Two-stroke help/advice needed please

[daaatomic]

Soooooo, I have a gasgas 50cc motard. The last week, while on my way up the harbour bridge, it lost power. It still managed to make it up the bridge, but when I pulled the clutch in, it just died and now it wont start.

It still turns over on the starter, but won't fire up.

There is definitely spark, and I've pulled apart the carb which seems to be fine(jet is all good), but I don't really want to go much further.

Is there anything else I can check before I load it in the van and take it top the mechanic?

Here is a picture of the carb, incase it helps.
http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=97459&d=1212648766

Thanks.
Dave.

[awayatc]

Wel.....spark and fuel is a runner....(if you still have got compression, i.e not run out of 2 stroke oil or so..)
So you are poitive that the spark is ok? because 2 strokes are very picky and peculiar about sparkplugs....

Well if you have got a spark, then you must make sure you got fuel as well...
start from the top and work your way down....Does the bowl in carb fill up?

one drop of water inside your carb bowl will prevent it from starting actualy....

Fuel problems are all easily fixed....spark can be a bit harder..

Good luck

[vinnieh]

Hey man,

I am by no means a mechanic but this is the exact problem I had. I have a little 50cc Nifty Fifty that died in the same way, at the top of a hill. I pulled it to bits and found that it had seized due to lack of air reaching the top end.

I had never pulled an engine apart before either, but unless you have ZERO concept of how an engine works I would say just pull the top end off to check that it hasn't seized. Just make sure you make careful note of what goes where. I don't know what a gasgas motard is like but 2-stroke 50cc engines can't be that complex.

If you DO decide to take apart the top end, be super careful with the rings on the piston because they might be quite brittle. It might pay to read up on some other forums on the net regarding taking a 2stroke engine to bits. If you had the ability to take apart a carb and reassemble it ok, then I can't see you having THAT much trouble with the top end. Just make sure you have the right tools.

Basically if you have a steady flow of fuel and a good spark and it's not starting, you probably don't have compression. The mixture and all that could affect it I suppose, make sure no air pipes or anything going to the carb aren't clogged but that's pretty unlikely. If you take the carb to bits again, make sure you don't push anything through the jets to clean them cause the slightest muckup can ruin them for good. You could always take it in and see if some kind mechanic will test it to see what compression you are getting.

That's my 2cents. I have only ever had one engine to bits before so I may not know 100% what I am talking about haha I am mostly repeating what I have heard elsewhere.

Good luck!

[daaatomic]

Thanks for the advice, I dont think it is siezed, as it still turns over okay. Fuel is definitly getting to the bowl, but i suspect thats where it stops.

Think I will just take it to someone, I'm sick of catching the bus already.

[Teezer]

Hiya. Just seized my 2-stroke, but the rear wheel locking up told me that it was definately the engine that had let go!

Many engines will still turn over even when they've seized - it's the lack of compression that stops the mix igniting on the spark. 2 easy ways to check for the obvious visible signs of seizure:

1) take spark plug out and look at the tip - squashed/ damaged/ bits of aluminium swarf on it = seized

2) take off exhaust, shine torch up the exhaust port and look at the piston. If anything other than a smooth side profile with 2 nicely seated rings, then it may well have seized. If you see obvious scratching/ wear/ chunks missing then that'll give it away - see attached pic.

You may need to turn the engine over a wee bit to get the piston visible - especially if it is at the bottom of its stroke.

If nothing is obvious then go back to fuelling & sparks, and if still nothing then strip the head off for a proper look.

Then throw hands up in despair and take it to a mechanic

The joy of strokers!

[vinnieh]

Many engines will still turn over even when they've seized - it's the lack of compression that stops the mix igniting on the spark.

Agreed. My 2-stroke still turned over fine and sounded OK, but when I took the top end off the barrel was scratched to shit and the piston was utterly knackered.

[Racey Rider]

Could possably be a bit of carbon flaked off and blocking the exhaust.
Gasses not getting out = fuel mix not getting in.

just a thought.
Racey

[Conquiztador]

U need 3 things for the sucker to go:
Spark
Fuel/air mix
Compression.

Spark is easy: Plug out, turn motor over, you will see if there is spark. Sorted. (Assuming here that the timing of the spark has not moved, but unlikely)

Fuel/air mix is not tricky either: Get some "Start Ya Bastard" in a spray can. Spray some in to the cylinder, plug back on, and try to start. If it does start, (will only run for a second or two) then U have a problem with fuel not getting there. If not, read on...

Compression. This is something that small 2 strokers are very relient on. A big 4 stroke can live with very low compression and still run. A 50cc two stroke can't. Plug out (again... U are getting good at it by now!) thumb on hole. If air wants to squeeze out from under your tumb (and make that funny farting noise) then U have compression. If there is a strange "suck" and no air comes past your thumb your compression is gone. Broken rings probably. Or a common fault is that the circlip that holds the pin in the piston has given up and now the pin has hit the side of the bore and has damaged the bore and your compression is gone.
If this is the case:
New piston + rings about $100
Re-bore about $60.
Workshop time about 2 hours at $60.

All up U will be $300 - $450 poorer if you can't do it your self.

Good Luck!