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Proper settings for Gold Star carburetors #529670 02/22/14 12:48 pm
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Magnetoman Online Content OP
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Since this comes up periodically, rather than everyone starting from scratch to provide answers each time, I searched for jetting information posted over the past 5 years. I simply cut/pasted relevant information from a number of posts (without credit and/or blame for the authors) of what appeared to be successful settings, making only minimal changes in some places to improve readability. Consider this post to be a first draft of a Wiki-carburetipedia for people to modify wherever needed.

To be most useful I think such a list should consist of a list of "best" suggested settings, possibly followed by comments on the effect of changes to those settings (e.g. use of a weak needle in a GP). However, tuning information common to carburetors used on all motorcycles (e.g. the importance of setting the the float level; how to read a plug; etc.) is dealt with in quite some detail in other threads so repeating it here would only make it harder to find GS-specific information.

Amal 1-1/2" GP
Needle 3GP (set at the middle notch)
Needle jet 109
Main jet 360
Throttle slide cutaway 4
The settings for your carb are correct for the Clubman specification with 2442 and 2446 cams.

a #3 or #4 is commonly used on a muffled road GS.
Most GPs work well on road GSs with a #350 main jet at sea level.

Standard size air jet is 0.125", 1/8"

a racing GS with an open mega works the best with a #6 or #7 slide used along with a leaner GP6 needle.

The weaker needle should be marked 3GP6 at the top (you may need a magnifying glass to read the markings)
this needle measures 0.075" at the thinnest point.
The part nr. for this one is 316/408.

The std needle (this one is prefered for road use with silencer) is marked 3GP at the top.
This one measures 0.095" at the thinnest point at the bottom.
The part nr for this needle is 316/465

GP1 mixture screw adjusts air and the GP2 mixture screw adjusts fuel. Usually you adjust this in neutral with a warm engine, try to hold at 2500rpm and adjust in and out untill highest rpm is found,

Stock 1 1/2" GP needle jet is a 109, Lift the needle up a notch if you try to use a 108, for a start.
stock book main jet is 350.

I did try the 3GP6 needle last summer, though it was clearly not the right move. Legend has it that if you can get them to run on the (leaner) 3GP6 needle, they are better, but I didn't fiddle with the needle jet or slide to make it work. Assuming it does. (standard silencer - leaner needle usually used with open megaphone

My engine was running rich at 1/2 throttle, so I changed from a 109 to a 108 needle jet.
That resulted in a little stumble at low throttle openings, so I changed from a 4 to a 3 slide and that cured it. Unfortunately I can not remember if I tried to change the needle setting before changing the slide.

Amal 10TT9
1-3/32" for the BB32GS, CB32GS and DB32GS
1-5/32" for the BB34GS
1-3/16" for the CB34GS, DB34GS, and DBD34GS

The BSA Gold Star Maintenance manual has the same settings for all of the above for both touring and scrambles:
Main jet 360
Needle Jet .l09
Needle Position 3
Slide 7

Amal Monobloc
3-1/2 slide is a good cutaway to begin with.
A 240 main, 25 pilot and .106 needle jets should be good. Start with the needle clip in the middle notch.

BB Scrambles
Gold Star literature calls for a 1 /16 Monobloc, with a .1065 needle jet, 260 main jet, 4 slide and needle position 3. Modern fuels seem to like things a little leaner.

Amal Concentric Mk 1
The rule of thumb when moving from Monobloc to Concentric was to drop the main jet size by 10% so 300 became a 270.

to use a 2-stroke carburetor change spray tube to straight and order up date kit #622/235 called conversion kit 4 stroke

Here's what's worked for me on my 1038 at sea level.
main jet 380, needle jet 622/122/108, needle 622/124, jet holder 622/128, pilot jet 30, slide 3.

only difference is my throttle valve is 3.5 so you may want to try that.

common baseline for the 38 is:
#4 slide
standard needle (start in the middle)
108 needle jet
main jet anywhere from 300 to 390
pilot jet 25 , 30 or 35

DB34 with a DBDhead and AMAL 1038 carb. 3,000 ft. there are 2 different jet holders for the 1000 series . The shorter holder and 4 stroke needle do not work well, the needle can foul the main jet. I am now down to 106 needle jet, needle in the middle. 107 jet was loading up on the over run. Main jet is my issue now, 330 was not too bad, 350 misfires as soon as the needle clears the jet, currently trying 320 main, no verdict yet. I have a 3.5 air slide, but feel a 4.0 might be better. Current. settings give me great acceleration up to 6,0000+ in the lower gears, a little rough on the overrun just off throttle, not sure of the main jet jet.

Amal Concentric Mk 2
The standard jetting is pretty close, 3.0 slide, (only one needle) needle in the middle position. 30 ro 35 pilot jet, 49 starteer jet, 320 main jet...

