question about Amal Mk 2 reassembly--and cold start

Hi All: Firstly, thanks for the help over the past months getting my '74 Commando up-and-running. It is still diabolical to start when cold, starts well when warm, but I think I've figured out why, and I'd like some advice:

So I checked the plugs after kicking the bike over more than a dozen times when cold. Absolutely dry! Thus it is not getting fuel into the cylinders. I blocked off one of the plastic overflow pipes from the carb bowl, and sucked the other. This created a vacuum in the bowl, and drew fuel into the bowl. One kick, and by gawd, the bike fired. Thus my suspicion was a stuck float needle (I have one with the Niton tip). I previously determined that the float level was too low, but fixed that so that the top 1/16" of the float is visible along the top of the float bowl, and parallel with the rim, when I put a little pressure on the float needle. I just stripped the carb again, and the float needle appears to be absolutely fine without any apparent stickiness at all, but I'm wondering whether modern fuels may affect the Niton and after a day or two of sitting, the needle sticks in its orifice.

Here's the thing: when I first stripped the carb, the needle clip was attached to the needle at the bottom slot of the needle, as per the photo, and there was also a 'C' clip there, wedged between the needle clip and the needle retaining disc (you can see the round stain on the retaining disc where that 'C' clip sat (and it is in the photo)). On the Amal diagrams I only see one needle clip, but I can't see which slot it should be in. Which slot is the correct one? Is it possible that my whole problem was caused by the needle clip being in the wrong groove on the needle, and that was ultimately lowering the needle too far and closing off the inlet for fuel to the bowl? In other words, could the problem be with the placement of that needle clip, rather than the float needle sticking?

Please chime in--and be aware that I am a noob with Amals and Nortons, and thus need clear guidance. [/URL

I believe that the big circlip you show is actually out of a mk1 carb. The mk2 should have the small one.

The small circlip sits directly on the bottom of the slide, the large washer you show then sits on top of the circlip and the spring holds it all together.

I think the small lip you show on the large washer faces upwards, but check to see if it aligns with anything as I'm only working from (a poor) memory here!

Try this link to an exploded diagram of the mk2 carb.

As to which groove the needle circlip goes in, the different grove are to alter the needle mixture, lowering it = weaker, raising it = richer. If the bike ran well previously, put it back where it was. If you've never run the bike properly, and are starting from zero, put it in the middle.

The fact that you have some mk1 parts in your mk2 carb would worry me. how do you know the rest of the parts are correct? The needles are different for the two types.

Thanks, Fast Eddie. Interestingly, now that you mention it, I notice that the small circlip sits nicely in a hollowed-out centre section of the slider. The big needle clip (which you think is from a Mk 1) is too big to sit nicely in the same space. The small circlip is the wrong one regardless, because it won't sit tightly in one of the grooves of the needle. I'm going down to my local Norton parts guy on Thursday and will ask him to check and rectify mix-and-match parts.

Any thoughts on my issue with the float needle?

Nielsen said:

Thanks, Fast Eddie. Interestingly, now that you mention it, I notice that the small circlip sits nicely in a hollowed-out centre section of the slider. The big needle clip (which you think is from a Mk 1) is too big to sit nicely in the same space. The small circlip is the wrong one regardless, because it won't sit tightly in one of the grooves of the needle. I'm going down to my local Norton parts guy on Thursday and will ask him to check and rectify mix-and-match parts.

Any thoughts on my issue with the float needle?

Click to expand...

Well, if you think the float needle looks fine, it may be wise to check out that the cold start system is working correctly. mk2 carbs dot have ticklers, so do need a properly working cold start system.

I think your best plan is to take the entire carb to your local man for a thorough inspection.

My thinking too. I have the float bowl on my workbench, with the float and float needle in place, the bowl full of petrol (I note you are in GB, so saying 'gas' may make you think I farted in the bowl). Will leave it like that for a couple of days, then suck out the petrol and see if the float needle opens or is stuck.

Nielsen, you did not mention when discussing your cold start reluctance if you depressed both carb's ticklers to the point of gas leaking out, this is a necessity!

also, you are not using the chokes for cold starting or your carbs do not have them inside and working?

No ticklers on this carb ( the bike was converted to a single carb). It's an Amal Mk 2 with the cable-operated cold start system--which seems to be in good working order now.

Fast Eddie is correct, the small circlip is the correct one, they can get worn and a bit loose, so I'd get a new one.

The small lip on the large washer faces down.


Since the fuel union is on the bottom of the float bowl it's very easy to check the float valve operation.. simply remove the float bowl, attach the fuel line to the fuel tank and with the float and float valve fitted, turn on the fuel. You should see the fuel flowing in and stopping at the correct level.

