bloody thing

B

brooky

Junior member
Location
PETERBOROUGH
Hi all after plenty of help from members the jota now sparks well (broken wire in heatshrink) had an hour spare this afternoon so thought would put some fuel in and see how the thing runs , it doesnt !! pops and bangs throws flames from the carbs , with a dmc 2 can i get a spark on each cyl while turning by hand at the timing mark? if the pugs are resting on the valve cover? all three plugs have a good spark when winding over also when the dmc box is in test position. tia
 
Is the wiring from DMC to the coils is correct? White goes to the twin lead coil for cylinder 1&3, grey to the single outlet coil for the middle pot.
What wire did you find had broken?
 
brooky said:
Hi all after plenty of help from members the jota now sparks well (broken wire in heatshrink) had an hour spare this afternoon so thought would put some fuel in and see how the thing runs , it doesnt !! pops and bangs throws flames from the carbs , with a dmc 2 can i get a spark on each cyl while turning by hand at the timing mark? if the pugs are resting on the valve cover? all three plugs have a good spark when winding over also when the dmc box is in test position. tia
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If you read my similar post “This bloody Bike” there is lots of info on similar issues. If you can get the flywheel off (assuming it’s the same as my 76 3C) l/h tread torqued to 100Nm, look at the orientation of the pulse cam on the crank. Could be sending a message to fire at the wrong timing, ie when the inlet valve is open. I have Ignitech ignition which uses the original pulse cam, your DMC may have a different timing trigger but it could be out of time, the symptoms are very similar.. For the spark to ignite in the carb the valve must be open.. If not the trigger then look to the timing of the cams..

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Rob said:
Is the wiring from DMC to the coils is correct? White goes to the twin lead coil for cylinder 1&3, grey to the single outlet coil for the middle pot.
What wire did you find had broken?
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Rob thanks for the reply . from memory the wires are colour to colour but will check in the morning, broken earth but inside of some thick heat shrink only lost earth when loom was cable tied back on the bike so checked out continuity then lost it as soon as pulled onto frame again. only found when stripped off all the heat shrink , was a soldered join that pulled apart.
 
Sounds like mixed plug leads or coil wires causing firing at 180 deg out. A hunch ...

A quick check; remove the plugs, fit them in the caps and ground them, then turn the motor on the starter while holding a finger over a plug hole and observing if the spark for that cylinder occurs basically when you feel the high pressure of compression stroke.
 
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Rob said:
If you don't find anything after checking as above then I'd consider checking any other soldered joints.
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Rob . sorted and starts ok, not so good when hot tho, few other jobs and can give it a run, fuel related issues now. start fault was assuming black wires (dmc) BOTH BLACK AT COILS . chased them back to colour under good old heat schrink and wrong way round .
 
Bingo!
Bloody annoying when folk use a single colour for their wiring mods. And so unnecessary when the DMC loom is supplied long enough in the first place.
 
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