bike running superbly rough

[wurlyvalve]

Hello all. I've just ridden 160 miles from week place accommodation to home. All was well but for 2 miles from home the engine cut. I went to re start it but the neutral light was off. Battery has 13v but with ignition on 7v, 166 ohms across the ignition circuit. So, I get new battery. Lovely, 12.7v ignition off, 12.4v igntion on. The bike starts.

However, it runs rough as rats. It sounds like it's a single but it has got exhaust gases out of both pipes. It will only do 30mph Max. And if held in neutral, revved to 3000 rpm it will suddenly clear and run like an engine again, momentarily.

Help, need to ride Sunday. I'm using my phone which I find rubbish for the internet, so sorry for port writing it mal corrects words for me.

Cheers,
.Glen

[wurlyvalve]

Left hand cylinder not running. Right hand exhaust hot but left is cold. As I'm away from my base I'm manual less. Resistance between the low voltage terminals on the left hand bank coil is 4.4 ohms, which seems right. Resistance from the both tension post and the low voltage pins is 85k ohms. Is this right? Is take the right hand one of to compare but that stems to be an arse to get to.

Thanks.

[dicky]

I can't help you with the electrical stuff at the moment, but given that 90% of electrical faults are due to the carburetor it might not hurt to drain the float bowls and check if there is any crap or water in them.
Easy to do and might help eliminate one potential cause of the problem.

dicky.

[wurlyvalve]

Right hand coil is 13k ohms. So that tells me the left hand one is goosed. Me walking back Sunday

[dicky]

Bugger.

[cobbadiggabuddyblooo]

Usually when your voltage drops you will draw more amps.
So could this have something to do with the coil damage??
With the battery not supplying a constant 12v because now it's supplying an irregular and lower lower voltage.
Am I correct to think from this principal that a 4 Ohm coil taking more current would overheat it???

[davamb]

Nope, Ohm's law states that the current is the voltage divided by the resistance, so as the voltage drops, so will the current.

[cobbadiggabuddyblooo]

Nope, Ohm's law states that the current is the voltage divided by the resistance, so as the voltage drops, so will the current.

Ok time for a lesson in resistance..

Is this only on a DC system?
If I use 110v and 240v sytems as an example,usually the amps are doubled ?

[wurlyvalve]

For a given power. P=VI.

[davamb]

Nope, Ohm's law states that the current is the voltage divided by the resistance, so as the voltage drops, so will the current.

Ok time for a lesson in resistance..

Is this only on a DC system?
If I use 110v and 240v sytems as an example,usually the amps are doubled ?

I'll post a brief tute up in another thread when I get a mo' Cobba - don't want to hijack Wurly's thread.

[dobbslc]

Halve the voltage = double the current.
Now to the coils...

Primary resistance should be between 3.1 to 4.6 ohms measured between the two terminals on the side of the coil.
Secondary resistance should be between 10.4 k ohms and 15.6 k ohms. Between the ht lead and the red / black coil terminal. But take the plug cap off as this will have a resistance of 10k ohms on its own.
If it's really hot weather or the ignition has been switched on you might get a slightly higher reading as resistance goes up with temperature.
Taken from the Haynes manual and verified on my bike last week.

[wurlyvalve]

Yeah all fixed now, thanks. A pair of new pattern coils from m and p saved the day. Shame my petcock and tank cap didn't seal, the leaked petrol stripped the pain off the tank and a spare alloy from my 7 that i had lying around. Still, barking as she should do now.