Mk2 carbs with cold start issues first check for a blocked cold start jet

this is located in the float chamber gasket face ( looks the same as a pilot jet ) and very easily blocked

It will also be worth checking the Viton tip has not become detatched from the cold start plunger and is blocking the orifice ( been caught my self with that problem )

remove the cold start plunger and blow out with carb cleaner through both the upper body drillings and the float chamber internal pick up orifice and cold start jet ensure they are all clear any of any blockage

if the float bowl has fuel present and all the drillings jets are clean it should pick up Gas at kick starter speed ( don't forget to remove the feed banjo and check for blocked filter )

Also might be worth checking fuel flow in to the carb by by connecting fuel pipes

then remove the float bowl drain plug switch on fuel taps place a container under the drain plug and collect the fuel

it could be a blocked tap filter and not a carb issue

if you are running say a 200 main jet the flow rate should be greater than 200cc per minute

Thanks for the replies! I'll be going in to the city tomorrow to have the carb checked over, and new parts where needed. Will report back. Is it really possible that my problem could be caused by the wrong clip holding the needle in place. Seems so unlikely--but then I'm far from expert. It is so weird that the spark plugs are absolutely dry after multiple kicks. Once the bike is warm, it starts OK with one or two kicks. Then when I sucked gas into the float bowl it started second kick from cold. Still suspect the float needle, but it looks to be in perfect condition. A head scratcher...... (which may explain my baldness).

I did clean out the entire cold start system, then did it again. It was clean. No guck. Viton tip on the plunger looks OK (not brilliant) and is certainly not coming apart.

Nielsen said:

Thanks for the replies! I'll be going in to the city tomorrow to have the carb checked over, and new parts where needed. Will report back. Is it really possible that my problem could be caused by the wrong clip holding the needle in place. Seems so unlikely--but then I'm far from expert. It is so weird that the spark plugs are absolutely dry after multiple kicks. Once the bike is warm, it starts OK with one or two kicks. Then when I sucked gas into the float bowl it started second kick from cold. Still suspect the float needle, but it looks to be in perfect condition. A head scratcher...... (which may explain my baldness).

I did clean out the entire cold start system, then did it again. It was clean. No guck. Viton tip on the plunger looks OK (not brilliant) and is certainly not coming apart.

Click to expand...

No, the wrong clip is most definitely not causing your problem, something else is.

IF everything in the carb is correct (for the model) and correctly specified, then my money, despite it looking good to you so far, is still on some fault in the cold start system, or pilot system.

But, the wrong clip shows that someone has mix n matched from their parts bin. It is very easy to mix n match bits that fit... but are wrong. eg, mk1 and mk2 have different needles, the mk 2 also has different needle types, they have different needle jets, to complicate matters further, and there are many different types of emulsion tubes, there are different parts for 2 and 4 strokes, they all look similar and fit, but won't work as intended in the wrong application.

So, it is a real possibility that you have some wrong components, and this will need to be determined by someone who knows these carbs very well.

Nevertheless, for my money, lack of fuel when kick starting still points to either the pilot fuel circuit and / or the cold start circuit and / or a general blockage... or empty tank!

I did check the tank!

Nielsen said:

I did check the tank!

Click to expand...

I once had a race bike splutter and eventually cut out. I had been having carb trouble for a while, so immediately got stuck into stripping them down again.

Whilst I had the carbs partially striped, I noticed I had forgotten to turn off the petrol taps... yet no petrol was coming out... I had a millisecond of confusion until the embarrassing truth dawned on me. What a reason for a DNF !!

Don't tell anyone this story though...

Your secret is safe with me, and think: it was better than running out of oil!

Fast Eddie said:

Nielsen said:

I did check the tank!

Click to expand...

I once had a race bike splutter and eventually cut out. I had been having carb trouble for a while, so immediately got stuck into stripping them down again.

Whilst I had the carbs partially striped, I noticed I had forgotten to turn off the petrol taps... yet no petrol was coming out... I had a millisecond of confusion until the embarrassing truth dawned on me. What a reason for a DNF !!

Don't tell anyone this story though...

Click to expand...

You were just following the great tradition of the Norton factory team. (P Williams Isle of Man)

Fast Eddie wrote;

the mk 2 also has different needle types, they have different needle jets

Click to expand...

I knew the needles were different but I was unaware that the needle jets were different to mk1's. Thanks for that, that'll save me "economising" and putting new spare Mk1 needle jets in my Mk 2's

Reggie said:

Fast Eddie wrote;

the mk 2 also has different needle types, they have different needle jets

Click to expand...

I knew the needles were different but I was unaware that the needle jets were different to mk1's. Thanks for that, that'll save me "economising" and putting new spare Mk1 needle jets in my Mk 2's

Click to expand...

If (and I mean IF) I recall correctly, the mk2 jets are taller, and have a groove machined around the outside for identification purposes.
However, I've no idea what the effect is of fitting the wrong ones!

I have heard that the needle jets are different for Mk1 and Mk2 but they have the same part number on Amal's website.

pommie john wrote;

I have heard that the needle jets are different for Mk1 and Mk2 but they have the same part number on Amal's website.

Click to expand...

Here are the numbers. 122-105 are the same, but the model designation are different, 622 2928.....so are they different :?:

MK1 Concentric
Product No: 622/122-105,
Name: Needle Jet - 4 Stroke - Size 105

MK2 Concentric.
Product No: 2928/122-105
Name: Needle Jet - Size 105 - 4 Stroke

Reggie said:

pommie john wrote;

I have heard that the needle jets are different for Mk1 and Mk2 but they have the same part number on Amal's website.

Click to expand...

Here are the numbers. 122-105 are the same, but the model designation are different, 622 2928.....so are they different :?:

MK1 Concentric
Product No: 622/122-105,
Name: Needle Jet - 4 Stroke - Size 105

MK2 Concentric.
Product No: 2928/122-105
Name: Needle Jet - Size 105 - 4 Stroke

Click to expand...

I looked at he 2000 series Mk2 ( which is the carb I have ) and it is listed with 622/122-105