Vehicle Bucking at 40 mph

[McFerg]

Hey y'all. My '86 720 has started to buck at around 40 mph and loses power/fuel and bogging down. What are the possibilities for why?

New Weber Carb installed 8 months ago.  New spark plugs, wires and distro cap 7 months ago. 

[McFerg]

When it gets back below 40 mph the power/fuel comes back.

 

[Gluteus Maximus]

My old 720 did the same once...ended up being a clogged fuel filter.  If I remember, there was one in or next to the fuel tank that was the problem.

[datzenmike]

Agree. If it doesn't help it probably needs to be replaced anyway. (every 3 years) It's cheap and easy enough to do.

[Thomas Perkins]

Also replace all your rubber fuel lines,starting with the one coming out of the gas tank and the two by the starter.Also drain your gas tank,it has a drain plug.Get a new gas cap too.Check the filter in your Weber.Also check the Weber bolts holding it down.Replace fuel filter at fuel pump,replace filter in fuel pump,12 bucks on Ebay.Pump could be going out.I had one that went out before.Always use OEM fuel pumps,Nissan still sells them,got me a new spare.Make sure your rubber fuel line going to Weber is not restricted.Also check your throttle linkage,could be too tight.If you are using a idle cut off solenoid,it could be loose.I am using one on my Weber.Check the O ring on it.Could be something simple.I also have replaced the fuel pump relay under glove box years ago,it was 50 bucks.

Edited May 26, 2022 by Thomas Perkins

[McFerg]

On 5/26/2022 at 12:53 PM, Thomas Perkins said:

Also replace all your rubber fuel lines,starting with the one coming out of the gas tank and the two by the starter.Also drain your gas tank,it has a drain plug.Get a new gas cap too.Check the filter in your Weber.Also check the Weber bolts holding it down.Replace fuel filter at fuel pump,replace filter in fuel pump,12 bucks on Ebay.Pump could be going out.I had one that went out before.Always use OEM fuel pumps,Nissan still sells them,got me a new spare.Make sure your rubber fuel line going to Weber is not restricted.Also check your throttle linkage,could be too tight.If you are using a idle cut off solenoid,it could be loose.I am using one on my Weber.Check the O ring on it.Could be something simple.I also have replaced the fuel pump relay under glove box years ago,it was 50 bucks.

I changed out the fuel filter and drained the tank 6 months ago. I decided to change the filter out again three days ago. It's my sons truck and he changed it while I was at work.  He thought the fuel pump was the filter so he disconnected the hoses and the wiring, then he realized it wasn't the fuel filter.  He reconnected it and Now it won't start at all. The motor turns over but acts like it's not getting any gas.  I will look at it later today but perhaps the fuel pump has gone bad. What's the best way to know if the fuel pump is bad? I'm currently going through the youtube rabbit hole of how to determine if the fuel pump is bad...

[datzenmike]

Just to be sure check the engine tag under the passenger side hood hinge on the inner fender. Is it Z24 or Z24i????? Each use a different pump. If a Z24 then there is a filter in the twist off bottom of the pump body in addition to the in line one.

 

Can you hear the pump working? with the key on?

 

Pull the hose off and direct into a suitable container. Pump should deliver 1.4 liters or more, of fuel per minute

[McFerg]

On 5/29/2022 at 5:19 PM, datzenmike said:

Just to be sure check the engine tag under the passenger side hood hinge on the inner fender. Is it Z24 or Z24i????? Each use a different pump. If a Z24 then there is a filter in the twist off bottom of the pump body in addition to the in line one.

 

Can you hear the pump working? with the key on?

 

Pull the hose off and direct into a suitable container. Pump should deliver 1.4 liters or more, of fuel per minute

Z24 Engine. Replaced the fuel pump today and it turned over like a champ.  It hasn't run this well for months.  Thank you all for the input.  This forum is the best.

[waddlin]

Mine was doing the same thing but at different speeds.  I changed the pump and it ran good for a while but then started acting up again. It ended up being the float and needle and seat sticking.  

[McFerg]

Ill Keep an eye out for this.  Thanks waddlin

On 6/2/2022 at 4:04 PM, waddlin said:

Mine was doing the same thing but at different speeds.  I changed the pump and it ran good for a while but then started acting up again. It ended up being the float and needle and seat sticking.