The plug in ALL the photo's is/was a Nippondenso W22EP-U. and a new plug was used each time
Martyn
Martyn
New Amal Premier 900 series Carb for Comets
- Thread starter craig
- Start date
OK so I thought the last run with the 105 needle jet, needle in its mid position, with the clip in the centre goove looked a wisker lean
SO
I moved the needle clip to the bottom groove, which is the richer setting, still with a 105 needle jet then I installed (yet another) brand new plug and went for a 20 mile ride - towards the end the motor had developed a small miss. No wonder, here is the plug at the end of the run. Its almost as bad as the 106 needle jet with the needle at full rich.
Clearly, from all I have tried so far the best setting seems to be as follows: Amal 930 Mk1 Premier, 250 main, 105 needle jet with needle in the centre groove. Idle mixture screw is at 1 1/2 turns. Once the engine is run in I will be able to do some work on the main jet size - for now I figure that a 250 main will NOT be too lean. I do know that a 210 main is destructively lean - just ask my wallet!
Martyn
SO
I moved the needle clip to the bottom groove, which is the richer setting, still with a 105 needle jet then I installed (yet another) brand new plug and went for a 20 mile ride - towards the end the motor had developed a small miss. No wonder, here is the plug at the end of the run. Its almost as bad as the 106 needle jet with the needle at full rich.
Clearly, from all I have tried so far the best setting seems to be as follows: Amal 930 Mk1 Premier, 250 main, 105 needle jet with needle in the centre groove. Idle mixture screw is at 1 1/2 turns. Once the engine is run in I will be able to do some work on the main jet size - for now I figure that a 250 main will NOT be too lean. I do know that a 210 main is destructively lean - just ask my wallet!
Martyn
Last edited:
The Norton 850 type of spray tube "creates localised low pressure and turbulence over the jet which helps break-up and distribute the fuel stream. For a given needle, fuel jet and air jet, a screened nozzle will deliver more fuel than a plain nozzle". that's a quote from Haynes "Motorcycle Fuel Systems Techbook" which was written with the help of Barry Johnston from Amal. Do you think your choice of spray tube may be the cause of the persistent rich running you are experiencing?
Check back to my earlier posts, especially number 40. Having experienced the destructive potential of running too lean, I deliberately started out with a very rich condition and have been methodically making small changes as I worked towards the best carburetor settings for my engine.
I have now settled on the following settings BUT with a near new motor I have yet to perform any high speed runs, which are required to determine the optimal main jet size. For now I suspect that the main jet is on the rich side though I am comfortable I have the rest of it nailed.
Amal Mk1 930 Premier
#3 Slide
250 Main Jet
105 Needle Jet
needle in middle groove
idle screw 1 1/2 turns
I have not seen the text you refer to, but based on what you have to say, it seems that the screened nozzle I am using should give a more reliable and consistent air/fuel mix (and possibly a tad better fuel economy) than a plain nozzle and in so making the tuning process easier, not harder.
Here is the state of the plug with the settings I have settled on.
Martyn
Hi Martyn, Can you post exactly what pieces are in this Amal Premier now?
If your spray tube is modified, can you post photo? I don't know what a "screened" nozzle is exactly.
needle markings?
idle screw "as supplied with carb"?
#3 slide standard or hard anodized?
Pilot jet? 622/502-19?
Gasoline brand and octane and ethanol percentage.
Ignition type details?
Ignition advance setting? maximum advance?
type ATD?
Spark plug gap?
Thank you for all the follow up on this issue
Craig
If your spray tube is modified, can you post photo? I don't know what a "screened" nozzle is exactly.
needle markings?
idle screw "as supplied with carb"?
#3 slide standard or hard anodized?
Pilot jet? 622/502-19?
Gasoline brand and octane and ethanol percentage.
Ignition type details?
Ignition advance setting? maximum advance?
type ATD?
Spark plug gap?
Thank you for all the follow up on this issue
Craig
Last edited:
There is NOTHING modified in my carb. It is a new AMAL Concentric Mk1 Premier 930.
The term "screened" refers to the needle jet being screened by the spray tube from the air flow within the carb body. In the pictures you posted only the spray tube labeled "4 Stroke" is screened. On the advise of a number of folks, including the late Big Sid I elected to use the "Norton" style of spray tube as it is (alleged) to provide better atomizeation of the fuel and thus a more even burn within the combustion chamber; all I know is that it works.
Here is the EXACT specification that I ordered from Burlen in the UK.
AMAL Concentric Mk1 Premier 930 Carb, configured as follows:
Slide = 3.0
Needle Jet = 106
Main Jet = 210
Pilot Jet = RJ19
Emulsion Tube = Norton 850 with cutaway facing inlet valve (as depicted in post #45 from Craig)
Left hand configuration
Mixing Chamber top with 2 adjustors
A 55 degree double banjo
After extensive (and at times unexpectedly destructive!) testing the follow has been found to be the optimum configuration for my standard Comet
Slide = 3.0
Needle Jet = 105 (Changed from what was originally delivered, but using replacement jet from Bulen)
Main Jet = 250 (Changed from what was originally delivered, but using replacement jet from Bulen)
Pilot Jet = RJ19
Emulsion Tube = Norton 850 with cutaway facing inlet valve (as depicted in post #45 from Craig)
Left hand configuration
Mixing Chamber top with 2 adjustors
A 55 degree double banjo
For completeness - I found that the best position for the mixture adjusting screw is 1 1/2 turns out (from fully closed)
Here is what Burlen has to say (on their web site) about their new design: “The new unit The 900 Series AMAL Carburettor has been re-designed to improve performance and wear. The new carburettor incorporates changes in materials which reduce the rate of slide and body wear and a precision engineered idle circuit which improves the pick up performance from idle and reduces fuel consumption. The precision manufactured forged alloy, hard anodised throttle slide has a low friction surface for smoother operation and greater wear resistance. The material of the carburettor body has a “passivated” finish which resists corrosion, whilst the ethanol resistant, puncture proof StayUp float and viton tipped alloy needle valve improve control of the fuel flow. A new easily removable pilot jet provides precise metering of the idle circuit. The jet, which is located in the opposite position to the pilot air screw, is manufactured to tight tolerances allowing it to be replaced with minimum disruption to the adjustment of the carburettor.”
