Single Amal 932Carb main jet and needle position.

baz said:
Yep I could have the wrong setup
I can only go by what I have tried on my own commando
I've had a single 32mm concentric a single CV 32 mikuni a single VM 34 and a VM 36 and my final single setup is a TM 40
None of these setups have started better than twin concentrics so far
My b50 would generally start first kick ,that was running a 32mm concentric
You darent open the throttle whilst kicking that bike over !
Click to expand...
Mikuni enrichener requires more engine motion to draw the fuel through and get the required fat mixture for cold start.

Saw this for decades on snowmobile engines.
The sleds with a hand pump type primer would start FIRST PULL, in any temperature, provided the operator knew when & how much.

Enricheners would take several pulls when cold.
 
concours said:
Mikuni enrichener requires more engine motion to draw the fuel through and get the required fat mixture for cold start.

Saw this for decades on snowmobile engines.
The sleds with a hand pump type primer would start FIRST PULL, in any temperature, provided the operator knew when & how much.

Enricheners would take several pulls when cold.
Click to expand...
Yes and don’t open throttle while kicking to start when cold.
 
Nothing wrong with grey plug tips . The needle and needle jet wear after mileages pile up .
 
I suggest most guys do not tune systematically. The main jet should alwas by over-rich slightly. A 260 main jet should be big enough. The rest is about needle jet, needle taper and clip position. If you lower the needle one notch, you should get a miss when you ride the bike. If you cannot get the motor to miss by lowering the needle, the needle jet is too big. Once you get the motor to miss, raise the needle one notch, and the miss should go away. That is the point at which you get best prformance without doing damage. I would buy two needles of different tapers, and try each one independently. The taper affects the rate at which the throttle can be opened - it compensates for loss of vacuum. With a single carb there will probably be more vacuum, so the needle jet might need to be slightly smaller. If you set the idle correctly, the motor should start first kick when hot, with the throttle closed. The slide cutaway is usually a number 3, which usually represents a height of 3mm when measure on a flat surface.
 
Schwany said:
Unleaded pump gas burns better than gas did 40 years ago. If your motor runs well, I would not worry about the grey color. If it pinks and/or coughs and falls on its face when the throttle is quickly opened near WOT, then it may be lean if the timing is good.

Below is a chart that shows where the parts in a carburetor work in relation to throttle opening. Not an Amal but close if you can read between the lines. There is some overlap in fuel delivery even with an old Amal. (I am guessing that I.M.S. in the chart is idle mixture screw.)

Single Amal 932Carb main jet and needle position.
Click to expand...
This chart has some erroneous information in it. The clip position either lifts or lowers the needle so, according to the chart, how come the clip has an earlier (from 1/8th open throttle) but the needle taper has a later effect? Is the clip in the airflow???
 
dobba99 said:
This chart has some erroneous information in it. The clip position either lifts or lowers the needle so, according to the chart, how come the clip has an earlier (from 1/8th open throttle) but the needle taper has a later effect? Is the clip in the airflow???
Click to expand...
You'll have to discuss this with Keihin or SUDCO, since it is a chart that came in the Keihin FCR User's Manual.

The clip is not located in the air flow.

Edit: I apologize for posting a chart that came out of another carburetor user manual. Although when I tune, the chart makes sense to me regardless of the carburetor model.
 
Last edited:
Seems like as the position of the clip determines the needle position, it mainly affects mixture strength from 1/8th to 3/4 throttle. Maybe even when the needle taper is still down in the main jet, the fact that it’s raised slightly allows more fuel to pass up to where it is less restricted by the reduced amount of the parallel portion still in the needle jet?
 
Stevo said:
Seems like as the position of the clip determines the needle position, it mainly affects mixture strength from 1/8th to 3/4 throttle. Maybe even when the needle taper is still down in the main jet, the fact that it’s raised slightly allows more fuel to pass up to where it is less restricted by the reduced amount of the parallel portion still in the needle jet?
Click to expand...
If you look at the needle, you will see the straight part and the shoulder where the taper begins. Where the taper begins is extremely important. When the parallel part is in the needle jet at low throttle openings, that is the leanest mixture you get under normal riding conditions. If you open the throttle quickly, you lose vacuum, and there is less depression on the needle jet, so you need more fuel flow. The rate of taper determines how fast you can open the throttle. A heavy handed person often needs quicker taper needles, but richer needles usually mean less power. The best power is achieved by using slow taper needles and feeding the throttle on slowly. With either quick or slow taper needles, if you raise the clip one notch, you should get a miss when you ride the bike - raise the needles one notch by lowering the clip. That is the smallest adjustment you can make with a normal carb. When using petrol as fuel, that adjustment is still too big to get best power, however it is as good as you can do without moving to fuel injection.
Many guys who road-race do not know this stuff - it comes with age. Plenty of guys run their motors miles too rich -it is a common mistake.
My 850 motor is on methanol, but the principle is the same - I use 6D Mikuni needles in Mk2 Amal carbs - the leanest.With methanol, the jests flow twice as much as with petrol, so raising or lowering the needles gives a much finer adjustment - I get closer to the optimum. It makes a really big difference.
 
Last edited:
You must log in or register to reply here.
Back
Top