No spark? Checked CDI, plug and magneto.

[Ollie]

Hey y'all, does anyone know what's up with my engine? Recently it made a strange sound then stopped working. When I try to start it, it seems like it has no spark. I have another working MB so I've been able to swap out components to check if they're faulty. So far, the CDI, spark plug, magneto, carb, pipe and throttle are all fully operational.
However, the engine won't start. When I try to jump-start it, it seems to be cycling air so I assume the piston is working properly. My wife reckons it could be a loss of compression from somewhere that's causing it not to spark, but I'm wary of tearing apart the engine until I know what I'm looking for.
Any ideas?

Ollie

 

[skyash]

If you put the plug on the out side of the motor and turn the motor over do you see spark? Think I have had a week spark and it doesn't work. Or no fuel? If you herd a noise mybe the rings broke I think it won't start if thay do go. If there is a big air leak it won't start. So maybe spray some wd40 on the motor when you are trying to start it not every where you don't want to much so you can't see where its leaking.

 

[danlandberg]

Air leak or broken rings will not affect spark. With plug out and grounded against the head or frame, pedal with cluch lever out (engaged) to turn the engine over as fast as possible. Watching for spark. I have a center kick stand, so it's pretty easy to do. If no spark, it's probably the magneto. (I've had more trouble with them than CDI's) My NO spark problem was the magnet It self. (One lost strength) √ all components with a multi meter. There are several threads on here that have the procedure.

 

[HeadSmess]

unless the wife works on race cars or something in her spare time, ignore her. and given her opinion...she doesnt


No (read it, its NO) loss of compression due to ANYTHING will cause a loss of spark.

well, you have checked basically everything and still no spark?


strange noise + no spark, sorta sounds to me like you may have lost/snapped, etc the woodruf key that holds the magnet in place on the crankshaft.

if its just free to do what it wants and isnt locked to the crankshaft...sure, youll get no spark.

you should notice if anythings up when you remove/swap the magneto.

the other suggestion made above...could have lost its magnetism...unusual, but not necessarily impossible. ie, check it.

you gotta turn them over pretty fast... usually i just hold the rear wheel off the ground and give the pedal a good kick...

there is the possibility that the head isnt earthing itself to the rest of the engine.

 

[crassius]

hold spark plug in your hand while turning the motor - if you feel nothing, you have no spark & can work from there

if you feel the voltage, then you need to check fuel and compression (unless timing somehow changed)

 

[danlandberg]

unless the wife works on race cars or something in her spare time, ignore her. and given her opinion...she doesnt


o loss of compression due to ANYTHING will cause loss of spark.

well, you have checked basically everything and still no spark?


strange noise + no spark, sorta sounds to me like you may have lost/snapped, etc the woodruf key that holds the magnet in place on the crankshaft.

if its just free to do what it wants and isnt locked to the crankshaft...sure, youll get no spark.

you should notice if anythings up when you remove/swap the magneto.

the other suggestion made above...could have lost its magnetism...unusual, but not necessarily impossible. ie, check it.

you gotta turn them over pretty fast... usually i just hold the rear wheel off the ground and give the pedal a good kick...

there is the possibility that the head isnt earthing itself to the rest of the engine.

 

[danlandberg]

Plug in open air (out of head) this is a no compression situation. Compression has nothing to do with a NO spark problem. No compression gives a NO start problem.
If all ignition components are in good working order, you WILL have spark, compression or not.

 

[danlandberg]

Strange noise, then NO spark, sounds like the magnet came loose. If the magnet grounds on the magneto, you will not have spark. √ the woodruff key that holds magnet on crank in its proper timing position.

 

[Ollie]

Thanks for all the suggestions guys! The engine is no longer on the bike, as I used it's working magneto to get my other dead engine running (water ingress killed it) and installed that instead.

I had previously looked for a spark like you suggested and didn't see one, but maybe I wasn't turning it over fast enough. I'm not sure how I can check it again without putting it back on a bike (which I don't have the patience for), so I'll open it up and have a look at the piston rings.

It's my oldest engine and noticably more powerful than the others, so I'd love to get it going again.

 

[HeadSmess]

Plug in open air (out of head) this is a no compression situation. Compression has nothing to do with a NO spark problem. No compression gives a NO start problem.
If all ignition components are in good working order, you WILL have spark, compression or not.

yeah yeah, my keyboard tends to miss the odd letter here and there...i meant "No loss of compression, due to anything, will cause a loss of spark..."

sheesh, one letter...cant you figure out what i meant?

richard...