Amal Carb Jetting

[Duccout]

I have just come upon some jetting recommendations from Amal that they sent me back in 1977 which may be of use to someone.

30mm carb for a 350 Ducati:

Main jet 210
Needle jet 106
Needle 622/124
Slide 3 1/2
Pilot jet bushed 622/107.

32mm carb for a 350 Ducati:

Main jet 230
Needle jet 106
Needle 622/124
Slide 3
Pilot jet bushed 622/107.

Colin

[themoudie]

Thank you for posting Colin.

Good health, Bill

[Duccout]

Here is a bit of a head's up regarding the fitting of new carburetors.

All things considered, in spite of the fact that Mikunis are better made, more accurate, easier to fit and work on and rubber-mounted, I think that an Amal may be the more sensible choice, because they have definite settings available from the Spanish Mototrans models, whereas Mikuni settings are a minefield. All four shops that I have looked at who are Mikuni experts - Sudco, Allen's, Motocarb and Mikuni Oz, recommend different jetting for the same bike, with the result that you just chase your tail the whole time.

Anyway, in case anyone is looking to fit a new Amal, here are the Mototrans jettings for the 250 Strada, a wide-case engine, but with small valves (which may make a difference)
27mm Amal
Main jet: 180,
Pilot jet: 25
Needle jet: 105
Needle: 622/124
Slide: 2.5

And here is the jetting for the 350 Forza, a wide case engine identical to the Italian big valve engines:
30mm Amal
Main Jet: 220
Pilot jet: 25
Needle jet: 105
Needle: 622/124
Slide:2.5.
Recamiousado in Spain has the correct rubber manifold spacers in stock to fit these carbs. It will be noted that Burlen has different jettings on their website to these, but these are the ones used by Mototrans for these models, although there were slight differences from the earlier Road models, possibly due to different exhausts or bore and stroke measurements, or due to air filters.

Cheers,

Colin

[George]

Interesting post Colin. I bought new Amal 30 for 350 Mototrans Road from Burlen with jetting as per their recommendations.Eengine starts and runs OK without any alterations to carb.
I have yet to try on the road. Until this weather improves I am unable to paint tank and side panels. Getting impatient.

[blethermaskite]

The jetting on my 350mk3 with an Amal concentric mk1 and a Dunstal decibel silencer is fixed (non adjustable) pilot jet, 3.1/2 slide, 106 needle jet, std. needle, 210 main jet, all running very sweet on this, previous setting on a straight through reverse cone (as F3) megaphone,...... same but with 220 main, 3 slide.
Moved house into the suburbs a couple of years ago from a very isolated rural location so had to quieten it down a bit
Cheers,
George

[Duccout]

It is funny, but Amal (the old company) tended to recommend a bigger needle jet (106 as opposed to a 105 used by Mototrans) and a larger slide cutaway (3.5 as opposed to 2.5 as used by Mototrans). Obviously, the end result appears to be the same.


Cheers,

Colin

[Dave354]

I will be running a mk1 30mm concentric with 210 main 106 pilot and number 3 slide on my 350….. just got the carb rebuild kit so no idea how that will fare? I am running standard Sebring valves and piston and Electrex ignition.
As yet I’m a little way off kicking her over.
Will there be a difference with the no3 slide rather than 3 1/2? Also it never had a choke fitted, should I fit one?
Regards
Dave

[Duccout]

Hi Dave,

Your settings should be fine, but you may have to do some fine tuning as there is a relationship between the needle jet, slide cutaway and pilot jet, and the air filter (or lack of one) and how open the exhaust is will affect the carburetion. I am assuming that you have a no 20 pilot jet? If you get a lot of spitting back as you pull away you may need a 2.5 slide. If you have not got it, download a copy of the Amal tuning guide. You will not need a choke, but Amal recommend blocking up the hole for the choke cable in the carb top.

Colin

[Dave354]

Hi Colin, I plan to run a standard silentium but do have an open megaphone as an option. Not sure what you mean by a no 20 pilot?

[Duccout]

Hi Dave,

The older carbs used a pilot jet of various sizes, from no20 up to no30, and these affect the way the bike runs at low revs, but newer Concentrics have a plain bush so it does not matter. When you get to ride the bike you can fine tune the way it runs - hopefully it will be perfect as it is.

Cheers,

Colin