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Genuine question 2 stroke

Posted by Expat Stu <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Expat+Stu' width='330' height='300' border=0 style='border:none;'> on November 11, 2025, 7:13 pm

I have just about finished prepping the Ossa, brakes being religned etc. BUT it won't start. It ran before I took it apart, and the only real change is to a pod type air filter. Could that be the cause? Yes it has fuel and sparks...

Re: Genuine question 2 stroke

Posted by DBDBrian <iframe src='https://members5.boardhost.com/classicbikemart/info/user=DBDBrian' width='330' height='300' border=0 style='border:none;'> on November 11, 2025, 8:56 pm, in reply to "Genuine question 2 stroke"

< Yes it has fuel and sparks...>

Are the sparks occurring at the right moment ?

Brian
Made In England

Re: Genuine question 2 stroke

Posted by the old one <iframe src='https://members5.boardhost.com/classicbikemart/info/user=the+old+one' width='330' height='300' border=0 style='border:none;'> on November 11, 2025, 9:11 pm, in reply to "Re: Genuine question 2 stroke"

< Yes it has fuel and sparks...>

Are the sparks occurring at the right moment ?

umm , timing 180 degrees out

Re: Genuine question 2 stroke

Posted by Lannis <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Lannis' width='330' height='300' border=0 style='border:none;'> on November 11, 2025, 9:58 pm, in reply to "Re: Genuine question 2 stroke"

Is the fuel being compressed?

Lannis

Do you remember, before the Internet, when people thought the cause of stupidity was lack of access to information?

Yeah, it wasn't that.

Re: Genuine question 2 stroke

Posted by Andy C <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Andy+C' width='330' height='300' border=0 style='border:none;'> on November 11, 2025, 11:00 pm, in reply to "Genuine question 2 stroke"

Stu

"It ran before I took it apart, and the only real change is to a pod type air filter."

So what bits did you take apart?

IMHO a pod filter probably would not make a lot of difference to it starting, but would probably affect the running under throttle.

Assuming timing is correct, I wonder if by coincidence the plug has decided to pack in - it has been known, perhaps it is not sparking under compression?

Who needs a signature anyway......

Re: Genuine question 2 stroke

Posted by Leon Novello <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Leon+Novello' width='330' height='300' border=0 style='border:none;'> on November 12, 2025, 3:57 am, in reply to "Genuine question 2 stroke"

Try taking out the filter as a test.

Leon Novello

Re: Genuine question 2 stroke

Posted by Expat Stu <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Expat+Stu' width='330' height='300' border=0 style='border:none;'> on November 12, 2025, 6:23 am, in reply to "Re: Genuine question 2 stroke"

The timing is electric from the flywheel, which I didn't touch. Mainly, the bike was stripped for tyres, brakes, cables (Venhills, superb service) etc. I did fit a new sparks plug though...? Thanks for all suggestions

Re: Genuine question 2 stroke

Posted by Andy C <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Andy+C' width='330' height='300' border=0 style='border:none;'> on November 12, 2025, 6:31 am, in reply to "Re: Genuine question 2 stroke"

"I did fit a new sparks plug though...?"

That could well be your problem, as you probably know you can sometimes get a rogue new plug.

If you still have the old plug that it was running OK with I would be iniclined to give that a go.

Who needs a signature anyway......

Re: Genuine question 2 stroke

Posted by Nigel B <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Nigel+B' width='330' height='300' border=0 style='border:none;'> on November 12, 2025, 10:21 am, in reply to "Genuine question 2 stroke"

Does it have a flywheel magneto ?

Once failed to get a Yamaha DT250 running that had a flywheel mag - it weakly sparked with the plug out, but would not start. Came to the conclusion that the spark was not strong enough when installed & under pressure. I guess that the issue was weakened magnets in the flywheel & that it needed re-magnetising. I understand that the magnets can get weak over time.

I have read of similar issues with flywheel mags in outboard motors (British Seagull particularly - though my limited experience with those suggested they were not keen to run period) & a "fix" suggested that could result in a stronger spark. Can't recall now if it was short out the plug lead and "motor" the engine with an electric drill with the plug out, or leave the HT lead open circuit & spin the engine. Something to do with the currents generated magnetic fields that helped boost the flywheel magnets & restored a stronger spark - or something !

IIRC Villiers Services can re-magnetise flywheels, though not used them myself.

Supposed to be a lot of counterfeit NGK & ND plugs around ATM - maybe try another plug from a different source ?

Nigel B.

Re: Genuine question 2 stroke

Posted by Greeves Rider <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Greeves+Rider' width='330' height='300' border=0 style='border:none;'> on November 13, 2025, 9:44 am, in reply to "Genuine question 2 stroke"

Is the plug wet? It could be a blocked carb jet due to standing unused. Have you tried a squirt of Easy start into the carb, if it fires and briefly runs then its a fuel problem.

Re: Genuine question 2 stroke

Posted by Expat Stu <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Expat+Stu' width='330' height='300' border=0 style='border:none;'> on November 16, 2025, 5:54 pm, in reply to "Re: Genuine question 2 stroke"

Belated thank yous!

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