Can ignition timing go faulty during use?

[Triton Thrasher]

If you want to be sure there is petrol in the combustion chamber, put a teaspoonful in through each spark plug hole.

[Ted_Flash]

I seem to remember that a colourtune plug lets you see if there's a spark inside the cylinder?

[owain]

I tried changing the main jet from .240 to .200 (the size that was last on the bike when it was running) but still nothing. I also checked the timing again and it seems spot on and checked the gap between the points. All seems fine there. The spark plug tester shows there is electricity getting to the spark plug i.e. bright orange flash. I can't check for sure whether there is a spark in the engine, however before I cleaned the points I was getting a bright light from the spark plug tester but no spark at the plug. Since then, I've been getting a spark when I've earthed the spark plug but I'm not quite as confident in relying on the spark plug tester anymore. Coupled together with the lack of any combustion, it led me to believe that I've not been getting any spark in the cylinder.

The fuel in the tank (which is definitely not air tight) is no more than 2 months old. I also tried spraying 'engine starter' through the carb today to try and get any sign of life out of it but still nothing. I'll check the magneto fibre gear again and will drain the tank and place new petrol into it. Plugs do come out slightly wet after several unsuccessful kicks and the magneto appears to turn as I would expect when the engine turns over.

[Swarfcut]

Owain.  With both plugs out, turn the engine over until one cylinder is on its compression stroke...finger in the plug hole trick. Then remove a magneto pick up. Look down the hole.  If the brass slip ring segment is visible, that is the the lead that goes to the cylinder about to fire.  No brass segment....that lead goes to the  other cylinder. Easy to mix the leads, could be as simple as that. Forget the carb, should easily fire a few times on a spray of " start yer bas***d."  Leave the points cover off in case there is an unintended earthing of the magneto.  Test plugs by simple substitution.

 RD and Klaus' observations are well worth considering, before you take it all apart.

 Ted...you would need good eyes to kick and look at the same time, but once running a colourtune is fascinating to see in action.

 Swarfy.

[duTch]

 I was also going to suggest switched plug leads, but Swarfo had it ccovered, nevertheless.....

 For what it's worth, and without going back to the beginning- if I recall, the problem started when the bike was running fine but cut out suddenly while riding....

[berger]

owain have a look at the points spring thing and make sure its not sometimes catching the cam ring. get hold of the centre bolt with some pliers and when it is nearest to the cam ring see if you can shake it about and make it touch the cam ring, if you can get a fag paper between the two without it gripping it -that isn't your problem--. just a thought I had after I had read previous posts and noted you had constant 15 thou valve clearances, otherwise I was going to say your followers had worn out and no valve lift

[ironhead]

owain,
you mentioned an "orange' flash with your plug tester.
It should be blue/white for a good ignition system, usually orange is a sign of a failing condenser.
I use a Briggs n Stratton 3 point spark tester. If the spark doesn't jump this, the engine , no matter what kind, will not start. The best test tool I've ever bought for finding ignition problems.

[Swarfcut]

duTch..  You're right. I re-read the whole thread and watched also watched Owain's  video again.  I reckon it is all down to the lack of sparks under compression, and a nut and bolt inspection of every part of the magneto is needed.  Ignition is the number one place to look when an otherwise well performing motor just stops. A Thorspark type of system is starting to look more attractive.

 Owain.. We all assume the motor is OK mechanically and the magneto is being driven.

 bergs.. Good timely reminder if you have  later type points with a steel backplate. Yup, another fine penny pinching design.

 Swarfy.

[BSA_54A10]

owain,
you mentioned an "orange' flash with your plug tester.
It should be blue/white for a good ignition system, usually orange is a sign of a failing condenser.
I use a Briggs n Stratton 3 point spark tester. If the spark doesn't jump this, the engine , no matter what kind, will not start. The best test tool I've ever bought for finding ignition problems.

He is using a red neon in line spark tester.
I have 4 of them because I am always leaving them on customers mowers.
The logic behind them is you can use them outside to check if a spark is being made and grounding through the plug
A good spark is of course blue white so a bit hard to see in daylight even with a 3 point tester.
If it gets a flash at compression then a spark is grounding via the plug, although it can be running down the side of a contaminated middle electrode and not jumping the gap.
For testing the strength of a magneto the best tool is the sliding electrode gap spark tester, however the longer the jump, the thinner the spark.
A good magneto will jump better than 1 full inch in air.

And the easiest way to make said same tool is to poke the ends of 2 HT leads into an old Bic Biro tube.
secure one side and allow the other to slide.
Gently & slowly pull one wire back till it no longer sparks then measure the distance between the two wires.
Back in the day they were called spark intensifiers and the favourite bodge was 2 firemans brass buttons 1/2 inch apart inside a garden hose.

[Swarfcut]

Trev.. I remember them, usually found on  Evinrude and Johnson 2 Stroke Outboards. The idea was that if a plug fouled, the spark would jump the internal air gap in the booster and this would clear the fouled plug somehow. Bit of a disappointment if you opened one up to see what was inside. Lifting the plug cap from the plug to make an air gap was the way we cleared fouled plugs on cheap knackered 2 strokes, James, Bantams, Fanny B's, and these days the same trick can be used on your reluctant mower or strimmer.

    Before the days of vehicle emission tests I made my own (a couple of pointed nails in a plastic tube) to keep a real oil burner running, rather than having to take the plugs out when the oil fouled them.  They were also hyped as a fuel saving power boosting wallet emptying must have.   

 Swarfy.

[owain]

UPDATE: It's alive and running again!!! 

I switched the cables over this morning and it started first kick. I tried switching the cables over much earlier on during this process with no luck. I think when I took the mag out of the bike and thoroughly cleaned the points, slipring, etc cured the non-sparking/weak sparking problem but then attached the cables to the wrong spark plug. This issue has caused no end of frustration for me and it seems so simple now. Thank you all for the troubleshooting advice, I think I would have given up if this problem had persisted for any longer!

[RDfella]

Glad to hear that. Sounds like you had two problems, which invariably confuses. Fortunately, forums like this give one the moral support to carry on whereas otherwise one might give up.

[Swarfcut]

Owain... Well done for getting a runner. After all the doom and gloom you were foiled by an error we all have made at some time. Check the oil and give it a little local run... just in case.   

 Spring is here, happy days.

 Swarfy.

[duTch]

 Good stuff- lets just hope it keeps running well...

[BSA_54A10]

Trev.. I remember them, usually found on  Evinrude and Johnson 2 Stroke Outboards. The idea was that if a plug fouled, the spark would jump the internal air gap in the booster and this would clear the fouled plug somehow. Bit of a disappointment if you opened one up to see what was inside. Lifting the plug cap from the plug to make an air gap was the way we cleared fouled plugs on cheap knackered 2 strokes, James, Bantams, Fanny B's, and these days the same trick can be used on your reluctant mower or strimmer.

    Before the days of vehicle emission tests I made my own (a couple of pointed nails in a plastic tube) to keep a real oil burner running, rather than having to take the plugs out when the oil fouled them.  They were also hyped as a fuel saving power boosting wallet emptying must have.   

 Swarfy.

Yep thems the things and that is exactly where they get used.

And the real funny bit for me is the number of times I get called in for a "Mower won't start " service.
Put the plug tester on and that tiny bit of extra resistance is just enough to make the spark jump the gap on a fouled plug  & the engine fires right up