Testing a Coil

[yosini]

Hi,

I'm trying to get to the bottom of the running problems I'm having with my twink - it seems as if it is not firing on all cylinders, there is definitely fuel and the twin 40 are pretty new and balanced, but it's a bit spluttery - much better an smoother at higher revs. to me it seems electrical, I've tested the spark on all plugs and had them all out to clean and check the gaps but still the same.

I thought the other day though that I used to have an old Sunbeam Stiletto which had similar symptoms and that ended up being the coil or the condenser - is there a way of testing a coil rather than just replacing? I know they aren't expensive items, but would be good if there was an easy test before I did.

Or any other suggestions? car is big valve, running electronic ignition but most other engine/electricals are standard. The engine was rebuilt about 500 miles ago by Spyder so will be going back to them to check, they mentioned something about it might be the timing chain (it had a new one) possibly relaxing and putting the timing out, but as the problem seems to suddenly disappear as they revs get higher I doubt it. It's almost as if one cylinder suddenly starts firing again and you get full smooth power rather than lumpy spluttery...

Cheers

Joe

[Grizzly]

Hope this helps. https://www.youtube.com/watch?v=FIx4dxew_UU

I believe 6v Ballast coils should be around 1.4-1.8ohms and 12v Un-Ballast coils 3-4ohms.


Just as a suggestion, have you removed and inspected the Carb jets? i don't know your situation but when mine has been stood a few weeks it gets a white deposit on the end of the jet, mine tend to be pump jets so it splutters when you try to pull away or accelerate (Rubbish modern fuel for you). I bought a cheap hydrosonic cleaner and give then an hour in there every time they start to play up.

[RogerFrench]

Failing coils usually get worse at high revs, not better.
I'd look elsewhere - Grizzly's s a good suggestion.

[Matt Elan]

Pm sent

[jerryh]

Maybe worth changing the rotor arm as well, there's so many dodgy red and black rotor arms being sold and these can give the symptoms you've mentioned.

[alan.barker]

Yosini,
i suggest you try a HT coil from one of your other cars as i do and you will soon know if it's the coil
Alan

[yosini]

Grizzly, good shout on those pump jets.I did as you suggested and have just put it back together now and she runs as sweet as before. Certainly will make me use it more now!

Brilliant, thanks all

Joe

[Bruce Crowthorne]

Funnily enough I have just cured a mis fire. In my case it was the rotor arm.
Of course I did HT leads and coil before I got to the rotor arm.

If you are anywhere near Portsmouth I have an extra coil .....