Starting the scooter
Flat spot. Delayed response to the throttle movemement or a flat spot signifies a weak mixture. This may be rectified by taking the connecting link down the threaded jet lever, having the lock nuts already finger tight only so that the adjustment may be made with the engine running.
Heavy smoke. Uneven running (eight-stroking) plus black or heavy blue smoke form the exhaust signifies an over rich mixture. This may be corrected by adjustment up the threaded lever. This allows the jet, which is in effect a jet-sized petrol tap, to shut off a little in relation to the butterfly, thus weakening the mixture.
Tuning the top half
Recommended Jet sizes
Starting the machine: 1. Open petrol tap.
2. Kick over the engine as normal.
3. Should the engine flood, switch off petrol, open the throttle wide and kick over the engine a few times.
4. Always stop the engine by turning off the petrol, leaving the injector dry for instant starting.
The Phillips Fuel Injector is a very simple design. The jet assembly is in effect a petrol tap. The butterfly is in effect an air tap. The levers are arranged so that the tuning of the first half of the throttle - taking the link down the long threaded lever for richer, or up for weaker - does not upset the basic full open setting. The second half of the throttle travel-top end-tuning is controlled by the throttle stop - say by one turn - and then lengthening the connecting link to bring the butterfly back again to the fully open position. This will weaken the mixture right down through the range, and call for a richening of the first half of throttle travel (bottom end). Tune the bottom end with the engine running, and when a clean pickup is obtained (lagging response and spitting back means too weak. Wight stroking and black smoke means too rich) open the throttle fully very quickly and watch the exhaust. Should black smoke appear as the revs mount well up the range the top end is too rich. Adjust weaker as described (not forgetting to reset bottom end) until black smoke has cleared. Then road test and finally tune top end to plug reading.
The idling stop should be set and at the same time the throttle cable must be adjusted precisely without slack, otherwise the throttle return spring will overcome the spring in the link thimble, and allow the jet to shut right off, so stalling the engine.
Bias on the side of vertical turns (on one unit) may be located by slackering off one side flange nut - with the other side not fully tight, and puching the unit over to make an air leak. If this is done with the engine running at near idle and the bad cylinder begins to fire this is the rich side. Now remove unit and make a small air leak that side, by cutting a little groove in a fibre manifold gasket (which may be fitted if one is not already there). All this is well worthwhile to get the superb instant response, and clear cut power gain that the injector will give.
Twin injectors: Fit separate pipe and tap to each unit so that after starting up, one side may be switched off whilstthe other is tuned to run clear, right up the range. Then switch over to the first side and tune it likewhise. Level butterflies with cable and adjusters. Tune top-end to plug readings.
Basic setting: Your injector is adjusted to a basic setting and the clamps should not be disturbed. If, however, by accident the clamps are moved use the following procedure:
1. Insert a ..... drill shank through the fuel feed hole, so that it is visible in the injector bore. This lines up jet in open position.
2. The left hand clamped lever must be hard against the throttle stop screw and the jet block.
3. The butterfly must be in the horizontal fully open position. Adjustment is carried out by altering the length of the connecting link
4. Arrange that connecting link is at approximately right angle to threaded lever when is fully open position. NO END FLOAT at jet spindle.
This never happens and so you have to look around and decide just where your money is best spent. The answer is to improve the engine, but this usually means buying very expensive parts and also spending long weekends in stripdowns and testing. But we have found an item that you can buy and bolt on which will give a reasonable increase in performance, and that is a Wal Phillips fuel injector. M M has tried these out in the past and found them to be just as clean running and realible as a carburettor but correctly unied, they will give a higher top speed, increase acceleration and sometimes both. We had a pair of Lambrettas on test this month and this was an opportunity to try out a new injector designed specially for scooters.
Made by the sane firm, this injector is similar to the existing types, but it is much shorter so that it can be fitted to a Lambretta or Vespa without having to cut a hole in the side panel.
Having a stub fitting, is fitted straght on to the SX200 that we were trying out. The tubing which normally servers as an overflow pipe to the Dell'Orto carb can be used as a petrol pipe from the tap to the injector. Wal altered the adjustment very slightly and then the bike was tried out. These are the times that were recorded:
We did not
to check the fuel consumption but it was not more than a couple of
per gallon up on standard. This is a very small price to pay for a top
speed increase of nearly 15 per cent. With the injector fitted, the
gave a standing quarter mile time of 20.8 sec. and a terminal
of 65 mph. This was only 1.6 sec. slower that the Royal Enfield GT,
the Enfield would continue accelerrating while the Lambretta run out of