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Discussion Starter · #1 ·
I have an old Suzuki ap50, a simple 2 stroke moped. And I have a slight problem... As In the title; the sparkplug gets wet, but it runs briefly with some starter fluid.

So I thought: Maybe there is no spark? So I held the spark against the cylinder and bam, there is spark. I tried spraying in a tiny amount of starter fluid and then it ran for about 2 sec until the starterfluid was gone.

What is the problem? Has the fuel gone stale? Maybe the timing is off, but would it really run at all then? Helpld be really appreciated ?
 

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Check the compression. Sometimes a plug will spark outside the engine, but not inside. Sign of a week coil or wyres or points. You can damage parts with starter fluid.
Use an NGK plug. They are easier to follow the heat range. If you are using a 9 or higher number, it will probably foul. Check the manual. Probably says to use an 8 or 7.
It could be too rich. Hard to get more fuel thru a restricted hole, but easy to block the air. Check the air filter.

UK
 

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Discussion Starter · #4 ·
Yeah, I know that starter fluid isn't the greatest, that's why I only use a very little bit of it. But if compression was bad would it really run at all? But I do suspect that the spark is too weak to ignite the fuel but powerful enough to to ignite the starter fluid.
 

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Discussion Starter · #6 ·
Oh, the fuel is probably from the middle of July or something, so it's not that old. But I've heard people saying fuel goes stale after 2 weeks and other saying fuel never gets stale at all...
 

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Oh, the fuel is probably from the middle of July or something, so it's not that old. But I've heard people saying fuel goes stale after 2 weeks and other saying fuel never gets stale at all...
Just like beer does not go flat. Middle of July is old, but it depends where you live.
For the road race bikes, we would only use fuel in the tank, if it was less than two weeks old. Otherwise it went in the truck, even if it was mixed with oil.
Flat fuel smells a bit like rotten eggs, and turns to orange in colour. Pour some on the ground and put a lighted match to it. Fresh fuel goes poof, flat fuel may not burn at all.
When I was in Penticton BC, the new Honda XL175 bikes would not fire, after sitting outside for over one month. We would drain some gas from the carb, and then they would run.
They also would not run with the original plug in them. The preserving stuff in the tank from the factory, would prevent them from firing. The residual from flat gas may do the same. For the cost of a plug, bung in a new one.

Back to heat range. On the two stroke race bikes, we would always start them with a hotter plug. After warming the engine we would switch to a colder plug. Trying to fire a bike with a plug that is too cold, will result in a fouled plug.
NGK has articles on heat range. Your bike should fire with a number 7 plug. 6 is too hot. The manual may say an 8 for normal running.

UK
 

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I had a 1979 Honda PA50 for my first bike, and I ran the heck out of it. Actually took the wire off it once and it ran with out a spark plug after trying to get it to shut off once. Compression, reed valves, elementary carburetor and spark is all that runs them little smokers. Timing for most designs are hard designed into the head and is not a factor so I would focus on what UK's path he is leading you down.
 

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I am not a fan of firing the spark plug under no compression. That is why I just use an inexpensive harbor Freight timing light to check the spark. An old school timing light is even better, because it will flash more brightly with a strong spark.

Cranking a bike in the dark can be a good thing as well. Poorly insulated wires can show flashes of light. My Cb750 Honda will let the gas go stale in the carbs in about a week. I drain the bowls out and it starts much more easily. Every bike is different, but these are observations living with a stable of rides. A fully charged battery will also give a much stronger spark.There can be some pretty good voltage losses through things such as ignition switches on the older bikes. That explains why a bike can turn over without being able to fire.

What you need to do is everything that everyone has suggested as it relates to spark. Then drain the carb bowls and fill them with fresh gasoline. Make sure the fuel is fresh. Once all that is done and only then, you can suspect that the carbies might need some cleaning. Also, you can make a little squirt bottle or buy a bottle with a tiny hose used to oil furnaces. Put some gas in it and use like starter fluid. Be careful and just use a little as you do not want to make your bike fire and not catch your bike on fire.
 

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Discussion Starter · #10 ·
Yeah, I do suspect it's something with the fuel. I believe so because it does run for a couple of seconds when I spray in a bit of starter fluid. And then when the starterfluid is gone it dies... So yeah, it's probably fuel or something in that area.
 
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