Amal mk2 v Mikuni

Hi All.
I have the opportunity to purchase a Mikuni carb providing I know what I want, I've used all sorts of Amal over the years am now on the mk2 which seems ok, is it worth changing I ask myself therefore I would appreciate advice from members who have experience of the Mikuni.

Thanks and a very happy new year for 2016.

Les2012.

Les, I think Alan brown knows mikuni carb,also Andy ckeckly(most likely spelt that wrong) maybe they'll be along to post about them

Andy's 125cc has a 34mm TMX mikuni which works well, he also ran a 38mm TMX in the bike for a while with a blade across the inlet which he told me worked well too

I have been thinking about exactly the same mod on the 175cc Smithy Bantam. It runs a 36mm MK2 and I have a 36mm Mikuni TM which would, with a different manifold fit straight on.

I would love to hear what Alan Brown has to say but I suppose they are both based on a flow rate main jet and the most important factors are a) is there a good supplier of parts (Allen Performance Parts Tel:01949 836733 or Rex Caunt Racing for Mikuni) and b) are they straight forward to setup.

Others use Lectron and Dellorto but I nothing about them.

Happy New Year Edward

I must say that I have used many types of carb, and I look at the factors that I need as a list:

1. Price.
2. Availability of the size I believe I need.
3. Availability of spares, especially jets/needles/slides etc.
4. Ease of modification.
5. Ease of use.
6. If the reaction to settings is as expected.

I use the Mikuni TM-1 style as it fits all my criteria and the amount of spares available is VAST!
A good set up carb will perform regardless, but I do like the adjustability of this style so it is my choice.

You make your choice and get used to it!
Cheers,
Alan

That's really helpful Andy.

I am interested to know if you have any hints or tips for anyone using or trying to set up a Mikuni TM? I have found a couple of articles on line and manuals etc. but nothing from a bantam racer. I suppose I am trying to understand if there are any rules to follow or winning formulas I can adopt?

I am also interested to know if you used a power jet?

Thanks for your help

Edward

If your engine is piston ported... speak to Rexl or speak to robbie about lectron carbs. I have used mikuni 28mm on a 175 piston ported and it worked fine, untill i added the mikuni power jet kit and i couldnt get it to work. i have also tried the mikuni 32mm or 34mm flatslide on the 175 piston ported and i couldnt get it set right, but im no expert.. i think Rex has had good results with the mikuni on his engines, the engine spec and carb jet sizes are on this web site somewhere. should i be inclined to experiment again, i would probably use the amal mk2 on the 175 piston ported as these carbs are from the piston port era of engine developement . seems these mikuni carbs where designed mostly during the reed valve era. Bit like most pistons today are designed for alloy nickacil coated cylinders not cast barrels.

Thanks for your comments Nigel

I have two Bantams, the ex Andy Moulden bike which I used last season which is a 125cc crack inducted reed valve engine. It uses a 34mm TMX mikuni with a power jet and a pressurised air box. All works really well, thank god!. (black bike with mono shock used to be red)

I also bought Edward Smiths 175 at the end of last season which used a Amal Mk 2, I am not going to change anything until I have a few miles on the bike but I would like to move to a more modern carb at some stage in the future, hence the post about 36mm Mikuni TM. Just trying to understand how best to make the change.

I am going to ride the 175 this season and Andys going to have a few days on the 125 and when he is not ridding it will in reserve.

Thanks again Edward

The Mk 2 Amal has an elongated oval formed by the bell-mouth radius around the air correction jet feed-hole. In this original state air accelerating through the bell-mouth will subject the air corrector to increasing negative pressure. This is caused by air velocity increase lowering pressure, the same principle that keeps aircraft in the air. Exactly the opposite is what is needed to lean out the fuel curve that naturally enrichens in carbs like these with the increase of air velocity.
After realising this, I modified the Amal on my w/cooled engine, and it works very well!
I slightly enlarged the bore in the feed hole and slipped in a thin walled brass tube that was long enough to extend to the lip of the bell mouth, problem gone! I also did the same mod to the idle orifice as well.
Just one more point, the bell radius form a sharp edge to it`s o/d; as sharp edges are anathema to fluid flow I formed a 6mm blending radius to this edge. It is also a good idea to fill the screw holes with silicone to form a smooth blend, never neglect easing turbulent air flow, it always pays!

Trevor

If anyone needs/wants any tips on either Lectron carbs, easy to set up but not easy to get the
metering rods/parts for I'm happy to help advise.

Also I've been running Dellorto VSHB carbs for the last 5 years and have 'got a handle' on them
too now..

Regards Mike