correct set up for amal

hillbone

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Hi.
Im running a 932 single amal on my Atlas. All standard engine and pipes.
Does anyone have the basic configuration for his carb ?
Main jet. Pilot. Needle position. Needle. Needle jet. I know it will take mucking around from there. Also what is the best plug?
I also have a spare Mikuni from my Commando . Is it a good bet on the Atlas in lieu of the Amal.?
Cheers Hillbone
 
This has been a topic earlier on this forum. Try a search on "932 + atlas".

Unless you find a report from someone who has good success with a single 932 on an Atlas, I would use the stock single carb Atlas configuration as a starting point, and "fettle up" from there. Amal jet numbers refer to the fuel flow in ml / min, so I would expect the same jet no. in a concentric would deliver the same fuel flow in a monobloc.

My Norton Owners Manual Publication P106/P lists for the 750 Atlas and Scrambler the following data: (No publication date is listed)

Twin carbs:
Monobloc type 389/88 RH
389/87 LH

Main Jet 350
Needle Jet 106
Pilot jet 20
Throttle valve 3

Needle taper D
Needle position 3

Single carb:

Monobloc type 376/294

The remaining data is 400, 106, 20, 3 1/2, C, and 4 respectively.

A handy reference for bike and carb set ups is:

http://porklips.org/~mason/moto/amal_specs.html

For plugs, I have not heard of anyone doing better than the standard heat range 6.

Slick
 
Thanks again Tex.

I will use that guide. Also I will remove my oil tank and rebuild a new tower at the top with all your good advise and photos from the last post.
The bike is slowly getting there and is quite nice to ride. The plugs looked like the inside of chimneys so I will pull them down as soon as I get them off the bike.
Thanks again mate.
Cheers Hillbone.
 
Triton Thrasher said:
Don't use a Monobloc guide, for your 932.
Click to expand...

Indeed.
A concentric will positively drown your engine with a 350 main jet !!

Amal jet numbering for all but the later monoblocs was entirely different to concentric jet numberings.
Tex should know that, its been mentioned here before.

A 932 is also a shade larger than the 930 the Atlas came with.
The setup is listed in Roy Bacon, can quote it later today if no-one is there before.
 
Rohan said:
A concentric will positively drown your engine with a 350 main jet !!

Amal jet numbering for all but the later monoblocs was entirely different to concentric jet numberings.
Tex should know that, its been mentioned here before.

A 932 is also a shade larger than the 930 the Atlas came with.
The setup is listed in Roy Bacon, can quote it later today if no-one is there before.
Click to expand...

Rohan, you have challenged Amal jet numbering before, but you have never explained this quote from the official Amal web site. The following is a cut and paste from the Amal website, and the same notice is given for Monobloc and Concentrics:

All genuine AMAL jets are calibrated to a flow rate. The number e.g. 100 indicates that it will flow 100cc`s of fuel in one minute at a specified head. Beware of imitations as they are just drilled to a size. All our jets are branded and packaged with the official AMAL logo.

http://amalcarb.co.uk/monobloc-series/3 ... e-210.html

Slick
 
Try fitting a 450 main jet to a concentric, like is listed for some years/models of Norton monoblocs !!
Thats too big for alcohol even... (well, almost)

Somewhere in the small print is mentioned that Amal back in history somewhere (1966 ?) standardized the jet sizes between concentrics and monoblocs.
Perhaps Burlen have forgotten that prior to that, THE JET SIZES ARE TOTALLY DIFFERENT, and certainly not interchangeable.
 
So...........

I have a main jet of 270 and its as rich as. The needle has no markings on it so i cant tell if its a type C. It also has only 3 grooves so I cant select position 4 which I assume is the bottom groove.

My Roy Bacon book is on loan and thedude who has it is on holidays so I'm still a bit lost here.
Cheer Mark
 
hillbone said:
So...........

I have a main jet of 270 and its as rich as. The needle has no markings on it so i cant tell if its a type C. It also has only 3 grooves so I cant select position 4 which I assume is the bottom groove.

My Roy Bacon book is on loan and thedude who has it is on holidays so I'm still a bit lost here.
Cheer Mark
Click to expand...

The main jet really only applies to full throttle or thereabouts.
270 sounds pretty big though, long term a 750 commando 932 is more like 220

If its too rich at less than full throttle, the needle needs dropping down.
Try the clip in the next highest position from where it is now.

Always watch for signs of heat when playing with carbs, it doesn't take too much wrong to melt a piston...
 
270 for a single Amal 932 sounds about right. I run two 240 on the road and two 260 on track days with my 850 racer.

The original 1960's-1970's specs are NOT directly applyible with modern petrol. Certainly here in Belgium.
 
Jagbruno said:
The original 1960's-1970's specs are NOT directly applyible with modern petrol. Certainly here in Belgium.
Click to expand...

I have sent an email to Burlen Fuel Systems (Amal) Tech Support to get a clarification on this issue. Have not yet received an answer .... maybe never will.

Slick
 
Triton Thrasher said:
hillbone said:
Don't use a Monobloc guide, for your 932.
Click to expand...
Click to expand...

+1

As far as I am aware Norton never fitted the single carb manifold with a 32mm /932 carb to the Atlas.
The equitant to the single 1 13/16 Monoblock fitted was the 930/ 30mm Concentric.
So it looks like you are on your own here.

BTY, did you know that when Norton fitted the single carb manifold with the Monoblock from the factory they fitted a split inlet port reducing collar.
This enabled the bike to run a non snatch top gear speed all the way down to 15 mph, ( this would be even lower with sidecar gearing) which allowed the engine to achieve a near 100mph range in top gear.
I had a GM 2.3 litre van with a single carb that also had split collars in the inlet ports which allowed a low non snatch top gear speed like my Norton Atlas- and stupidly I removed all of them. I can tell you, in both cases, that they knew what they were doing.
 
I don't think too many guys would ride their bike with the carbs jetted too lean on the needle jet. The motor would cough and miss on every gear change. However I also don't think too many pistons are burnt by running too lean on the needle jet - it usually occurs through having a blast at full throttle with the main jets too lean. I tend to run slightly rich on the mains and lean off on the needles as much as possible without causing the cough. You need to check that at full throttle the metering is being done by the main jets and NOT the needles. Fit the next size mains and do a plug chop - if it doesn't richen, you have a problem which can be rectified by recessing the mains so the tip of the needle remains trapped. (It is possible to have the metering done off the tip of the needle at full throttle. That can burn a piston. )
The numbers on the needle jets are thousands of an inch hole diameter. The numbers on the mains are flow measurement, however they are radically different for the various types of carbs. Late model concentric main jets are smaller than early monobloc main jets.
 
Sorry if I sounded long-winded in my previous post. My brother and I have been tuning 750cc two strokes on methanol and we have almost come to blows over jetting carbs. If you get it wrong with a two stroke you immediately cop the big bill. The Commando is easy - just fit main jets that are too large until you get the rest right.
 
acotrel said:
The motor would cough
Click to expand...

Alan I've not heard a motor on petrol 'cough', no matter how it was jetted.
Unless it ran completely out of fuel....

If they are really lean, the motor 'hunts' and won't pull.
If they are really rich, they blow black smoke and 8 stroke.

You've been racing with methanol too long ??
 
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