Technical stuff

Additional Amal Info
STARTING from cold. Flood the carburetter by depressing the tickler sharply three or four times, and close the air valve: set the ignition, approximately half retarded. Then shut the throttle and open it a little, e.g.: about one eighth open, then kick-start. If it is too much open starting will be difficult.

STARTING, engine hot. Do not flood the carburetter, but close off the air lever. Set the ignition and close the throttle, then open the throttle about one eighth of its travel and kick-start. If the carburetter has been flooded and won't start because the mixture is too rich - open the throttle wide and give the engine several turns to clear the richness, then start again with the throttle one eighth open, and air lever wide open. Generally speaking it is not advisable to flood at all when an engine is hot.

STARTING, general. By experiment, find out if and when it is necessary to flood, also note the best position for the air lever and the throttle for the easiest starting (some carburetters have the throttle stop fitted with a starting position on to which the throttle must be shut down).

CABLE CONTROLS. See that there is a minimum of backlash when the controls are set back and that any movement of the handlebar does not cause the throttle to open; this is done by the adjusters on the top of the carburetter. See that the throttle shuts down freely.

PETROL FEED, verification. Detach petrol pipe union at the float chamber end; turn on petrol tap momentarily and see that fuel gushes out. Avoid petrol pipes with the vertical loops as they cause air locks. Flooding may be due to a worn or bent needle or a leaky float, but nearly all flooding with new machines is due to impurities (grit, fluff etc.) in the tank, so clean out the float chamber periodically until the trouble ceases. If the trouble persists, the tank might be drained, swilled out, etc. Note that if a carburetter, either vertical or horizontal, is flooding with the engine stopped, the overflow from the main jet will not run into the engine, but out of the carburetter through a hole at the base of the mixing chamber.

FIXING CARBURETTER AND AIR LEAKS. Erratic slow running is often caused by air leaks, so verify there are none at the point of attachment to the cylinder or inlet pipe, check by means of an oil can and eliminate by new washers and the equal tightening up of the flange nuts. Also in old machines look out for air leaks caused by a worn throttle or worn inlet valve guides.

BANGING IN EXHAUST may be caused by too weak a pilot mixture when the throttle is closed, it may also be caused by too rich a pilot mixture and an air leak in the exhaust system, the reason in either case is that the mixture has not fired in the cylinder and has fired in the hot silencer. If the banging happens when the throttle is fairly wide open, the trouble will be ignition not carburation.

AIR FILTERS. These may affect the jet setting, so if one is fitted afterwards to the carburetter the main jet may have to be smaller. If a carburetter is set with an air filter and the engine is to run without it, take care not to overheat the engine due to too weak a mixture; testing with the air valve will indicate if a larger main jet and higher needle position are required.

If the trouble cannot be remedied by making the mixture richer or weaker with the air valve, and you know the petrol feed is good and the carburetter is not flooding, the trouble is elsewhere.

