Ideas for jetting a Dommy 99 600 with Amal Mk 1s

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CJSP

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I have just acquired a cafe racer (62 model 50 frame, 1960 Model 99 600 motor) with dual Amal Mk 1s fitted. Main jets are different (200/220), needles are 105 and pilot jets are 15. Plan to try 220/105/20 based on what I have seen from various threads. Am I about right? Thx
 
CJSP said:
I have just acquired a cafe racer (62 model 50 frame, 1960 Model 99 600 motor) with dual Amal Mk 1s fitted. Main jets are different (200/220), needles are 105 and pilot jets are 15. Plan to try 220/105/20 based on what I have seen from various threads. Am I about right? Thx
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According to Amal it came with dual 376, 1-1/16" carbs. 250 main jets, 106 needle jet, clip in bottom position on needle, 3 cutaway. Those jets should be close for a pair of MK1 626 or 928 carbs but neither of them will normally mount as they have 2.00" between centers of the mounting flange and the 375/376/389 series has 1.625". Since they are already mounted, I guess there were manifolds to make that happen. What are the carb numbers on the carbs?

If you want them, the correct carbs are out of stock, but you could ask AMAL if they will have them: https://amalcarb.co.uk/su/21/ack316.html
 
CJSP said:
I have just acquired a cafe racer (62 model 50 frame, 1960 Model 99 600 motor) with dual Amal Mk 1s fitted. Main jets are different (200/220), needles are 105 and pilot jets are 15. Plan to try 220/105/20 based on what I have seen from various threads. Am I about right? Thx
Click to expand...


Hi CSJP
May be able to help a little as I am running a 1959 Dominator with twin Mk1 non Premier 26mm Amals but bike has a later 650ss downdraft head fitted. Air filers are foam pods

When I got the bike it ran reasonably well on 106, no3 slide, middle needle notch and 210 mains. But fuel consumption was poor at about 50mpg.

I then tweaked the settings using experience from running a 1974 Triumph Daytona which also runs a pair of 26mm Mark 1s.

Currently running 106 no3 needle top notch with the pilot bush drilled to 17 thou. Fuel level set to 6mm below the float bowl flange. Now runs much better mid range and at higher throttle openings fuel consumption out to 70-75mpg.

There may to be more to be had from the bike yet and so I will be doing further work as follows

1/ See if it will run / pickup smoothly on a pair of 3.5 slides.

2/ Try 190 mains to see if that further improve top end response

3/ This later head is circa 28.5mm inlet diameter which must have been a compromise for Norton as all the parts list show a slip in 26mm diameter liner was offered / fitted to 500ss and 650ss bikes. Rather like the current debate on RH4 inlet tract sizes I feel 26mm diameter sleeves will be beneficial on a mere 600. These sleeves are available from Roger at RGM motors.

Recent tuning experience on a1960 500 which ran well in every respect to 75mph showed too big a main jet by just 1 or two sizes kills to end performance.

Finally I used plug gauges / number drills to check all jets / needles were on size.

So my view on your bike check fuel height bin the 105s for starters then tweak as required.

Cheers Keith
 
TT
I have just bought it as a non-runner so cleaning the carbs out and discovered different jets. So plan to get a rebuild kit from Amal and ultrasonic the carbs and rebuild. So yet to fire!

Greg

There is a manifold to mount the Mk 1s. The numbers are Left: 626 L301, Right: 626 R50 with a random 54 stamped to the left of the carb number.

Keith,
So try 210 main, 106 needle, and 17 pilot? I already have 3.5 slides. Needles are 3 cut aways set in middle position currently.

As an aside the crankcase has a 99C followed by a number stamped on the left rear below the barrel. This is separate to the 14 R and engine number. What does this designate?

Thanks all,

Charlie
 
CJSP said:
Greg

There is a manifold to mount the Mk 1s. The numbers are Left: 626 L301, Right: 626 R50 with a random 54 stamped to the left of the carb number.
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626 carbs are all basically the same except jetting.

