New to the Ossa but after 1 trial on it enjoying it so far.  Fitted with a Mk2 Amal Concentric but seems rich on the bottom end.   Anyone have recommended jetting or alternative carb recommendations?

Mk1 and Mk2 AMAL  concentric are notorious for wearing the slide needle and needle jet, causing the motor to run rich. The standard jetting works fine when nothing is worn. Yes there are lots of alternate carbies that will fit and work well and not suffer rapid wear. Keihin, Mikuni, Dellorto and OKO are all popular and are reliable and long-lasting. I don't want to recommend a particular brand, just that you should buy one that has been pre-jetted for your bike by someone who knows what they are doing.

I fitted a Mikuni 26mm purchased from Motocarb to my TR77, tho other option might be a 26mm OKO but buy genuine from scooter assasins or mid atlantic trials then follow their set up guide.

Edited March 26, 20188 yr by trialsrfun

8 hours ago, feetupfun said:

Mk1 and Mk2 AMAL  concentric are notorious for wearing the slide needle and needle jet, causing the motor to run rich. The standard jetting works fine when nothing is worn. Yes there are lots of alternate carbies that will fit and work well and not suffer rapid wear. Keihin, Mikuni, Dellorto and OKO are all popular and are reliable and long-lasting. I don't want to recommend a particular brand, just that you should buy one that has been pre-jetted for your bike by someone who knows what they are doing.

You could try just replacing the needle and jet. This will cost less and may sort out the bike. If you want to keep the bike original, the Amal is still available as a complete carb jetted to your bike, google will show you where. Shame the Jap carbs are so good.

The OKO I fitted to my Explorer from Mid-Atlantic trials worked great.

12 hours ago, feetupfun said:

Mk1 and Mk2 AMAL  concentric are notorious for wearing the slide needle and needle jet, causing the motor to run rich. The standard jetting works fine when nothing is worn. Yes there are lots of alternate carbies that will fit and work well and not suffer rapid wear. Keihin, Mikuni, Dellorto and OKO are all popular and are reliable and long-lasting. I don't want to recommend a particular brand, just that you should buy one that has been pre-jetted for your bike by someone who knows what they are doing.

Couldn't agree more,replaced the slide which was worn worse than the body,needle and guide and full gasket kit,I'am really happy with it now,saves the hassle of guessing jetting with a 2S....could be scary and expensive ,I understand the jetting for other Japanese carbs is quite different than the Amal.

Besides the jetting theres the issue of buying a Mikuni,Keihin and others is you don't know what you are getting is it made in China,Taiwan or Japan ????,I searthed around in Aliexpress and Ebay and asked questions,carbs advertised as genuine in some cases were knock offs,a guy on YouTube found this when he ordered, genuine carb ran better as he tested on the same bike.

I think if you are changing its better to buy the setup kit,correct jetting (or close) right manifold to carb adaptor etc...worth the extra $$$$.

Thanks for the inputs guys.   May persevere and try to get the Amal right assuming it is the correct carb.  Markings are L2627 401, jets currently fitted are Pilot 20, Main 150, Needle 106.   Do these sound right for a 250 Ossa?