	Tech Talk
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Tuning your Amal 1st If at full throttle the engine runs 'heavily', the main jet is too large. If at full throttle by slightly closing the throttle or air valve, the engine seems to have better power, the main jet is too small. With a correct sized main jet, the engine at full throttle should run evenly and regularly with maximum power. If you are testing for speed work, ensure that the main jet size is sufficient for the mixture to be rich enough to keep the engine cool, and to verify this, examine the sparking plug after taking a fast run, de-clutching and stopping the engine quickly. If the plug body at its end has a cool appearance, the mixture is correct, if sooty the mixture is rich, if however there are signs of intense heat, the mixture is too weak, and a larger main jet is required. 2nd With the engine idling too fast with the twist grip shut off and the throttle shut down on to the throttle stop screw, and ignition set for best slow running; a) loosen the stop screw nut and screw down until engine runs slower and begins to falter. Then screw the pilot air screw in or out to make the engine run regularly and faster. b) Now gently lower the throttle stop screw until the engine runs slower and just begins to falter, then lock the nut lightly and begin again to adjust the pilot air screw to get the best slow running. If this second adjustment makes the engine run too fast, go over the job again a third time. Finally, lock up tight the throttle stop screw nut without disturbing the screws position. 3rd If, as you take off from the idling position, there is objectionable spitting from the carburetter, slightly richen the mixture by screwing in the air screw sufficiently, but if this is not effective, screw it back again, and fit a throttle with a smaller cut away. If the engine jerks under load at this throttle position and there is no spitting, either the throttle needle is too high or a larger throttle cut away is required to cure the richness. 4th The needle controls a wide range of throttle opening and also the acceleration. Try the needle in as low a position as possible, eg: with the clip in a groove as near the top as possible. If acceleration is poor and with the air valve partially closed the results are better, raise the needle by two grooves. If much better, try lowering the needle by one groove and leave it where it is best. NOTE, if the mixture is still too rich with the clip in groove number one (nearest the top), the needle and needle jet probably needs replacing due to wear.
Additional Amal Info STARTING from cold. Flood the carburetter by depressing the tickler sharply three or four times, and close the air valve: set the ignition, approximately half retarded. Then shut the throttle and open it a little, e.g.: about one eighth open, then kick-start. If it is too much open starting will be difficult. STARTING, engine hot. Do not flood the carburetter, but close off the air lever. Set the ignition and close the throttle, then open the throttle about one eighth of its travel and kick-start. If the carburetter has been flooded and won't start because the mixture is too rich - open the throttle wide and give the engine several turns to clear the richness, then start again with the throttle one eighth open, and air lever wide open. Generally speaking it is not advisable to flood at all when an engine is hot. STARTING, general. By experiment, find out if and when it is necessary to flood, also note the best position for the air lever and the throttle for the easiest starting (some carburetters have the throttle stop fitted with a starting position on to which the throttle must be shut down). CABLE CONTROLS. See that there is a minimum of backlash when the controls are set back and that any movement of the handlebar does not cause the throttle to open; this is done by the adjusters on the top of the carburetter. See that the throttle shuts down freely. PETROL FEED, verification. Detach petrol pipe union at the float chamber end; turn on petrol tap momentarily and see that fuel gushes out. Avoid petrol pipes with the vertical loops as they cause air locks. Flooding may be due to a worn or bent needle or a leaky float, but nearly all flooding with new machines is due to impurities (grit, fluff etc.) in the tank, so clean out the float chamber periodically until the trouble ceases. If the trouble persists, the tank might be drained, swilled out, etc. Note that if a carburetter, either vertical or horizontal, is flooding with the engine stopped, the overflow from the main jet will not run into the engine, but out of the carburetter through a hole at the base of the mixing chamber. FIXING CARBURETTER AND AIR LEAKS. Erratic slow running is often caused by air leaks, so verify there are none at the point of attachment to the cylinder or inlet pipe, check by means of an oil can and eliminate by new washers and the equal tightening up of the flange nuts. Also in old machines look out for air leaks caused by a worn throttle or worn inlet valve guides. BANGING IN EXHAUST may be caused by too weak a pilot mixture when the throttle is closed, it may also be caused by too rich a pilot mixture and an air leak in the exhaust system, the reason in either case is that the mixture has not fired in the cylinder and has fired in the hot silencer. If the banging happens when the throttle is fairly wide open, the trouble will be ignition not carburation. AIR FILTERS. These may affect the jet setting, so if one is fitted afterwards to the carburetter the main jet may have to be smaller. If a carburetter is set with an air filter and the engine is to run without it, take care not to overheat the engine due to too weak a mixture; testing with the air valve will indicate if a larger main jet and higher needle position are required. If the trouble cannot be remedied by making the mixture richer or weaker with the air valve, and you know the petrol feed is good and the carburetter is not flooding, the trouble is elsewhere.
