Which carb for a Sherpa?

[trialsrfun]

My Bultaco Sherpa 250cc Model 124 has the original fitment Amal 627 carb which is quite worn. The bike still continues to run ok with it, but I must assume that a better carb would improve things somewhat.

The question is though what replacement carb would be most suitable,

Amal Concentric Mk1 as now

Amal Mk11 as used on the later Sherpa's which I think are stub fitting only

Mikuni VM26

I think there is an OKO flat slide available

Is there anything else that I am unaware of that may be better than the above, what have you tried and how did it work?

[woody]

Assuming all carbs are new and functioning as they should:- The bike will run fine on the MK1 Amal 26mm (or 27mm if still available) the MK2 Amal isn't worth the extra expense, an OKO 26mm will work virtually straight out of the box with minimal changes (it did on my M92 and 199b) a 26mm Mikuni will be a sea of misery to jet unless someone can give you the spec.

A new MK1 Amal is the original fitment so will bolt straight on. The MK2 Amal, OKO and Mikuni will need an adaptor or manifold change as they are all push-on fitment not bolt on.

It's a personal opinion but I doubt that if you were blindfolded and tried the bike with each of those carbs correctly set up, you would be able to tell any significant difference between them. The OKO and Mikuni probably run a little smoother off the pilot but it's subjective to be honest.

For what it's worth, my old M92 325 which my mate now has runs very well with a 26mm MK1 Amal, silky smooth off the bottom and revs to the moon. I've tried a 28mm Mikuni and now have a 28mm OKO on my 340 and can't tell any difference.

[trialsrfun]

Smooth power delivery is the goal, the bike runs very well as it is yet the carb is in rather poor condition with definite and pronounced body wear, a carb in better condition must surely improve things further. I cannot really fault the Amal Mk1 other than for its lack of a choke, relying on messy overpriming for a cold start.

As I said the bike rides really well with plenty of power and although I have only yet ridden it in one trial (a slippy one) it seems to find grip better than the 325 and is much easier to start than the bigger bike.

Starting when hot is good so I guess after the carb job another decision is whether or not to fit an electronic ignition to it. To date I have heard good and bad about the various ignition systems from other Bultaco owners.

Edited November 7, 2010 by TrialsRfun