When you time a BTH magneto you lock it with the rod and set the engine to your desired advance, tighten the pinion nut and job done. If it's set on full advance how does the magneto retard itself for starting? What is the advance range and if you set the advance at 36 degrees what is the retard setting? A mechanical A/R is easy to understand, I don't understand this electronic wizardry.
E: Engine BTH magneto
- Thread starter Sakura
- Start date
The electronics cannot predict the future engine speed and advance to match it but can measure actual time between trigger pulses and introduce a delay if the programming demands it.
So, if I understand, the longer time between the trigger pulses (low engine speed) a delay is introduced retarding the ignition? Conversely, as pulses get closer it moves towards the set full advance? If that actually makes sense!
Yes, I think that is how electronic advance works , but no-one seems to know the actual delay, in degrees, for the BTH.
The BTH website shows an advance curve, or rather a retard curve, that indicates 38°. To me, that means an advance setting of 36° means a retard setting of 2° ATDC. Hardly conducive to good starting! But what do I know about electronic ignition.
I have 34º set on my BTH fitted to a standard B Rapide and it starts and idles just fine. When fitting an electric starter it is strongly advised to set ignition advance at 34º to prevent any chance of backfire which would break the shear pin.I will do this on my Shadow with electric start.
Dear Sakura,
Echoing what Alberevin says. My Rapide settings are as above. It always started easily on the kickstart and the same now I've fitted an electric start. It has only ever had the new BT-H magneto fitted since I built the bike. It has never "kicked back" in 40,000 + miles.
If the bike runs fine when you have it going but you suspect that the ignition timing is making your bike hard to start then it is very easy to adjust the timing a little by slacking three three fixings on the magneto and turning the magneto body a little. The slots in the magneto flange allow for several degrees of adjustment either way if you originally fitted the magnet with the fixings central in the slots. A small mark on flange and crankcase beforehand will lt you set it back to where you started. Try it a little at a time and see if you notice any difference. It is not usually critical to 1º or 2º.
If you suspect a weak spark first check that your plug gaps are set to no more than the 0.018" listed in the handbook. Also check that the plug leads are firmly fixed onto the screw on the coils and that the screw goes down the middle of the lead and not to one side of the centre wire. Check the same at the plug cap end too. Non resistor plugs should be fitted and preferably unsuppressed plug caps. You can remove the spark plugs and with a plug cap removed hole the end of the lead away from the engine while someone spins it over. You should see a thin spark that will jump over 1/4" or so. Don't expect to see a bright blue spark, that is not what is produced by this system.
You said: "But what do I know about electronic ignition" Sometimes we have to accept that something just works even though we don't understand why. Many drivers only know that you turn a key, press some pedals and miraculously their vehicle moves.
Plug gaps 18 thou, How strange, My electric thing," Rita", Says not wide, I would have thought this new stuff could go much bigger, When I packed up mending Cars, The plug gaps were getting Huge !.
One of our blokes told me to go bigger, For better starting, But it didn't work for me. Cheers Bill.
One of our blokes told me to go bigger, For better starting, But it didn't work for me. Cheers Bill.
Hi BigEd,
Thanks for your reply. You are right that much of today's technology is inscrutable to the average person. There was a time when I could understand and repair most items that I owned, domestic, vehicles etc. Now I understand very little of the items I own, particularly "domestic". However, the one area I am still on top of is classic bikes and things mechanical of that era, I worked for many years on mechanical maintenance in a Nuclear Power Station. So I am still curious about the BTH technology, as far as I can understand it. If they publish a retard curve showing 38°, it means just that to me. b'nighted gave me good insight into how the retard process works, perhaps someone has an explanation of how the retard range works. Every day's a school day.
Thanks for your reply. You are right that much of today's technology is inscrutable to the average person. There was a time when I could understand and repair most items that I owned, domestic, vehicles etc. Now I understand very little of the items I own, particularly "domestic". However, the one area I am still on top of is classic bikes and things mechanical of that era, I worked for many years on mechanical maintenance in a Nuclear Power Station. So I am still curious about the BTH technology, as far as I can understand it. If they publish a retard curve showing 38°, it means just that to me. b'nighted gave me good insight into how the retard process works, perhaps someone has an explanation of how the retard range works. Every day's a school day.
My understanding is the BTH electronic mag counts the delay between pulses to determine RPM. When it is very low at kickstart speed it sets itself timing wise to a predetermined figure x degrees retarded from the 34 degrees advance that you timed the bike to. This is a set point seperate to the curve graph. When the bike fires up (above the kickstart RPM) the unit senses the rpm by the delay between pulses and follows the graph on their website. Note the graph goes to approx 38 degrees retard from full advance for a twin, but that is at 400 RPM. I bet your Vincent ticks over a bit higher than that so the actual operational advance-retard figure is less than 38 degrees.
Also the graph says "typical" twin ignition curve so it could be slightly different for a Vincent twin.
That is my understanding, but I may be wrong.
Simon
Also the graph says "typical" twin ignition curve so it could be slightly different for a Vincent twin.
That is my understanding, but I may be wrong.
Simon