Think you can diagnose these issues?

[Slowdus]

Hello, I've got a 86 720 KC 5speed 2wd; In the 6 months that I've owned it, two issues have come up that I just wanted some opinions on, from those who know these trucks well. 

 

 

 

- Let's say I'm merging onto a fast NYC highway where there's very little run-up and need to get up to 60mph quickly. If I floor it through 1st and 2nd gear...by the time I reach 3rd, the truck starts bucking like it's not getting fuel. I then have to get off the gas, wait like 3 seconds, and slowly roll into the gas. After that happens, the truck is more prone to bucking as I try to maintain highway speeds (60-75)... It makes upgraded slope highways tricky... Is the fuel pump getting overworked? I have a Weber 38.... Is it flooding the engine? Are there any fixes? 

 

 

 

-Next issue, very recently when I am accelerating through 1st and 2nd gear at a fast pace, the shifter moves damn near all the way to the right side of the center console. I come off the gas and it moves back to the left. The bushing for the left side of the stick was never great, but it never started doing this until recently. This is my first manual car so I'm not sure if bushings would do this... Maybe it's the mounts? 

 

Thanks.

 

[powderfinger]

40 minutes ago, Slowdus said:

when I am accelerating through 1st and 2nd gear at a fast pace

you lost me with this line lol, you ain't doing a god damn thing fast in a 720! As for the bucking under hard acceleration, try changing the fuel filter. A clogged fuel filter will first causing issues when the engine needs the most fuel like hard accelerating or pulling a hill.

 

As for the shifter moving when on and off the gas, I would have someone get in the truck and rev it up and down while you watch the engine. Maybe the motor mounts are trash and everything is shifting?

Edited September 19, 2024 by powderfinger

[datzenmike]

My guess is also the fuel filter between the tank and the electric pump mounted on the outside of the frame just forward of the right rear wheel.

 

Certainly the engine rubber isolators in the mounts and the rubber transmission mount should be looked at. Also take the console out and expose the shifter where it connects to the transmission. Are the plastic shifter bushings damaged or broken? Try lightly moving it side to side. In neutral it normally it should seek a resting position between the 3 and 4 gears.

 

 

[datzenmike]

I might add: look at the fuel level in the glass sight on the front of the carburetor. It should be in the middle. If float set too low you might be able to use it faster than it can get in. There is also a filter in the twist off base of the electric fuel pump. It should be fine as the main filter is before it.

[EDM620]

Definately sounds like starving for fuel, change the filter then check fuel level in the carb after running a bit.

 

Based on your descrition, not sure how much the shifter is moving, but the 2 key points are the shifter bushings and the mounts. You can quickly identify bad mounts by having someone rev & release the throttle while you watch the engine. Under normal use, the engine will "rock" slightly under rev then return to rest at idle. All engines do this. Excessive movement indicates worn out mounts, and they can fail completely. There is a mount on each side of the engine plus the transmission mount. If one is bad, change them all.

[Slowdus]

So it's been over a year and I forgot about this post, but I don't wanna be those guys that don't wrap up threads to help others lol.

 

The bucking and stalling out issue turned out to be a leak from a fuel hose that was not noticed by me. After a while the leak got so bad that I had a shop replace the line, among some other unrelated things; The symptoms completely stopped which points to even a slight leak having a big effect when flooring the truck.

 

The shifter jumping around was the driver side engine mount failing. Upon inspection, I was able to see the rip in the rubber, and it completely broke in half when I removed it. I replaced it and the issue is no more. Thanks for the replies.

[datzenmike]

So I suppose air was being sucked in between the tank and the electric pump? This would lessen the pump suction. If between the pump and the carburetor it would leak fuel under pressure.