Amal Mk2 Carb - simple question

Hi Chaps - the pilot mixture provided by the single Mk2 Amal on my 920 Commando is far too rich (I always suspected this and a Colourtune confirmed it) - I intend to alter the pilot jet - my question - the numbers on the jets - is a higher number a larger or smaller size i.e does a larger numbered jet supply more or less petrol ?

Cheers,

Mark , As far as I know you only have a 20 and a 25 available for the mark two. The 25 being richer. If you remove the air correction bushing you may find that helps. How many turns out are you on your air screw? Anything beyond three and you will need to change something basic. Are you sure that the cross drilled air bleed hole is clear?, it can be enlarged to further weaken the idle signal strength. Lots of ways around the kind of problem. Buy Panic's Amal tuning book.

Hi Norbsa - the pilot screw is nearly full out (any more turns and it will fall out !!!) - the carb is fairly new and clean.
I gather the pilot jet can be fitted in two alternative positions depending on whether it's for a two or four-stroke engine.
Cheers,

As far as I know you only have a 20 and a 25 available for the mark two.

Click to expand...

There's certainly a 15 available and possibly a 10. Check the blanking screws are in the other pilot jet positions and the choke plungers are working cos boy the carbs are rich.
Cash

Cash we are talking about Mark two's here. No pressed in jet in a mark two.
Go Here: http://www.hitchcocksmotorcycles.com/
Click on mark two under the Amal image see parts 41 air jets and 26 pilot jets

Or go to the Amal website: http://www.amalcarb.co.uk/


15cc to 200cc.

After a garage fire I replaced the two amal mkI's by one Amal MkII which I bought from RGM. The old carbs were lacquered with roasted petrol deposits and I just couldn't get them to run right. First off with the standard RGM settings and jets the tick-over could be set but with the air screw practically wound right in! The bike would run OK from 1/8 throttle onwards, but would spit and cough on run over. My problem proved to be my tank was dissolving, (I thought I was immune to this problem as I have run on unleaded fuel for a few years now, but unfortunately there was the brown deposits in the intake tubes. So back to Internet to find a product (some sort of epoxy resin) to treat the tank with, which could be found easily in France! I found http://www.restom.net/traitements-reservoir-1.htm which I applied to my tank and after a week's curing I refitted the tank and filled up with unleaded. I thoroughly cleaned the carb with Wynn's and for the moment all goes well and the original richness is either gone or since I am driving the bike through the throttle range, the overall color of the plugs is brown (OK).
I'm impressed with the new setup, starting has never been so easy, and the tick-over is very reliable, there is nothing worse than not been able to rely on the tick over at a red-light.
I don't notice any less power for the moment, early days.

I've had a lot of trouble with running rich on the pilot circuit with twin 34mm Mk2's. My problem turned out to air leaks on the slides which was disappointing because all parts were brand new.
At the beginning I had the slides bottomed out completely and couldn't get the idle under control. I tried all the usual stuff before playing with slides.
I found a big difference between aluminium including the anodised ones and the chromed brass type. My simple test was to drop the slide to the bottom and suck on the outlet, there was a very noticeable difference between the two types.
Chromed slides are a bit heavier but its worth the extra wrist load to get a working pilot circuit.

Where did you buy your chromed slides Rich_j, I would like to try one, as my air screw is only a 1/4 turn out to get a decent tick-over.

Surrey Cycles?: http://www.amalcarburettors.co.uk/carb_02.htm

Cash we are talking about Mark two's here. No pressed in jet in a mark two.

Click to expand...

Sorry if I mislead you I was talking about Mk2's.
There are two positions to fit Mk2 pilot jets, one in the float bowl usually for 4 strokes the other in the carb body usually for 2 strokes. The unused hole is plugged by a blind pilot jet. My thinking was, perhaps if this plug was missing the carb might run very rich at tick-over requiring the air screw to be wound right out.

Cash

Norbsa,
I've just looked at Hitchcok's site and if you look carefully it shows the two places where the pilots 26 can be fitted.

Cash

Geoffrey Chapman said:

Where did you buy your chromed slides Rich_j, I would like to try one, as my air screw is only a 1/4 turn out to get a decent tick-over.

Click to expand...

I got mine from Hitchcocks in UK, they list them as part number AM/2928/170

http://www.hitchcocksmotorcycles.com/

Almost forgot, if you're heading for the Hitchcocks site it's also worth getting a deep float p/n AM/622/196 if your carb isn't fitted one already.
Helps keep the float valve under control with the engine bouncing around on its isolastics at idle.

I stuck a new MkII from RGM on my 72 Combat in August. After fitting, the bike fired up but as I was needing some work doing to the bike (power box, rewire, belt primary etc etc) I gave it to a chap who came recommended (and who has turned out to be the real deal) for some mods and setting up.

He commented that he wasn't happy with the tick over but adjusting the pilot was having little or no affect. The overrun was also not ideal. The bike ran well but following some further work to the bike (not carb related) and a few miles the bike started playing up. The plugs are fouling and the bike no longer runs on the pilot so it looks like the pilot has 'come out'.

It's getting stripped down this week so I'll report what we find but I'm less than impressed with the MkII and wish I'd gone for a Mikuni ;( The build quality is suspect in my opinion and I also had the float stick (I think) resulting in petrol pouring out of the over flow.

d

Cash,
Yes I see that now that you point it out. Something about your wording on the first post made me think you were off onto Mark ones, it would not be the first time this has happened. I have never checked mine to see if a blocked off jet is in that spot. But not now, it runs well and I never question good results. And yes, I have the brass slides and the two cycle floats and removed bushings as well.

Apparently there's a batch of these carbs with dodgy choke mechanisms. The choke doesn't seat correctly......equals much richness and an ineffectual pilot jet.

d

It's getting stripped down this week so I'll report what we find but I'm less than impressed with the MkII and wish I'd gone for a Mikuni ;( The build quality is suspect in my opinion and I also had the float stick (I think) resulting in petrol pouring out of the over flow.

I had the same issues and I find i don't trust the tickover when pulling up to a stop (say at a junction) as it has stalled a few times. I t will tick over at stand still fine, and when I get home! Apart from all that, it does start first kick or on the starter and it runs fine at anything over 10-20 mph.

No doubt further fiddling will sort it in the end......

The choke mechanism was taken off and sure enough the small rubber seat was marked clearly showing the choke had not been seating correctly. The forked choke lifter was putting side force onto the plunger meaning it wasn't seating correctly allowing fuel to be drawn in even with the choke off.

A small file was used to create more clearance in the fork and this seems to have sported it.

d

Had the same problem with the choke mechanism and had to slightly bend the fork to make sure the choke closed properly. I'm waiting for 20 and 25 pilot jets to experiment with (I have a 15 at the moment). I have noticed a range of throttle, about 1/8 - 1/4 where I get absolutely no variation in speed (I need to check again to be sure) then the bike takes off like a rocket!. I've marked-up my twist grip with white "corrector fluid" to better see where I am with the throttle opening.