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[Chris Tindal]

Hi all, over the last few weeks I have been fettling a 59 Bighead bullet. It was running very rough but I've almost got it sorted with new cables, plug, condenser, oil change and brakes. It has an SR1 for ignition and 12v conversion for the lights. It now starts first kick and will tickover smoothly and evenly. The clutch works fine and the gears all change well. The problem is when it's hot, if I stall it and kick it immediately, it starts again. If I leave it just a few seconds, it will just not start. It takes about half an hour of kicking before it finally fires up, and when it does, it runs well again. If I turn the petrol off immediately after I have stopped it, it's easier to coax back into life, but still a pig, no matter what the throttle position. It has an open 389 Amal (new), and the plug colour is dark brown although I don't know what jets are in it yet. It doesn't need the air leaver at all to start, even when cold. My initial thought is that it seems to flood, but should it flood so easy? (it has the original brass push-pull tap) Could it be jetted a bit rich, so that when its hot there''s not enough air?, or could it be the winding in the SR1? Any thoughts would be helful, cheers Chris.

[WDCO42]

Hello Chris, Have you fitted an heat spacer between the carb and the head ? It looks more for me to some fuel issue than ignition one, the same that affect some side valve singles reluctant to fire when hot.
Hope it will help you. Claude

[Dennis C]

This is typical of what happens when the SR1 mag armature needs to be remagnetised, as they get older the magnets get weaker.

[Dennis C]

An easy cure is to convert to coil ignition. Inside the mag two wires connect to the stop terminal connector one is the coil the other is the points, disconnect the coil wire and earth it on the condenser mounting screw run a lead from the external stop terminal to a 12v coil, and supply switched 12v to the other coil connector. You now have coil ignition. You can hide a coil under the petrol tank on the frame tube, lead the HT lead from the mag up under the tank and it will look like it is still in use.

[Adrian]

If the problem is due to fading magnets in the magneto, how come the engine still starts well from cold? I would have thought a tired magneto would have made the bike a consistently bad starter at all times. If the bike can be re-started with a hot engine immediately after stalling, that suggests the sparks are still fine.

[Mark M]

Respect to Dennis but I agree, a failing mag would show symptoms at other times. The re-start procedure you describe and the fact that you never need choke suggest very rich mixture, as does the plug colour. I'd look at the carb. There have been quality control problems at Amal in the recent past, i've seen some myself. First, make sure there is no fibre washer under the tickler valve (easy,) then check the carb internals. I have found that the "new" Viton tipped needles can lead to flooding, the brass type are better. Also check that all the specs for jets and slide are correct. Good luck!

REgards, Mark

[PeteF]

Worth checking the float height. OK the carb is new but.......
The clues might be "If I turn the petrol off immediately after I have stopped it, it's easier to coax back into life" and "It doesn't need the air leaver at all to start, even when cold. My initial thought is that it seems to flood"
http://www.reochumber.co.uk/

[Presto]

There are a number of anomalies in this situation. Immediate re-start is said to be ok. Any delay and the re-start is problematic – requiring ½ hour of kicking. That is extraordinary! Petrol off helps re-start but only marginally. I would have thought that if the problem was a flooding carburetor at the carb then ½ an hour kicking would result in a fatally flooded engine with the expected result of a total failure to start, until the plug is removed and dried off. Equally that it idles well doesn’t suggest a flooding carb and also suggests that the pilot system is ok. The dark brown plug colour is not so extreme that it points to folding of an order that would make hot starting so extremely difficult. In the 389 Monobloc the float height is not adjustable and is rarely incorrect. I would look to the jet sizes – which are not known at this stage. I also wonder where the new carb was bought and if it was correctly set-up from the start.

[PeteF]

Presto, I've found quite a few to be wrong over the years. The problem is usually because people fit the supplied washer under the needle seat but older Monoblocs don't have one. That shouldn't be the case here but it's a quick check.

[Presto]

Very true Pete, good advice - as usual!