prodding it gently to TDC.

To save getting to way off track in another thread i have had the experience occassionally where there has been a "backfire" when prodding..

Of course it is accepted that the desired position of pistons is just prior to TDC.. So my question is,

How man revolution will the engine do with an initial first kick and non starting.. ie how many times will the ignition have a chance to ignite whilst the piston sails past on TDC. This is only to satisfy my curiousity

Depends how hard and fast you can get it rolling...

guessing 2 or maybe 3 complete revolutions with a normal fairly healthy kick?

concours said:

Depends how hard and fast you can get it rolling...

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I agree with Concours, but would also add...it depends where in the 4 stroke cycle you first get it rolling.

I don't think the engine turns over more than two and a little more times....I do not have any data on this, just guts, and the sound it makes (when it doesn't start).

With my magneto ignition, I rarely get kick backs, and when I do, I suspect (no proof here) that the AAU "stuck" in the advanced position....they do that occasionally, and frequently if the springs are weak or broken. I cannot speculate on why the modern EI's will do it, except to say they may not be velocity dependent like a magneto. I would say each type of trigger sensor has its own velocity characteristics.

Moreover, if the engine fires a piddling 4 deg BTC with a very slow rotation and low inertia to carry over TC, a kickback can occur.

Does anyone know the spec on timing advance at idle rpm?

Years ago, when autos where hand cranked, they had cable retarders that pulled the timing to AFTER TC to prevent such kickbacks.

Slick

We can only speculate in generalities w/o knowing your type of electronic ignition. Stuck worn AAU's is fast idle and kick back starts is main reason for the electronics revolution. Analog black box boyah's can fire on two revolutions which gives one revolution of cam trigger coils and have on occasion just turned on boyah key for a start at dead slow idle. Some electronics may fire before 2 revolutions and if too slow a turn will back fire. Another factor is low voltage seems to advance the electro brains bonkers.

Does anyone know the spec on timing advance at idle rpm?

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around 5 degrees at 1000rpm idle for most electronic ignitions like my TriSpark

https://www.google.com/search?q=boyer+e ... B800%3B450

olChris said:

To save getting to way off track in another thread i have had the experience occassionally where there has been a "backfire" when prodding..

Of course it is accepted that the desired position of pistons is just prior to TDC.. So my question is,

How man revolution will the engine do with an initial first kick and non starting.. ie how many times will the ignition have a chance to ignite whilst the piston sails past on TDC. This is only to satisfy my curiousity

Click to expand...

I have an old trispark. Many a time I have tickled the carbs and whilst trying to get pistons where I want them, the thing has just either gone like pfut out the carbs or fired and run on the first prod. If you visualise taking like 5 seconds for 1 stroke of the kick start, you realise how slow I'm going when it catches. It has never, ever kicked back so I am not concerned.

If everything is set up correctly, when the pistons are pushed gently toward TDC and you feel compression, all it should take to start the motor is a solid push over compression. If you are using carbs with ticklers, you might get flooding which can make the start difficult, however the Mk2 Amal and Mikuni type chokes the motor should should always start as long as there is fuel and spark. I've seen guys jumping on the kickstarter - usually totally un-necessary. If it doesn't start first kick - it is back to the drawing board.
The only time I've had trouble recently was after I left the bike standing for about a year and the plugs died. I replaced them and it started immediately.

If it doesn't start first kick - it is back to the drawing board.

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Amend to that Alan as its been my experience too, Cdo should be one kick offs cold to hot and if not can try another attempt but likely wasted effort before checking key, fuel on, wire connections or bad plugs or water in bowls or out of gas. The electro brains can fire out of time of need on first rotation if turning very slowly and hopefully during the valve over lap to just a puff out pipes not much piston force. The best reliable single kick Norton I had was the points fired killer diller super hi tune dual Amal P!! drag strip only 'street' bike. It was so spark advanced would fracture bones feet ankle or knee and/or lift me up tossed to ground a couple bike lengths away > if I was too timid on first karate like kick down KIYAAH. Every start hurt me some. Most lasting memory of its 1st KicK start was after 9 mo away with it stored in a cycle shop, tickled the hi test ethyl lead 100+ octane pump gas and jumped down on it for blasts of soot shot out the open headers leaving a dinner plate size mess on the white hard bags of a police Harley parked behind it, likely one sent out to get me, so nailed in a few more times to leave more lasting impression and left. I have diagnosed and number of analog boyah power issues by leaving key on and tugging/flicking wires/connections till a spark heard/seen on plugs on head. Do not do this on side of road *in gear* on stand- with fingers near moving items or on a slope it could cough off stand a few inches then carry on down w/o you.

