so that the subsequent compression and firing will be weaker than the carburettor settings would indicate.
At some throttle, this may not make a lot of difference, but on a mostly closed throttle at low idle/rpms it might.

Worst case scenario is when the seals are totally trashed, and the engine will only run in short bursts or not at all even.
As many an owner of old worn 2 strokes may be familiar with !
A spoonfull of petroil down the gullet will/may produce a short burst of running, and then - silence !
Aaaayyyyeee !

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