Engine racing on start -5500 rpms!

Hey folks! I have a a1990 Mazda B2200. Its been running great, but all of a sudden when I started it this afternoon, the engine immediately raced up to 5000 rpms. I checked the throttle cable and it seems to be fine. Any suggestions as to what this is or how to diagnose the problem?
Thanks in advance.

Sounds like it can POSSIBLY be a vacuum leak... vacuum leaks can tend to have opposing effects... if the vacuum leak is pre-venturi in your carb it will accelerate the engine... if it's post-venturi it will run very poorly or not run at all depending on how big of a leak.

You can test if its a vacuum issue quite easily in your case, since it's running that is... Get some starter fluid, and while the engine is running spray some carefully around the vacuum hoses and carb... try not to get it in the carb directly... If the engine revs up that's a tell-tell sign that it's a vacuum issue. You should be able to isolate where the leak is using this method.

Be careful... don't spray too much, just little bursts at a time because you are already revving pretty high @ 5,500rpm, and if it is in fact a vacuum leak, the you will be increasing your rpm speed every time you spray.

If when you spray around the engine does not change in rpms, then it's safe to say it's not a vacuum leak.

Is the throttle return spring still in place? The only way this could happen would be for the throttle to be wide open, Vacuum leak has no fuel in it.

When it does this, are you physically able to move the throttle arm back up to its idle position with your hand?

I hate to argue on forums becuase for the most part it doesn't accomplish much... Nevertheless a vaccum leak can and infact does cuase engine acceleration if you have a carburetor and if the leak is pre-venturi... As i mentioned in earlier post... Under these conditions the extra airflow will cause carb to generate more fuel... No different than opening the throttle...

Truth will be in the fix.

I think the throttle just "has to be" wide open to approach 5500 rpm. My $2 bet is on something stuck.

Thanks folks! As it turned out, the secondary throttle plate was stuck open due to the arm from the servo on the carb becoming detached and wedging itself into the mechanism. Pretty simple fix. This is my first auto with a carb, so it was a giid learning experience about how it works.

$2 please.

Lol, put on my account. Account that I has no money.