Hitchcocks Forum

Can someone help me with the ignition timing on my SR1? This is what I've done so far but it's clearly a mile out as it won't start. So, piston 0.8 ml before TDC using a homemade tool, points cam turned so the points just open, put the aa unit on without turning anything and tighten up. It' has a new condenser and points and sparks when kicking over so all looks OK, but with the plug in there's nothing, no firing apart from the odd loud backfire. I'm a bit baffled at the moment but maybe missing something obvious.

I haven't timed an SR magneto but I have timed a K2F with advance/retard unit on my Mk1 Interceptor. I think 2 things, you need to lock the A/R unit at full advance (bob weights in "flung out" position, turn and lock with a piece of wire,) then time at 3/8" - 5/16" BTDC. 0.8mm is way too small and what you are doing is effectively timing fully retarded so your spark is probably arriving ATDC hence the backfire!

REgards, Mark

Or are you possibly timing it on the wrong TDC?.

Thanks Mark. I got the 0.8 mm from the guide to setting the timing with the distributor, I assumed the mag would be the same. Anyway, I tried 3/8", which cured the backfire, but it's still as dead as a dodo. I think I'm using the right TDC Dennis, the exhaust pushrod is at the bottom. Am I getting the points cam in the right position in conjunction with the piston position? I turn it so the points just open when the mark on the stick is at 3/8" before TDC, but it's open to wide variation. Should the points be about to open, just open or fully open? It all seems a bit crude and inaccurate.

We used to use a fag paper and as soon as the points let it move that was far enough, I now use a one thou feeler gauge to detect as the points just start to open, always turn the engine forward to the correct TDC position and make sure both valves are closed.

Hi Chris, you could use the old trick of cigarette paper ( the best one for that is Rizla +, the thinnest). You put it between the closed points, then, holding it with a small traction, you turn the cam, when the points begin to open, you feel the paper mooving. I do that for decennies without troubles. Otherwise, there is a kind of buzzer that you can use, that changes tone when the points beggin to open ( much easier on a SR than a MO1) A question: is your mag ( or the cam), the good one for your sens of rotation ?
Hope it will help you. Claude

Hi Chris, if that is the magneto you bought from me recently, it was set up with the wrong rotation for a Bullet, but this can be reversed by removing the cam from the armature and repositioning it so the other ramp on the cam becomes the opening ramp. You also need to set it so as the points are just breaking open, the maximum magnetic flux is felt. Your initial timing setting of 0.8mm btdc with points just opening would be about right, as the auto advance unit will take care of advancing the timing further - certainly it should be able to start and run and be somewhere 'near' like that. Regards, Paul.

Claude & Dennis, I'll try that method, it narrows it down a bit and gives me something more precise to aim for. It's ok Paul, I know yours is the wrong way, I bought that for spares and to have a spare coil to swap. All useful info, I'll try again, thanks all.