Concentric Modification

[Bill Thomas]

I had 3 sets off Ron,
He also told me , His carb's work better with 2 into 1 Exhaust pipes,
That and seeing what Ray Elger did with his sprinter,
May have talked me into what I did.

 

[Nigel Spaxman]

The Amal Concentric MkI is not a suitable carb for racing. It is unable to supply enough fuel at full throttle. That said, there are tuners who do mods to make the Concentric work well. I don't feel right about using a carb that is not designed to deliver sufficient fuel at full throttle.

I am pretty certain that none of the round remote floats made by Amal deliver enough fuel at full throttle. They are huge, but they do not flow well. I think that these float bowls needed mods to flow large quantities of fuel.

The Amal 510/1 float bowl flows more fuel than any other Amal float bowl, according to Tom Ullman, Amal's chief engineer. I think the best set-up for a Comet is the stock Flash or Lightning set-up. It will go pretty fast without fuel starvation. If you want absolute top performance you will have to customize any carb you choose.

View attachment 52217

This set-up works well on a Vincent.

I think the MK2 carbs are pretty good. I don't have much experience with them because AHRMA banned them after Carleton and I started using them. I believe Roy Robertson uses MK2 carbs. But, I think I agree with Greg that any carb with a float bowl attached below the main jet may be prone to fuel starvation. This is why I picked up a double float bowl MK2.

View attachment 52218

View attachment 52219

These float bowls used to be made by Amal of Spain for the super flat tracks where the bike would be leaned to one side for an extended period of time.

David

A friend of mine had a Speedway Jawa that used this type of float bowll. It ran on Methanol.

 

[Bill Thomas]

I like the look , But never seen one,
No need for one now , Just a slow poke !.

 

[Chris Launders]

I seem to remember hearing eons ago the methanol Mk1 float chamber used the bigger Mk2 float needle and housing with the slot, I've just looked and there is just enough alloy to do this.
Can anybody confirm/deny this ?

 

[Phil Davies]

I had 3 sets off Ron,
He also told me , His carb's work better with 2 into 1 Exhaust pipes,

I did some work with fluid dynamics on Ron's carbs, sadly after I had paused racing, because I liked Ron's thinking and his approach to fuel flow.
Because of the presentation of the metered fuel to the venturi air flow the fuel is more readily mixed within the air, resulting in better conditions for combustion-hence the power lift when using them.
The fuel metering is more accurate than that of amal's, the only item that the amal scores on automatic weather compensation, whereas Ron's carbs have to be adjusted on the day to suit - not the biggest job in the world.

 

[Bill Thomas]

As you say, Always playing with them, like the Wal Philips Injectors / Drip feed !,
I never cured the sticking problem low revs, Can't remember what pistons ,
11 s or 12 s But they had a hell of a sucking on the slide,
And the petrol mist /drip after start up ,
Messed up my polished Crank Cases !!,
I polished the outside of the later Carbs, Looked good and the power was good,
But for me the 36 mm Dellortos was the real fix, But not easy to tune and, Cost a lot !.

 

[erik]

The effect of fuel starvation should be much more sufficient on the singles than on the twins because full throttle is more often when riding with less power!If the Concentric works perfect on the Comet it should be no problem on the twin.With my standard Comet I have no problem using a 930 Concentric.But I will cut the slot in the floatchamber and checking a different mainjet again.After my journey to the far far north rallye. Erik

 

[Bill Thomas]

That's funny, So I am not the only one , Far behind the times !,
Must be because we ride Vincents .
That's why I posted the mod ' on here, In case anybody else didn't know.

As you said before , Not many of us ride that hard anymore, Unless Racing,

I would have thought Ben would use something better than Monobloc Carb's ?,
I know the AUS Horner thing used them, But they put so much money into there racing,
I doubt there monobloc is anything like the factory ones ?.

 

[Trickymicky]

Float Chamber Bowl 0.125" - High Flow Seating - The AMAL Carburetter Company

Float Chamber Bowl 0.125" - High Flow Seating

amalcarb.co.uk

Float Chamber Bowl 0.156" Alcohol Seating (4.0mm) - The AMAL Carburetter Company

Float Chamber Bowl 0.156" Alcohol Seating (4.0mm)

amalcarb.co.uk

 

[Bill Thomas]

I wonder what that size is for ?, Can't be the hole where the petrol goes through the Float jet ?,
Which is where I have found the difference ?,
And why would the Alcohol one be smaller than the Fast flow ?.

Sorry getting my inches mixed up with metric and everything else,
Back to school for me !, Do they take 75 year olds .