To actually mount the carb onto the motor I used a stainless steel manifold that I purchased from James Mosher in the USA. This is significant as the original Comet (and rapide) manifold has a 26mm bore. The Mosher manifold has a full 32mm bore!
UPDATED Jan 9, 2014.
Following further extensive testing here is what I finally settled on; only variance from above are noted.
main Jet 220
needle in centre groove
Ignition fully advanced at 31 BTDC
Martyn
The term "screened" refers to the needle jet being screened by the spray tube from the air flow within the carb body. In the pictures you posted only the spray tube labeled "4 Stroke" is screened. On the advise of a number of folks, including the late Big Sid I elected to use the "Norton" style of spray tube as it is (alleged) to provide better atomizeation of the fuel and thus a more even burn within the combustion chamber; all I know is that it works.
Here is the EXACT specification that I ordered from Burlen in the UK.
AMAL Concentric Mk1 Premier 930 Carb, configured as follows:
Slide = 3.0
Needle Jet = 106
Main Jet = 210
Pilot Jet = RJ19
Emulsion Tube = Norton 850 with cutaway facing inlet valve (as depicted in post #45 from Craig)
Left hand configuration
Mixing Chamber top with 2 adjustors
A 55 degree double banjo
After extensive (and at times unexpectedly destructive!) testing the follow has been found to be the optimum configuration for my standard Comet
Slide = 3.0
Needle Jet = 105 (Changed from what was originally delivered, but using replacement jet from Bulen)
Main Jet = 250 (Changed from what was originally delivered, but using replacement jet from Bulen)
Pilot Jet = RJ19
Emulsion Tube = Norton 850 with cutaway facing inlet valve (as depicted in post #45 from Craig)
Left hand configuration
Mixing Chamber top with 2 adjustors
A 55 degree double banjo
For completeness - I found that the best position for the mixture adjusting screw is 1 1/2 turns out (from fully closed)
Here is what Burlen has to say (on their web site) about their new design: “The new unit The 900 Series AMAL Carburettor has been re-designed to improve performance and wear. The new carburettor incorporates changes in materials which reduce the rate of slide and body wear and a precision engineered idle circuit which improves the pick up performance from idle and reduces fuel consumption. The precision manufactured forged alloy, hard anodised throttle slide has a low friction surface for smoother operation and greater wear resistance. The material of the carburettor body has a “passivated” finish which resists corrosion, whilst the ethanol resistant, puncture proof StayUp float and viton tipped alloy needle valve improve control of the fuel flow. A new easily removable pilot jet provides precise metering of the idle circuit. The jet, which is located in the opposite position to the pilot air screw, is manufactured to tight tolerances allowing it to be replaced with minimum disruption to the adjustment of the carburettor.”
To actually mount the carb onto the motor I used a stainless steel manifold that I purchased from James Mosher in the USA. This is significant as the original Comet (and rapide) manifold has a 26mm bore. The Mosher manifold has a full 32mm bore!
UPDATED Jan 9, 2014.
Following further extensive testing here is what I finally settled on; only variance from above are noted.
main Jet 220
needle in centre groove
Ignition fully advanced at 31 BTDC
Martyn
Last edited:
Thanks for this info - I have just ordered a set to have "on the bench" for possible future use.
Martyn
Martyn, I thought you pushed out the spray tube and cut it down, I see you can just order this from Burlen. How many grooves on the pilot jet?
So premium means hard anodized slide, standard needle for pilot (not extended), standard two groove main slide needle, etc.
Using the Jim Mosher manifold, did you alter the head opening? make it bigger?
http://www.performanceindian.com/VinMenu.html
Thank you for this testing and explanation.
I am looking over this Premium 928 I tried and it appears it had a pilot with no grooves when I was told it would a -17.
Cheers
Craig
So premium means hard anodized slide, standard needle for pilot (not extended), standard two groove main slide needle, etc.
Using the Jim Mosher manifold, did you alter the head opening? make it bigger?
http://www.performanceindian.com/VinMenu.html
Thank you for this testing and explanation.
I am looking over this Premium 928 I tried and it appears it had a pilot with no grooves when I was told it would a -17.
Cheers
Craig
Had not actually removed the pilot jet - but for you I just did so. The one in my 930 premium has 3 grooves. Also my needle - the one that came with the carb as "standard" has 3 clip grooves
ALSO FYI today did a run of around 220 miles and during it there was a steepish hill over 1 1/2 miles long so I hit it at the bottom with wide open throttle and held it like that (at around 70 mph) till I got to the top then in with the clutch, in with the decomp lever , stop on the side of the road and a plug check. Sorry no photo this time but the plug looked just fine, not rich, a nice tan colour on the ceramic - this was with a 250 main. I will be seeking out a 260 main to try on the next run as my ($$$$) experience has me preferring to be a tad on the rich side.
Oh yes, I did profile the inlet port to eliminate the step between the port and the Mosher manifold - DREMEL are wonderful things but must be used with utmost care
Martyn