I have a Keystone K75. The film will not stay in a loop after going through projector so it goes through too fast and you cannot watch the movie. Any ideas of what is wrong?

Sears 8mm projector with 1950's & 60's films - YouTube

? 13:24
https://www.youtube.com/watch?v=7-IIS8ti7Ig
Jul 5, 2011 - Uploaded by drh4683
Vintage sears automatic projector. ... All 8mm and 16mm movie film, even going back to the 1920's and 30's ...
Sears Du-all Eight - Demo - YouTube? 0:37https://www.youtube.com/watch?v=WHbqCMKUGkoNov 13, 2007 - Uploaded by fierorcr86Buy This Now at www.mycurrentauctions.com I demo a Sears Du-all Eight super 8 ... How to load a Bell ...Sears Du-all 8 auto thread projector - YouTube

For a projector to run right, the motor has gear teeth in it that engage with the hollow points on the film itself. The motor has to turn at a steady speed with no friction or hesitation. It is possible the motor on the inside of the projector needs to be oiled or cleaned out...or rebuilt at worse.
There is also the motor that pulls the film thru the projector and winds it onto the receiving spool. Sometimes that motor is out of synch with the projector drive motor and trys to pull the film thru to fast or turns to slow and the you get that "clicking " sound when the receiving spool isn't winding the film up fast enough and the film gets dragged on by those projector teeth and make that plastic clicking sound.
Watch the film while it is running between the two reels and the projector lens. The film should be slightly taunt going into the projector and slightly taunt coming back out of the projector. If you see the film grouping up in front of the projector drive or after, then you know your spools are needing greased up or there is a drag on the motors causing things to be unsynchronized.

This is definitely a mechanical problem and you need to watch the film being fed into the projector and how it is wound up n the receiver spool to see where the fault lies.

I assume you haven't put a reel of film onto the projector and looped it through to the back spool. The front spool usually 'freewheels' whilst the film is pulled through the projector and taken up by the motor driven rear spool.
It is possible that the friction drive and/or drive belt have deteriorated with age, as the mentioned projector is a rather elderly 'classic' of the dual 8mm series.
If in doubt, don't risk your family pictures. Try the unit with an old piece of film on small spools.

There is a black and silver knob under the keystone label( right above the automatic label ) on the side of your projector. turn this knob counterclockwise to loosen the covering over the housing unit for the lamb. once the knob is loosened lift the housing unit off of the side of the projector. You wlll see the enclosure where the lamp fits into beneath it.
Make sure the power is off for your projector while doing so. Screw the lamb into the enclosure , then replace the covering and screw the black knob in clockwise until it tightens.

Old film projectors are sometimes challenging to operate.
I have an old Bell&Howell and have to stop and think whenever a friend asks me to transfer a film to DVD. (Fortunately not often anymore.)

I just Googled keystone k100 and got several sites including several videos on Youtube.

I'm sure you'll find something in your flavour.

Good luck! Have fun.

Check this Website and see if one of the manuals doesn't give you the answer:

http://www.paulivester.com/films/projector/BH273man.htm

it won't go to factory default settings until you select it from the settings menu.

Re Keystone 68 projectors:
I join the growing throngs of folks who wish to view their family archives in 8 mm before submitting the reels to the digitals for conversion. Doesn't anyone have an answer for us? I continue to search, if I find, I'll post.
Fauvette