Misc: Everything Else Starting Problem - Series 'C' BIG Single

[Jez Nemeth]

Hi Bill hope don't mind opening up this thread again and adding to the question.

Have similar issues trying to kick start a large capacity single cylinder unit in my bike, with a BTH electronic mag, hardly getting a spark on kickover. Carb 36mm/fuel/AMC box, etc... all that stuff is good. Start she will not, hell of a lot of compression- it's the ex-Renwick dev engine fettled to fit (833cc).

What magneto would folx recommend to get that low engine speed strong spark? And where might I get one and bits?

 

[Peter Holmes]

Well it is not a magneto, but I would go distributor and coil.

 

[billirwinnz]

Hi Bill hope don't mind opening up this thread again and adding to the question.

Have similar issues trying to kick start a large capacity single cylinder unit in my bike, with a BTH electronic mag, hardly getting a spark on kickover. Carb 36mm/fuel/AMC box, etc... all that stuff is good. Start she will not, hell of a lot of compression- it's the ex-Renwick dev engine fettled to fit (833cc).

What magneto would folx recommend to get that low engine speed strong spark? And where might I get one and bits?

Hi Jez
I tested my BTH in my lathe at 190 and 300rpm corresponding to 380 and 600 engine rpm. At 190 the spark was intermittent and weak. At 300 it was great. My A twin would start well when the oil was warm but a combination of cold oil and a geriatric rider just couldn’t spin the motor fast enough. I replaced it with a rebuilt Lucas Magdyno and starting is usually first kick hot or cold as long as I don’t flood it.

For an A single there is less choice because of the 35mm deck height. As I said above Marelli made many different 35mm magnetos although the common Guzzi ones (MCR4) spin anticlockwise and have auto advance. Is this for an A single or something else? Do you need a magdyno or a separate mag? For a single cylinder 45mm deck height I would choose a BTH but a well rebuilt Lucas will work reliably too.

It’s not cheap to rebuild a mag these days so the Thorspark points replacement is an excellent solution if you don’t mind relying on a battery.

Bill

 

[Jez Nemeth]

Hi Bill, It's a C engine -so wrong part of the forum TBH, but the thread seemed to fit.

When it comes to non-electronic Mags, complete newbie and willing to listen and learn. What you've outlined above seems to be what we're aiming at, like the independence of the electronic unit, but this is all a balancing act/compromise when you leave the factory designated path. Be just the Mag, so for a single a well renovated K1F with good coil + Thorspark points may be a good direction to look, that's really useful to know as a starting point, thank you.

 

[greg brillus]

Tim touched on it earlier, but with the AMC gearbox you need to adopt a slightly different method of starting........ I found this after building a 600 Norvin a few years back now.......Instead of pushing down the kickstart lever till it just passed TDC then kick........You need to go further, get the engine up to compression, then with the k/s lever at about the 9:00 o'clock position, and decomp lever squeezed in, push the k/s lever fully down to the bottom, then come back up fully with the lever and kick with a full stroke........This is because the AMC boxes have a different quadrant to ratchet ratio than the Burman boxes........this should help.......As for the new BTH mag's well sometimes they are great and have no issues, and sometimes they are not.........The weak spark at kicking speed is a common thing........But try the different starting approach as suggested and this should start it ok........Good luck.

 

[Jez Nemeth]

Thanks Greg -will give it a go, hell of a lot of compression in there, stroke is 106, piston 100mm and a worked TP head...quietened them down a bit with smaller carb, etc.. will keep trying on it, having to rest the leg at the mo -hate to give up on it, but part of me still suspects, as you've said, dialling the right kickstart procedure would do it, feels annoyingly close too, but just not fast enough -I'll keep persevering, cheaper than buying more bits!

 

[brian gains]

i know nothing about electrics or ignition but, does the spark improve by removing the suppressor cap, ie HT lead direct to plug?.

 

[Chris Launders]

Would one of the chainsaw decompressors help

 

[timetraveller]

I would echo Peter Holme's advice. There can be a huge spark with a coil ignition at almost zero revs. The distributor that would do it is from a C12 BSA I think. Single cylinder and the correct direction of rotation. A bit like hen's teeth now. Royal Enfields also had the same direction of rotation with their mags as Vincents. It might be worth looking at some of the newer India Enfields to find out what their sense of rotation is. Remember, you only need one cam and one set of points, a coil, and a capacitor to get it going but then you need some form of advance/retard system.

 

[Peter Holmes]

If using a BSA C12 Lucas distributor, the advance and retard is integral within the distributor base, but you have to increase the amount a little, which is easy to do with a round file, or send it to the Distributor Doctor.