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Hi folks,

My mate has a GPW or MB (can't remember which!) which won't start. It has been a chassis up restoration but having got nearly to the end it won't start.

It has a new (6 volt) battery, leads, coil, condenser, point, leads and plugs. Power is getting through and there is a spark on each plug. He has tried pouring a small amount of fuel directly into the carb and has even tried Easy Start but still no joy. All earthing leads are good.

I've no experience of 6 volt systems, can you have a weak spark?! Could it be a dodgy component? Has anybody had a similar problem got any ideas?

Cheers

Mark

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Does the engine have a chain or gear driven cam? Spent ages trying to get mine to start before reading the gear driven distributor spins in the opposite direction so 2 plug leads need to be swapped.

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It could be any number of issues from mechanical to electrical to static or ignition  timing.

As Chris notes above it will need a methodical investigation starting with the easy to do stuff first do not be tempted or persuaded to start ripping things apart until you (or your mate) have gone through all the basic checks including making sure that the valve train and distributor drive are functioning correctly. 

When you mention a weak spark with a 6volt system I'm guessing your referring to the potential for coil robbing as a result of a tight engine after a full rebuild?. 

If everything else checks out OK above disconnect your main light feed and also the generator wires to the CVC box and try a 12 volt battery direct to the starter switch with a 12 volt coil, the 6volt starter will be fine as long as you don't hang on the starter button for extended periods and don't run the engine too long with the generator wires disconnected as it can overheat the wingdings a few minutes is OK.

Pete

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Mark,

If you have a spark and fuel is getting through (plugs will be wet), then the likelihood is that the problem is the same as you had a while ago with your QL - the timing has probably been set 180 degrees out ie set to no4 top dead centre instead of no1 top dead centre. The result of this is that each cylinder has a valve open when the ignition tries to fire. To check that you have no1 tdc, remove the plugs and turn the engine on the starting handle with a finger over the hole for the spark plug and watch the timing marks. If you can feel pressure with your finger as the timing marks line up, then you have no1 tdc.

The reason it's so easy to get wrong is that no1 and no4 cranks are in the same plane, as are no2 and no3, so you always have two pistons at the top of their stroke. the valve timing, at 1/2 crankshaft speed, is such that when no1 is on the compression stroke, no4 is on the exhaust stroke. If you are 180 degrees out, the ignition fires with a valve open and the fuel charge gone!

Check the timing first, and that should sort it out. If the timing is correct, check the main earth from the engine to the chassis, a faultless connection is critical with a 6 volt system.

If that doesn't solve the problem, then I would begin to suspect that the valve timing is amiss due to an error in reassembling the engine, although it would need to be pretty far out not to run at all.

Hope this helps and that I haven't confused you too much!

Mike

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  • 3 months later...

How fast does it turn over?

GPWs are apparently renown for having bad earths as the frame mount for the earth is connected by rivets.

I'd run an earth lead directly to the starter on the block - see if that makes a difference.
That fixed mine.

 

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  • 4 weeks later...
On 7/11/2019 at 12:15 AM, Spencer54 said:

How fast does it turn over?

GPWs are apparently renown for having bad earths as the frame mount for the earth is connected by rivets.

I'd run an earth lead directly to the starter on the block - see if that makes a difference.
That fixed mine.

 

thats good advice

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