I've kicked over a 1000cc Vincent which was running 12 to 1 comp. ratio with no problem. If you bounce the piston off compression and leave a bit of slack as you do it, then you can get badly bitten. If you push the piston slowly towards TDC you can always hold any kick-back. The firm shove over the top is enough to activate the spark, all it needs to do is move the piston enough to generate the spark and have a bit of inertia. It normally doesn't take much velocity as the piston goes past TDC to start the bike. If you watch any bearded old fart start his bike, it is always a casual no-fuss event. Only the very inexperienced have a problem kicking a bike over, they often go at it 'like a bull at a gate'.

I learned, from starting big singles, that every kick start should begin with slowly bringing it to TDC, then kick it firmly to use compression to allow a lot of force to be built up before the piston passes TDC. That ensures that the engine is spinning as fast as can be. IMO, using a compression release to "get it past TDC" throws away this additional speed. The same applies, but less so, to twins.

You could find TDC with the ignition off then turn it on and kick. Not sure why you would have a backfire tho...never experienced that with my EI.

On both my commandos I don't bother finding TDC ,I just kick them and they start. But it wasn't always like that , they seemed to get stuck at the top of the stroke and it was like the kickstart was jammed hellish to move it. Now it is easy as pie, don't know why but it is and I ain't complaining!

J

But it wasn't always like that , they seemed to get stuck at the top of the stroke and it was like the kickstart was jammed hellish to move it. Now it is easy as pie, don't know why but it is and I ain't complaining! J

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Ah man J you can't just leave us hanging on such vital mystery tuning factors that protect both kicker biomechanics and the kickee shock load paths, so go out and fart with the timing to make some real sense we can use. I don't know of a more disadvantaged kicker ratio than a Commando. Pity any that are so likely made tractor size fitting. Sometimes mine start on creeping up to TDC & is something to be prepped for, ie: kicker out racing your stomp down so over extension shock loads pull knee open & against boney hard stops. Only takes ~ 70 lbs to break a knee by over extension, ie: like a kick into the knee cap could. Yep Sir Commandos are a thinking man's stupid motorcycle.

I found when I first got an 850 that if its was all tuned and set up correctly,
it would start the 1st time one of the pistons went past TDC on the firing stroke - with even a half reasonable kick.
Takes all the effort out of it.
That was with stock points and amals.

If it wasn't tuned - dirty points, out of synch carbs etc,
you could do a lot of kicking...

BTW, in the early days of motoring (cars), before electric starters were invented,
the brits had a secondary ignition system of trembler coils and distributer that
would send a spark to the NEXT cylinder that was going to fire in sequence -
- and the engine would just start on the press of a button.
Magic, when you see it done.
Engine just bursts into life from nothing.
Thunk about that one !

Peel with boyah twice started like magic on its on by key on after i'd gone into a store and back out in under 10 min summer time. Really would like to work out repeatable conditions or put in a tremblor starter too. I can't figure out the logic of how this happened but engine turned enough w/o spark to leave enough mix to fire off with pistons past TDC.

Boyer sparks when the ignition is turned on ?
If the spark occured when the piston was at least over TDC,
so the engine turned forward (not kick back) then it could possibly start.

Complicated business having 2 ignitions, one just for starting....

auldblue said:

On both my commandos I don't bother finding TDC ,I just kick them and they start. But it wasn't always like that , they seemed to get stuck at the top of the stroke and it was like the kickstart was jammed hellish to move it. Now it is easy as pie, don't know why but it is and I ain't complaining!

J

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When I first got my 850, it was easy to kick over but never a really good starter. Leaked like a f....g sieve as well. Tthen I blew the left hand piston. After fitting 2 new pistons, I could then stand on the kick start and it would hardly move. Shit did it go like a rocket as well. Doesn't leak now either especially with the modified Jowet breather valve.
Maybe your engine is wearing out and the compressions a getting low.
Dereck

Maybe your engine is wearing out and the compressions a getting low.
Dereck[/quote]

No Derek ,I think you are wrong! It's always been shit. But it'll still do eighty odd on soft tyres with no issues.
J

Without seeming to be rude, kicking it over from just before TDC is asking for trouble. If you've got a charged cylinder i.e.. full of fuel air mix, then a kick from there is asking for a kick back as it fires but sends the piston back down the bore. The method used to start a single is to bring the piston up to compression, lift the valve and ease the piston over TDC then kick it to allow the flywheel to carry the piston down, up (exhaust stroke), down (induction), up (compression) and fire as it goes over the top. The same technique applies to a Commando, ease it over compression then give it one, The racing single guys (without kickstarts obviously) put the bike in gear and put it in first or second gear, release the clutch and drag the bike backwards to bring the piston up to TDC backwards. This ensures a fresh charge and the inertia of the flywheel to fire up first go. Yes I know a Commando has another cylinder but that one will be going down on the induction stroke so has a chance of catching. Back to school chaps (or the orthopaedic ward)