Wanted: 74/75 850 Commando

[Paul in NZ]

Any more info/thoughts behind these mods Voltaire?

I've had untold frustrations around idle and twiddling/balancing etc has just resulted in going around in circles.Fueling above idle is fine.No probs to start either.
.

Hi - AMAL concentrics look dead simple but there are a lot of things that upset them. They are super sensitive to air leaks for one...

I'd start with hauling them off the bike and giving them a good clean. If you have a compressor blow through the idle cct air intake on the atmosphere side (small holes below main intake) and watch that you can see it appearing through the small hole in the bore of the carb just behind the slide.

While the very first concentrics had a removable pilot jet they soon switched to a fixed bush which gets blocked/damaged very easily. They also tend to run far too rich on modern unleaded which I think is a global problem because the new 'premium' concentrics have reverted to this removable pilot jet. If its running too rich at idle try a hotter plug. (you can go 2 grades hotter and to an extended tip plug with the 650 TR6's and T120s to counter this)

While you have the carbs off - check the float levels are right. I personally like them on the low side but if you lower it too much the tickler does not work any good. Also check the flow through the taps and lines at this point.

Check the floats for leaks and make sure you have the later version of the float needle (the little rubber tip stops excess fuel flowing in at idle.)

Don't over tighten the carbs when remounting them - you will warp the bodies (check by winding the slides right to the top an see if they stick)

Once everything is clean and 'right' go through the set up as in the manual - if the battery is good it should idle OK. If all else fails go to a single carb set up....

Change the needle/needle jet. They cost peanuts and wear out fast.

[Paul in NZ]

Oh - I have some amal set up booklets if required

[Voltaire]

Good Post Paul, I was on a run last year to the 'naki and the guy behind said he could smell the unburnt gas.....he could not believe when I filled up the huge 12 litre tank I was getting over 60 MPG.
" They' say you should have the chokes working too...yes?

[Paul in NZ]

Good Post Paul, I was on a run last year to the 'naki and the guy behind said he could smell the unburnt gas.....he could not believe when I filled up the huge 12 litre tank I was getting over 60 MPG.
" They' say you should have the chokes working too...yes?

Erm - well I have the choke fitted on mine... Cos I like the sweet little choke lever and it looks naff without doing something... Some people hate them but - in my case to get the bike to run right at idle/low speed I've leaned it out as much as I can. The choke definately makes it start a little easier IN MY CASE.... Plus I have a single carb bike...

If you do ditch the chokes make sure you seal up the hole in the top of the carb.

Once AMALs are right they are pretty good. But you need to undo 40 plus years of bodging.

[BIG DOUG]

Funny just reading on another forum about this,you need a #74 drill bit as this is the size of the jet.Hey paul do you want to buy a brand new pair of genuine heated triumph grips I have a pair new in the box.

[BIG DOUG]

correction to the above it is a #78 drill bit.

[eelracing]

Cheers for all the feedback chaps,a few of the tips I have already tried,i've even replaced the slides but thems are pearls thanks Paul.

[Paul in NZ]

Funny just reading on another forum about this,you need a #74 drill bit as this is the size of the jet.Hey paul do you want to buy a brand new pair of genuine heated triumph grips I have a pair new in the box.

Argh splutter froth gurgle.... Too late (but thanks) Doug... I have the hot grips by Mr Oxford...

[Paul in NZ]

Cheers for all the feedback chaps,a few of the tips I have already tried,i've even replaced the slides but thems are pearls thanks Paul.

The bodies wear as much if not more than the slides and will sometimes leak enough air around them to make idle adjustment a real PIA. Having said that - IF everything else is right, ie ignition, valves, charging etc then you should be able to get some sort of idle...

Speaking of such... What sort of ignition system are you running? If not already some kind of electronic one will definately help.

[swarfie]

The bodies wear as much if not more than the slides and will sometimes leak enough air around them to make idle adjustment a real PIA. Having said that - IF everything else is right, ie ignition, valves, charging etc then you should be able to get some sort of idle....

When I restored my Velocette Venom MKII Clubman in 1997 I put a NOS Amal MK 1 body and new slide and it was sweet for a few miles...18 months and 10,000 miles latter it was as sloppy as and wouldn't idle reliably. I bored the body and sleeved the slide with Alumec 89 tooling plate and it was sweet for another 28,000 miles. Slide wasn't worn bugger all (due to good material) but the body was shagged again so I got another slightly worn body, bored it to suit my slide and was back to good mixture and idle. Its done 42,000 now and is still okay. The bodies don't wear as much as the slides but still wear out ...having a better material on the slide certainly seems to make them last longer though. Good advice about the needle and needle jet Paul, they wear out and upset the idle mixture. I compensated by giving one of my bikes more slide cutaway but then eventually replaced them and had to go back to the original slide cutaway as it was then too lean at idle and spitting back through the carb.

[Paul in NZ]

I have found that the concentrics are super sensitive to slide cutaway changes. Even a half size seems to make a huge difference.

You can get an improved concentric now with a modern materials slide. This should improve matters.

FWIW - AMAL back in the day were quite aware of the silliness of making the body and slide of the same material and proposed several times upgrades to cure this. The british industry though would not pay more than a pound a carb so it never happened... Ah! the good old days!

On the up side - even a flogged out concentric will keep working rather well from just off idle to WOT

[Paul in NZ]

When I restored my Velocette Venom MKII Clubman

Argh... Jealous MUCH

[Paul in NZ]

These links might help

http://www.ingfatrygg.se/amal.html#toc

http://www.britcycle.com/Manuals/amaltune.pdf (not using boiling water in a bowl is great when adjusting float height - not keen on naked flames around carbs)

http://www.britcycle.com/Manuals/Ama...691_622069.pdf

http://www.hitchcocksmotorcycles.com...mk1-concentric

[Kickaha]

I have found that the concentrics are super sensitive to slide cutaway changes. Even a half size seems to make a huge difference.

You can get an improved concentric now with a modern materials slide. This should improve matters.

I'm going to improve matters by binning the amal and fitting a mikuni

[Motu]

FWIW - AMAL back in the day were quite aware of the silliness of making the body and slide of the same material and proposed several times upgrades to cure this. The british industry though would not pay more than a pound a carb so it never happened...

The Monoblock was a better carb, with a thin brass slide, internally supported, and the needle clip at the top of the slide. Main jets easy to replace, separate pilot jet, easy access float. In the mid '70's I scored two brand new monoblocks and fitted them to my Rickman with T100C engine - a whole new wonderful world compared to concentrics. Funny, I was comparing brand new Monoblocks to worn out Concentrics, when most people were fitting brand new Concentrics to replace worn out Monoblocks and saying it was an improvement.