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E: Engine Comet Amal MK1 Concentric


Tony Wilkinson

Active Website User
VOC Member
I have only recently acquired my 1950 Comet and am generally pleased with it. I have had a number of issues and am slowly through them. The mag was weak and would die when the engine got hot. I have since replaced with electronic coil ignition which seems to work very well.
The bike was fitted with it's original 229 carburettor but despite rebuilding still suffered from flooding and constant leaking. I have recently purchased a used but excellent condition Amal (Burlen) MK1 carburettor 928/L301. It is said to be set up for a Comet and had indeed been fitted to one as it has the correct inlet stub.
It has a 200 main jet and before I install it, I would like some advice please. does this seem correct ?
 

erik

Well Known and Active Website User
VOC Member
I have a 30mm concentric mk1 and a 200 main Jet fitted.No Problems since 10000 km
 

Tony Wilkinson

Active Website User
VOC Member
I will fit it this week and trial over the weekend. I know this can be a bit of a minefield as lots of differing opinions and by the way what oil should I use .............. Joking.
 

James B

Website User
VOC Member
Following with interest. Also have a comet. I believe I have got the 229 working acceptably ( still leaks though ) but of course am currently struggling with the mag instead...
 

greg brillus

Well Known and Active Website User
VOC Member
Any side bowl type 276 or 289 carb will drip fuel if the machine is sat on it's side stand, and also if the fuel taps are leaking internally...........Disconnect the fuel pipe connection and leave a small container under the tap overnight and you will find a lot leak internally...........This is the primary cause of leaks from these carby's............No amount of replacement gaskets and sealants will stop it.
 

Tony Wilkinson

Active Website User
VOC Member
Following with interest. Also have a comet. I believe I have got the 229 working acceptably ( still leaks though ) but of course am currently struggling with the mag instead...
My 229 works OK, petrol taps do not leak (they are new). I gather most of them leak. I am not surprised as 70 years old. I will fit the Concentric at the weekend. Going back to main jet sizes, my 229 also has a 200 main jet so I am going to try that first. On the subject of the mag, I have fitted a Thorspark coil ignition from Sussex motorcycles. The unit fits inside the mag which does not need to be removed. You will have to find a place to fit the coil, I have fitted mine on the engine support next to the battery. You will also need a switch so it can be turned on and off. I made a bracket to fit in existing holes in the rear engine mount for the coil and the switch. This unit uses very little from the battery. I have a gel type battery in a dummy case (like most people I suspect).
 

James B

Website User
VOC Member
During high? speed use mine weeps under the float bowl cover and down the outside of the float bowl - presumably due to fuel being vibrated and splashed around inside. Is there supposed to be a gasket here? I don’t see anything on the exploded diagram at burlen

(Apologies for inadvertent thread highjack)
 

Tony Wilkinson

Active Website User
VOC Member
Any side bowl type 276 or 289 carb will drip fuel if the machine is sat on it's side stand, and also if the fuel taps are leaking internally...........Disconnect the fuel pipe connection and leave a small container under the tap overnight and you will find a lot leak internally...........This is the primary cause of leaks from these carby's............No amount of replacement gaskets and sealants will stop it.
I have new fuel taps which do not leak but carb leaks as soon as fuel is turned on. Still hopefully this will be cured once I have the Concentric carb fitted.
 

James B

Website User
VOC Member
Note the weepage telltale down the back of the float chamber, and the throttle stop that had decided to unwind itself :)
 

greg brillus

Well Known and Active Website User
VOC Member
It is generally set at the base of the mixture screw thread, this is open to opinion on account of the angle some carb's are mounted to the engine, but your method of checking works best.
 

Tony Wilkinson

Active Website User
VOC Member
I am happy to report that the Amal MK1 (Burlen) Concentric is now fitted. I had to wait for a new throttle cable with a longer inner to get the bike running again. From first startup the bike sounded better and ticks over like a Swiss watch.
The seller said this carb was all set up for a standard Comet and he was not wrong. It runs cleanly throughout the rev range, starts easily and importantly does not leak, happy days.
 

MartynG

Well Known and Active Website User
VOC Member
I am happy to report that the Amal MK1 (Burlen) Concentric is now fitted. I had to wait for a new throttle cable with a longer inner to get the bike running again. From first startup the bike sounded better and ticks over like a Swiss watch.
The seller said this carb was all set up for a standard Comet and he was not wrong. It runs cleanly throughout the rev range, starts easily and importantly does not leak, happy days.
Hi Tony,

That was my understanding when I purchased and fitted a 30mm Mk1 to my comet. It came fitted with a 190 main. 3 pistons later I am now on a 240 main - it is amazing how well these bike run lean - till the piston fails!

Do you know how the carb is set up? What main, what needle jet, needle etc. ? Care to share?

Martyn
 

Mike 40M

Well Known and Active Website User
VOC Member
When I bought my Comet it was fitted with a 930(?) Concentric. The seller mentioned that the idle jet has been drilled a bit. As it runs, idles and starts well, I haven't bothered to examine it closer.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I have only recently acquired my 1950 Comet and am generally pleased with it. I have had a number of issues and am slowly through them. The mag was weak and would die when the engine got hot. I have since replaced with electronic coil ignition which seems to work very well.
The bike was fitted with it's original 229 carburettor but despite rebuilding still suffered from flooding and constant leaking. I have recently purchased a used but excellent condition Amal (Burlen) MK1 carburettor 928/L301. It is said to be set up for a Comet and had indeed been fitted to one as it has the correct inlet stub.
It has a 200 main jet and before I install it, I would like some advice please. does this seem correct ?
The Britbike web site says 28mm 180, and 30mm 200 Main jet as a start setting, With standard Silencer and air cleaner !!!!?. As Martyn says, Worth going up a bit for safety, And with the petrol as it is ?.
Also if you have a straight through silencer, It will need a bigger main jet. Cheers Bill.
 

Tony Wilkinson

Active Website User
VOC Member
Hi Tony,

That was my understanding when I purchased and fitted a 30mm Mk1 to my comet. It came fitted with a 190 main. 3 pistons later I am now on a 240 main - it is amazing how well these bike run lean - till the piston fails!

Do you know how the carb is set up? What main, what needle jet, needle etc. ? Care to share?

Martyn
Hi, sorry for the late reply, I have been away.
It is a 928 L301 carb, 200 main jet, 106 needle jet and a no 3 cutaway slide, running with an Amal no 900 bell mouth, sorry can't remember what needle but clip in middle groove.
 

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