Stumble, hard start, and backfire...

[dwire]

Good sleuthing, dwire. There is a picture of such a thing in an OLD handbook I have. When I say your photo, I recalled it.
Something like this was used in the dark ages when magnetos and early kettering ignition systems got used on autos!!
Easy to build now using a slice of polyethelene thick-wall tube or some such. The original was in hard rubber or Bakelite. I think Prestolite made one.
On the other hand, it eliminated all that FUN I mentioned where YOU hold the wire and draw the spark.

Yes, it takes a lot more moxie to spark in the compressed atmosphere of the combustion chamber, that's why you need to see about a 1/4 inch spark outside!
PS. Did you make this or is it something you bought or inherited? The ring looks like formica.

Frankly, myself I've always had or fashioned a tool of some nature, as I am no stranger to high tension shocks, but more of the deadly nature, like TV fly-back transformers, or several brushes with full three-phase 240 - so I "try" to avoid such things as much as I can these days. Not to say in a pinch standing on carpet, wood or the like in a house with no one around, no test light or meter and assuredly not touching a ground wire, run my finger across unknown house wiring one by one to find the hot wire by the 60Hz vibration in the shock it will give you...

These spark testers are production items and have been for many, many years - this one is pretty new, only about 15 - 20 years or so. We had one that was black and it likely was 100% Bakelite, but just warn down from serious use - and just like Bakelite it had snapped in half; it was used for many years with a careful safety-wire job to hold the brittle thing together. We finally broke down and bought a new one at some point for the shop years back. It is not Bakelite, but is tough stuff that is for certain.

These date back as you mention, but no homework for me as that is what was always provided; sure they are still for sale today enough places; particularly small engine suppliers as they are standard fair for magneto get-ups... This one would have likely come through our then supplier as a Briggs&Stratton authorized dealer/warranty repair etc... Surely Tecumseh and all the others still in biz. likely have similar items; unless, well there is always the possibility "THERE'S AN APP FOR THAT" now...

Anyway, you think that's neat, you'd really get a kick out of my timing lights; when I move the big chest and get a bit settled, I'll post you or something; talk about flash from the past - and don't drop; ALL Bakelite!

[dwire]

I understand the need for the clamp and the pin opposite it, but why is that third pin there and coming in at an angle?

Good question Tim, I know what it has been used for - that is several things; I also am pretty darn sure when I set that thing up once that there was a specified gap between the long and short electrodes as well, but I am having a brain fade moment and would prefer check in the big book before giving you as they would say on that game show "The final answer." I know it's been used on twins, for the dimensions are close enough to observe both at once and one gets a good visual comparison, but It would simply be best if I pulled the book for you as I only wish to post facts and obviously the facts machine in my brain is on strike tonight; for it has been a super long day.

[Roy Gavin]

Gunsons, the makers of the Colortune spark plugs also made a Flashtest device, which was just a pair of plastic dividers about 5" long, with a pair of contacts about an inch up and a scale at the end.

They had three ranges for the maximum gap the spark would jump without misses- 0-4 mm , fault exists, 4-8 mm , fault developing,and 8-15 mm ,all OK, system normal. As long as it wasnt made by Lucas, of course

Wouldnt be hard to make something similar with a couple of bits 1/2" square timber lath with half lap pivot joint at one end and a couple of 1 1/2" brass screws through each lath.

Handy elimination tool in the days of Lucas electrics, as it shows up coil ,capacitor, or lead problems easily.

Fitting the large 22 mf capacitor from the Hitachi distributor from a Datsun L series engine in place of the OEM 15 mf Lucas item made a ,err, electrifying difference to the spark on my BSA B44 - changed it from a weak white to a blue that you could hear, and so far hasnt caused any problems with the remainder of the system.

[Major Softie]

Fitting the large 22 mf capacitor from the Hitachi distributor from a Datsun L series engine in place of the OEM 15 mf Lucas item made a ,err, electrifying difference to the spark on my BSA B44 - changed it from a weak white to a blue that you could hear, and so far hasnt caused any problems with the remainder of the system.

That's very interesting. Why, if simply changing to the higher mf condensor/capacitor would make such a difference, would they have not done so in the first place? I know that, in spite of the terrible problems in Lucas electrics, their engineers were not ignorant. Not having any background in electrical engineering, I have no idea what the possible negative impacts would be, but I do understand enough to see why the higher mf unit would yield a hotter spark.

