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Check the vacuum pipe which goes from the fuel tap to the inlet manifold. If the tap is faulty the fuel will flow down the vacuum pipe straight into the engine.

Indeed, there were some small bits of debris in the oil tray when I drained it, but I`ll be having a poke around in the engine with an extendable magnet next week in case anything larger pops up.

Haven`t done much with this one today as I`ve been delivering other scoots. I have checked the nut and threads and they are fine. The washer only butts up against the roller bearing and in turn holds that and the starter clutch firmly on the crank. The washer can`t butt up tightly against the outer gear as that would make the outer gear move constantly with the crank, therefore making the idler and the starter motor move constantly as they are all in mesh.
Is it possible that under normal operation the friction of the starter clutch holds the outer gear in place ? I did notice that to place the outer gear into the starter clutch I had to rotate it in one direction which obviously provides the 'grip' to turn the crank when the starter motor is activated and alternately allows freewheel in the opposite direction once the starting phase is completed.
I`m just wondering if something is broken inside the clutch which has weakened the spring or friction tension to hold the outer gear in position. This might explain the rattling noise which I`m getting ?

One of our Sym fleet bikes developed a knock/rattle from the engine. I`ve stripped the top end but found nothing obvious. Same goes for the transmission side of things.
So I popped the left crankcase side off to examine the starter clutch and oil pump. Again nothing was immediately obvious but on putting it all back together I noticed something odd about the starter clutch. With the washer and nut in place and tightened, I can move the gear towards me, so that it slides over the washer. I can`t say I`ve noticed this on any of our other GY6`s. I don`t think it`s normal as the gear would be flopping in and out onto the nut.
Anyone come across this before ?
Sorry about the hazy pics


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I`m building a custom project in work and have seen a nifty looking LED tailight on fleabay. Unfortunately I have no experience with LED lights so I`m wondering if they can be wired in just like a normal light or do I need something else like a relay ? The bikes a 50cc ped with a 12v system and will be wired to run without a battery.
Any info from those in the know would be much appreciated.

The popping could be due to a leaky gasket, instead of putting your finger over the exhaust hold something like a bunched up rag over it to block it completely. I generally stick the sole of my work boots against the hole as it`s quicker. The engine should die eventually as it can`t breathe. There are a few types of gasket, the copper ring, and a ring made of metal and fibre which has a flat face. Both do the same job.
It could be that the exhaust isn`t correctly mated to the cylinder, loosen the mounting bolts a couple of turns and the exhaust nuts at the cylinder. Give the exhaust a wiggle then re tighten the nuts at the cylinder first, then re tighten the mounting bolts last.
If you need another gasket there`s loads on ebay under '139qmb exhaust gasket'.

The part in your first pic is the starter bendix. When you engage the electric start, the bendix pushes the small gear to engage with the outer part of the variator. The bendix should all be in one piece, I`m not sure by looking at pic 2 but it looks like it`s broken apart. If this is a 50cc gy6 then you can get them on ebay www.ebay.com/itm/New-GY6-50-Starter-Bendix-Clutch-139QMB-scooter-49-50-cc-/320977686297