Intermittent Cutting Out/Misfire

[Frosties]

Hiya fellas, hope you can help with this one.

On start up and on tickover, the bike will blip down/misfire as if 1 of the coils is breaking down/firing intermittently. This intermittent firing can get better or worse throughout the day. This can lead to the bike cutting out when pulling away or even when changing down from speed - has dropped from 3.5k Rpm to off once or twice on changing down.

Bike pulls hard and clean above 3k Rpm.

Once the bike has cut out you can hit the starter until the cows come home & the bike will not start. However, if you turn the ignition off then on or hit the kill switch off/on then the bike will always start immediately   

Remembered it only started happening after I had a new throttle cable fitted but thought it was just coincidence.

Was just about to get a set of coils/leads when by chance I had to park in a dark service tunnel this morning.....the bike still blipping down so sat and watched it for a while. I noticed for the first time that when the bike blips down, like it's missed a cylinder, the temp gauge blips down quickly and returns to normal and neutral light also blips dimmer ...... all in conjunction with the misfire.

Played around with cables/looms to kill switch and ignition and tried massaging the kill switch & ignition key but could not improve issues nor make them worse.

Question is, are the 2 issues (won't start after cutting out and semi misfiring) linked?

What component which could have been disturbed is along the same run as the throttle cable?

As a note, carbs are ultra clean and recently balanced. Valve clearances done and new plugs fitted. Could a coil/lead that's breaking down give me these symptons??

Any advice on this would be much appreciated fellas 'cos apart from new coils and leads i'm totally lost!

Cheers

[rf9rider]

Sounds like you have a problem with either the ignition switch or wiring, if it was the coil problem, it wouldn`t re- start until it had cooled down.

I`d start by checking the wiring to the ignition switch, especially the connector block, then the wiring around the stem.

The throttle cable runs alongside the wiring down by the stem, so look around that area?

You could also check the main fuse for corrosion etc.

[akendall1966]

Ignition pickup sensor common failure point on these motors with some of your symptoms in common.

[Frosties]

Thanks for the replies fellas, much appreciated 

Will start with the connector block mentioned which could answer why it coincided with the new throttle cable being fitted.

Failing that will source a new sensor...........actually thought these bikes were sensor free 

Any other thoughts welcome, need to get this sorted...it's my main commuter!

Cheers

[rf9rider]

Keep us posted

[Solon]

Agree with rf9rider on this, coil or ignition pick up sensor failure wouldn't be affected by the "restart" you give when you hit the kill switch.
If the temp gauge goes down altogether with the lights going dimmer, it sounds like when misfiring, smth. happens to all electric circuit. You might have a short circuit somewhere, two wires or smth touching intermittently due to vibration, sometimes tending to stick together due to electrical charge, thus killing the engine. When you stop the ignition, electricity no longer travels through them, allowing them to separate, so the engine starts again after you hit the kill switch.
Just a guess here, keep us updated, sounds curious.

[HeavyHustler]

Where's a good place to get a new ignition pick up sensor?

[Frosties]

UPDATE

Checked all connections throughout, cleaned and ensured they were a nice snug fit - still had issues.

Re-checked carbs for any debris - all good.

Drained tank and ensured clean along with the fuel tap - no issues.

Came back to the electrical possibility and changed the plugs - still issues.

Replaced coil packs and leads - ALL SORTED 

Bike runs sweet and pulls clean from tickover to blood line. Can even start bike after stalling it on purpose so no need to hit kill switch.

Happy is a bloody inderstatement!!