running rich

[royblackburn1@btinternet.]

Hi all my a65L is running rich it has concentric carbs on i believe the mixture screw is just for slow speed {tick over} so if i lower the needles should this run less rich I also know theres a lot of variations why running rich so thought i would start with the basic, would I notice a difference in performance with needles being lowered, thanks Roy

[rhyatt]

Carb issues are always fun to sort,
When bsa and amal got together 70 years ago , they would always start at the main jet and work backwards to idle.
So, are your jets and needles and clip positions correct to spec?
The Burlen /Amal site is helpful and of course your own riders manual to check .
Lowering needles into their jets will weaken the mixture , but plug chops at different speeds are vital.
Very often, the needle jet wears oval with the needle flapping in them , so consider replacing.

[Allan G]

Hi Roy,

You haven't said what year your A65L is or if the carbs are original or not?

A brief history, in 68, carbs were fitted with what was later called the 2 stroke setup, the bikes ran fine but were fairly rich. A 2T carb can be identified by the slanted (towards the engine) spray tube, which is the little brass tube you see when you look down the throat of the carb.
The setup for these carbs was:
20 pilot jet (screw in)
106 needle jet (2t type)
Needle in middle clip (2t type)
190 main jet
Throttle slide #2.5

However in 69 revisions were made, the 4t carb was born and is noticeable by the spray tube being squared off at the top. Needle jet also had revision for 4t applications as did the needle itself. These are the settings I advise for anyone buying a A65L carb (pre oif)

Pilot jet - bush type , or if premier #19 pilot jet (the pressed in bush was equal to about 17 thou, however through my experience, and those of people who I have sold carbs too, #19 seems the better way forward.

Needle jet 106
Needle position -1, this is the top clip position which sets the needle lowest.
Main jet 180
Throttle slide #3

If your Lightning is an OIF, then change your main jet to 200.

All of these carb setups are 30mm applications.

Then if you have deviated from the standard Intake and Exhaust setup then you may need to tweak those settings again for optimum running.

[royblackburn1@btinternet.]

Thank you both very much a lot of information given the bike is 1966 like said I bet amal over the years had headaches with what jets to use and different cut outs and tubes, I have a lot to go at I wonder if Amal have sorted every thing out with their Premier, Roy

[ChrisG]

What a lot of folk don't realise is that once running and up to speed, the bike is running on pilot jet most of the time. It's taken me decades to work that one out. As such, it's always worth getting the tickover, i.e. pilot and throttle screw right first.

[scifi]

Many years ago I tweaked an Amal carb and found that a 145 main jet was best for my 250.   However now I see that the jets are only available in 10 increments, i.e. 130, 140, 150 etc.    Maybe I have not found the correct supplier.

[chaz]

an eye opener for fuelling is the modern car use of a fuel consumption gauge.

Amal used to produce a booklet showing which part of the slide is in use at what part of running.

with my Insignia, you drive it normally and you can see the gauge lights shoot to the right and into the red when accelerating. but once you have hit your required speed and are cruising the gauge lights drop to normal  green, economical. turning on cruise control, foot away from the pedal, the set speed shows when more fuel is needed , say to go up hill lights up the red scale  , then if "free wheeling" down, the gauge drops well into the green.

As Editor says, once the speed is hit, the carb will breathe itself, until more fuel is needed..