L301 left carb with means generic jetting. Came with 160 Main Jet, 106 Needle Jet, 3 cutaway and needle clip in middle position.
R50 is not a number listed by AMAL which normally means never made but errors do exist. 54 is a left-hand carb so that makes no sense.

Unless you're going to ride at 3/4 throttle or more, the main jets you have are fine for now as long as they are the same. 3-1/2 slides are probably too lean, but they only have real effect at 1/8 to 1/4 throttle so use what you have for now. Most riding is 1/4 to 3/4 throttle and 106 needle jets are almost always the right jets. I would start with the needle clip in the middle. If they are premier carbs, AMAL says #17, but most use #19 for just about everything. #17 will work fine but good idle is easier to get with #19 and they help a little with starting.

 
Greg
The slides are worn so I was planning to replace, hence you recommend 3's rather than 3 1/2?
Many thanks
Charlie
 
Pay particular attention to the pilot jet bush
It needs to be rodded out
The ultrasonic won't touch it
 
CJSP said:
Greg
The slides are worn so I was planning to replace, hence you recommend 3's rather than 3 1/2?
Many thanks
Charlie
Click to expand...
If you go for the 3 cutaway you can change it to a 3 1/2 with a couple of swipes of a barstard file
 
CJSP said:
As an aside the crankcase has a 99C followed by a number stamped on the left rear below the barrel. This is separate to the 14 R and engine number. What does this designate?
Click to expand...
99C - 600cc coil ignition. Can be from a Dominator or Nomad

14R - Dominator 99 code

The number under the 99C is a factory assembly number, may or may not be in sequence of when built as compared to other numbers.
 
baz said:
If you go for the 3 cutaway you can change it to a 3 1/2 with a couple of swipes of a barstard file
Click to expand...
Baz
baz said:
Pay particular attention to the pilot jet bush
It needs to be rodded out
The ultrasonic won't touch it
Click to expand...
Baz, are you refering to the removal pilot or a bush pressed into the body of the carb? I have read references to the use of 16 thou drills held in a WD40 spray tube..
Thx
Charlie
 
All just a further point. I do not have premier carbs hence the pilot is screwed up into the base of the carb body and Amal recommend a 25cc for this app.
 
CJSP said:
Greg
The slides are worn so I was planning to replace, hence you recommend 3's rather than 3 1/2?
Many thanks
Charlie
Click to expand...
I would. That's what it would have had with a pair of 1-1/16" 376 carbs which are 27mm bores and you have 26mm bores so close.
 
CJSP said:
All just a further point. I do not have premier carbs hence the pilot is screwed up into the base of the carb body and Amal recommend a 25cc for this app.
Click to expand...
Wow! Those are VERY old. AMAL quit using those very soon after the concentric carbs came out. They switched to the hidden jets that have cause so many issues.

I would live with the current slides, get the jetting figured out and then buy a set of Aluminum Premier 626 carbs with the jetting you figure out. While doing that I see how it runs between 1/8 and 1/4 throttle to determine whether 3 or 3-1/2 slides are best and if a toss-up, I would get 3.
 
CJSP said:
Baz

Baz, are you refering to the removal pilot or a bush pressed into the body of the carb? I have read references to the use of 16 thou drills held in a WD40 spray tube..
Thx
Charlie
Click to expand...
Yes
 
Take a look at bushman's carb tuning secrets to get a good Idea of how the mk1s work
And what to look out for
626 carbs can be bored to 27 mm
That's basically what they did for the trident/rocket 3
You could of course go for the 928 MK1s
It all depends on what you are going to use the bike for
I love a single carb on a Brit twin but there are many opinions on this and plenty of options
 
The bike is being built to ride locally, with pace but not a race bike, good quick (for the model) and a reliable starter and runner. Bit of fun really, different to my shovel with apes and my KTM 890 which goes literally anywhere!!
 
Hah, just found one of the concentrics has a two stroke brass bush in the centre of the car, it is chamfered off as on amal website. I'll see if i can get a 4 stroke one to press in or see if Amal will do it..
 
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