Petter A1 backfiring through exhaust.

[disco2]

Hi it’s Will hope you are well I have recently bought an air compressor set made by Ben Patent it has a Petter A1 engine driving the air pump via a belt drive. The machine is complete but the engine will not start. It backfires through the exhaust with no attempt to start. The person I bought it from said it had a stuck exhaust valve because it had been stood for several years so he had freed it up. He said he thought the valve needed lapping but when I turn it over there is no obvious leak from the exhaust. I have watched a video on checking the ignition timing but it talks about the magneto clicking just before tdc but mine does not click. It is producing a good spark and is igniting the fuel in the exhaust. It is a wico mag .I wondered if anyone has any thoughts on how I can check the ignition timing without a click from the magneto.
Thanks for any help
Best wishes William

[charlie]

William, the click you are listening for is the magneto impulse. Not all magnetos are fitted with them, it nay be that it is the wrong magneto. There should be a small plate on the magneto giving type, if you could post that up on here it will help identify what magneto you have. Also which model of Petter A, and serial number as looking at the Wico magneto information I have several different magnetos were fitted over the years.

[disco2]

Hi Charlie thanks for your reply I will get those details later today.
Best wishes William.

[disco2]

Hi it’s Will I have just had a look and these are the numbers I can see. It’s a wico mag looks like 676B it could be a 5 not a 6 at the start but I can’t see it well enough to be certain. The engine is a Petter A1 3hp @ 1500rpm serial number 1522000. I had a look at the points opening times and it appears the points are opening with the piston a bottom mot top dead centre. If my understanding is correct they should be open just before tdc. So perhaps the mag has been off and re fitted half a turn out.
Thanks for your help and advice
Best wishes William

[charlie]

The information I have does not list a 676B, it does have a 576B which was fitted to JAP 4/2, 5 & 6 engines. I have copied what information I have, see attached, it could be someone has fitted an alternative magneto.

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[disco2]

Hi Charlie thanks for your reply that’s really helpful. Reading through it definitely looks like the timing is out so I will pop the magneto off and have a go at resetting it. There is a click which seems to occur at the time the points open and there is also a tdc marking on the flywheel so fingers crossed it will start.
Thanks for your help and advice
Best wishes William.

[disco2]

Hi it’s Will I thought I would share my happiness I have got the Petter running and it’s running perfectly 😁 it was as simple as the ignition timing was 180 degrees out so took of the mag and rotated the flywheel half a turn and re fitted the mag and it started up. One word of advice though make sure when ‘re fitting the mag that the little clip that holds the points cover on is not trapped between the mag and the valve chest because you have to take the mag off again to free the clip. I found out the hard way.
Thanks for your help and advice
Best wishes William

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