So I've got a 75' hilux 20r. It drove fine a about a week ago besides the usual light mis-firing. After two days of straight rain I decided to take a cruise on this nice day.
I try to start it up to no avail, nothing new, maybe I flooded it. I pull out the spark plugs to wipe them and let them dry out a little. I put two back in fine but notice the 3 and 4 plug holes are pretty gnarly. I know I'm looking at a helicoil job soon but for now i got them back in and i think i got most of the metal shards out.
Now, I go to start it and it somewhat fires up but is mis-firing worse than usual, figure I'll let it warm up.. Shuts off on me. I keep trying to start it up and it gets worse and worse. Now it's like a mean thud and violent motor movement when i try to start it.
This all seemed to happen pretty quickly and escalated fast! Could it be a tranny thing? Could i maybe not have gotten all of the metal shards out? but would it cause a violent start-up attempt? Please someone chime in, I'm lost right now.

 

Check cam pin make sure its not sheared had that happen once

 

And while the valve cover is off, look for vent valves, cracked rocker arms, things that look bad.

 

I gave it a solid tune-up including that gunked up fuel filter. Got her running good again!