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DBD34 Scrambler carburator problems #710317
10/02/17 7:54 pm
10/02/17 7:54 pm
Joined: Jul 2013
Posts: 27
Switzerland
M
mf-zh Offline OP
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mf-zh  Offline OP
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M

Joined: Jul 2013
Posts: 27
Switzerland
Hi everybody

Maybe somebody can help me on my carb problem. My bike:

1957 DBD34 500ccm
Standard gear box
New scrambler head (ABSAF)
New AMAL Premier 932 Carb with a heat insulator
New Magneto (electronic VAPE)
High level exhaust

My problem: When the bike is hot, the idle goes up and down a lot. You drive 1 mile stop,the bike nearly dies on you. After your next stop, say 300 yards it idles at about 2000rpms. I have put on a other AMAL, the problem is +/- the same. Due to the high level exhaust, I can't fit a Mikuni. The quality of the AMAL is not great, for example the screws and threads don't look as if they match on idle and mixture. And I imagine it is pulling air where it shouldn't. The heat insulator is good and tight.

What carbs you have on your scramblers?

Greetings for Switzerland,

Mike

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Re: DBD34 Scrambler carburator problems [Re: mf-zh] #710361
10/03/17 2:51 am
10/03/17 2:51 am
Joined: Mar 2017
Posts: 20
Iowa
9
99cyclone Offline
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Joined: Mar 2017
Posts: 20
Iowa
Does your bike have an adapter manifold to fit the 932 on the DBD head?

My DBD didn't run right with a 932, was too lean. It had quite an idle rise as it warmed up (no air leaks) and ran hot. I didn't bother much with the jetting, as it already had fairly large jets.

Instead, I found a 1036 AMAL that bolts right up to the head. I got the jetting right and filed the slide cutaway until it ran right. These carbs are scarce, but still out there.

It's a bit more work, but it was well worth it for my bike.

You might contact Mark at British Only Austria. He had a 1034 when I visited in August.


Buells and Brit Bikes
Re: DBD34 Scrambler carburator problems [Re: mf-zh] #710364
10/03/17 3:49 am
10/03/17 3:49 am
Joined: Nov 2011
Posts: 4,734
U.S.
Magnetoman Online content

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Magnetoman  Online Content

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Originally Posted by mf-zh
New Magneto (electronic VAPE)
The heat insulator is good and tight.
It doesn't look like VAPE makes a magneto replacement so please give more details about what you have for an ignition system, and especially if the control unit is mounted somewhere where it can get hot.

"Good and tight" makes me wonder if maybe you tightened it too much and warped the carburetor flange or the insulator, allowing air to leak in. The mounting nuts should be "snug" not "tight," with loctite rather than brute force holding them in place.

Re: DBD34 Scrambler carburator problems [Re: 99cyclone] #710528
10/04/17 7:00 pm
10/04/17 7:00 pm
Joined: Jul 2013
Posts: 27
Switzerland
M
mf-zh Offline OP
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mf-zh  Offline OP
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M

Joined: Jul 2013
Posts: 27
Switzerland
@99 cyclone

I will ask Mark, i know him well. Thanks for the tip.


@Magnetoman

This is the Magdyno I have from Vape: http://www.powerdynamo.biz/eng/systems/7197/719710main.htm. It is not the problem, I am aware about the warping of the AMAL Carbs.

Re: DBD34 Scrambler carburator problems [Re: Magnetoman] #714382
11/09/17 3:11 pm
11/09/17 3:11 pm
Joined: Jul 2013
Posts: 27
Switzerland
M
mf-zh Offline OP
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mf-zh  Offline OP
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Posts: 27
Switzerland
Hi Magnetoman

https://www.powerdynamo-shop.com/shop/show_product.php?cPath=2_36&products_id=259

sell the VAPE Magdyno.

Cheers, Mike


Originally Posted by Magnetoman
Originally Posted by mf-zh
New Magneto (electronic VAPE)
The heat insulator is good and tight.
It doesn't look like VAPE makes a magneto replacement so please give more details about what you have for an ignition system, and especially if the control unit is mounted somewhere where it can get hot.

"Good and tight" makes me wonder if maybe you tightened it too much and warped the carburetor flange or the insulator, allowing air to leak in. The mounting nuts should be "snug" not "tight," with loctite rather than brute force holding them in place.

