Talk to me about coils

So, here’s the problem.Haven’t used the bike for two or three weeks. Its just sat, nothing has been touched, moved, wiggled or jiggled.Last couple of days I’ve had it out and its really playing up.Lots of back firing across the rev range and at any speed. I changed the plugs but still the problem occurs. Took it for a rip down the motorway and I’m scaring drivers as I overtake them.So I checked the spark - it seems very erratic, not strong and not always blue. Kind flickers around and goes from blue to orange.So, I suspect my coils are on the way out. I have two of them, both at 6V.Pulled them out and tested them, multi meter set at 200 ohms and I’m getting a reading of about 2.4/5 on both of them.Checked a known good coil and I’m getting about 4.9.Does this reading suggest that the coils are on the way out and would therefore be the cause of all the back firing?Any other ideas?(I know nothing about coils any information I have gleaned is from watching youtube videos which may or may not be a good idea!).Thanks!

Do you have the points ignition? If so try the condensers first.

On the primary side they should be both be the same resistance a 2.5 ohm differance leads me to think one is faulty
you must be using electronic ignition if you have the two 6 volts so a fault on one coil can show up on both cylinders so replace the pair or if you have a good one i would replace the one at 2.5 then they are about both 5.0
my mistake thought it said one was 2.5 and other 5 apologies Ex smokingbiker2013-05-03 17:55:02

Ignition barrel.

Just because the LT coil winding shows up OK (and both seem to) it doesn’t mean that the HT coils are good. I assume you have Rita ignition. 2.5 ohms on a 6 volt coil is correct. The other coil you are comparing with must be a 12 volt one, so no use.Suggest you get a couple of new 6 volt coils. Loads on Ebay.You can check the HT side of each coil, but the resistance will be quite high.

ooh, its getting a bit complicated!Bike has Newtornics electronic ingnition.Both coils are showing 2.5 or thereabouts.Am off to buy a couple of new coils and will report back.I’ll give everything electrical a good clean and a scrub to ensure not dodgy connectionsThanks

A spark in air should always be blue, never orange. Don’t know what that’s about. 2 x 6V coils, 2.5 Ohms each, suggests nothing wrong with them, therefore occurs to me bad connections from pick-up to amplifier. Possibly. (?) The pick-up signals are typically very low power so doesn’t take much to stop them getting through. Water ingress in the connector is an absolute no-no.

What’s the starting like? Battery OK? I’ve known symptoms not unlike yours when a battery is beginning to fail, though it would still spin the engine over well.

Battery is fine - cranking like a big cranking thing.When I picked up my newly shod wheel from the garage they checked the coils and thought they seemed fine at 2.5ohms each.So, its back to the really simple things - new plug caps have been bought and will be fitted tomorrow.Just watch, when I get it all back together it’ll start up fine with no hint of a problem - sometimes these bikes can be very wilful!Will update tomorrow.Thanks!!

I’m no mechanic, but I would have thought that backfiring could be caused by a number of things, and dodgy coils wouldn’t be my number one suspect (and the coils don’t sound that dodgy anyway).

You might want to retitle the thread, or start a new one about backfiring, to get a wider range of views.

Newtronics eh, have you cleaned the optical pickups in the distributer housing?
Mike, the LT coils may well look good, but it’s usually the HT coil which breaks down, often only when hot, guess how I found that out?Brian UK2013-05-03 19:13:45

The 6v elektrikery 'gnitions seem to use up coils more readily than the points maybe as they fire every time and Waste a spark, RiTa scared me to death when I first got it if you flick the ign off sometimes you get a “woof” or even LOUD backfire as the wasted spark fires any unburnt fuel.

Personally backfiring after it has been left i would check

Connections
Fuel
Plugs
plug caps
zorst for any 'oles or leaks
THEN the coils

But then I do not like throwing £££ at stuff , usually cos I aint got any pare really.

OK yes fairy nuff, needs a coil tester to be sure. Other possibilities ~ all electrical connections to ignition system OK? Ignition / kill switches OK? Amplifier is getting 12V OK? Amplifier’s earth to frame is OK? Plus what Brian said.

not sure its coils with what you have said but as the insulation gone on coil causing arching to frame .

You say it has Newtronics ignition. Is that not the new version of the old Piranha system? That always used the standard 12V coilsLucas Rita uses 6V coils.

silly question, but have you made shure that the fuel tap is fully open/not blocked at all. my cali3 (rita ignicion) cost me new coils and plugs+HT leads turned out that the fuel tap wasent opening fully, she would start and run but as soon as it warmed up it started back fireing. it drove me bloody mad.

Well, thought I’d update this.As I said coils were checked by the garage who said they were fine. So I cleaned them up, wrapped them in inner tube rubber and reinstalled. I bought new NGK plug caps.Installed new fuel filters on the carbsInstalled new fuel lines Installed new carb rubbers and put on a new rear tyre (not sure this affected the back firing problem)And now she runs like a top!!I did a run over to Hastings yesterday and not a squeak or a fart there or back. Running as smoothly as ever, if not more so.Just in time for the sunshine!!I reckon she was telling me that a little TLC was in order!!Cheers

Nice one. That is what they call character!