BSA C10 C11 C12

BSA C10 C11 C12 Forum => Technical Section => Topic started by: Owen on October 17, 2020, 08:53:53 pm

Title: Distributor v Combined contact and advance/retard mechanism
Post by: Owen on October 17, 2020, 08:53:53 pm
There I was looking through some Lucas information on distributors (C10/C11) and the combined contact and adv-retard mechanism (C11G-C12ohv). I noticed the advance angle for the distributor versions is 9 to 11 degrees, yet the C11G/C12 ohv unit is 11 to 13 degrees. So the question is would making the distributor version go to 13 degrees make any difference?
Title: Re: Distributor v Combined contact and advance/retard mechanism
Post by: Tman on October 17, 2020, 09:35:02 pm
In these days of crap petrol less advance is better than more advance, but would 1' be noticeable on a lowly iron-head plodder like a C  ranger? I rather doubt it.
Title: Re: Distributor v Combined contact and advance/retard mechanism
Post by: Cosmikdebriis on October 18, 2020, 08:16:32 am
I would guess that the advance retard mechanisms are likely to be so well worn out by now that neither would be near the original spec.

Most of us (I should imagine) set ignition at fully advanced so it's only going to affect the retarded timing (who really cares about that)?

Personally. I just wind my dizzy backwards and forwards until I get it to run how I like it and don't really have a clue what that might be.

As has been said, Couple of degrees here and there isn't going to make much difference on such an engine.

No harm in trying though.
Title: Re: Distributor v Combined contact and advance/retard mechanism
Post by: timsdad on October 18, 2020, 08:30:33 am
The difference between the two models may be because the later bikes are turning direct off the cam and the early ones go through the skew gears.

As has been said, these are different times so the bikes need timing to where they need to be with the modern petrol and, perhaps, different compression ratio of a replacement piston. I set all my bikes at full advance, at the manufacturers' recommendation where possible, and then tinker with it to a better running position. This will be as advanced as possible to avoid pinking.


Ray
Title: Re: Distributor v Combined contact and advance/retard mechanism
Post by: Cosmikdebriis on October 18, 2020, 08:55:22 am

I set all my bikes at full advance, at the manufacturers' recommendation where possible, and then tinker with it to a better running position. This will be as advanced as possible to avoid pinking.

Ray

To be fair and as I said, I couldn't tell you what ignition timing I have but where Ray and I may differ is. I like mine to chugg up a hill or round a corner at low revs so set mine so that it doesn't get "snatchy". That position is in there, somewhere, and it can take a bit of roadside fiddling to find it but eventually I'm more or less happy.

Either approach seems right to me though.
Title: Re: Distributor v Combined contact and advance/retard mechanism
Post by: timsdad on October 18, 2020, 09:23:53 am
My bikes, the cooking models, all chugg up hills and trundle around at low revs when needed, Cosmik, because they're running at full retard.

The only way we differ, I'd think, is that I usually know what my timing is set at and you don't. When my 650 Triumph is running to my satisfaction, after it's engine renovation this month,  I'll check where the timing is set with a degree plate so I can replicate it easily if the points have to come apart.


Ray
Title: Re: Distributor v Combined contact and advance/retard mechanism
Post by: hampshirebiker on October 18, 2020, 09:30:47 am
I assume that with rising octane levels in the 50s a slight advance of timing was a logical step.
Title: Re: Distributor v Combined contact and advance/retard mechanism
Post by: chaterlea25 on October 18, 2020, 06:10:39 pm
Hi All,
Agreed with worn partscits a matter of experimentation.
Back in the day when I ran my C12 as everyday transport I found that a static timig of app  1/32 In after tdc gave better running thzn the 1/32 before tdc recommended in the book
On my C10  dizzy I would  leave the clamp loose enough so I could "adjust" it while riding to get the best out of it then tighten up once backb home
Not recommended in 2020 :o

John