Motoscrubs.com

Having trouble getting the idle speed consistent on my 69 450. It has an amal type one concentric carb on it. Slide seems to be a close fit, but it is old, so I might be wrong. can't make out the numbers but it is stamped 32mm. does this seem like it might be the original carb, or was it smaller? Does anyone know the jet sizes and slide needle for the original? this carb does not have a choke slide in it. Plug reading is showing a slight rich condition. After tickling it starts easy but occasionally pops through the exhaust when coming off idle which I interpreted to be a lean condition in the low speed circuit. The bike generally runs well pulls consistently from just off idle to the top, no dead spots, cruises without surging. I'm sure I'll get it sorted but thought I'd try not to re-invent the wheel. Thanks in advance.

My Mototrans 350 has an Amal 930. The 30 in the 930 refers to 30 mm. It also does not have a choke. My tickler is not working, so the bike is very hard to start when cold. Once it is running, there are no problems. If you think it would help, I could check the jet sizes. Thke a look here for everything you wanted to know about Amal carbs.

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=42112#Post42112

Pete

" does this seem like it might be the original carb, or was it smaller "

____ No Italian-made 450-DUKE came-stock with Amal-carbs. _ As they all came with the common 29mm square-slide DelLorto.
So it's a guess that your carb came from some Brit-bike.
The 32mm-Amal is a better suited size for the 450. _ And it should be jetted pretty much the same as the same carb on a 1974 Norton-850, (so look-up those specs).
__ I don't know of any Spanish-made Amal-carbs larger than 30mm ever stock on any DUCATI-model.
And I've never heard of any 450s made in Spain. _ Does yours have Spanish-made forks or something? _ Otherwise if not, I wonder why you ever got the thought that yours could possibly be Spanish-made?


DUKE-Cheers,
-Bob

Thanks

So how do I tell if my bike is Italian or Spanish? It has "Made in Italy on several parts, but I guess they could have been bolted on. The Clymer's manual allows that an amal carb is fitted but doesn't say it is Spanish only. The case is stamped DM450 on one side of the seam and 450xxx on the other I think.

As far as I know, Mototrans never built the 450 engine.
Cylinder head castings are different on Mototrans engines too. Some of the Spanish timing covers have 'Made in Spain' cast into them, although early ones do not. They do not have any 'Made in ---' markings at all. Clutch inspection cover castings only have Ducati cast into them, not Ducati with Made in Italy underneath.
Most Mototrans engine numbers will have MD stamped on them, for Mototrans Ducati, as opposed to the DM of Ducati Mechanica.
You've almost certainly got an Italian motor.
As to Amal carbs, try main jet about 220, needle jet 106, pilot jet 25, slide with 4 cutaway on a 450.
350's run OK with a 3 1/2 slide but 450's seem to prefer the bigger cutaway on the slide.
You might have to experiment with the needle position a bit.
These are only settings to start to set up your carb. Depending on where you are in the world, altitude etc., they can vary a bit.
I can set a motor up at home and have it running fine. Go to the Isle of Man and it's all over the place due to the cooler, damper climate.

I will be curious to see what you finally settle on.

Someday I may upgrade from my Dellorto VHB on my 40SCR.

I agree with Bob - the 450 Scramblers seem to all come with the VHB square body Dellorto 29mm carbs.

The parts book on motoscrubs.com also shows this from a parts perspective.
Tony

thanks everyone for your help.

I didn't say I thought it was a spanish bike, but wondered how you can tell the difference. Seems somewhere years ago, I saw a picture of a spanish scrambler with a dunstal type pipe and an Amal carb. I never learned if this was original, but my bike had Dunstal type pipe and Amal carb when I bought it.
No spanish markings at all that I can find.

Bob, you may be right on the brit bike connection, as I got the bike from GP motorcycles in San Diego. At the time about 17 Years ago, they were a small struggling shop with a heavy preference for british iron and they might have fitted those parts to make the bike run. Or who knows.

Jon, I'll take a look at those jets next time I get it apart. will wait till the service gasket kit arrives. I don't know why I didn't record the sizes when I had it apart. I will take a look at the jets and see how close they come to your recommendations. If it comes to changing slides I will probably just replace the carb with a DellOrto. I see that Bevel Heaven sells a new 30mm that seems like it would fit the bill and doesn't seem priced crazy.

Pete thanks for the link. interesting reading.

regards, all
Mike

____ A 32mm-carb on any 450-model is certainly better suited (to such a large cyl.displacement) than the stock 29mm-size.
However, neither of the two main cam-types which were stock in most 450-models were very well suited for their displacement_+_intake-tract ! _ And the working-theories of how each of those two extremely-different cam-designs may best make use of available intake-plumbing, differs quite considerably ! ...
__ While the (relatively very mild [for a 450!] ) SCR-cam would most qualify for the 'big-gulp' theory, the wild std.DESMO-cam works more-so with the 'air-ram' theory.
So while with the std.DESMO/(Blue&White)-cam, ya ought prefer a longer intake-tract,, with the SCR/(White)-cam, ya ought prefer a larger carb onto a short as possible intake-tract.
Although a dynamo-meter may be needed to measure any differences, it would seem that a 450 with the mild-cam would be the most likely to benefit from the use of an even larger (33 to 36mm) carb, that's directly-mounted without any extended-manifolding (like that used on 850-Nortons).

____ It would be very nice to see pix of all the various carb & plumbing set-ups that any 450-owners have come-up-with for their 450s !
(MotoMike has indicated that he'll do so soon... Will anyone-else beat him at posting such pix of their 450's intake-tract?)


DUKE-Cheers,
-Bob

OK, here are a few shots of my Amal Upon closer inspection I can make out "RB 932, 32mm" Not sure about the RB as it is faint. I have an Emgo filter on it. Because of the extra bracing on the 450 frame, I had to crush the filter to make it fit, but will try to find a K&N with a canted inlet so that it fits properly.







A little reluctant to take close ups as the "blush is off the rose" and the old girls flaws are obvious under close scrutiny

Mike