Amal Mk2 air jet question

fiatfan

fiatfan

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Since I´m having an inconceivable (at least to me) problem with my new single Mikuni 34mm on my -73 850, I thought that I´d give an old Amal Mk2 34mm, made in Spain!, a go. It´s my only alternative at the moment. After a lot of reading I was going to remove the air jet, but of course it wouldn´t let go. Tried to use a screw to pull it out but no luck. So I tried to carefully drill it out, but after I got about 2-2.5mm in it is just solid aluminium, no hole. Should I drill deeper? The jet looks pretty long on pictures. The hole in the jet was 2mm diameter, unfortunatly I didn´t check how deep the hole was but it should go all the way through the jet?
I also have to replace several parts since it have probably been used on a 2-stroke.
\Tommy
 
You definitely have to remove that air jet.

But your description scares me as to the risk of swarf etc getting into the airways.

Once you’ve done this, you need to revert to standard 4 stroke settings and you must replace all needles, jets, jet holder, etc in order to be sure you are starting from the correct / known, baseline.

What’s the problem with your Mikuni? I would suggest your time and money might be better spent resolving this? They’re a nice carb, and if yours is brand new you have the perfect base.
 
Last edited:
Fast Eddie said:
You definitely have to remove that air jet.

But your description scares me as to the risk of swarf etc in getting into the airways.

Once you’ve done this, you need to revert to standard 4 stroke settings and you must replace all needles, jets, jet holder, etc in order to be sure you are starting from the correct / known, baseline.

What’s the problem with your Mikuni? I would suggest your time and money might be better spent resolving this? They’re a nice carb, and if yours is brand new you have the perfect base.
Click to expand...
I´m trying....:D The carb is in pieces and I hace had it ultrasonically (?) cleaned, a friend has a proper machine so I´ll use that again when I´m done with the jet, and blow it through with compressed air. I think I´m on track with an initial set-up for my bike.
Now the Mikuni.... something is not right with the low speed circuit, can´t get it to idle properly, little or no impact when turning the blending screw. Been all the way down to 25 low speed jet, but then I had no idle at all. And the worst thing is, and this is difficult to explain in another language than my own; if I for example drive say 60/70 mph in 4:th gear and change down to third, when the revs goes down to about 2500 rpm and lower, and I still have no gas, the engine starts igniting and the bike starts twiching. To me it seems like fuel somehow is drawn in through the carb though the slide is all the way down. Where and how I don´t understand. I have just had it cleaned in my friends machine, not driven the bike since.
 
fiatfan said:
I´m trying....:D The carb is in pieces and I hace had it ultrasonically (?) cleaned, a friend has a proper machine so I´ll use that again when I´m done with the jet, and blow it through with compressed air. I think I´m on track with an initial set-up for my bike.
Now the Mikuni.... something is not right with the low speed circuit, can´t get it to idle properly, little or no impact when turning the blending screw. Been all the way down to 25 low speed jet, but then I had no idle at all. And the worst thing is, and this is difficult to explain in another language than my own; if I for example drive say 60/70 mph in 4:th gear and change down to third, when the revs goes down to about 2500 rpm and lower, and I still have no gas, the engine starts igniting and the bike starts twiching. To me it seems like fuel somehow is drawn in through the carb though the slide is all the way down. Where and how I don´t understand. I have just had it cleaned in my friends machine, not driven the bike since.
Click to expand...
Are you sure your enricher is not leaking?
 
marshg246 said:
Are you sure your enricher is not leaking?
Click to expand...
That´s the choke right? I have had it out and measured the length of it and compared it with how deep the hole is. As far as I can understand the plunger should bottom out against the tube that comes up in the bottom. There is also an imprint in the rubber end of the plunger. I have also checked that the slide isn´t too high when in the bottom position, I read somewhere that if it is too high, fuel can leak up through the needle jet. I also tried lowering the needle one step, but then it was almost impossible to drive when I turned the choke off.
 
Don´t know what this is called, does it also need replacing when going from 2-stroke to 4-stroke?
Amal Mk2 air jet question
 
Yup, “spray tube”.

And yup, 2 strokes and 4 strokes are different. There may be other different types as well, for example on mk1s Amal made special spray tubes for Triumph triples, late Commandos, etc.

Best to fit a new 4 stroke one IMO to be sure.

For reference, this is a NOS 36mm 4 stroke MK11… the spray tube is quite different to yours…

IMG_3906.jpeg
IMG_3905.jpeg
 
Last edited:
fiatfan said:
Since I´m having an inconceivable (at least to me) problem with my new single Mikuni 34mm on my -73 850, I thought that I´d give an old Amal Mk2 34mm, made in Spain!, a go. It´s my only alternative at the moment. After a lot of reading I was going to remove the air jet, but of course it wouldn´t let go. Tried to use a screw to pull it out but no luck. So I tried to carefully drill it out, but after I got about 2-2.5mm in it is just solid aluminium, no hole. Should I drill deeper? The jet looks pretty long on pictures. The hole in the jet was 2mm diameter, unfortunatly I didn´t check how deep the hole was but it should go all the way through the jet?
I also have to replace several parts since it have probably been used on a 2-stroke.
\Tommy
Click to expand...
Recently went through two Mk 2's.
One jet popped out, the other needed a soak in some carb cleaner. then dropped out.
This is what I used. It's about all we can get in California.

Berryman® Chem-Dip® Carburetor Parts Cleaner

www.berrymanproducts.com www.berrymanproducts.com
 
fiatfan said:
That´s the choke right? I have had it out and measured the length of it and compared it with how deep the hole is. As far as I can understand the plunger should bottom out against the tube that comes up in the bottom. There is also an imprint in the rubber end of the plunger. I have also checked that the slide isn´t too high when in the bottom position, I read somewhere that if it is too high, fuel can leak up through the needle jet. I also tried lowering the needle one step, but then it was almost impossible to drive when I turned the choke off.
Click to expand...
I had fougth with a mik for days , then I bougth a chinese plunger and problem solved ....(about 2 quids!)
 
Why should a two-stroke carb be different from a four-stroke carb when they both do the same thing ? A two-stroke carb is usually jetted leaner than a four-stroke carb - but the tuning sequence is the same - start rich -then lean-off. When the motor is warm, it should idle when the throttle is closed. wind the petrol control screw in until the engine misses then richen slightly. - Same when setting the needle and needle jet - lower the needle until the motor misses, then raise it one notch. Main jets should always be slightly too rich, so fit the bigger recommended size. If you use this sequence and an air or pilot jet needs changing, you might find the need more easily.
 
Fast Eddie said:
Yup, “spray tube”.

And yup, 2 strokes and 4 strokes are different. There may be other different types as well, for example on mk1s Amal made special spray tubes for Triumph triples, late Commandos, etc.

Best to fit a new 4 stroke one IMO to be sure.

For reference, this is a NOS 36mm 4 stroke MK11… the spray tube is quite different to yours…

View attachment 121219View attachment 121220
Click to expand...
That is quite a bit smaller, well not as high anyway. I haven´t seen anyone who sells those.
 

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