Misc: Ignition Mysterious Meteor misfire - what am I missing?

vibrac

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VOC Member
There was a lot about the BTH cut out wire interference with the HT lead on here a few years ago I know it convinced me enough that I cut out my cut out wire on the racer
 

Martyn Goodwin

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From what I have read in this thread so far it seems to be heat related. I would be checking EVERY electrical connection associated with the ignition.

Change/clean/fix ONE THING AT A TIME.

Here in no particular order is what I would suggest next. I would start with the spark plug lead - actually I would replace it even if it looks OK, just in case. You want a copper cored lead and a non-resistor plug cap.

Check where the HT cable connects into the BTH coil for any sign of oxide or corrosion (or oil) and clean all that up. If you have a spare coil, put that on and see if matters improve.

Check all 12V wiries including the earth wires to be sure they do not have any trace of corrosion or oil in their connections and clean them up
 

Martyn Goodwin

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Just wondering. Once the mis-fire starts happening have you reached down and felt if the carb itself is getting warm or even hot?
 

LoneStar

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It seems to worsen as the engine warms up. It doesn't seem to be RPM-related. I haven't tried revving in neutral. It doesn't seem to matter if the engine is under load or not.
If it idles well, yet misfires at speed, the misfire relates to either higher rpm or greater throttle opening.

By revving the engine in neutral you can raise rpm with very little throttle - misfire at this point suggests ignition rather than carburetion; lack of misfire the reverse.
 

CoreyL

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VOC Member
From what I have read in this thread so far it seems to be heat related. I would be checking EVERY electrical connection associated with the ignition.

Change/clean/fix ONE THING AT A TIME.

Here in no particular order is what I would suggest next. I would start with the spark plug lead - actually I would replace it even if it looks OK, just in case. You want a copper cored lead and a non-resistor plug cap.

Check where the HT cable connects into the BTH coil for any sign of oxide or corrosion (or oil) and clean all that up. If you have a spare coil, put that on and see if matters improve.

Check all 12V wiries including the earth wires to be sure they do not have any trace of corrosion or oil in their connections and clean them up
I've swapped out the BTH coil and HT lead. Non-resistor plugs and cap. I'm now planning to send the BTH back to the manufacturer in the UK to determine if there is an internal problem. It's happened before.
 

CoreyL

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Just wondering. Once the mis-fire starts happening have you reached down and felt if the carb itself is getting warm or even hot?
The inlet manifold is hot but the carb body is not. There is a thick insulator between carb body and inlet manifold.
 

brian gains

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VOC Member
classic condenser / short failure in the vid'.
in CoreyL's situation given the symptoms i'd look for something simple; is the misfire affected if the choke is applied judiciously at high revs, are the points in good condition ie spring, pads square nothing shorting at high revs.
 

Simon Dinsdale

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classic condenser / short failure in the vid'.
in CoreyL's situation given the symptoms i'd look for something simple; is the misfire affected if the choke is applied judiciously at high revs, are the points in good condition ie spring, pads square nothing shorting at high revs.
Brian, The magneto CoreyL is using is a modern BTH which is actually a self generation electronic ignition system so no condensor and no points used.
I had a modern BTH fitted to my Rapide 10 years ago. It ran great for a few years and then slowly got harder to start hot or cold and eventually would not run. The BTH would still generate a spark though but not a bang from the bike and so I suspect its internal timing was faulty and sparking at the wrong time even though the shaft & hole ofr the timing pin was lined up. I sent the BTH back but the guy running BTH at the time and he said he could find nothing wrong with it and it must be a problem my Rapide. Strangely when I took the BTH off I refitted the old twin points coil ignition and the bike fired up straight away and has run great ever since. I could never get that BTH to run on a bike again so it was thrown on the shelf.
 
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