What do I do? 12VDC 100w motor

[panic mode]

current is not measured by feeling wire temperature, even then we don't know what is the size of the wires.
do you have some current readings with and without load?

i am still firm believer that this motor is toast... why don't you open it and take a look at windings and brushes. they must be mess.

one of my colleagues decided to fix kids 'barbie car' and replaced the busted motor with one from power seat (we had lots of those).
it worked fine for little girl, it even worked for bigger girl who really took it for a spin (off road, up and down hill then through the bushes,).
well, it worked for good 20 maybe 30min and that is when the motor melted (most car motors like seat, mirrors, windows etc are not rated for continuous duty).

windshield wiper motor is rated for continuous duty but since already geared, speed is low.

 

[stk2008]

The motor is sealed I had a quick look and I really cant see any way to open it up.

 

[tcmtech]

How big is this go-cart and how heavy is it with and without the rider?

100 watts is just over 1/7th of one horsepower and a normal go-cart for small kids with a gas engine is around 3 HP or more.

 

[stk2008]

I have not really weighed but will do tomorrow.

I am thinking like you say the motor is dieing because my mate got it from a scooter and he is a big old boy and he said it went fast with him on it though he did have it connected to a 12v car battery.
Maybe after he got off it and stripped it down the damage was done.

 

[tcmtech]

Most electric scooters have small batteries in the 5 -7 ah range that run dead just before the motor cooks itself.

If he had a car battery on it he probably had 10 times as much battery capacity which would have been more than enough power to run the motor in an overloaded state long enough to cook itself.