850 Spider Starter cranks slow when warm

[ablewood]

I have a 1973 850 Spider. Starts right up when the car is cold. After driving for awhile and the engine warms up, the starter begins to crank slower and slower until it barely cranks at all. Once the car cools, it starts right up again. The engine is not overheating and running at normal temp. Battery cables are very clean at battery and starter. Hmmmmmm???
Ideas?

 

[Mark]

I had the same problem on my '68. I installed a gear-reduction starter and its been starting fine ever since.

I have a 1973 850 Spider. Starts right up when the car is cold. After driving for awhile and the engine warms up, the starter begins to crank slower and slower until it barely cranks at all. Once the car cools, it starts right up again. The engine is not overheating and running at normal temp. Battery cables are very clean at battery and starter. Hmmmmmm???
Ideas?

 

[kmead]

I did the same thing Mark did. I bought a gear reduction starter from AutoRicambi, they are also available from Mark Allison and I assume the other vendors.

Installing it requires removing the radiator and preferably the water pump, at least for me as I have a Coupe with more limited access from above.

 

[NM850]

Another vote for the gear reduction starter. For the cost you can't properly rebuild the original and there is the added benefit of weight reduction.
Also when you install the new starter it helps to run another ground cable from a starter bolt to the chassis.
I like to use those braided flat cables.