38mm AMAL Mark 2 Concentric
Main Jet: 320
Pilot Jet: 30
Needle Jet: 107
Throttle Slide: 3 Heavy chromed brass type
Throttle needle: middle position

Mikuni VM
i HAVE A 38 mikuni...is the jetting still 25 pilot 220 main R0 needle jet 6dh3 needle #3 slide?

Jetting is the same for both 36 and 38. Some years ago, Allens told me the jetting they set the carbs up with is:
Main Jet: 240
Pilot Jet: 35
Needle Jet 159 series 'P8' (though I suspect the 38mm would possibly need the 247 series needle jet, in the same P8 size, depending on the carb body)
Needle: 6DH3 (pretty standard needle for a 4 stroke)
Slide - forgot to ask

Last edited by Magnetoman; 02/23/14 1:34 am. Reason: Added specs for TT carburetors
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Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #529673 02/22/14 1:18 pm
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No settings for a 10TT? I'm working on my '53 BB/ZB now and would like to know the standard settings to start with.


Bill B...


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Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #529679 02/22/14 1:51 pm
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Nicely condensed information Magnetoman, thank you very much.

James.

Re: Proper settings for Gold Star carburetors [Re: limeyrider] #529682 02/22/14 2:25 pm
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Don P. Offline
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Here are standard settings for TT carbs for earlier models:
TT 1 5/32" Main 360/slide 6/clip 4/Jet .109
This is from my book.I have not tried it yet.

Re: Proper settings for Gold Star carburetors [Re: Boomer] #529699 02/22/14 4:12 pm
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Magnetoman Online Content OP
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Originally Posted by Boomer
No settings for a 10TT?
Although someone already answered this question, certainly "book values" for various settings can be added to this thread. However, where I think it will be most useful is for carburetors where book values don't exist. For example, when for reasons of either cost or convenience someone wants to replace their TT or GP with a "modern" Concentric or Mikuni.

Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #529709 02/22/14 6:11 pm
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Thanks Don for the info. Do you know what pipe that was for?

Nice job MM. Something to add to the sixth edition.

I picked up this '53 bitsa last year. It's a BB34A frame with a ZB34GS engine that has a BB head attached with a 10TT9 carb. Haven't tried to start it yet as I've sent the magdyno off to Doug Wood. When I pulled the exhaust pipe and replaced the bellmouth of the carb both ends appeared sooty. The PO was using a 1 7/8's pipe with an open mega. I'll be going to a 1 3/4" pipe with a muffler so I'm probably looking at leaning it out


This is what it looked like when I brought it home:

[Linked Image]

Bill B...


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Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #529766 02/23/14 12:53 am
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Thanks for your labors Magnetoman... well done mate.

Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #529768 02/23/14 1:26 am
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Here are what I have for different Mikuni's. I do not know where some of these specs came from, some I did use on one of my bikes. At least this is good to compare or start from.

...........P.J Slide N.J. M.J. Needle Air jet
VM32 - 25, 3.5, Q-8, 190, 6FJ11, no air jet
VM34 - 25, 3.5, R-0, 220, 6FJ6, 2.0
VM36 - 25, 3.5, R-0, 220, 6DH3, 2.0
VM38 - 25, 3.5, R-0, 220, 6DH3, 2.0
TM41 Pro - 10, 5, R-2, 240, 6FJ40, none

Hope this info is helpful..
Ron

Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #529770 02/23/14 1:29 am
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Agree - thanks for the data mining.

I try and add data to an exel spreadsheet for the same purpose (though mostly for 1 1/2" GP and 36/38mm M1 and MkII Concentrics) for the Gold Stars and Thruxton...which seem to end up with very similar settings -enough that I think you could swap carbs over and be very close to the mark (for tjose with a foot in both camps..!)


No generalisation is wholly true, not even this one.
Oliver Wendell Holmes
Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #529772 02/23/14 1:31 am
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Ron - interesting data - the R nozzle is pretty big, though I will give them a try in the coming months myself. The 2.0 air jet would be good for 2 strokes, though I'd expect to see something more like 0.7 or less for a 4 stroke..whatever works, I guess..there are dozens of ways of getting the same results..


No generalisation is wholly true, not even this one.
Oliver Wendell Holmes
Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #540945 05/02/14 6:43 pm
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MM, what is a good starting point on the GP3 as far as unscrewing that knob on the starboard side of the carb. Somewhere, sometime, I heard someone say that 17 clicks out is a good starting point. Does that reconcile with your experience?

Regards,
Stubb


Hate is a poison which one consumes hoping for another to die.
Re: Proper settings for Gold Star carburetors [Re: stubbicatt R.I.P.] #540946 05/02/14 7:05 pm
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Originally Posted by stubbicatt
what is a good starting point on the GP3 as far as unscrewing that knob on the starboard side of the carb.
Port or starboard doesn't matter with a GP, but fore and aft (or bow and stern) do. If the knob is on the engine side of the carburetor it controls the fuel, so screwing it out makes it richer. If on the air filter side it controls the air, so screwing it out makes it leaner.

