amals

Ever since I bought my 1974 mk 11a 850 it has had a mind of its own when at idle. Sometimes its ok , then when you want it to idle,say at lights, it stalls. Also if you give the throttle a quick blip, it will splutter. Its ok if you rev it gradually, just not too fast.
I`m assuming the carb slides are worn out, as when I fit them there is a good 0.5 to 1mm side to side movement in the throttle body. Is this normal?
The motor has had new valves ,guides and springs plus a pw3 cam. This made no difference to the idle which will not go below 1100rpm.
The carbs are amal 34mm and have only done 9000 miles. I have replaced all jets and needles.
Any ideas,
thanks

blacklav said:

I`m assuming the carb slides are worn out, as when I fit them there is a good 0.5 to 1mm side to side movement in the throttle body. Is this normal?

Click to expand...

Yes, that's normal-for worn out!

I believe the standard Amal slide clearance is 0.0035" (0.0889mm).

blacklav said:

...it has had a mind of its own when at idle....
...the carb slides are worn out, as when I fit them there is a good 0.5 to 1mm side to side movement in the throttle body....

Click to expand...

Yikes! Borrow from Steve's bag of tricks, and grease up the slides. If your idle is suddenly much improved, you might get away with replacing just the slides. If you do, please let us know how well this works, as I'm in the same boat with mine (10k miles). However, I'd venture to guess that 0.5 - 1.0 mm is a combined slide/body issue.

Nathan

I replaced the slides in my 13K mile 930's with some anodized slides and the improvement was noticeable, but not acceptable. I finally sent them to Lunds and he sleeved/honed them and now I can take my hand off the throttle and it idles perfectly. Go for it, about $200, it's worth it. Or if the both carbs need rebuilding, you might as well buy new premiers. Then I sold the anodized slides.

When I bought my Combat, idle was very erratic.
It had an old Boyer EI, and even older Amals.

After much trial and error, I now have a smooth idle, superb acceleration, easy startup, and a very happy owner.

The magic formula for me:
Amal Premiers
Tri-Spark ignition,
Moroso resistor spark plug leads
Non-resistor NGK plugs.

blacklav said:

Ever since I bought my 1974 mk 11a 850 it has had a mind of its own when at idle. Sometimes its ok , then when you want it to idle,say at lights, it stalls. Also if you give the throttle a quick blip, it will splutter. Its ok if you rev it gradually, just not too fast.
I`m assuming the carb slides are worn out, as when I fit them there is a good 0.5 to 1mm side to side movement in the throttle body. Is this normal?
The motor has had new valves ,guides and springs plus a pw3 cam. This made no difference to the idle which will not go below 1100rpm.
The carbs are amal 34mm and have only done 9000 miles. I have replaced all jets and needles.
Any ideas,
thanks

Click to expand...

Hi blacklav.
If the carbys have only done 9000m I struggle to see how they could be worn 0.5 to 1.0mm. Could you please measure them per the last pages of the thread 'Needing Air'.
Tuning is about air control and the addition of fuel to that airflow. 34mm carbys must have slower airflow above idle simply due to diameter once the slide lifts (why 34mm?). I am looking at AMAL carby improvements at present and have sorted out idle by the installation of a Viton seal. Next, I found airflow control from pilot circuit to needle jet fuel draw transition difficult to achieve due to poorly designed airflow. This is resolved on my bike but tests are still being quantified. I will keep you posted. What size slide cutaway and needle jet are you using?
Ta.

Are you sure they are 34mm? Most are 32s.
Jaydee

My 930's were worn out in about 5K miles and wouldn't maintain a decent idle. Pazon helped but the sleeving did the trick. YMMV.

Just about anything you can do to improve the original bike will help. There are so many good options available now.

Sorry to hi jack but my commando is in the same boat. trying to figure out a place to send my old ones to be honed/sleeved. Any suggestions?

You might want to stay original but the single Mikuni works just fine for me and the conversion is reasonable.

jaydee75 said:

Are you sure they are 34mm? Most are 32s.

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Yes, that needs looking into.
Amal don't make 34mm concentrics.

Unless they are the Mk 2 type ?

Rohan said:

jaydee75 said:

Are you sure they are 34mm? Most are 32s.

Click to expand...

Yes, that needs looking into.
Amal don't make 34mm concentrics.

Unless they are the Mk 2 type ?

Click to expand...

AMAL 1000 series Concentrics are/were 34mm, 36mm, 38mm.
Ta.

