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Hi all,

I figured I'd start a thread for the new carb I got for my bike - an Amal concentric 930. These are the setting I'll be running:

MAIN JET 220

PILOT JET 30

NEEDLE JET 105

NEEDLE POSITION 2

THROTTLE SLIDE 3.5

If anyone has suggestions please let me know, otherwise I'll post how the install (and running of the bike) turns out.

Let us know how it runs.

At 30mm, the 930 seems a bit big for a 250 street bike. A smaller bore — 28 or even 26 — would give you better response in the low- and medium-rpm ranges. Also, a 926 will bolt on to the stock mounting studs with very little modification; a 930 is going to require a custom manifold of some sort.

If possible, maybe try to use a longer than stock intake manifold with a nicely tapered inlet tract.

Thanks Nick.

Did you mean a 626? I haven't been able to find any information on an Amal 926.

Yeah, a 626 is what you want. For jetting, look up the jetting for a Triumph T100R Daytona (500cc). It's really just two 250 singles stuck together, so that jetting should be pretty close for a 250 single like yours. 930 is too big.

Founds some settings for the T100R, which are:

MAIN JET 150

NEEDLE JET 106

THROTTLE SLIDE 3.0

The 626 carb comes with a 160 main jet, 106 needle jet and a 3.0 slide so I think I'll just use those first and see how the bike runs, and then maybe swap for a 150 main jet later on to see if there's an improvement.

In my experience, an Amal 930 (30mm bore) works very well indeed on a roadgoing 250 Ducati with a 29mm inlet flange - a Mark3.
But it might not be perfect for the smaller Monza inlet. I don't have any data on this but an Amal 626 (26mm bore) might be a better match for a standard Monza. That has a 24mm inlet, doesn't it? Good idea to use Triumph Daytona settings as a start point for tuning.

Both 930 and 626 Amals, both called Concentric, have the same mounting flange detail, with 2 inch stud spacing. They easily attach directly to a Ducati 250 head, preferably with a heat insulating spacer.

Thanks, Jordan. I'll be using one of these for a spacer:

http://www.eurojamb.com/ducati-bevel-in ... -2905.html

halfpast wrote:Thanks, Jordan. I'll be using one of these for a spacer:

http://www.eurojamb.com/ducati-bevel-in ... -2905.html

OK, but I see the hole size is 29mm, so there would be an undesirable gap between the carb and head.

Also available are simple Tufnol spacers with 26mm hole and 3mm thickness, from many sources including this one:
http://www.hitchcocksmotorcycles.com/am ... cellaneous

I've seen these Tufnol ones in various thicknesses between 1.5 to 20 mm.

Thanks Jordan for the suggestion. Unfortunately that outfit won't tell me shipping costs to the States until *after* i enter my credit card info on the website. And I haven't been able to find a place stateside that sells a 26mm gasket.

I hope to get the assembly together in the next few weeks and I'll post an update then. Thanks all.

Well, the carb has been installed. I went with a 150 main jet, 106 needle jet and a 3.0 slide. Took the bike for a couple runs up and down the street and it ran well, but the darn thing still doesn't want to idle. I also found that the motor won't start (even when warm) unless I use the tickler. So that made me think that the bowl wasn't being properly filled when at low RPM's. I therefore checked the petcocks and their flow, which seemed okay. Next was the tank vent. I opened the filler and saw the motor still wanted to die, so that's out. Anyone have any other thoughts?



(PS - photo taken before I put the air intake tube back on)