Amal Concentric Mk2 R2934/3

[DewCatTea-Bob]

" I have posted a picture of the carb fitted. "

____ Thanks for your pix ! - (I have zoomed-in on the specific area of particular-interest.)
__ What size is that Mk2-carb, (34mm, or what ?),, and where did you acquire the manifold, (which you have your Mk2-Amal mounted to the cyl.head with), from ?
____ I'm unsure if that newer Amal-model employs the very-same jetting-scale numerical-labeling as the older Concentric-models were given, but if it has remained the same,
then the jetting employed in the 30mm-Amal that's stock on 350-Mototrans models
should get you as close as Mototrans had bothered to tune that carb for a 350-Duke.
__ However if Amal has actually updated their jet-labeling with a new set of numerical-labeling, then (depending on your Mk2-carb's size), the jetting employed within the Mk2-AMALs mounted on the 1975 750-Triumph model, should provide a fairly-close starting-point (for you to possibly end-up with, if your carb isn't too-much bigger than 30mm).


Duke-Cheers,
-Bob

[lloydy1]

__ What size is that Mk2-carb, (34mm, or what ?),, and where did you acquire the manifold, (which you have your Mk2-Amal mounted to the cyl.head with), from ?

Hi Bob, it is a 34mm. The manifold was already fitted to the head when I got the bike.

[DewCatTea-Bob]

" it is a 34mm.. "

____ Well since a 34mm-carb is 28.5% larger than a 30mm-carb, it's then not very likely that the same stock-jetting within the 30mm-AMALs (on either the 350-Mototrans or pre-1974 750 L-twins) would result with a perfect (or even ball-park) air/fuel-mixture for your 34mm-Amal.
So hopefully someone who has installed a 34 or 36mm Mk2-Amal on a 4-stroke cylinder (ranging from 320 to 450cc), can help set you straight with more perfect jetting-specs.


Hopeful-Cheers,
-Bob

[lloydy1]

Hi Bob,

Thanks for your guidance, I will make some more enquires and hopefully I will get it near to somethink right.

Cheers, Dave

[DewCatTea-Bob]

" hopefully I will get it near to somethink right. "

____ If you can find-out what the jetting is within the Mk2-carbs on the 1975-model 750-Triumph, then you could go with (at least) a step or two richer jetting than that, because I believe that those carbs are only 30mm and your 34mm carb should require richer fuel-metering as it would be expected to flow more air (and so thus require more fuel to go-with),, AND since your larger venturi results with relatively slower air-flow and-thus lower vacuum (to suck-up fuel into the flowing-air), then-thus richer jet-settings should need to be employed in order to compensate for the weaker vacuum so as to still be able to pull-up the same/required amount of fuel.
So you know WHICH direction (from the 750-Triumph's metering) you have to go but, not exactly how FAR,, however it's safe to figure (at least) one-step richer on the metering-sizes, and that should get you fairly close.
____ Sorry I'm not of more help with this,, and while there's no-doubt that somebody-else here has also fitted an Amal-Mk2 to their-own Duke, they're probably not offering their help because they also still haven't dialed-in & pinned-down the best jetting either.


Hopeful-Cheers,
-Bob

[lloydy1]

Hi Bob, you have been a great help thanks.

I have come across this site, which seems to have some settings and lots of info.

http://www.postdiluvian.org/~mason/moto/jetting.html.

Cheers, Dave

[DewCatTea-Bob]

" you have been a great help "

____ No need for any attempt at flattery, as my help with this has certainly been much less than "great" !


" I have come across this site, which seems to have some settings and lots of info. "

____ Yes, that w.site does indeed seem to have some fairly well related data which may be all you'll need to learn of.
I haven't looked-through it real well but, I did soon find the following lists which ought-to be compared to the current jetting in YOUR Amal-carb. .....

850 Triumph:
34 mm Amal Mark 2.
320 main jet
.106 needle jet
25 pilot
50 choke
#3 throttle slide
2A1 needle.

Stock Pre-1980 T140E:
30mm Amal MKII
200 Main jet
25 Pilot jet
50 Starter jet
.105 Needle jet
2C3 needle - 2nd groove
#3 Throttle slide

Stock Post-1980 T140E and T140D:
30mm Amal MKII
200 Main jet
20 Pilot jet
35 Starter jet
.106 Needle jet
2C3 needle - 2nd groove
#3 Throttle slide

Triumph TSS:
34mm Amal MKII
Pilot Jet: 20
Cold Start Jet: 35
Needle Jet: 106
Main Jet: 230
Needle: 2C3
Slide: 3 1/2

350cc Aermacchi racer:
carb: 34mm Spanish Amal bored to 35mm
main jet 220/230
pilot 25
needle jet 105
needle 2C3 using bottom notch
needle 2A1 using top notch
slide #3

__ Now/next after you can list all the equivalent jetting that's currently in YOUR Mk2-Amal, then we should be better able to suggest the best jetting-sizes for your 350-Duke project.


Hopeful-Cheers,
-Bob

[lloydy1]

Hi Bob,

I will get the carb stripped down tomorrow and post the full break down of the jets etc.
Cheers, Dave

[graeme]

Dave, I have a pair of 32mm Amals in the cupboard that came off an 850 Commando that I can look and give you the jet sizes if you think that will help.
Graeme

[DewCatTea-Bob]

Hi Bob,

I will get the carb stripped down tomorrow and post the full break down of the jets etc.
Cheers, Dave

____ I've now spent some time looking-over & comparing the lists of jetting-sizes I posted and also that of which you've given so-far,
and it seems that your carb shouldn't be jetted too far off, already just as it is.
So I'm wondering if you might've been running your Duke with the carb left in it's starting-mode (with the starter-jet remaining in it's functioning-state) ?
If you're sure that that's not the case, then at what throttle-settings do you think your carb's jetting is running richest at, (near full-throttle running, or, at lower normal crusing-speed settings) ?
____ Also, I've been meaning to ask,, has your cyl.head's intake-port been ported-out at all, (so as to better match the size of your carb's 34mm bore-size) ?


Duke-Cheers,
-Bob