Do you know what complexities are involved? If not, maybe Rob?

[Jean]

If the capacitor is TOO big, electrically, it can mess with the spark timing.
You can watch this on a scope!
Back to EE 201, tank circuits and ocillators.
OH wait! They don't DO discrete components anymore.
DUH.
According to Bosch specs, the "normal" cap value is 0.3 to 0.4 mf...I think there is a decimal missing from those specs Roy listed!!

[Roy Gavin]

http://www.etoolcart.com/gunson-flash-t ... g4079.aspx

Found a link to a flashtest.

The Hitachi capacitor was fitted mainly because I had one lying around, and I suspected the 30 year old OEM Lucas item was the cause of the weak spark.
It was, but I dare say that a new 15 mf , either Lucas or Hitachi, would have been better too. Main point in stating the strength was to confirm that something other than the original specification can work well with the remainder of the OEM components.
According to Radco in his book- The Vintagents Workshop, elderly British two strokes with flywheel mags get the same sort of result from replacing the small internal Capacitor with a larger externally mounted one, and this may have also been in my mind .

[dwire]

If the capacitor is TOO big, electrically, it can mess with the spark timing.
You can watch this on a scope!
Back to EE 201, tank circuits and ocillators.
OH wait! They don't DO discrete components anymore.
DUH.
According to Bosch specs, the "normal" cap value is 0.3 to 0.4 mf...I think there is a decimal missing from those specs Roy listed!!

Yeah Jean, no question about that and a scope will show the time deviation for which you speak, though one needs use or make a detector and know its known effects on your measurement as well, for I have yet to see a scope that will tolerate tens to hundreds of thousands of volts. You could though get away with connecting the scope between the condenser and points and noting the deviation there... Hall effect sensor maybe - or whatever they use today for modern clamp around wire type timing lights. (Sorry I don't have any of those anymore I don't think; the ones from the 40's and 50's are just so much more fun and cooler! - Though just as Jean has lamented since they actually use the spark to trigger the firing of the strobe, the extensions and such one uses to keep the plug and wire connected, yet still grab the signal for the light make for a very wonderful place to get the sh1t knocked out of you...) And yeah Jean I've done plenty of the pull the wire deals; especially on vintage (like 30's through 50's cars) would prefer not as that is a recipe for get shocked!

Between designing passive EQ's for the audio industry and being an amateur radio op, one gets ample opportunity to learn the idiosyncrasies of changing time/domain with capacitors. lol they're not just for filtering 'ya know. And even for the layman should not be that hard to understand; a capacitor requires time to charge as well as discharge; without even getting into the other half of what mechanism or why the capacitor gives up said charge, in part or entirely, just knowing charging and discharging a cap delay's current movement forward is enough to know "something" about its characteristics.

Tim (Shepard), I will try and get you a real answer about the secondary electrode from the folks that knew (now likely long since gone) but I am in the middle of a move that is all consuming if you know what I mean... I can still say we used it on twins, either magneto or electric ala' tank circuit Tesla type (like our bikes) but I'm sure there is a diagram of that tool in one of the 100lb books over at the shops that likely identifies each electrode's initial and intended purpose back in the day; I just have not had the time and may not for a bit as I try and make this move. It's likely on the same page I had to refer to in order to set the thing up to begin with! ARGH!

[Roy Gavin]

Yes , I probably got the values wrong, it was 15 years ago, and my knowledge of things electrical stops at -Watts divided by volts gives amps

But the Bosch recommended values, - .30 to .40 , are in line with my observation that .22 works better than .15.

Might even dig out the Bosch one from the R75/7 and see how that works, assuming that it more than .22

[Jean]

dwire, I still have and use a Heathkit auto-diagnostic scope, and one of those inductive pickup timing lights. (Useful if you have autos from the 50's and 60's...still) The scope also uses an inductive pickup...
The wiggles on the scope tell you a lot about the condition of the capacitor and are actually lots of fun to show to "the kids" who are totally mystified by that sort of thing!
Big capacitors are good for more than what they are intended, too. When I was in college we had an EE lab with one of those 'furn boys for a lab assiatant who was terrified of electricity (!) SO...we charged up some of those tomato-can size caps and put them on a tall shelf where you'd have to just stand on tip-toe to reach them and most likely put your fingers over the terminals on top. He cleaned the shelves when he hit one. Still terrified, after 40+ years, I'm sure.

