Lazy to engage Starter

I'm making the most of this weather with the convertible at the moment, which has now developed a weird problem just when it was running right!

Sometimes when the key is turned from ignition to start the car nothing happens apart from the dash lights (oil, charging, handbrake and clock) dimming, wait a moment and then the starter turns the engine over nice and fast and it bursts into life.

This does not happen every time, sometimes it works perfectly but then on Monday morning leaving for work on the third turn of the key i held it there, and after about four seconds the starter burst into life and the car ran. I had thought the heat was causing it (it tended to happen when the engine was still hot from use), but Monday morning proved otherwise as the car had sat overnight.

So the battery is showing full charge (14.6v), and when the engine does crank it turns over fast, showing a battery with decent charge.
The starter is the original, if the solenoid was getting lazy then surely the starter would turn over but not be engaged? So make a whizzing noise?
Apart from those i'm considering the ignition switch, or wiring.

I am leaning towards the battery at the moment, i've had a not to dissimilar starting fault on my B3 Passat (fully charged battery that would intermittantly not crank over the car yet still show charge). Therefore i changed the battery in the Golf over to a spare last night, the problem has not shown today but being intermittant only time will tell.
Whilst i'm waiting for time to tell i wondered what other peoples thoughts were? I'd like to sort it before driving up to the AGM from Devon.

Thanks guys.

Clean up the connections to the starter motor, especially the main lead from the battery to the starter motor and see if that's any better before splashing out on new parts….

I had this years ago on a daily driver 1.3. Exactly the same symptoms.

Turned out to be the electric switch at the bottom of the ignition lock. Pretty cheap and easy bolt off/on. There is no need to drill out anything like the Haynes book of lies tells you to do.

https://www.ebay.co.uk/itm/VW-Ignition-Switch-T1-Beetle-Buggy-Ghia-Bay-Window-MK1-MK2-Golf-Jetta-Caddy-T25/161979721175?hash=item25b6be65d7:g:WPIAAOSwll1Wwxy8

 

Also install the heat soak relay, it off loads the high current off the ignition switch and places full battery power on the Starter Solenoid… The Starter really likes to spin then.

originally designed for automatics, but works great for manuals too.

http://www.cabby-info.com/Files/InstallingHot-startRelay.pdf

I am having the exact same issue with my ford ranger atm, it started by getting very slow and eventually would not start unless you hit it with a hammer, I couldn't find a replacement so took motor apart and it was full of dirt and carbon from the brushes, plus I had a leak above it so it had a bit of coolant getting in.

 I cleaned it all out and put back together but now occasionally does nothing for 3 seconds then starts fine. I suspect the brushes/holders but looked like they had lots of meat on them when put back together. might be worth checking the brushes in yours if you can be bothered to take it apart

Thanks guys, i'll look into those and i'll definitely clean up those connections tomorrow night.
Surely if it was the ignition switch then the lights would not dim when it happens? And if it was the starter then the starter would either click as the solenoid livens or whine as the motor spins without the solenoid working?

I have to say though (touch wood) a change of battery and so far the problem hasn't resurfaced yet. This includes pootling around tonight to see where houses are (we're house shopping at the mo, not just being creepy!) which included the fan cutting in and out and lots of starting and stopping of the engine. We will see.