New Amal Premier 900 series Carb for Comets

[craig]

Has anyone installed and tuned the "new" 900 series carbs on a Comet yet?
New carb has an externally changeable lo speed pilot jet #9, hard anodized slide #26.
new pilot sizes like
622/502-15
622/502-17
622/502-19
Anyone able to provide results from dyno tuning a Comet for touring?
Using a O2 sensor? results?
New gasoline mixes with Ethanol provides more O2, so AirFuel ratios are way off and the traditional jet sizes are not doing well when reading plugs.
Cheers
Craig

 

[roy the mechanic]

o2 sensors are great when diagnosing injection systems. Unfortunatly they aren't much use on a carburated dinosour like our bikes. You need to find on old school dyno operator who still has a co/hc analyser, like the one I used for 25 years. As for plug colurs, with modern fuels all the old tricks like a "lovely brown" insulator are totally "out of the window" you will find on the original scale that a deathly white plug is ,in fact , just about right! Be lucky + please report your progress, Roy.

 

[craig]

This new Amal 900 looks very promising to aid in tuning, due to quickly changing lo speed jet.
What is the proper way to tune a currently ridden Vincent Comet with 10% ethanol and having only plug readings to use for mixture/tuning?
I don't want to drag race 1/4 mile to check Wide Open Throttle only.
An internet search is frustratingly a mish mash of forum advice crap with poor graphics, nothing relating exactly to Amal equipped Vincents.
Everything relating to drag racing.
Any help ?
Craig

 

[roy the mechanic]

Burlen fuel systems (the guys that make them) have a down loadable tune it yourself guide on their site. I'm sure if you still have trouble they will advise you by phone or e mail.

 

[craig]

Thank you, searched Burlen, but I don't see anything but pre ethanol instructions, circa 1969.
nothing relates to unleaded gasoline with 10% ethanol soon to be 15%.

am I overlooking something? I want see "tuning with gasoline/ethanol"

Burlen fuel systems (the guys that make them) have a down loadable tune it yourself guide on their site. I'm sure if you still have trouble they will advise you by phone or e mail.

 

[davidd]

Craig,

While I have a great interest in what you are looking for, I am not sure that you will find a satisfactory answer on this forum. I have suggested that there might be tangible benefits from dyno tuning for street bikes quite a while, but I have not heard of any owner doing so. I am also cognizant of the reason why- it is costly and a pain, so I am not surprised at the resistance. All my work has been done with racers on race fuel, so they are of little use to the average rider. However, I am not certain that any testing other than your own will be of any use to you. I have only tested modern pump fuel twice in the last four years and the tests were done with over the counter products to determine the amount of alcohol. Both tests showed less than 5% alcohol. So, I do not believe that there is anywhere near the alcohol in the fuel that there could be. I suppose this is bad news because if this small percentage creates as many problems as we have all experienced, I would definitely fear a 300% increase. Let's hope that all the bad stuff happens with just a small amount and the effects plateau after that.

I do not think that you will find an owner who tested the fuel prior to dyno testing that will support the fuel ratio that you may be using. I am hoping that someone may have done so.

David

 

[Martyn Goodwin]

Amal Mk1 930/301PREM/A Carb for a Comet

I installed a "new" Amal unit on my Comet some 2,000 miles back and it has transformed my bike. Easily starting , smooth idle and loads of power (when compared to the knackered old original unit It is a “improved” Amal Mk1 930/301PREM/A concentric. After consulting with Big Sid, I had it configured as follows; #3 Slide (hard anodised), 106 Needle Jet, 210 Main Jet, RJ19 Pilot, a Norton Commando style spray tube (which has the entire rear section –that faces the inlet valve – cut away), viton tipped float needle, “stay-up” float and a K&N air filter. I installed the new carb using a flange to flange stainless steel manifold I obtained from Jim Mosher in the USA. I profiled the inlet port opening on the head to provide a smooth gas flow thru the manifold and into the inlet port. I also installed a Bakelite heat insulator from a Norton, between the manifold and the carb. Taking note of the Amal instructions I used Nyloc nuts when securing the carb to the manifold and tightened them to just 4 foot pounds. At first I could not be happier with the result.

BUT WARNING

December 9, 2013 update:: After a long run of a 100 miles or so at high speed the motor was overheating to the extent the the pipes blued badly and I lost a fair bit of compression. Internal examination revealed an overheated and damaged piston, broken top ring etc - so it seems I was running way too lean. Additional trials are underway following a rebuild and I started out with a 250 main jet and the needle in the bottom grove ( rich setting). .


Current RECOMMENDATION , DEC 9, 2013

After extensive road trials conducted over a number of weeks the following is the current suggested configuration for a Amal Mk1 Premier 930 carb fitted to a Vincent Comet. Also I have had the failed (melted) piston examined by an expert aeronautical engineer who specialises in combustion chamber physics. It was his VERY STRONG opinion that it was NOT a lean mix that caused the failure, but rather detonation. He recommended using the highest octane fuel available and also reducing the ignition advance to NO MORE then 32 degrees BTDC. So here is the conservative tuning configuration

#3 Slide,
Norton Commando style spray tube
Main Jet 240,
Needle Jet 105,
needle in centre groove,
RJ19 pilot jet
idle mixture screw 1 1/4 turns out.

Timing set to 32 degrees BTDC at full advance

Martyn

 

[chankly bore]

Very detailed information, thanks Martin. I have found Ethanol mixtures burn a little hotter-at least that is what I believe caused my old gasper to nip up. I now only run 98 octane with no jungle juice in it. What fuel are you using? Cheers.

 

[Martyn Goodwin]

Very detailed information, thanks Martin. I have found Ethanol mixtures burn a little hotter-at least that is what I believe caused my old gasper to nip up. I now only run 98 octane with no jungle juice in it. What fuel are you using? Cheers.

Either 98 or 100 octane but NO ETHANOL!!!!. I get it from Liberty or BP. Every 2nd tank I put in about 100ml of 2 stroke oil.

M

 

[roy the mechanic]

craig, I know this will not sit well with you, but I'm going to tell you anyway. Try to forget about the dreaded ethanol, for all practical tuning processes it really does not make any difference . Martyn's set-up, via Big Sid, sounds like the best starting point ! Turn the idle mixture screw all the way in-but don't force it, turn it back out by one turn. I'm prepared to bet it will start easy + run real good. Go have some fun, do tell how it goes, Roy. P S Ihave used the same settings in my new twin!