Having said that, I don't know what setting to start with on a GP3 so someone else will have to pitch in.

Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #550674 06/30/14 12:00 pm
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Hello All & MM,
MM you state for GP3 slide #3 or #4 for muffler, #6 or #7 for mega.
Just take the top off mine to fit a new cable and it has slide number 5 fitted with a goldie style muffler. Now I am confused!! Also the (worn) standard needle was fitted in the top groove.

As the slide is well worn and minus a small piece on the side I feel it should be replaced, but with what size? Will also replace the needle.
Not sure what the main jet as it is not out yet, but feel I should replace this also and having read on this forum that 330 is generally a good place to start with modern fuels - at sea level - I will start with this one.

I can then experiment a little to get a half decent set up.
Any comments will be very welcome.
RogerH.

Re: Proper settings for Gold Star carburetors [Re: Magnetoman] #608320 07/13/15 3:05 am
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My DBD was running much to rich with the standard settings. When I moved the needle to the top notch it ran OK except for an occational stumble now and then, which made me belive that it was still running too rich.

I tried with a 108 needle jet and had to put in a #3 slide as there was a stumble just off idle, but the result was more or less the same.

Now it was time for a more scientific approach, so I invested in an Innovate AFR meter.

The exhaust clamp they sell that fit in the end of the silencer does not work reliably. I suppose it is because in a single cylinder engine there is too long between the exhaust pulses, so I had to weld in a bung in the top of the exhaust pipe.


http://s1372.photobucket.com/user/oka33/media/L1010424_zpsd85faf53.jpg.html

http://s1372.photobucket.com/user/oka33/media/L1010425_zps134b0da9.jpg.html

As expected it was too rich at about 11:1 AFR with both of the two settings above.

I decided to aim for 12-13:1 for maximum horsepower. Perhaps I will later try leaner settings, but fuel consumption is not
that important.

As an experiment I changed back to the 109 needle jet and tried the GP6 needle in the bottom notch. It was actually fine
with around 12.5-13:1 AFR until 1/2 throttle, at whick point it jumped to 10-11:1.

So what is actually going on with the needle in the various positions? The taper of the needle is 17.5mm long and the GP
is 38mm in diameter, so it will be on the taper in the middle 46%. With the needle in the top notch it will be on the straight
part 17% and out of the needle jet 37%.
With the needle in the bottom notch it will be on the straight 4% and out of the needle jet 50%, which, I think, explains
the jump in AFR when the bottom notch is used.

I feel that the needle is too short. I think is has been designed for the smaller diameters and just been carried over when
AMAL enlarged the GP to 1".

So I cut an extra notch in the needle 2mm above the top one:

http://s1372.photobucket.com/user/o...0-afe5-7a78b696e88e_zpsf3hynzwr.jpg.html

It was almost perfect now except for a small leanness between 1/8 and 1/4 throttle. To eliminate that I sanded the needle the last 2-3mm up to 19.5mm to compensate for the extra notch.

For the main jet I have ended up with a 330.

The fuel consumption has improved from 18Km/liter to 23Km/liter and the spark plug is now light brown instead of dark brown.

The last thing was to set the idle speed. I did that by adding a blob of solder to the end of the cable. It is trial and error, but if it extents 3mm under the roof of the slide, it is about right. Aim for around 1500RPM with full advance, then you can regulate the speed down with the ignition lever.

http://s1372.photobucket.com/user/o...7-8069-b1191fe622e4_zps5oqwpjnp.jpg.html

I hope that these ramblings may be useful to someone.


Re: Proper settings for Gold Star carburetors [Re: Ole K] #608344 07/13/15 10:35 am
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Originally Posted by Ole K
Now it was time for a more scientific approach, so I invested in an Innovate AFR meter.

The exhaust clamp they sell that fit in the end of the silencer does not work reliably. I suppose it is because in a single cylinder engine there is too long between the exhaust pulses, so I had to weld in a bung in the top of the exhaust pipe.
Great information, Ole. Thanks very much for posting it.

I probably have written about it before, but I too have an Innovate AFR meter. As you mentioned, the problem is air gets sucked back a fair distance into an exhaust system on each revolution, and that air seriously distorts the A/F reading unless the sensor is well upstream.

Since I wanted to make it universal for all my motorcycles, rather than welding bungs on each of them I bought a piece of silicone-based high temperature "cloth" and had a seamstress add Velcro strips so I could wrap it around the end of exhaust pipes to effectively make the pipe longer. A support rod cobbled together for each different bike keeps the end of the cloth from dragging on the ground.


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