Those 1000 series don't fit in there though, do they ?

And were mostly ? sold as 2 stroke versions too, which is a trap for young players...

Rohan said:

Those 1000 series don't fit in there though, do they ?

And were mostly ? sold as 2 stroke versions too, which is a trap for young players...

Click to expand...

Refer original post e.g. "...my 1974 mk 11a 850 ... carbs are amal 34mm..."
Ta.

Yes, but a pair of them won't fit in there. (?) They are significantly larger (physically) than anything fitted stock.

So you'd expect someone to especially note if they had managed to shoehorn em in there, somehow...
Its more likely a case of mistaken identity (?).

Which is where the line "Yes, that needs looking into" comes into it.
We are likely to need some further info to decide if anything is 'normal' in this instance...

Rohan said:

Yes, but a pair of them won't fit in there. (?) They are significantly larger (physically) than anything fitted stock.

So you'd expect someone to especially note if they had managed to shoehorn em in there, somehow...
Its more likely a case of mistaken identity (?).

Which is where the line "Yes, that needs looking into" comes into it.
We are likely to need some further info to decide if anything is 'normal' in this instance...

Click to expand...

900 series vs 1000 series dimensions at https://www.google.com.au/url?sa=t&sour ... _lyni01f8Q
Ta.

NoiseyNorton said:

Sorry to hi jack but my commando is in the same boat. trying to figure out a place to send my old ones to be honed/sleeved. Any suggestions?

Click to expand...

This is where I sent mine. Took about 2 weeks. http://amalsleeve.com/ I think there's a fella in Canada that does them too.

needing said:

Rohan said:

Yes, but a pair of them won't fit in there. (?) They are significantly larger (physically) than anything fitted stock.

So you'd expect someone to especially note if they had managed to shoehorn em in there, somehow...
Its more likely a case of mistaken identity (?).

Which is where the line "Yes, that needs looking into" comes into it.
We are likely to need some further info to decide if anything is 'normal' in this instance...

Click to expand...

900 series vs 1000 series dimensions at https://www.google.com.au/url?sa=t&sour ... _lyni01f8Q
Ta.

Click to expand...

Needing, thank you fotr the document. It clearly show how the 1000" could never work.
Having to file or grind the inside blanks of the 900's to fit, the 1000's, being a 1/4" wider, would surely make these non applicable, unless of course you splay your manifolds.

Yeah man nothing like Norton Commando family feuds. My best ridding bud took me to my first INOA rally and as we set looking at the seeming heavenly scene he leans over and says It All About The Bikes, implying many of those attending would have nothing to do with each otherwise.

As thread ran off birdge now here one to ponder on air fuel mixing concepts. I got a 2.5 hp Duddle Bug last year for a rally pits and home runabout but found it too weak to plow through tall grass or climb much a grade ya would not notice walking up, so... after seeing lawn mowers to V8s running on pure vapors from air sucked though gas I used Boy Scout canteen, some car a/c tubing and rubber hose and foam seal and pulled and pulled and pulled with ether spray to fire off while moving sliding hose over a/c alu tube series of air holes till it started idled and was able to plow through grass and climb decent slopes - amazing like 30% more power. Trouble is each day and temp jumidity changed the combo of air fuel puzzle but did center on narrow range than first attempt not even knowing if worked. I disconnected fuel hose to feed vapor into carb to keep its throttle function. Another issue on these vapor type systems is the constant refriguration of the bubbled gas volume. Some go to great lengths to route engine coolant or direct exhaust at the gas tanks. I lucked out exhaust passed near tank so a thin perferorated alu plate half shield half deflector puffs enough on canteen to keep it slightly warm and fueling well. I tapped a T from normal gas tank into canteen which has sight tube to keep its gas level about right. If too full vacuum can pull air through and if not enough goes too lean and stalls. Could work on a Commando too pulling through Amal slides.

pete.v said:

Needing, thank you fotr the document. It clearly show how the 1000" could never work.
Having to file or grind the inside blanks of the 900's to fit, the 1000's, being a 1/4" wider, would surely make these non applicable, unless of course you splay your manifolds.

Click to expand...

There is also the minor matter that the 1000 series use 2.5 inch stud centres on the mounting flanges,
against 2 inch for the 900 series.

This makes it near impossible to get them side-by-side to fit to the head at all.
I nearly said totally impossible, but I'm sure someone somewhere has figured out something.

We note the OP hasn't come back with further details...