Normally reliable now it wont start!

[huddie]

Hi all, So whats wrong with it then, I am begining to struggle. Looks like my long ride this weekend is going to be a no no.
Got it out of the shed to prep it ready for this weekend. It started ok as it usually does I moved it into the garage ready to give it a good blast , it started fine, ran for about 30 seconds or so and then splutterd and stopped.
Checked the sparks, fine on both sides. Carb tickles up to flooding fine.
Stripped the carb blew out all the orifices with an airline still no good.
Drained the carb again, used some fresh fuel via an auxilary tank, still no good.
Checked the points gap, 12 thou ok.
Checked the timing thinking perhaps that had moved but dont know how. That looks fine. Set the right piston at 5/16 give or take a micron, points not open, piston in same position but with the timing cover off and the auto advance fully advanced  points just opening.
So Whats left, I am now beginning to suspect the MAG but dont know if there is any way to check it.
Should add that the mag was profesionally rebuilt Feb 2011 and has had very little use since.
Any ideas.
Regards Chris

[Goldy]

You sound really frustrated and the trouble is that the frustration spills over to the fault finding. Try to go through it logically . Earth the plugs to the head and see if there is a spark, yes or no. When you take the plugs out after trying to start it are they wet. Yes or no. After that you know if it's ignition or fuel. Then go through each function and try to keep it simple.
Keep calm.
All the best Goldy

[huddie]

Hi Goldy, Yea the plugs are wet forgot to add that, wet on the old fuel and wet on the new fuel, Earth the plugs to the head and they spark fine. This is why I am begining to suspect the Mag.
I believe it's possible for magnetos to work under no load as with the plugs out and earthed but to fail under compression?
Regards Huddie

[beezermacc]

Have you tried removing the petrol tank cap ?  Have you tried removing the cover off the mag to remove the kill switch provision?

[bsa-bill]

Change the plugs for new ones or some very old ones

[beezermacc]

It may just have run rich on tickover whilst cold and flooded the plugs. Try cleaning the plugs and starting it with the throttle fully open! If that doesn't work and if both cylinders shut down at the same time it sounds like carb or something in the mag like points or slip ring ....... contaminated slip ring? - worth cheking for carbon dust in the slip ring housing and clean the slip ring with some light emery on the end of a piece of rubber tube, with the kill button held down!

[huddie]

Thanks for the respones guys. There are a few things there to try that I haven't speciffically thought of, so some different plugs, the slip ring and wide open throttle.
I don't think it's the kill switch because the plugs are sparking when earthed aginst the head.
I will try these things tomorrow before condeming the mag internals and then give you some feed back.
Thanks Huddie

[iansoady]

It's sometimes worth trying some easy start as used on old Lister diesels and the like - although I don't know if you can still buy it. I have an old can lurking in the garage....

Petrol off, open throttle, squirt into carb intake then kick. If it's sparking you'll generally get some response.

[Topdad]

Hi Huddie , i echo the ideas of the others . Having had the same thing happen to my P&J , Re the plugs I'm told this supposed "Petrol "    in reality ethanol based muck damages the plugs after they have become wet , i had my car flood at Christmas and had to change them to get it running again. Wide open throttle is exactly the right procedure for a flooded engine and was used on both cars and bikes in days of yore . If still problems remember that it can only be 3 things ,electrical :- timing l ,sparks and magneto, mechanical :-,does the engine have compression ,did it stop with bang  and are tappets adjusted properly etc fuel:- carb:-kneedle still held by clip, jets clean  ,fuel lines do you have a filter in the line,my monies on new plugs curing it but look forward to hearing exactly what you find,regards BobH

[A10Boy]

I agree, if the plugs have been wet, they are probably scrap.

[huddie]

Hooray, It started first kick!!, So what was it eh, Well stand up Beezermac and take a round of applause. It was the B*@@!y slip ring.
It did look rather dirty and a good clean did the trick. Highly commended also goes to Goldy who said go through it logically. I thought I had mate, but my mental plan was obviously not up to it. Next time I get a problem i'll write down a plan of action. In my defence I was thrown by the fact that I had sparks when the plugs were out and earthed.
Interesting point about wet plugs. I didn't know that neat petrol ruined them. Mine got cleaned up thoroughly and put back in and as I said started first kick!.
Many thanks to all who replied.
Regards Huddie.

[bsa-bill]

Interesting point about wet plugs. I didn't know that neat petrol ruined them.

Trouble is it a some do some don't kind of thing, there's an interesting article on one of plug sites re the manufacture of plugs today stating they used to glaze the porcelain internal insulating bit, now they don't so if the plug gets wet it may absorb the fuel and become a poor insulator allowing the spark to track across.
I'm not saying this is correct at all but it does explain some of our starting woes

[beezermacc]

Ta! However, you may need to invest in some decent quality carbon brushes. Poor quality brushes erode very quickly and distribute carbon dust on the slip ring and in the slip ring housing.

[fido]

If it wont start, check the magneto.....next, check the magneto....thirdly, check the magneto....after that you can check the plugs, plug leads, carb, compression etc 

[Triton Thrasher]

The first symptom I've had, of a dirty slip ring, is difficult starting and bad running, rather than outright refusal. The cause, in my case, was the brush protruding too far on the spring and going sideways on the slip ring.

Don't replace brushes that are not worn out- new ones are a bit of a gamble.