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Monobloc Carb for Goldstar #758079 12/04/18 8:04 am
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LaurenSue Offline OP
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Hello. I have a 1958 DBD Goldstar with Clubmans cams and I was told it had a DB head.
The diameter appears to be 30mm (by my wife's dress making tape measure) and the studs are 2 inches apart.
I am putting an AMAL Monobloc carb on and have been advised to go for a 389/61 - 320 main, 30 pilot, 106 needle, 4 cutaway, needle position 4.
Does this sound correct? Thank you.

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Re: Monobloc Carb for Goldstar [Re: LaurenSue] #758121 12/04/18 5:12 pm
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slow learner Online Content
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Correct is what works on your bike as you ride it. It is a mistake to think that putting a carburetor in "stock" configuration will have it functioning with out fault. Research the procedure for tuning a Monobloc carb and start with what you have. Modify as required. Also, there was a small port DBD head produced. It would look just like a small port DB head other than the carb mounting flange is notably thicker.


Laurence Luce
Re: Monobloc Carb for Goldstar [Re: LaurenSue] #758138 12/04/18 7:17 pm
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Originally Posted by LaurenSue
958 DBD Goldstar with Clubmans cams and I was told it had a DB head.
The diameter appears to be 30mm (by my wife's dress making tape measure) and the studs are 2 inches apart.
advised to go for a 389/61 - 320 main, 30 pilot, 106 needle, 4 cutaway, needle position 4.
I have a 1-3/16" (~30.2 mm) 389 on my 1961 Catalina that has scrambles cams and the small-port DBD Catalina head. The settings you list are the ones AMAL listed for the 1961 "B34 Scrambler USA". After ~1000 miles of it running well with a 320 main jet the old silencer broke and when I put a different one on it required a huge change to the main jet

The settings used for the first 1000 miles are essentially the ones you listed (although, with the needle on the 3rd notch), but with the new silencer I now have:

pilot 25 (5/8 of a turn out from closed)
needle 106 (on 2nd notch from top)
4 cutaway
220 main (yes, not a typo, the main jet is 220)

The values you listed are reasonable for starting with, but the combination of small port with Clubmans cams and unknown silencer means that they're unlikely to be the ones you end up with. You will have to refine the jetting yourself.



Re: Monobloc Carb for Goldstar [Re: LaurenSue] #758207 12/05/18 11:08 am
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I ran a 32mm Concentric on a B33 we raced years ago (in Auckland!), with 2442/2446 cams...not exactly the same setup as you, though the settings for the Monobloc, with those cams and port sizes might be similar. My bike always ran with 330 or 340 main jet on an open megaphone (so a couple of sizes smaller, most likely, with a muffler). Needle jet was 106. Oddly, I don't have a record of the slide, though recall a 3 (I should be able to check next week if it helps - I'll be where the carb is - in the UK). Pilot jet was the usual 'fixed' Concentric thing, which is equivalent to a removable jet size that I don't remember.

Monobloc pilot jets are easy to change anyway, and the effort to try a couple of worth it - you'll know when you have the right size, as the air screw will be where the literature says it should be, and have an effect when you adjust it.

I'd start with something around these numbers and try it.

Here's some useful info I found: https://www.princeton.edu/ssp/65-cub-data/library/amalbritbike.pdf


No generalisation is wholly true, not even this one.
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Re: Monobloc Carb for Goldstar [Re: LaurenSue] #758239 12/05/18 5:39 pm
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I got mine from here https://www.feked.com/amal-389-monobloc-carburettor-15-32.html but I use a no.3 cutaway with a 25 pilot jet these were suggested to me by AMAL .

This was part of the Email from them . It sounds like your bike has the scramblers head which used an 1 5/32” Monobloc carburetter. 389/13 is the specification for the scrambler using a 320 Main Jet, .1065 Needle Jet, 25 Pilot Jet and a No 3 Throttle Slide .

Last edited by ducati2242; 12/05/18 5:43 pm.

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