The little lady's GP100 died on her last weekend and we had to get a mate to pick up her bike in a van. I thought the engine had flooded but that's not it. Am I right in thinking that the spark plug takes a beating on a 2 stroke and that's a probable cause of a sudden stoppage?

Well if MZ two strokes are anything to go by then I'd say they [2-stroke engines] are generally heavy on plugs probably because they have to fire every second stroke and also as they're burning an oil petrol mix at the same time which soon reveals a weak plug causing misfires and poor starting as the plug will tend to oil up easily. 1500-2000 miles as a maximum is about what I'd get before running problems with my 125, any ignition problems almost always related to knackered plugs but if you're saying the bike just ground to a halt while riding that doesn't sound like a plug problem to me as they don't [usually] go that suddenly while riding. More usually that'd be something like a carburettor jet being blocked by muck - have you checked? Either way £2 or so for a new plug won't hurt, why not check whether you're getting a spark across the head with the plug out the engine and kicking the engine over to see if the problem's ignition related? The colour of the plug also indicates a lot, if its throughly black or oily then you've probably got a bad plug in there - should have a nice chocolate brown covered electrode tip if its igniting properly and your carburettor isn't supplying too rich a mixture...

If you're not changing the plug and cleaning it regularly this is very prabably the cause - used to do mine weekly or thereabouts. Take it out, give it a good brush with a wire brush, and check the gap with a feeler gauge and bend the elctrode a little if the gap has got too wide. When you replace the plug put a little smear of copperslip on the thread, csrew it in by hand and just nip it up with the spanner.

A 2-stroke rider should always carry a spare plug and a plug spanner and know how to do the job. Afeter a certain distance tho (about 25000m for my Yam) a 2-stroke engine will need a rebore.

it hasn't run out of 2 stroke oil has it?
my rd350 did that at 80 going up the local bypass, i'd give that a sphincter factor of about 9.5

And i'm ever so glad I don't have anyone refrring to me as "the little lady" - yeuch!

BG, she is a lady, and she is very little...

But I mean no offence to the chicks and birds that are members of the forum

New plug in today- the old one was blackened all over and a little oily, but has made no difference.

Do you think I need to check the carbs?

As an almost engine illiterate person (learning slowly) what does "check the carbs" really mean?

If its oily then it could well be that youve got oil fouling your plugs!!!!!

So are you getting what appears a decent spark over the head (top of the engine) with the new plug? If you kick it over with the plug out of the engine (but connected obviously) you should be able to see whether or not there's a decent spark - if there isn't then there's a problem elsewhere within the ignition system.
However if the sparks good then most likely the carburettor jets may be blocked (the jets through which the engine sucks in petrol from the carburettor) with muck, to check them you need to remove the float bowl at base of carburettor then remove the brass coloured jet/nozzle you'll probably see in the centre of your carb - take it out (unscrew it) and blow through it, hold up to the light to check if its clear before putting it back in. Its not impossible for muck in the petrol/tank to end up blocking a carb if it can bypass the fuel filter though its not all that common a problem.
If you have a good spark and carb is found to be clear then chances are the crankcase oil seals have gone, this would agree with your plug oiling up as it has. Bad crankcase oil seals equal no induction compression on a 2-stroke so the motor will not function, and it also allows in excess oil from the gearbox so your plug will tend to oil up.
Start with checking for a decent spark at the head then I'd check for a clear carburettor before anything else more involved.

it sounds like there's a spark... but it was sunny so i couldn't see...

i'll take a look at the carbs too when I get a chance

cheers cheese

Erm - I spose you've checked the fuel tank..............


Yes of course you have, sorry!


Starting from the beginning - were there any problems with the way the bike ran before it stopped running?

check for two stroke oil, it's in a tank behind one of the side panels, if it's been allowed to run out the engine will have stopped being lubricated and the piston will have been nipped in the head, this can cause rough running and a reluctance to start.
Having said that if you suspect the plug buy a new one, if the original was badly fouled it's gonna be a bugger to clean, might as well replace it and remove the doubt from the equation.

We filled the bike up on the way, and i've checked the fuel tap and there's fuel coming out.

The bike was fine before, although it would always be fine to start 1st time, we'd get where we were going and stop, and then it would be really hard to start for the return journey...



Loads of 2-stroke oil, just filled it up recently.

New spark plug went in and had no effect on starting the engine...



Looks like I'm going to have to look at the carb and see if it's ok...

Ah! Doesn't like restarting when warm - when my little Yam did that it was a problem with the generator - it worked fine when cold, and appeared fine when rested when cold - but once warmed up it didn't work properly. Took it to the local bike shop who sent the relevant bit to a man down the road who rewinds them.

On the other hand, if the bike is high mileage it may be due for a rebore and new piston -this is general maintenance for 2 strokes. They rely heavily on the integrity of the seal between the piston and the cylinder wall and once either is too worn, they just won't go!

You don't say if, when the bike ground to a halt, there was any kind of noise involved in doing this? I'm wondering if maybe a piston ring may have broken up if that was the case, but it sounds to me more like crankcase oil seals going. As to rebores, you'd notice the need for a rebore with a gradual loss of power over thousands of miles rather than a total loss of compression and therefore the engine not running. If you've established that the carburettor is clear and fuel is entering the engine plus you also have a good spark therefore ignition is fine, then it would seem to me that the crankcase oil seals or something else causing a lack of compression (broken piston rings possibly) maybe even a poor head gasket seal could be to blame. Is there any play on the end of the crank? Before you get into the engine though I'd make sure that your carburettor jets are entirely clear.

Well you'd think so wouldn't you - but that's exactly what happened with my Yam - had a few starting problems then pffft! No go.

since we got the bike we've done about 20 miles, so there's no way to know if it's a gradual thing or was a sudden thing...