1961 ES2 + mk 1 Amal Concentric 928

Harry,

I have a 928 on my 1956 ES2, so apart from the ignition it should be similar. BTW it has a Triumph style pancake paper filter and I have removed the choke slide completely . I used plug chops to get the main jet size.

Main jet 180

Needle 106

Slide 3

Airscrew 1.25 turns.

It runs very well and idles extremely well.

Only issue is it is a Left Hand unit off an A65 I think, which is a bit of a phaff. 

Don Anson Australia 

I have a 61 big bore ES2 (530cc) with a 928 carb. Sorry I can't remember the needle position  or slide (Either 3 or 31/2) But the main jet is 240. (Smaller than the mono block 270)

I also have a poor man's Manx (59) on standard bore with a 3 1/2 slide and a 230 main jet. Again, sorry I can't remember the needle position. But this is a 930 carb.

The main jet on a concentric should be smaller than on a mono block, some say 20% but it is really what works best, as no two bikes are the same.

Hope this helps.

Hi Harry,

It will be very interesting to see what the top end performance will be with that 180 main jet.

Will it make 80?

I have two model 50's on 626's. The one with the air filter uses a 200 main jet and the one without, a 210.

Just a thought...

Neil, you may be onto something. 

I have not tried to get top speed from my ES2 yet, and I would be surprised if it does make the full 80mph.

The manual I use in tuning any carbies is ' Motorcycle Carburettor Manual' by Pete Shoemark. His last line in plug chops was along the lines of " when you find the ideal main jet size, keep increasing the jet size until power drops off AS THERE IS MORE POWER TO BE GAINED!

I followed this reasoning in my Mikuni equipped Atlas. But not on the ES2 for some reason. Maybe 200 or 210 would liberate a few more mph.

Also bear in mind all my bikes run aircleaner s. 

Hi Don,

I would still be interested to see what a 180 would pull on an ES2 with standard gearing. Engine 20T and G box 19T.

I reckon about 65.(Without wind or slope assistance)

I think 210 would be in the right direction (Model 50 with no air filter) But 240 open end and 230 with a filter on an ES2. (As in your case)  A lot more dust down under.......

Good luck and happy trails.....

I use a 200 main jet, 106 needle jet, needle in the top groove and a 3.25 slide on my ‘52 ES2 with a 928 concentric. Good for about 68 mpg on a recent trip, but no idea of the top speed - it cruises happily at 60 mph.

john

... start with a main jet that I know is too big then reduce the size. My thinking is that I rarely use wide open throttle so carburation further down the range is much more important to me - especially coming off idle (cutaway) and roll-on mid throttle (needle).

Actually, I often just leave the too-big main jet in as it doesn't do any harm for my riding "style"......

Neil,

I'm assuming my bike has standard gearing, it will easily pull 65 mph. It has a metric Speedo and I've had it to 110kmh which is the maximum legal speed here. 110kmh is 68 mph. I feel it has a good 5 mph left in it, but time will tell.

Hi Don,

Yes I forgot the more restrictive speed limits down under. 100 kph in NZ, that's just 62 mph. And camera's all over, especially in shaky City. In the UK it is 70 mph max (A shade under 113 kph)

I feel those max speeds are enough to make a difference though. As Harry said, his bike runs out of puff @ 70 mph. I would expect that from one of my Model 50's, but a little more than 10 mph extra for an ES2. Then there is the easy feeling aspect of knowing there is another 20 mph in the pot at 60 mph. If the performance is there you have a choice but without it you are constrained. 

A matter of choice but it seems the answer is in the main jet where size matters....If I can say that without offending anyone? 

.. runs very well and accelerates very briskly but 70 is the usual max in normal riding - sitting up, me at 110 kg. I'm sure it would do more if I was flat on the tank and with a decent run but I'm happy with that.