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Backfire when ignition switched on

Posted: Sun Apr 15, 2018 11:26 am
by Mudge
I have an issue with my 1976gl1000.
I had the points taken off and a dyna electronic ignition kit fitted, ever since this bike workshop fit the electronic ignition i have had an issue with the running of the engine.
As soon as i turn the key in the ignition i felt what can only be described as premature ignition from one of the cylinders on the left hand side.
This is before even pressing the start button, its as if the bike has an attenpt at starting without being told to.
And when it runs its uneven and lumpy.
I have asked my local south of england vjmc for help but unfortunately no one wants to help me out.
I cant find anyone local to portsmouth, u.k. who is prepared and i quote to work on any bike over 10 years old.
I am now struggling with this issue, the bike is rideable but obviously not running anything like she should and i am determined to get her running nicely again so is there anyone out there that you know of who can help me please.

Re: Backfire when ignition switched on

Posted: Tue Apr 17, 2018 12:09 pm
by WingAdmin
Does it do this if the bike has been sitting for a while? Or does it do it if you have just shut it off, and then turn it back on? Or both?

Re: Backfire when ignition switched on

Posted: Tue Apr 17, 2018 1:02 pm
by Mudge
Hi,
Yes It does this when its been sitting for a few days or more, also shes uneven when starting.
Any thoughts or jdeas as to whag may be the prkblem?.
Because right now im struggling due to the lack of professional help available to us oldie biky rideds within the portsmouth area.
I look forward to any help and advice with gratitude.

Regards
Vic

Re: Backfire when ignition switched on

Posted: Tue Apr 17, 2018 9:06 pm
by ekvh
I have a 77 that does this randomly. Dyna ignition? A suggested cause was that the ignition was turned off, but the motor still slows to a stop near a compression point. When you turn the ignition on, the points or electronic ignition has rotated into a position signaling it to fire. If it’s in the right position and there’s a little fuel, it will fire when you turn the switch on. Mine always sounds like it turns back just a little. I don’t recall it sounding as if it moved more than a quarter turn, just a WAG.

Never heard of a work around. If you have the kill switch on stop so there’s no spark, you can crank it and then release the kill switch to run and it should fire at the right time then.

Re: Backfire when ignition switched on

Posted: Thu Apr 19, 2018 3:35 pm
by virgilmobile
Never heard of a work around. If you have the kill switch on stop so there’s no spark
There is a simple solution.
Yes you need to kill the ignition power when the key is first turned on to prevent this..
One method is to get the ignition power to go on as soon as the oil pressure light goes off.
The same method used to delay turning on HID headlights.


Obvious and a good thing to..no spark till the oil pressure comes up.Usually just a few seconds of cranking.
There's another method too.A bit faster..Same relay and added diode to the start solenoid circuit.The relay is off when the key is first turned on and is energized by the start button.Its wired as a latching relay...Once the button is pushed it stays latched till the key is turned off.



Re: Backfire when ignition switched on

Posted: Sat Apr 21, 2018 10:23 am
by WingAdmin
Nice idea, and definitely the latching relay circuit (for safety). Not only will this help with this problem, it will help with engine wear - it means your crank and pistons won't be absorbing the massive power pulses of ignition without there first being oil pressure lubricating the cylinder walls and crank main bearings.