New Amal Premier 900 series Carb for Comets

[cinquecento]

Hi Martyn - can you go back in and delete your original post just in case someone does an archive search and stops at your last post using it as a starting ref' point.

In the meantime I'll delete the copy i saved for future reference.

Thanks.

 

[Martyn Goodwin]

Hi Martyn - can you go back in and delete your original post just in case someone does an archive search and stops at your last post using it as a starting ref' point.

In the meantime I'll delete the copy i saved for future reference.

Thanks.

Original post has been updated to indicate richer jetting is in order.

M

 

[chankly bore]

Phil Tainton, Stud Road WANTIRNA. raise needle one notch, 220 main for starters. Slide should be fine, as should the pilot jet. 98 R.O.N. fuel.

 

[vibrac]

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.

I use a rolling road for the racer and if I fitted a 'new' carb on the alphabet twin I would also use it I understood that the analyzers on a good installation pick up on five gases CO, HC, O2, CO2, NOx so how does that differ from just CO/HC ? I feel woefully ignorant on that subject can someone explain if you will

 

[Bill Thomas]

Am I the only one who don't think those filters ie 16 pass enough petrol, That is the first thing I throw away, If you are going to use a lot of power. Cheers Bill.

 

[Martyn Goodwin]

Am I the only one who don't think those filters ie 16 pass enough petrol, That is the first thing I throw away, If you are going to use a lot of power. Cheers Bill.

Would you not loose even more power when (not if) crud in the fuel starts to block the jets and passageways inside the carb?

On my Comet I have that filter in place PLUS there is also gauze filters on the top of both fuel taps (the bits that poke up inside the fuel tank). Around every 5,000 miles I clean out all 3 filters and have always found lots of crap on the fuel tap gauze filters plus a much smaller amount - but it is there - of crap on the filter in the fuel bowl that you refer to.

M

 

[davidd]

I use a rolling road for the racer and if I fitted a 'new' carb on the alphabet twin I would also use it I understood that the analyzers on a good installation pick up on five gases CO, HC, O2, CO2, NOx so how does that differ from just CO/HC ? I feel woefully ignorant on that subject can someone explain if you will

I think Roy is the man to answer, but I believe that the larger data collection helps narrow down what is happening in the combustion chamber. This site has some information:

http://www.ratwell.com/mirror/interro/techgas.html

David

 

[davidd]

It is always worthwhile to check your fuel flow when you have an opportunity, like the end of the season draining. I add a gallon of fuel and open the tap with the gas cap off and time it. I pour the gallon back in and do the same with the gas cap on tight. You can do it again through the float bowl If the time is much slower, I check the cap vent first then the float then the tap. If I were running filters, I would repeat the process with the filters. I get 38 miles to the gallon at full throttle with the 500. I carry a little over a gallon in the tank, so I carry just enough for the race. You have to remember that the average is not the only issue, but how quickly the fuel will flow during a quick twist of the throttle. The float bowl should take care of this (unless you are at Bonneville and Daytona). Say your vent is not keeping up, then you risk a lean condition at a steady open throttle while cruising.

It is good to know how your fuel system works so you can eliminate it as a factor when experiencing a lean condition.

David

 

[Martyn Goodwin]

Status Update November 15, 2013

Comet is back on the road today with a fresh rebuilt motor. Carb is a Mk1 930 premier configured as follows:

Slide = 3.0
Needle Jet = 106
Main Jet = 250
Emulsion Tube = Norton 850 with cutaway facing inlet valve
Left hand configuration
Mixing Chamber top with 2 adjustors
A 55 degree double banjo
Needle in bottom grove (ie rich)
Idle mixture screw 1 1/2 turns out

After 80 miles of running today I had a badly sooted up spark plug with hesitation and a tendency to misfire at small throttle openings - At wider (not full) openings it was much smoother. Not a trace of "blueing" on the exhaust or silencer. Tomorrow I will be re setting the needle to the middle groove then doing another 80 to 100 mile loop and will report back - I figure its best to change just one thing at a time.

The good news is with ignition at 2 BTDC fully retarded and 30 BTDC fully advanced the bike is a first kick starter - and as expected the compression is such that use of the decomp lever is a must

Re the Dyno check of the carb tuning that I have been trying to arrange - I have spoken to a few local dyno owners and while they are all happy to take my $$$ they - to a man so far - absolutely refuse to allow me to get involved in the tuning process, even though they (have all so far ) admit they have little ( i take that as none) experience with Amal Mk1's or Vincents. I am not prepared to risk my bike under those conditions. I continue to seek out a more sympathetic Dyno owner.

Stay tuned.

Martyn

 

[chankly bore]

Misfire at small throttle openings is evidence of richness in pilot jet and/or slide cutaway. Needle comes in at half to three -quarters throttle which you shouldn't be using yet if you are running a new piston and barrel in.