you are probably getting heat soak on your starter.
Remedy:
1. goto discount auto parts, auto zone and get a heat shield for your starter solenoid. It's the small round object attatched to your starter.
2. you could get a blanket that covers your starter and solenoid.
3. Do both.
4. You could get a mini starter which would move it farther away from your exhaust.
5. You could goto a starter shop, which rebuilds starters in America, not like the krap from the parts stores. You could install it, but the problem will come back again at some point.

I tried the above stuff. I ended up going to my local starter shop and purchasing a high torque mini starter. This made changing the starter much easier also. Before with a regular size starter I would have to unbolt the pass. side header, now I don't. There is also more room to get my large hands on the wires.

Theres my 5 cents worth.

 

thanks

 

Patrick covered it all,, I have ony 1 thing to add,, you mite try backing your timimg off a degree or two,,too much timing will also cause it to crank to hard hot,,let us know how you make out

 

I had luck with running the ground cable directly from the battery to the starter case. this took care of my hot start problems.

 

It could also be carbon build up in the cylinders. It causes increased compression. If the starter ideas don't fix it, there are water injection kits to clean the combustion chambers.

 

Also if the car was granny driven there could be carbon build up behind the rings. It causes just the symptoms you describe. A bottle of Blaster TVF in the oil will get rid of carbon and varnish that can cause rings to drag when hot. If a new starter only helps for a short time, try the Blaster.

 

If it's turning adding a shield on the solenoid won't change things. The solenoid isn't stuck and has engaged the starter.

 

I've never run a heatshield,,,just make sure that you've got to good battery cables and good connections,not the parts store cheapies,a little heavier. My timing is set at 16* initial and it starts first time everytime even in this 90 degree heat.