Hello so I have been having this issue with my 20r where when i fire it up the throttle is at full boar, like completely open. The first time it did it I just sprayed some carb cleaner in it and wiped it out a little bit and it stopped for a couple days. Then it did it again so I replaced the throttle cable which was pretty worn out and pulled off and rebuilt the entire carb replacing all the parts I could that came in the kit. I started it back up and it idled perfect for about 5 minutes then started doing it again. I don't know what else could be causing that. Even if I move the throttle back and forth manually it still will not bring the rpms down at all now. Anyone have any ideas? I have been looking on forums like crazy and can't find anyone with the same issue. Thanks!

 

What carburetor? What is your timing set at?

Does it just run away and you have to cut the key to keep it from destroying itself or does it run up to a certain RPM and sit there?

You're saying if you completely close the throttle plate it's still revving up really high? Can you put your hand over the intake with the filter off and kill it by starving it of air?

If it's a Weber carb, do you have a fuel pressure regulator in-line, between the pump and the carb? Also, if a Weber, how high is your float set and which jets are in it?

It could be multiple issues coming together to make this problem but I would start at the tank and work all the way to the intake manifold checking that fuel is flowing how it's supposed to be first and foremost.

 

Yeah it just keeps going and I have to cut the key. I'm not sure what the timing is set at but I don't believe that I changed anything in the way of timing and I didn't make any changes to the air/fuel ratio screws. I haven't tried holding hand over to kill it yet, just tried to move the throttle open and closed but I literally only have like 2 or 3 seconds before I have to kill it so it doesn't explode so I haven't been able to play with it much while it's on.
It is the Aisin carb which I believe is the same as the Weber. I set the float based on the specifications in the manual and I hooked up all the hoses and lines in the same spots for sure but I'm not sure if it has a fuel pressure regulator on it. I know I need to go back through it but I'm not sure what I should be looking for exactly when I do cause it started up fine after I put it back together. I'll tear back into and see what I can find out.

Thanks for the questions, gives me a little better idea what to look at!

 

The Aisan* is the factory Toyota carburetor and is not the same as a Weber. If I remember correctly, the 1980 trucks used an older style "round top" carburetor that I am not that familiar with. There is no need for a separate pressure regulator when using the factory carburetor.

Are you sure the throttle plates are actually closing? It does sound like the throttle plates are opening allowing for the high revving. Are you able to physically see that the throttle plates are closed prior to starting?

* Edit:
A little clarification (trivia) time:
There are two Toyota part suppliers with very similar names. Aisin makes water pumps, oil pumps, and hubs among other parts for Toyota, but do not make the OEM carburetors for Toyota.

Toyota sourced its carburetors from Aisan, not Aisin. Since the two company names are so similar, I did not realize they were two separate companies until today.

 

Yes I can see down in their that both plates on the bottom are fully closed when I start it. I haven't tried to look inside it while it's on to see if they are open because I don't have enough time to before I have to cut it.

 

Interesting I didn't notice the name differences either.

To the OP, does the throttle (cable, linkage and plates) operate smoothly when not running and when you operate it by hand? Do you have the right cable?
Where is the idle screw set (a pic would help here)?

Also, putting your vehicle info in you signature would help us help you. You location could too.

 

My 1980 20R Aisan carburetor is acting the same way. Turn on the key and the engine RPM goes to the tach's bottom of red line! I never had it that high and thank God the engine never destroyed itself. Yet.
Throttle cable position has nothing to do with it. Remains at Idle setting. Took a few seconds to look down the throat and gas was flowing OVER the left nozzle and feeding the "fire".
Could a stuck Float be the problem?
It's a rebuilt carb that's maybe only 4-5 years old.
Any help appreciated. Thanks folks.

Steve