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Lost my spark!!!


CBVFRbikeboy

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This 750 is doing my head in :wacko:

I've now lost all spark to the (new) plugs, and I can't figure out where or why it's happened. I've been fiddling with my carbs a bit, but not touched electrics, and now they're dead. Was running, and didn't (consciously) disturb anything.

I'm getting power to the coils (B/W side). Resistance across terminals is within spec, as is resistance b/w leads. Resistance across the pulse units is within spec. To test, I've replaced at different times both coils, and pulse generators with other good units. I've swapped a CDI unit from my 1000 in case that might work, but nup. I've run power to the coils direct from the battery (to by-pass the cut-out switch) - no change.

 

Just as a curiosity, I noticed the Clymer manual says right-hand coil is 1-3, and the wire should be yellow and b/w, but both the 750 and the 1000 have this coil on the left.

 

I'm missing something, but my brain hurts now, and I hope someone can give me a prod.

 

cheers

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download the honda factory manual from vfrd..

 make sure the plug caps and wires are screwed in properly.. sometimes the come off  or get loose when changing the plugs. 

 pull the wires from the coils  one at a time and clean the connections with sandpaper or 3m red or green pads .. squash the female connector on the wires to get a better connection. make sure you have a good ground from the main harness.. add extras ..:fing02:

 

 

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30 minutes ago, gll429 said:

download the honda factory manual from vfrd..

 

Thanks, yeah, got the factory manual as well, and have tested the pulse units according to their instructions. I've fitted new leads just in case, and the screw-in connectors look in good nick. All fit nice and tight. I've swapped coils with good units, and I've swapped CDI units with a pair off my running 1000F. The b/w lead to the coils looses about .5 volt compared to direct-feed from the battery, but that's normal. I've run out of parts to substitute :wacko:

 

Thanks for responding.

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you didnt mention the grounds.

   as crazy as it may seam.. find the closest green wire to the coils and splice it. add a wire straight to the frame. and even clean up any possible ground interference at the coils.. even running a wire to the frame from the coil mounts.

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1 hour ago, gll429 said:

you didnt mention the grounds.

   as crazy as it may seam.. find the closest green wire to the coils and splice it. add a wire straight to the frame. and even clean up any possible ground interference at the coils.. even running a wire to the frame from the coil mounts.

good point. I've just run a ground from the coil bracket back to the battery (seems closer than any frame-mount?)

 

Incidentally, I can't figure out how the rubber-mounted carb chamber gets its earth? As far as I can tell, the carb insulators should, well, insulate the lower air-box-thingy? I can't see any metal-to-metal contact anywhere, yet my multimeter tells me it's earthed?? I hate electrics sometimes :wacko:

 

no change :blush:

 

thanks again.

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hook your wiring back up to the proper way..  double check your fuses. put the stock cdi unit on .

Main ground is the bolt on the cross member on the frame right above the fuel pump. The same bolt holds the crankcase vent bottle to the frame. Pull that connection and clean it up.   make sure your battery is at least 11 v. 

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16 minutes ago, squirrelman said:

Did a dingo chew your wires ? :goofy:

 

yep. I see what you did ;-)

 

I think I may have solved it, although the spark is still weak, it seems to be enough to fire her up.

 

Now I just have to sort out my carb issues :-(

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