Jetting for a 350 Mach 3

I have an Amal Concentric Mark 2 fitted to my 1973 Mach 3 350 and I’m trying to order an overrhaul kit from Amal. I need to specify the jetting I require and though I have the original jetting and Mick Walker reccomended jetting in the Haynes manual, these don’t correspond with the Amal jet sizes?

The sizes in the Haynes manual state:

Pilot jet: original - 40, Mick Walker reccomendation - 50
Main jet: original - 115, Mick Walker reccomendation - 125
Needle jet: 265M

The sizes in the Amal list are nothing like these, the existing main jet I have is 230. And I don’t apear to have a pilot jet in the carb, just a pilot blanking screw, why would this be the case?

I don’t really want to just order what is already in the carb as these may be completely wrong, (I’ve never had the bike running).

Any help would be greatly appreciated.

Cheers, Martin.

Hi Martin,
Give Nigel Lacey a call I’m sure he can help you with a starting point as he fits Mk2 Amal’s to some of his bikes, Nigel is the "Top"man when it comes to tuning these old singles PERIOD!

Here’s a link…

The mach 3 came supplied with a Delorto carb as standard, so I don’t think you’ll be able to find jetting from any publication.
Back in the day owners and specialists like Mick Walker, Tony Brancato, John Smith or Vic Camp used to fit these bikes with Mk1 Amal concentrics.

My ‘74 250 Desmo came to me fitted with a rubber mounted Mk1 30mm Amal, part of a performance modification carried out by John Smith inc’ gasflowing back in the 70’s.
I’ve since had this carb converted to a 32mm Smoothbore by the late George Mansfield/aka Mez Porting RIP.

Steve R

Thanks for the info Steve, I’ll give Nigel a call as there are other parts I want to order from him too.

I have the original Delorto carb which look completely worn out but when I bought the bike it was fitted with the Amal. In the manuals I have they also list the Amal mark 1 as originaly being used (don’t know if it was on the Mach3 though) and I was told today by a guy at Amal today, that the Amal carbs fitted to Ducatis were Spanish built?

Cheers, Martin.

Yes Martin,
Spanish built singles (Mototrans) often came fitted with spanish made Amals, but all of the original Mk3’s I’ve seen have been fitted with Delorto’s.

It’s also been said over the years (by people who know these things) that the Spanish made Amal’s were of a poorer quality than those made in the UK.

Steve R

I spoke to Nigel this morning, thanks for the advice Steve. What a nice guy, I felt a bit guilty taking up his time but he is so knowledgeable and interesting to listen to. Needless to say I’m going to be ordering any parts I can from Lacey’s.

For anyone else who’s interested, his advice for jetting on the 350 Mach 3 with an Amal Mark 2 Concentric was as follows.

Pilot jet: 20 to 25
Needle jet: 106
Main jet: 220