Needles and needle jets

The needle jet is the critical component in Commando carburettors. It is interesting if you do a search to find out what is available.

There are different lengths of Mikuni needles to suit different size carburettors , #6 needles will fit 32mm Amal carburettors and they are available in many different tapers. Fitting leaner needles into Commando carburettor might be the difference between good and bad performance. 6D Mikuni needles are the leanest at 3/4 throttle.

Jets R Us, like all retail suppliers, are having trouble keeping their shelves stocked. Don't be surprised if whatever you need is out-of-stock.

The best way to fix amals and Mikuni's is to replace them with FCR 35's.

outawack said:

The best way to fix amals and Mikuni's is to replace them with FCR 35's.

Click to expand...

You will never get them at the optimum float chamber angle due to the frame.
The metering (if set up correctly) is more precise though even if a floored installation on a Commando given the cost.

Time Warp said:

You will never get them at the optimum float chamber angle due to the frame.
The metering (if set up correctly) is more precise though even if a floored installation on a Commando given the cost.

Click to expand...

A flaw in the floor ?

OUTAWACK. You sure are.

Nothing wrong with a well set up pair of Amals, even if they are worn.

Most of our riding is probably done using one-third to two-thirds throttle. The part which is affected by the taper on the needles. It might be the reason for poor throttle response which occurs with many commandos. The taper is there to compensate for momentary loss of vacuum as you open the throttle. Lean neeclles require slightly slower throttle opening, but the engine response can be better.
The first thing anyone should do after buying an old British bike is replace the needles and needle jets. The difference between poor and excellent performance is often bugger all in terms of needle clearance.

kerinorton said:

OUTAWACK. You sure are.

Nothing wrong with a well set up pair of Amals, even if they are worn.

Click to expand...

Anything will work, but some things are better than others.

The needle jet should be small enough so that the motor will cough as you lower the needle to the part where the parallel part begins. Then you raise it one notch. As you open the throttle, the metering is done by the parallel part of the needle and the low running jets until you reach about one-third throttle. After that, the taper takes over until you reach about two thirds throttle. Then the metering is done by the main jets. If the taper is too quick, the richer mixture can cause poor throttle response. Particularly when you use petrol as fuel.