Re: DBD34 Scrambler carburator problems [Re: mf-zh] #714408
11/09/17 7:19 pm
11/09/17 7:19 pm
Joined: Aug 2015
Posts: 1,266
Bolton Lancs UK
A
Andy Higham Online content
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Andy Higham  Online Content
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A

Joined: Aug 2015
Posts: 1,266
Bolton Lancs UK
32mm is very small for a 500 goldie
I have a 32mm Mikuni on my B31 and the same electronic magdyno, and DBD34 clubman cams. It idles well hot or cold, starts easily and works cleanly at part throttle

Last edited by Andy Higham; 11/09/17 7:23 pm.

BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: DBD34 Scrambler carburator problems [Re: mf-zh] #718090
12/07/17 10:05 pm
12/07/17 10:05 pm
Joined: Jul 2006
Posts: 224
SANTA FE
B
bsalloyd Offline

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B

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Posts: 224
SANTA FE
The DBD Scrambler came with a 1 5/32" Monobloc carburetor. The inlet track was smaller and had different bolt centers in the head. At least here in the colonies.


1951 ZB GS
1953 BB GS
1953 Super Flash
1954 Vincent BS
1963 RGS

Re: DBD34 Scrambler carburator problems [Re: mf-zh] #718313
12/10/17 11:23 am
12/10/17 11:23 am
Joined: Sep 2015
Posts: 315
Kent, England
J
John Alexander Offline
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John Alexander  Offline
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J

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Posts: 315
Kent, England
if you can possibly get a 1 5/32 Monobloc carb from say Auto Cycle in the Uk, they will correctly jet it for you.

Re: DBD34 Scrambler carburator problems [Re: mf-zh] #718495
12/12/17 4:24 am
12/12/17 4:24 am
Joined: Feb 2012
Posts: 1,266
Middle East,
Kerry W Offline
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Kerry W  Offline
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Posts: 1,266
Middle East,
You can still make plenty of power with 32mm... 1 5/32" is about 29.3mm and that would allow a scrambler to make 36-37 hp if I recall. I've run 32mm Concentrics on a Clubmans 350 and a road-racing B33. Results on both were good - the 350 idled at 800 rpm all day. The B33 was practically as quick as a DBD road-racer, except for perhaps the last part of a very long straight, though it pulled harder than most 500's (Clubmans cams, DBD spec flywheels/short rod)


No generalisation is wholly true, not even this one.
Oliver Wendell Holmes
Re: DBD34 Scrambler carburator problems [Re: mf-zh] #719218
12/18/17 11:54 am
12/18/17 11:54 am
Joined: Jul 2013
Posts: 27
Switzerland
M
mf-zh Offline OP
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mf-zh  Offline OP
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M

Joined: Jul 2013
Posts: 27
Switzerland
After trying another brand new AMAL 932, i went for a Mikulni VM 34mm. Problem solved. I now spell AMAL with a ā€œNā€œ. Thanks for all your tips.

merry x-mas to all,

Mike

Re: DBD34 Scrambler carburator problems [Re: mf-zh] #719236
12/18/17 2:22 pm
12/18/17 2:22 pm
Joined: Nov 2011
Posts: 4,734
U.S.
Magnetoman Online content

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Magnetoman  Online Content

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Posts: 4,734
U.S.
For people who come across this thread later I wanted to note that I strongly suspect the problem mf-zh had was do to worn slides and/or an air leak at the flange. I don't have this problem with any of my AMAL-equipped bikes, but I did have it years ago with my Trident. However, the inconsistent idle that caused huge anxiety for me every year when waiting my turn at the then-required, now-discontinued annual emissions test was cured by resleeving the worn carburetors.

For anyone interested, I have a 1-5/32" (~29.4 mm) AMAL 389 on my Catalina scrambler with the following jetting:

float level set at the tit in the center of the float bowl cover
pilot 25
pilot screw 5/8 turn out
cutaway 4
needle jet 106 (measures 0.1065"-0.1066")
needle on 2nd notch (i.e. 1 notch below the top one)
main jet 220

The 1961 AMAL catalog lists an infinitesimally larger 1-3/16" (~30.2 mm) as correct for the Catalina with its open exhaust (mine has a silencer), but with a much larger 320 main and the needle on the 4th notch (and an insignificantly different 30 pilot). The reason I mention this is that, while the book values can be a reasonable place to start, you can end up at a considerably different place before the engine runs well. But, running well wasn't mf-zh's issue, it was a wavering idle, which isn't a problem caused by the settings.

Last edited by Magnetoman; 12/18/17 2:38 pm. Reason: added that mine has a silencer

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