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Motoplat Ignition Boxes

R

rgakrill

Just got it firing!
Joined
Jun 7, 2009
Messages
24
I wonder if any of you can help me out with a bit of a problems.

I am trying to get my recently rebuilt V75 4-valve (1986) working. I have had a mystery problem where the engine wont rev properly and misfires when pulling away. I initially thought that it was an air leak or a carb problem but I have basically renewed all the fuel system including brand new carbs but the problem still persists.

So I have started checking the ignition system. My first point of call was to check the voltage at the coils. I was getting 12.5V on one coil and 11.5V on the other. So I swapped the wires round and the low voltage stayed on the same coil!! When I disconnected the Motoplat TCI Ignition boxes the voltage went up to 12.5V.

I have one 'new' Motoplat Unit and two old ones (I keep one plumbed in as a spare). When I connect the old ones I get 11.5V at the coils and the new one, 12.5V.

So I checked the wire which acts a the earth to the coils (the green and green/black ones that go from TCI to coil). The upshot was that there was a voltage of circa 1V going from the TCI to the coil. This seems wrong to me as it should act as an earth to the coils so the potential difference flow from coil to TCI and not the other way round.

On the newish Motoplat unit there is no voltage on the 'trigger' wire.

It seems strange that both units would fail at the same time but it would explain the misfire.

Any advice anyone?

cheers

Richard Akrill
 
Hi Richard,

Sorry for the tardy reply but I've been away.

I agree, its unlikely to be both modules simultaneously.

I'd hook the old modules up ad check advance with a timing light. It should be smooth and progressive.

I'd make sure the pick ups are clean.

I'd change the plugs. Get rid of any platinum/iridium/resistor plugs due to making it harder for the motoplat. All that fancy stuff has resistance that the 'plat doesn't like.

Check HT leads for continuity. Wriggle them and keep measuring.

Check plug caps. If resistor ones then measure. Should be around 5k ohm but I'd ditch them and go to standard nil ohm caps.

Check coils for resistance across the LT and LT/HT terminals. LT +/- should be either 3 or 5 ohms, I can't remember off hand but it will be one or the other. LT/HT should be lots.

cheers

Rod a happy 'platter

The 'plat gets a bum rap a lot of the time. Like anything they can fail but check all the normal suspects first.
 
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