Engine Won't Start

[Alan @Ncl]

Hello again from me.
I am back again on this since the plug tester arrived and has now been deployed.  According to it, I am indeed getting a spark with the plugs fitted as it gives a flash (dull red) everytime. Just a thought but are these testers infallible?  If a plug was tracking down the insulator, how would it know the difference?

Sadly, still no start though.  Only a few splutters and a resounding backfire at one stage.  So going back to my 6 point Q&A checklist in my post dated 8th Feb (instigated by Jim) the only unanswered question is number 2: i.e. is there a combustible mixture present?  

Perhaps one issue I have not made prominent enough is that there used to be a 'mild' anti induction bias washer in there that I left out partly because it was the wrong bore and partly because I forgot to note which way it was pointing when I took it off.  That seems to be the only thing that is different but its hard to imagine its a factor here?

Have not had a push yet.  My poor long suffering wife has volunteered (great lass, especially since she is fed up with the competition from my two wheeled mistress anyway) but I think I will wait for a heavier lift.

Alan

[lawnmowerman]

Hi Alan
I do not think the spark tester would indicate a spark tracking down the insulator nor would it give an indication of the voltage or the performance of the spark under combustion pressure, although I am prepared to be corrected.
Mags are great when they are working well which is why they are still used on aircraft engines, but when they start playing up they can get unpredictable producing random effects and many red herrings as I have found. Don't forget they were made by Joe Lucas, Prince of Darkness 

Jim

[Alan @Ncl]

Thanks Jim
For now, I am having to assume the Mag is ok as I have no evidence it is not (innocent till proved guilty, etc.). Certainly sparks well with plugs out and I was hoping the tester would provide the definitive answer that it is still sparking when the plugs are under pressure.  However, I think you are saying that this is not necessarily so.  In this case, what is the definitive test that a mag is working properly?

How are you getting on with your mag by the way?  Did you take it in for testing/ rebuilding and if so, what judgement was handed down?

Alan

[A10Boy]

Have you checked your valve timing yet. I once had an engine where someone had added a puchmark to a camshaft gear, so there were two timing marks. Guess which one I timed it to?

Remember that the gears are different sizes so the marks will only align every 64 [I think] revolutions.

If the valve timing is out, it wont draw fuel into the cylinders properly because the pistons will be in the wrong place when the valves are open. So you will have good sparks, good carb and no go.

Just a thought

[Alan @Ncl]

Have you checked your valve timing yet. I once had an engine where someone had added a puchmark to a camshaft gear, so there were two timing marks. Guess which one I timed it to?

Its a good and logical thought Andy and thanks for posting.  I think its ok though as I have not touched any of that since the engine was running fine, many years ago.  Only thing removed was the autoadvance when changing the mag.  Also it did run this time; briefly, unsuccessfully and hot (before I stripped the carb).

Had a look at the valves operating with the covers off and they seemed to be doing the right things (and had correct clearances).

Thanks again though.

Alan

[Sidcar]

Hi Alan,
A so so spark is not good enough under compression so this sounds to me like a mag problem. Mags don't like standing about doing nothing. They fire the bike up, get warm and then short out inside. I've just had my mag rebuilt after buying the bike when it had stood for a year. If you have a spark of sorts there is an old dodge you can try. Get a good graphite pencil and rub the lead over the spark plug electrodes. Many a bike with a weak mag has been coaxed into life by this method.
My mag was done by Dave Fisher down in Swanage. It's not cheap but it's money well spent.


Sid

[Alan @Ncl]

Thanks for your contribution Sid.  I will certainly try this.
Several members have flagged up the likelihood of the Mag as culprit but it seems to be giving a magnificent spark (I opened an old plug gap up to 60 thou and it jumped that with ease).  Also, the plug tester recommended by another member seems to indicate activity with the plug in the cylinder and under pressure.  As for fall off with temperature, can't tell as it has not had chance to get properly warm for 15 years.

I don't want to ditch or rebuild the mag till sure its guilty and my current focus is more towards the carb (currently awaiting new pilot jet).

Alan

[trevinoz]

Alan,
           .060" gap will not tell you much. A good magneto will throw a spark 8-10mm easily.
  Trev.

[Alan @Ncl]

Thanks Trev.  Glad you fellers have not given up on me yet.  I thought 60 thou spark at kickover speed might not be too bad (It also jumped the safety screw gap at over a 1/4 inch when spun fast by hand).  Do you think this is still no guarantee though?

Can I also ask about pilot jets.  When I look 'down the spout' it looks as though there are several smaller holes within the main hole.  Is this just my old eyes deceiving me (an illusion brought on by excessive blood flow to the brain due to overexuberant action on the kickstarter perhaps?)

Alan

[Sidcar]

Alan, Swallow your pride (you could wait til it's dark) and push the bugger. If the mag is dodgy getting it spinning faster will produce a better spark. You've done everything else twice over so it must be worth a go. I went out on my newly aquired A10 outfit last Sunday. When we came to leave the cafe we'd stopped at the bike was, a- cold, b-dead. We kicked it in relays, there was a unimpressive spark at the plugs. We then pushed it and away it went. I then rode it the 20 miles home and at low revs it spat and missed. I stopped it when I got home it would'nt start and the spark had disappeared. Sent mag away Monday got it back Friday. Bike now starts a treat.
The only thing you don't seem to have checked is the wear in the air slide/ venturi. When they get very worn (you can rock the air slide in the venturi) the air is drawn round the slide instead of over the jet. My Sloper got so bad it had to be push started, flooding it vigorously made no difference. Had the carb slieved and a new slide and it was a different bike.

Sid

[Alan @Ncl]

Thanks Sid. We did try a push but it was a rather half hearted attempt on the drive.  Will have to have another go when the weather picks up and I get another volunteer.The slide is a good fit but I suppose I could try a bit of oil as a temporary seal while trying to start.
Thanks again

Alan

[jfligg]

Hey Alan
   Any Joy?  Jeff

[Alan @Ncl]

Thanks for asking Jeff.

Have not been near it for a while as I have been diverted onto other issues.  When the weather warms up and I get round to it again, I will definitely report back, one way or another.

Alan

[duTch]

 So what happened....??

 Was looking for something , and came across this so read it go to whoa, all 4 pages, and no outcome...??

 My as well ask what I think I was looking for- thread size of the pilot jet, to maybe find/make a screw-on adaptor for the 'float level tube'....any ideas ??
 (just cos there's not much exposed thread to plug onto, and it leaks a bit)

[Derby Rob]

just done the same as Dutch........what was the out come ?, its like reading a who done it with the last page missing!