backfire

aquila · Post by **aquila** » Tue Apr 17, 2007 12:08 pm

Hey guys! I have a Ty250 mono that wont run just backfires what sounds like every second stroke? I was looking at the timing/stator plate and noticed two indicator marks next to each other. I'm not sure which one I am meant to line it up with when i set the timing? Can anyone enlighten me please?

Post by **David Lahey** » Tue Apr 17, 2007 4:20 pm

If there are two marks on the flywheel close together, one will be the spark timing mark and the other will be top dead centre. If you rotate the engine using the kickstart while looking at the flywheel, you will know which way it should rotate when running.
The timing mark will be the first one to pass any given point on the casing when it is rotating the correct way.
Are you saying the motor runs but backfires every second power stroke? Sounds pretty weird. More info needed if you want a better diagnosis.
My guess at this stage is you have sheared the flywheel key in which case any timing marks on the flywheel are meaningless.

aquila · Post by **aquila** » Tue Apr 17, 2007 6:07 pm

I am talking about the two marks inside the case that the stator plate mark lines up with at the top of the plate?? confused? I am. How do I set the timing at 2.6mm BTDC if I can't get it to run? Would it backfire if the reeds are not closing? Maybe I am looking in the wrong place.

Post by **David Lahey** » Tue Apr 17, 2007 6:40 pm

Ok so it doesn't run. What do you mean it is backfiring on every second stroke? (stroke of the engine or stroke of the kickstart lever?)

Is your backfire an explosion in the exhaust pipe or an explosion that blows flame backwards through the carby?

One cause of backfiring is when the ignition timing is way out.

Backfires can also be caused by an intermittent ignition system fault that allows the exhaust pipe to fill with fuel/air mixture when there is no spark and then ignites it when there is a spark.

What is the recent history of the bike?

What was happening when the problem first started?

If you want to check the timing using a strobe light on a bike with electronic ignition then yes you need to be able to have it running. You also need to make marks on the flywheel and engine casing that line up with 2.6mm BDTC (piston position).

aquila · Post by **aquila** » Wed Apr 18, 2007 9:02 am

Hi Dave, I bought the bike with this problem as a spare bike but got stumped. The seller told me it ran fine untill it just stopped due to no spark. He then had someone else work on it and changed altenator?? what he actually changed I am not sure but there is plenty spark, compression, timing marks on the case seem to be right. I have tried moving the timinig both ways with no firing at all away from where it set now. when it does start it whill just backfire very slowly thats why is was thinking every second stroke but I think it is every stroke. I am picking up two other running bikes this week so I will try comparing stator etc and even swap the parts, CDI, stator plate and so on untill I am certain it is not the ignition................ Good Brain Exercise!

Thanks for your thoughts Dave.

Tee-Why · Post by **Tee-Why** » Wed Apr 18, 2007 11:33 pm

aquila, you are located in "Peel" as in Mandurah?
Did you see the bike for sale in last weekends Sunday Times?

aquila · Post by **aquila** » Thu Apr 19, 2007 8:51 am

Yes I did subinator. This is that bike.

aquila · Post by **aquila** » Sun Apr 22, 2007 10:20 am

Problem solved!! I was convinced for whatever reason the timing was drasticly out, so I was looking at when the pulser was being excited by the magnets thought it may reversed wiring or magnets? Looking at the pulser realised that the unit is one wire and grounded no chance. Got me looking at the stator coil, if that is around the wrong way pulser would trigger on the opposit pole of the magnet causeing the timing to be way out. Flipped it over, bingo!!!!!!!!!!!!!! two kicks and purring away...

Thanks for your hepl guys!

Aquila.