BSA Villiers won't start

Not sure what you have got, although electronic ignition suggests that it's at the more recent end of classic!  - a few images will be useful.

A bit of crankshaft end float should not be the cause of your problem unless it is excessive, and an indication of more serious general engine wear.

The A15 at the start of the engine number gives it away, it is the last version of the sloper with electronic ignition and a Villiers carb instead of the slide type. Now as to whether it is  the original engine or a replacement is another question.

Hortimech's identification of the engine as a Sloper  suggests that your example may have an incorrect plug ,  but I don't have any info specific to the electronic ignition version. If I'm interpreting my NGK catalogue correctly the H in BP7HS signifies a 12.7 mm reach, whereas the normal plug for a Sloper was a Champion N8 , the NGK equivalent being a B6ES with a 19mm reach. So the first thing to do is to fit a plug of the correct reach.

Thank you I have changed the plug to a B6ES and tried again but it won't start. I have also taken the flywheel off and replaced the HT and it won't start. It is generating a spark. I bought an inline spark testing neon and there is a visible spark but it won't start. I am not sure why. When I took the flywheel off to replace the Damaged HT cable there were alignment marks for the magneto backplate it was aligned so I think the timing should be correct.

I don't know what to try next ?

How much float is acceptable ?I will measure it , I don't have any history on the machine so have no idea of the condition of the engine. 

I take it that you are using fresh fuel?

Surprisingly the F12 manual does not give a figure for crank end float but I would think that 2 to 8 thou would be about right but I can't see that excess of this would be the cause of your problem.

You have said that the compression is good but it may be worth checking the valve clearances - 6thou for both , and possibly remove and inspect  the valves and re- seat as necessary.

You say that you know that fuel is reaching the cylinder. Presumably it's wetting the plug but not being ignited. So it would seem that it's either too rich or that the spark isn't strong enough to ignite it. Try removing the air filter element and opening the throttle wide. Also remove any plug cap / connector and stuff the end of a straightened paper clip into the end of the HT lead and wrap it around the plug terminal.

I bought new fuel at the weekend and have only used that. When I talk about end float on the flywheel I it's in the thrust direction not rotational and it millimeters  not a few thou.

I have not tested the compression only really what I can feel when pulling the recoil up to to top of the stroke. can you tell me what compression I should have in the cylinder, I will test it with a compression tester.

I have replaced the plug leans plug cap and spark plug with brand equipment from Villiers so I think they are now good. It has the wipec magneto  and electronic ignition module. I am not sure it there is anything that can effect the ignition timing. ?

I can check the valve clearances, but may have to remove the engine to do that. If I need to take the head off to check the cylinder bore am I likely to be able to keep the head gasket intact or will I need a new one straight away?

If you have a good spark and can feel compression when you pull it over (and by this, I mean it doesn't pull over very easily), it is probably a carb problem. Does it try to start, if you take the sparkplug out after trying to start it, is it wet.

Check that fuel is getting to the carb from the tank, try putting a drop or two of fuel into the carb inlet before pulling it over, does it fire then ?

If you do remove the cylinder head (and I not convinced you need to), you will need a new gasket.

I have cleaned the carb blow all the jets out  and when I take the plug out it  smells of fuel I checked the float chamber and it has fuel in it.

It doesn't try to start 

One other question what is a good spark I bought an inline spark tester and can see a spark but I don't know how good is good ?

Not sure of the answer to your "good spark " question as I've had points ignition  Villiers running quite happily with a tiny anaemic spark that would fail The Briggs and Stratton 1/4" in free air test but we never saw many Villiers with electronic ignition. As a rule engines with electronic flywheel magnetos do require a faster cranking speed than their points ignition equivalent.

As far as I know Villiers never published cylinder compression figures and as Hortimech says some resistance is probably enough. As you have a compression gauge it may be worth taking a reading "dry" and then after putting a squirt of engine oil down the bore and comparing the two readings. Any marked increase will probably indicate ring or bore wear. The compression test should be done with a fully open throttle (or even with the carburettor removed)  and over several compression strokes allowing the engine to pump up. Ideally a compression test is performed on a fully warmed up engine but.....!   

On small single cylinder engines a leak down test in which the cylinder is pressurised is probably more meaningful than a compression test as it makes it relatively easy to detect leaking valves, a failed head gasket or piston blow by.

I have spent today trying to start a Villiers F15 attached to a generator, which has a B10/2 carb.  I found that it was very fussy to start the first time after I had cleaned out the carb.  I used a strand of electrical wire to poke out all the holes in the jets.  I had to use full choke and spin it on the drill whilst adjusting the pilot jet screw between each attempt by no more than a quarter turn until it went.  Then I was able to slowly remove the choke whilst adjusting the pilot screw until the choke could be opened without it stalling.  Once set it starts on the pull cord no problem.  The spark isn't great, but it doesn't seem to be a problem - so I would concentrate on the carb.  If the engine hunts you still have muck in the carb.  I found a lot of muck behind the brass seating that the float needle valve goes into.  I also had to clean up the governor wire lever so that it could move freely. 

Good luck

Al