Hello, i have a 86 toyoya pickup with a carb. 22r. It runs great most of the time except when i am driving around 55-60 mph and i let off the gas just a little while going down a hill it starts to cut out. If i give it more gas it quits doing it or if i let of the gas completly it quits. It just starts to stumble right when your giving it enough gas to hold your speed going down hills at high speeds. I have changed spark plugs,wires,cap,rotor,fuel filter. This truck is copletly stock. Thanks for any help.

 

The first things that come to mind are the vacuum advance and the EGR. Both of those things are changed at partial throttle. I had a broken vacuum line going to the main diaphram on my vacuum advance and it cause a slight bucking at light throttle. Make sure all of your vacuum lines are in good shape and going to the correct place. Also check that both diaphrams on your vacuum advance hold vacuum. Check your timing, also.

 

your carb could be giving you the issues too, i dont know alot about carbed trucks but it is a thought.

 

when it "stumbles", does it lurch, an irregular stumble, or is it more like you've run out of gas, a even, constant lack of power or speed?

 

Its more like running out of gas. It happens real fast. When i let off the throttle all the way it dosnt do it or if i give it more throttle it dosnt do it. Just when your trying to keep a constant speed at 50mph or higher. It dosnt do it at all under 50mph. Thanks for the help.

 

if you've replaced the fuel filter, i'm going to agree that you probably need to rebuild the carb. it may be gummed up, and if you're going to clean it might as well spend the cents necessary to replace gaskets, orings, etc. easy job.

 

Maybe the fuel cut solenoid system is acting up. It cuts fuel while decelerating so the cat does not overheat. When the throttle is closed, vacuum is applied to a vacuum switch on the passenger side fender. If the vehicle is above a certain speed and RPMS, which you would be at 50 MPH, then it cuts fuel to the idle circuit of the carburetor.

I am not ruling out the carburetor, as that is a good possibility, but I would check the little things first. I have found that smog controls acting wierd can seem like carburetor problems.