Roy, the general observation for ignition service is if the capacitor is a "little bit bigger" it's OK, so if you actually did some sort of calculation for the oscillation coil-cap tank circuit, you'd get a smaller value than the installed capacitor. The 0.15mf DOES seem small tho. How old is your BSA B44? It could be the voltage on that particular system is lower than what we are used to. If the spark voltage was on the order of 12K to 15K volts, a 0.15-0.22mf would probably work OK...the Bosch coils I am working with make about 20K-22K volts and the Blues claim 26K-28K volts.

Anyhow, the whole point of my original "historical" post was to put forth the observation that a faulty capacitor can make starting a pain, not only poor performance once you are running, and can be troublesome for a while before total failure leaves you at the roadside. Backfiring and missing at random is a sure sign of capacitor trouble.

[dwire]

dwire, I still have and use a Heathkit auto-diagnostic scope, and one of those inductive pickup timing lights. (Useful if you have autos from the 50's and 60's...still) The scope also uses an inductive pickup...
The wiggles on the scope tell you a lot about the condition of the capacitor and are actually lots of fun to show to "the kids" who are totally mystified by that sort of thing!
Big capacitors are good for more than what they are intended, too. When I was in college we had an EE lab with one of those 'furn boys for a lab assiatant who was terrified of electricity (!) SO...we charged up some of those tomato-can size caps and put them on a tall shelf where you'd have to just stand on tip-toe to reach them and most likely put your fingers over the terminals on top. He cleaned the shelves when he hit one. Still terrified, after 40+ years, I'm sure.

Roy, the general observation for ignition service is if the capacitor is a "little bit bigger" it's OK, so if you actually did some sort of calculation for the oscillation coil-cap tank circuit, you'd get a smaller value than the installed capacitor. The 0.15mf DOES seem small tho. How old is your BSA B44? It could be the voltage on that particular system is lower than what we are used to. If the spark voltage was on the order of 12K to 15K volts, a 0.15-0.22mf would probably work OK...the Bosch coils I am working with make about 20K-22K volts and the Blues claim 26K-28K volts.

Anyhow, the whole point of my original "historical" post was to put forth the observation that a faulty capacitor can make starting a pain, not only poor performance once you are running, and can be troublesome for a while before total failure leaves you at the roadside. Backfiring and missing at random is a sure sign of capacitor trouble.

Yes, I was a HeathKit kid myself among other things.. Not sure what the analyzer my father built back in the 60's/70's was called or it's model number - wait, perhaps I can become Google smart as so many do... Incidentally, the first timing light he made actually USED the spark itself as the trigger and voltage to excite the stobe bulb; one to ground and one to if I recall little stiff bent over wires you could jam into the boot from the other clip - vary archaic, but worked well enough. My old Sun Bakelite units require 6 or 12 volt input (depending on the model) to fire the strobe and the extensions and such you connected in series with your pug wire for one to connect to were there to tell the strobe system when to release - a bit more modern design and common in shops through the 40's-50's...

Ah, wouldn't you know without even having to take time out to take a picture, this one came up instantly when I typed "old HeathKit Engine Analyzers..." in Google. We still have ours setting in a safe place for posterity. No "scope" as such included; simply mere dial and needle operation, but this model could test anything from starter current draw to, dwell and - well just about anything one looked at in that era... Here's a pic:


But... when I was just about six or seven and Microsoft dropped their first product on the market to small vendors in the form of "BASIC" (see OSI Challenger IP/with 6502 CPU) I learned it over the 78-79 winter and as well spent the rest of my non school hours out of the electronics college of our local rather well accredited University. At that time, a professional oscilloscope (Tek) was a giant machine on a cart that weighed more that I do today; chock full of valves and other technology long since gone for THOSE sort of applications. I miss those big roll-arounds with 60 plug-ins in them!

What happened to me anyway? I should not have been the least hesitant in answering Tim's question about the second connection on that spark tester, but I simply cannot right now and will have to just look it up. Maybe the impending birthday pushing me into my 40's and living a very fast life until all "the fast" was pretty well extinguished from me is some to blame. Likely I am largely at fault. Yet I'm unsure on that, I've had a rough ride that still continues sometimes - as it does for all of "us" mortals.