TOPIC:

Ever since I had this bike it's been hard to start when hot. I press the button and only sometimes does it turn over. Luckily the slightest movement of the starter motor usually fires the bike in to life. But Now this issue happens even when it's cold.

 I thought, "try the solenoid first" So I disconnected the large cables on the solenoid, to the starter motor and battery. and hit the button. I got a few clicks here and there, then nothing.

I rebuilt the handle bar switches when I refurbished them...That didn't help.

I bought a new solenoid, that didn't help either.

I tested the wires from the starter button at the solenoid connections. I get power every time the starter button is pressed. Yet almost no clicks when the solenoid is connected. .
With a "Power Probe", I powered up the solenoid on it's own, and it clicked happily every time.   I could have tapped out some really bad swear words in morse code.

I don't get any voltage drop on the battery when pressing the starter button. (starter disconnected). I even used jumper cables with a spare car battery to see if anything changed...no change.

I made some temporary earth leads using the jumper cables...no change.

I'm completely stumped. I'm not the best at electrics by any means but maybe I've missed the obvious?
Thanks in advance.

If I am reading this right , and difficult not being there and actually seeing the problem  , if It was Me , I would be checking that there is a  Good Earth from the Solenoid .

Thanks yes I'll have a look, and put in a temporary earth to the solenoid and see if it helps.

If all connections and Grounds are good.....At this point, I'd be removing the starter motor.  Worn brushes?, Dirty commutators (not Russian potatoes) and/or possible corrosion between starter-motor and block.  A good time to clean and lube the bearing and bushing !

I wish we knew what year and model you are working on. It's not as simple as .......
You say you struggle with electrical issues and lots of guys have a problem figuring out electrical. This particular "problem" you have here is a great example of a simple circuit. We have a power source of 12 volts from the battery. We have a ground. We have a solenoid which is an electrically operated switch that does some work, in this case, operates a high amp switch to power the starter.
In order to perform the function of turning over the starter, we need to "complete a circuit". Power at one end of the circuit has to travel through the circuit to power the (in this case) solenoid and come out the other side of the solenoid and find its way to ground. Simple.
So in order to follow the circuit we need a road map which is the electrical diagram. We know its a simple circuit so it's a matter of tracing the road map and following the power from the battery through the circuit and back to the ground of the battery. Simple.
There are 3 main electrical diagrams for this motorcycle depending on whether its a European, UK, USA or Canadian model and in this case, it's important to know which model so we can trace the circuit.
From what I see, the circuit involves more than just a starter button, battery, solenoid and ground. We also have the engine stop switch and a starter interrupt switch which is in the side stand of the bike. 
We know that in order for the solenoid to function it needs power. Just having 12 volts means nothing if there's enough resistance in the circuit to restrict the amperage, then there won't be enough power to "drive" the solenoid.
So where might we find resistance? Any connection in the circuit be it a wiring connection, switch connection, ground connection could restrict the power in the circuit enough that the solenoid flutters and won't switch on the high amp power to the starter.

One of the best "tools" I have for troubleshooting electrical is a 11" x 17"  laminated copy of the electrical circuit that I can use a dry erasable marker on and "mark up" a circuit and follow the "road map" and test my circuits. I took a PDF file of the electrical diagram to my local Business Depot and asked them to enlarge it to 11 x 17 and then laminate it. Cost me $8.00 Canadian. It's worth every penny. Trying to trace it out on the computer and not being able to mark it up first is a major pain in the ass. Take the time, spend the money and get a copy. when your done, wipe it off and hang it in your garage as wall art till the next time you need it. your buddies will be amazed that you did it and that you actually use it because it all above there knowledge base. It just might inspire you to learn a new knowledge base to work with. I had a Porsche 928 with 3 fuse panels, 4 relay panels and 2 on board computers. Want to trace a circuit for me?

Once you get simple circuits under your belt, you can move on to more complicated circuits like ones involving resistors, capacitors, transistors, diodes and eventually computer circuits but you need to get a simple circuit understood first. The electrical diagram is nothing more than a road map showing you all the possibilities. Just map out a route and follow it. Think of an area on the map where you find resistance and think of it as "road construction" jamming up the highway.

Hope this helps.
KB

Thanks for the help and suggestions. It's a 1979  Z1300 European model.
I had stripped and rebuilt the starter motor twice now which apart from a little bit of rust seemed in fairly good/clean condition. But as I wasn't even getting a solenoid click most of the time, I thought get the up stream issue fixed first.

I really do want to learn about it,  but I seem to have a bit of a mental blockage when it comes to electricity. I have dealt with and fixed many electrical issues on bikes and cars over the years but I still make stupid, basic mistakes.  It's getting better but very slowly.  I'm just finishing up rewiring my Z1000 from scratch using non original clocks, gauges, handle bar switches etc. I did it, but I still managed to fry my starter button at one point.  I knew the smoke wasn't a good thing...

I don't seem to have a side stand switch but I do need to pull my clutch in to start it.

I like the laminated diagram idea, a good way to get my head around it all.

I'm going to test the earth lead to the solenoid now as it seems like an easy one to check first.