Tuning Twin Amal's To start with, slacken the throttle stop screws and put the twist grip into the shut off position, to allow the throttle to shut off. There should be a slight back-lash in the cables where backlash can be obtained, if necessary, by screwing in the cable adjusting screws on the top of the carburetter. Then, with the handlebars in the normal position, and with the throttles closed, adjust the cable adjusting screws so that on the slightest opening of the twist grip, both throttles begin to open simultaneously. Main jet sizes are selected by checking the effect of the mixture on the sparking plugs, after taking a run at full throttle over a straight piece of road. The smallest pair of jets that give the best maximum speed is usually correct provided that the plugs do not show any signs of excessive heat. It might be that for really critical tuning, one carburetter might require a slightly different jet size from the other. For slow running, set the twist grip to make the engine run slowly but just faster than a "tick over". Then gently screw in the throttle stops to just hold the throttles in that position, and return the twist grip into the shut position, leaving the engine running on the throttle stops. The next thing to do is set each carburetter by screwing down the throttle stop screws and adjusting the pilot air screws accordingly. Regarding the setting of the pilot jets, a fairly satisfactory method is to detach one sparking plug lead, and set the pilot air adjusting screw on the other cylinder as a single unit, and then reversing the process to the other cylinder. It may be found that when both leads are connected to the sparking plugs, the engine runs slightly quicker than desirable. If this happens, a slight adjustment of the throttle stop screws will put this right. It is essential that the speed of idling on both cylinders is approximately the same, as this will either make or mar the smoothness of the get-away on the initial opening of the throttle. It is essential with twin carburetters that the throttle slides are a good fit in the bodies, and also that there is no suspicion of air leaks at either of the flange attachments to the cylinder. With regards to the lower end of the throttle range, which is always the more difficult to set, one can only take excessive pains to make quite sure that the control cables are perfectly adjusted, without any excessive backlash or difference in the amount of backlash between one carburetter and another, otherwise one throttle slide will be out of phase with the other, and so resulting in uneven running. To check the opening of the throttles simultaneously, shut the twist grip back so that the throttles are resting on the throttle stop screws in their final position of adjustment. Then, insert the fingers into the air intakes and press them on the throttles. With the other hand, gently open with the twist grip and feel the throttles lift off their stops at the same time. Even more Amal info RE-ASSEMBLING after dismantling. See that the washer on the bottom of the jet block is in good condition, otherwise fuel will leak across its face causing rich erratic running. if the washer is faulty it should be replaced by a new one. When replacing the throttle see that the jet needle goes into the centre hole in the jet block and once in, check the throttle works freely when the mixing chamber cap (2) is screwed down firmly by spring clip (18). When re-assembling the float see that the narrow leg portion of its hinge is uppermost, as this operates the float needle. Care should be taken to see that the joint faces of the side cover and body are not damaged or warped and that the joint washer is in good condition, otherwise difficulty will be experienced in making a petrol tight joint. HOW TO TRACE FAULTS There are only TWO possible faults in carburation; either RICHNESS of mixture or WEAKNESS of mixture, so in case of trouble, decide which is the cause, by; 1. Examining the petrol feed. Verify jets and passages are clear. Verify the banjo gauze is clear and allows ample flow. Verify there is no flooding. 2. Looking for air leaks. At the connection to the engine. Or due to leaky inlet valve stems. 3. Defective or worn parts. Slack throttle or worn needle jet. Loose jets. 4. TEST WITH THE AIR VALVE, to see if by richening the mixture, the results are better or worse. INDICATIONS OF RICHNESS Black smoke in exhaust. Petrol spraying out of the carb. Four strokes, eight stroking. Heavy, lumpy running. Heavy petrol consumption. - If the jet block 16 is not tightened up by washer and nut 14, richness will be caused through leakage of petrol. - Air cleaner choked up. - Needle jet worn large. Sparking plug sooty. INDICATIONS OF WEAKNESS Spitting in carburetor. Erratic slow running. Overheating Acceleration poor. Engine goes better if; - throttle not wide open or air valve is partially closed - Has air cleaner been removed - Jets partially choked up REMOVING the silencer or running with a racing silencer requires a richer setting and a larger main jet. NOTE: Verify correctness of fuel feed, stop air leaks, check over ignition and valve operation and timing. Now at throttle position shown on sheet 7, fig 5, test to see if the mixture is rich or weak. This is done by partially closing the air valve, and if the engine runs better weakness is indicated, but if the engine runs worse richness is indicated. TO CURE RICHNESS Fit smaller main jet. Screw out pilot air screw. Fit a throttle with larger cut-away Lower needle one or two grooves TO CURE WEAKNESS Fit larger main jet Screw pilot air screw in. Fit a throttle with smaller cut-away. Raise needle one or two grooves. NOTE: It is not correct to cure a rich mixture at half throttle by fitting a smaller main jet because the main jet may be correct for power at full throttle, the correct way is to lower the needle. CHANGING FROM STANDARD PETROLS TO SPECIAL FUELS, such as alcohol mixtures will, with the same setting in the carburetor, certainly cause weakness of mixture and possible damage from overheating.