Weak spark help please

[Mike on a bike]

Hi folks, I have a problem with a weak spark. After trying to start the engine and not succeeding we went on a process of elimination coarse of action. I have replaced with brand new the following....Points, Condensers, Coils and Battery. After doing this I still have weak sparks at the plugs and points. We have connected the battery directly to the coils to bypass everything else but with the same result.
Can anyone tell me if the generator comes into play in any way to boost the amperage to create a better spark? Don't want to strip that if it is not necessary. Got no hair to pull out anymore so your help will be gratefully received. 

[marvo]

Hi there, if you have not had the engine running for a while then the first thing I would do is drain the float bowls and tank and put brand new good quality fuel in flushed through the drains and only then can you consider starting to look elsewhere, apologies for going back to basics but it's often the fix! Cheers Marvo.

[Mike on a bike]

Thanks for your reply Marvo No disrespect intended but the problem is electrical and nothing to do with the fuel. Holding the plugs to earth on the engine shows up the weak spark so at this point nothing to do with the fuel system.

[Lobo]

Hello Mike,

The HT leads are typically a source of trouble if aged; you say you replaced the coils... can we assume this includes the HT leads... and even better the caps?

Other areas to check is the set-up correct... points gapped @ 12-16 thou", plugs (NGK D8ES) at 24-28 tho"

Is the points back plate clean /  well earthed? Are all the leads / connectors clean & in good fettle?

In answer to your alternator question, the battery voltage will nominally be around 12.4V, and rise to abouts 14.5 by 4000 RPM. I guess this 20% increase in low circuit voltage will directly increase the HT voltage by 20%.... but whether this means a 20% better spark I'll leave to smarter folk than me to say...

What will be very relevant is the starter motor cranking will drop the voltage significantly... is this your problem perhaps? Off the top of my head I reckon it'd drop to 9 v or so; and even less on a bad battery or with worn starter motor.

(a trick used by manufacturers to overcome this was to fit ballast coils... which typically ran at say 6v via the resistor. Except when you cranked the starter.... the ballast resister was removed from the circuit allowing 9v or so to the coils... and bingo a big spark for starting. Once running / starter motor off ... the resistor switched back in & coils now back at 6v)

I digress...

An option to consider might be fitting an electronic ignition to boost your spark... definitely pros & cons to these... a few threads around this website if you look.

I've a breakerless electronic ignition on my '750.... I can't tell you it particularly runs better. But, it certainly starts more easily... via the starter motor regardless of months standing.

Simon

[Bryanj]

(1) there should not be a spark at the points
(2) generator has an effectonly when the engine is running
(3) spark, i find, always looks weak to me

[steff750]

why do you think you have a weak spark?
as bryan says the sparks aint that bright anyways as long as its blue i dont think thats your problem you need to retrace what you have already done you do need fuel aswell as the spark at the right time to get the motor to fire up