Time to take a look and see what's wrong.

The Chinese scooter is home and in the garage. It's a Direct Bikes DB50QT-11. Romantic name eh?

These are as generic as they come, they're made in various factories in China to a vague specification and sold by the container load to dealers who get them badged up with whatever brand they sell them as. The exact same machine can be bought as a Baotian, a Lexmoto, a Longjia, a Znen - you get the idea. What you're actually getting in all of these cases is a scooter chassis with the 139QMB engine fitted.

There are some decent workshop manuals available to download from the internet relating to these machines and so long as you remember that what's fitted to your machine may vary a little from what's in the manual, then there's plenty of information available to help you undertake looking after or repairing one of these bikes.

Now it's time to take a look and see what I've bought.

First, the bodywork.

It's obviously been ridden by the ubiquitous impoverished teen. With balance issues. The front mudguard has the front snapped off. There is the odd scrape down either side and the seat has a torn cover. The glass is broken in one of the mirrors, and the front brake lever has the end snapped off. Overall, it's in poor cosmetic condition for something just over two years old. However, none of that can be blamed on the fact that it's a cheap Chinese bike - the finger of blame points at the previous owner and how they'd looked after it.

Mechanically, the electric start doesn't turn the engine, although it turns over on the kickstart fine. All of the locks are a little stiff, although they do work. The electrics mostly work, apart from the horn. The brakes aren't dragging, and stop the bike when rolled along. Giving the bike a good shake produces no ominous noises, and the suspension moves freely at both ends. Front and rear tyres are both legal and are a brand that I've at least heard of, Duro. Overall, better that expected.

As the bike's stood for a couple of months, I put the battery on charge. Surprisingly, it's a branded battery (Lucas), rather than the un-named one I was expecting. It's in good condition and takes a charge. Unfortunately, there's still no action from the starter motor, apart from the click of the starter relay.


Back to first principles - if you've got fuel, compression and a spark at the correct time, the engine should at least fire. Whipping off the seat and under seat storage box, I can now get to the engine to check for the presence of all three.

Running down from the tank to the carburettor is the fuel line with a big fuel filter in it. It's dry inside. It can't be that simple can it? With the starter out of action, the vacuum operated fuel tap won't get enough suction to open when the engine's turned over on the kick start, so I remove the vacuum pipe from the inlet manifold and suck on it enough to open the fuel tap. The filter fills, could this be all that it needed?

No.

Many kicks later with no signs of life at all, I move onto the next thing to check and remove the plug. It's a brand new NGK. Someone's been down this path before, apparently unsuccessfully. There's a nice big spark when it's turned over on the kickstart, so let's park that one for now.

Compression. I know it's only a tiny engine, so the kick start won't put up much of a fight, but if I put my finger over the plug hole, it struggles to blow my finger off. Compression is low, why? With a four stroke engine, low compression can be due to bore, piston or ring wear, a blowing head gasket or valve problems. Checking the valves is the easiest and first thing to check. Off with the valve cover (noting that the engine seems spotlessly clean inside, and that the valve cover uses a reusable neoprene gasket, rather than a one shot paper one) I rotate the engine until both valves are closed on the compression stroke  and check the clearances.

Inlet - fine. Exhaust - there is no clearance. We have a smoking gun, if not a running engine. If the exhaust valve has no clearance it'll not be closing properly so the engine will be losing compression. This will be worse when the engine is hot, so the performance must have been very poor when it actually did run.

A quick adjustment, so that the exhaust valve has the required clearance, and a few prods on the kick start and the engine is attempting to start. Time to put the valve cover back on, this time with a little copper grease on the bolts to make future maintenance easier. This done, and a few more prods on the start lever, and the bike bursts into life, burbling away at a slightly high tick over.

It lives!