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

The carbs need to be identical in all respects. The slide cutaway usually only affects throtlle openings below one third and usually works in conjunction with the idle circuit., and it is nornal to have main jets which are slightly too rich. THe thing you need to get correct is the needle jets and needles. When you lower the needles, you should be able to cause the motor to miss, then raise the needles one notch. If you cannot induce the miss, fit the next smaller needle jet. If the clip is in the bottom notch of the needle, you are either too rich, or you have run out of adjustment- need the bigger needle jet
 
CJSP said:
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..
Click to expand...

Hi again CSJP,
Apologies I missed the 20 indicating the carbs were the very early Mk1s.

These carbs were modified by Amal soon after introduction to improve slow running on some bikes Triumph Daytona for one.

Your carbs are old and didn't work well when new. The slides are worn and possibly the bodies too. They are made out of a zinc alloy which distorts for fun. Flange face, float bowl face and carb body all to be checked for being flat / not distorted on the slide bore. Look really closely before spending on spares for what are likely scrap bodies.

The original type of slides are not worth fitting monkey metal and they will wear very quickly. The anodised slides are much better but a chunk of money.

I am thinking you could end up spending a chunk of money on spares and still end up withe uneven idle due to body wear.

The Aluminum bodied Premiers work really well don't distort and no slide wear 10k+ miles.

If you need 26mm slide diameters measured I can do that on some new anodised slides. Not sure what clearances Amal build into the bore but believe it to be circa 2 or 3 thou. Some one should be able to confirm either way.

If you elect the spares option then no 3 slide, 25 pilot jet, 200main and top needle notch get my vote.

Lot to think about.

Keith
 
Henrynorton said:
Hi again CSJP,
Apologies I missed the 20 indicating the carbs were the very early Mk1s.

These carbs were modified by Amal soon after introduction to improve slow running on some bikes Triumph Daytona for one.

Your carbs are old and didn't work well when new. The slides are worn and possibly the bodies too. They are made out of a zinc alloy which distorts for fun. Flange face, float bowl face and carb body all to be checked for being flat / not distorted on the slide bore. Look really closely before spending on spares for what are likely scrap bodies.

The original type of slides are not worth fitting monkey metal and they will wear very quickly. The anodised slides are much better but a chunk of money.

I am thinking you could end up spending a chunk of money on spares and still end up withe uneven idle due to body wear.

The Aluminum bodied Premiers work really well don't distort and no slide wear 10k+ miles.

If you need 26mm slide diameters measured I can do that on some new anodised slides. Not sure what clearances Amal build into the bore but believe it to be circa 2 or 3 thou. Some one should be able to confirm either way.

If you elect the spares option then no 3 slide, 25 pilot jet, 200main and top needle notch get my vote.

Lot to think about.

Keith
Click to expand...
Spot on.
 
Kudos for running twin MK1s on your cafe racer for looks
But you may be better off running a single 28 or 30 MK1 on your 600 twin
I don't want to turn this into a twin verses single carb debate
This is just my opinion
And you'll end up with a great b road scratcher
I'm guessing you won't be holding it flat out on a motorway,so a single carb would be my choice
It'll make the bike nicer to live with and a great contrast to your Harley and KTM
 
I don't think we have motorcycle wreckers in Australia these days. Sometimes when I was building bikes, I would visit the wreckers to buy something better than I already had. You probably would not want Mikuni carbs on a British bike. Whatever carbs you use, you always have the same tuning problem, so there needs to be a convenient source for jets
 
Belated thanks to all that contributed. In the end I bought a couple of new permiers from Amal direct. So need to find some time to fit them and fire her up!!
 
Congrats on acquiring your cafe racer! It sounds like you've done some good research. Running 220 main jets is a solid starting point for your setup, especially with dual Amal Mk 1 carbs. Your 105 needles should work well for mid-throttle response, and increasing the pilot jets to 20 should improve low-speed fueling. However, since jetting can vary based on altitude, climate, and the condition of the engine, I'd suggest trying out your setup, but be ready for some fine-tuning based on performance. Check for smooth throttle response and avoid any signs of lean or rich running. Keep an eye on your spark plugs too—they’ll give a good indication of how your jetting is working.
 
Back
Top