Induction/compression pressure

Short answer is no. Some depression in the inlet system will allow atmospheric pressure to "push" fuel through the carburettor jets and atomise it. It does not need as much suction as you may be expecting.

You have a spark in free air (ie not under compression) You have compression. You believe that the carb is functioning.correctly. Bear in mind is that it needs a better functioning ignition system to fire the plug when under compression than when laid on top of the cylinder head so the spark that you are seeing may not be there when the plug is installed.

A possible problem area in an old two stroke is air leaking into the crankcase either around worn main bearings or, in the case of a two piece crankcase, gasket failure. Air leaks into the crankcase interfere with the mixture strength being transferred from the crankcase to the cylinder and often shows up as poor hot starting.

Try starting it with a few drops of fuel injected directly into the cylinder via the plug hole. If you get signs of life it suggests that the igniton is OK and only leaves crankcase depression and carburettion! So then try some fuel directly into the air cleaner or carb throat. Signs of life , then give the carb a good clean. and see where it gets you. Still no joy, possiblya well worn engine in need of a thorough overhaul or reconditioning.

All said and done, a worn two stroke can give you a lot more grief than a four! Hours of fun and frustration!

Many thanks for your suggestions Wristpin. I will give them a shot and hopefully get a bit closer to sorting the problem. Hopefully not a full restoration job required!

While I think about it, your engine was designed to run on a petrol / oil mixture using a straight (non detergent mono grade) oil. Possibly Castrol XL SAE30 or the equivalent from Shell or Esso. I would suggest that you stick with an oil of this specification and not be tempted into thinking that you are doing better for your engine by using a modern synthetic mixing oil designed for high revving chainsaws etc. So make up your mixture using a straight non detergent SAE30 or 40 at the ratio originally recommended by Villiers. Be aware that the SAE30 oil commonly sold as "Lawnmower oil" will probably be a detergent oil and is not suitable for making up fuel mixture for older engines. A suitable oil will probably be one sold for classic cars. If you look on the Millers oils website you will see that they do a Classic 2-stroke oil specifically for older machinery and I expect that other firms such as Morris Lubricants do the same.

Thanks for posting this hsu139 . I'm having a similar problem.

2 stroke lightweight "1449" started well on the kick start (didn't use the cordless drill with a socket!) and ran beautifully for half an hour. It was left on slow tick over for 5 minutes before being choked to stop it.

When trying to restart it a few minutes later, would it run? would it heck as like.

Spark, fine.

Compression, fine.

Fuel, fine.

Cylinder to crank case bolts all tight.

Had carb off as hsu 139 did etc etc.

After 20 mins frustration !!!, she finally woke up with the aid of a drill and after running badly on tick over for a few minutes, kept stalling, went on to resume service as usual.Grrr.

Has the condensor got any roll in this?

Regards Andy

Thanks again wristpin, will make sure I get suitable oil to mix with my petrol. Keep you posted on my progress. No dout will have more questions if this approach doesn't work!

Ok, so I put a few drops of fuel into the plug hole and then put a new spark plug in. To my delight it spluttered into life for 3 or 4 seconds before cutting out.

I'm thinking therefore that the problem might be with the carb. When I prime the carb it overflows with fuel, suggesting that fuel is getting into the carb fine. The problem appears to be with whatever mechanism sends the fuel from the carb into the piston chamber (beyond my technical knowledge!). Is this a reasonable conclusion?

I'm going to remove the carb and give it a good clean out. Is there an advised technique for this/anything in particular I should be looking out for? In particular, should the centerpiece with jet be hollow all the way through? I.e. if I try to push a thin piece of wire up through the middle, should it go all the way? If the piece of wire gets stuck would this indicate a blockage that may prevent fuel getting into the piston chamber?

Hope this makes sense. Again, any guidance appreciated.

So, you've proved that the compression and ignition are capable of life when "doped".

Now try a little fuel straight into the air cleaner or carb throat . If that works you will have proved that the induction side and crankcase are capable of drawing in the fuel/air mixture and transferring it to the cylinder. I have been known to put some fuel on a rag and hold it over the carb inlet or air filter. There is a risk to this - if the engine backfires it will set fire to the rag,  so not too much fuel on it, fire extinguisher handy and your bulk supply of fuel outside the work area - you have been warned!

If that is successful you either have an engine that is so on the margin that it is past running normally or the carburettor is the culprit. Most Villiers/Amal carbs have identifying numbers on them such as B10  -  has yours got any id numbers? If we can id your carb I may be able to post an illustrated parts list which will give you an idea of what goes where. As a general rule we were all taught never to poke things through carb jets but sometimes needs must!  One can use a strand from a wire brush or even the gas welding nozzle cleaners but what you should avoid doing is enlarging the calibrated jet orifices.

Got it working! There was some gunk stuck in the jet. Managed to get it out with some WD40 and a bit of gentle encouragement from a piece of wire.

I have the same non start problem with the Atco villiers engine. If I put a few drops of petrol in the cylinder head,screw the plug back in, it will fire up and run for a couple of revolutions, but otherwise it would appear that vapour is not reaching the cylinder.There seems to be a lack of suction on the carb, which I traced to a worn crankshaft bearing on the driving end. If you can get the engine to run it will continue to run,where the loss of suction may not matter so much. Is there any way to seal the bearing,????

Air ingress  via the main bearing seals is possibly the major cause of starting issues with two stoke engines.; more often when hot than cold. The sealing on early two strokes can be pretty rudimentary relying from the fit between the crank and plain bush  type main bearings sometimes assisted by additional spring loaded  thrust seals.

in most cases the steel crank wears at a lesser rate than the (bronze?) main bearings so where they are available replacing the bushes may improve matters but if the crank is badly worn the situation can only be recovered by having it re-ground and fitting under sized bearings/bushes to match.

When it comes to the "suction" side of the engine it should be considered that what is actually happening  is the action of the piston (ascending on a conventional two stroke and descending in a four stroke) is the creation of a low pressure area that allows atmospheric pressure to push the mixture into the engine ; hence the use of turbo or super chargers to increase the performance of an engine .  So on a conventional two stroke anything that reduces the creation of inlet tract depression also reduces the engine's ability to take in the fuel air mixture - equals difficulty or failure to start.

If the coil is failing this can cause problems particularly with a hot engine but start ok when cold. Check the coil on a multi meter. I had a midget engine from a Qualcast sixteen which started every time when cold but if you tried to restart when hot would never run. A friend with good knowledge of 2 stroke engines told me if there is a leak in the crankcase this will compromise compression and efficiency of how the fuel is drawn from the carburetor round the crankcase and into the cylinder. I purchased some new crank seals from an online Villiers supplier and had the old seals pressed out on a hydraulic press and the new one pressed in and this sorted the problem. Engine now runs sweet and starts from hot every time.