Friday afternoon bike?

Hi there. New to the forum so will introduce myself before I start with the questions.
I am 38 and have been riding bikes since my first little italijet when I was 4. I then ventured into schoolboy grasstrack and then onto motorcross. In my early twenties I had a short burst at road racing in the super stock class on a RGV250.
I have had numerous road bikes, mainly super quick sports bikes. When my children came along I decided to hang up my leathers and take up a more family orientated past time - we now have a VW campervan.
Untill recently, I had all but forgot about bikes and my passion for tinkering and riding them. My nephew then turned up on his recently restored CT70 (albeit with a lifan 125 big valve head engine installed) and convinced me to join him on a road trip from Kent to Cornwall this coming summer.
I found myself a little 1978 6volt ST70 that had been standing in a shed for the last 20 years and bought it home. Quick Clean of the carb, oil change and new battery - 5th kick and it fired up! A bit lumpy but running all the same.

Then the problems start - or not start as the case now is!

I noticed I had a weak spark, so that is what I based my problem on. So far I have carried out the following :-

New spark plug
New coil and plug cap
New points
New condenser

I now seem to have a reasonable spark - I'm not convinced it is 100% though
Still no joy, so i decided to check the piston rings. The middle ring had infact broken but remained within the piston grooves and had not caused any damage.
Installed new piston rings - now have good compression (as much as can be expected on a 70cc engine)
I believe I have the timing right - I set the points using a light bulb connected to black lead coming from the stator and to a battery and a third lead to earth. When the bulb dims the condenser is charging meaning the points are just opening.
I have set the O mark in line with the correct notch on the timing cog whilst the flywheel is lined up with the T mark. I believe this has all been done on the right cycle of the engine ( valves both closed, with flywheel easy to rock back and forth)
Whilst the head was off I checked the valves were seated correctly and all appeared fine. I have set the valve clearances on the tappets also.

Could this be a Friday afternoon bike? Before It came into my hands it had 4 previous owners, laid up for 20 years and it has only clocked up just under 3000miles! The points adjustment screw shows signs of substantial wear, which points to historic problems with this bike.
I really have enjoyed tinkering with it so far, but I am now running out of avenues to expire
I know I can send it away to be sorted, but I am set on sorting it myself.
Any ideas would be kindly appreciated.
Thankyou.

Hi and welcome,
About the only thing left ignition wise is the L.T'.coil in the stator,but first,to check the quality of your spark,remove plug cap and you should have a fat,blue spark that will jump app.10mm.when you kick engine over.
Condensers have a finite life dont forget.
Bikes that have stood a long time usually suffer from internal corrosion in the carb which can restrict drillings and passages as well as jets etc. A clue maybe is 'a quick clean of the carb'(try a couple of cc.of fuel down plug hole perhaps)
To clarify valve timing - zero stamped in cam sprocket to align with notch at uppermost in head casting @TDC ('T' mark on flywheel)
With your bike history I'm sure a 'Honda 70' wont beat you!!!!!!!!
Good luck,
Dave

A couple of small thoughts:

- no excessive wear on cam shaft?
- check the valves for leaks. Pour some fuel in the inlet (remove manifold) and check the level after 15 minutes.
- no excessive play on crank shaft?
- cam chain tension is correct?
- correct spark plug gap?
- good earthing on coil?
- the condensor didn't become too hot while soldering? (They are VERY fragile!)
- Good ignition coil and no signs of damage to the flywheel magnets?
- No play on the flywheel or crank shaft connection?
- New gaskets fitted after removing head / cylinder? Don't forget the manifold gaskets either.
- No rust in gas tank or old fuel? Always fit an inline fuel filter!
- No vacuum in the gas tank? Try with the seat open and fuel cap off.

This should keep you busy on a rainy night
The standard engines are bullet proof, so you should be able to get it going properly again.

Most common faults with these little bikes , vent in the fuel cap and the valves