New Owner of a 720 (with many problems)

[datzenmike]

Alternator case is grounded through the mounting bolts... but it never hurts to have that ground wire on properly.

 

Take the cover plate off the front of the carb and bend the float down very slightly. Test it and try again. Have rags to soak up the gas as it spills out. Watch for small parts to fall out when the cover comes off.

[Brandon.fair]

Watch for small parts to fall out when the cover comes off.

 

Like actual parts or like debries/sediment?

[datzenmike]

Inside the chamber is a horizontal hinge pin for the float to swing on. On the very end is a tiny brass spacer to space the float away from the front cover... it is very easily dislodged and it drops out the front. Have rags under the front to catch the gas and this will catch it if it does.

[Brandon.fair]

What will happen if the carb is too full of fuel?

[datzenmike]

It will run slightly over full but they do have a correct level so I would try for that. The fuel level in the bowl also affects the fuel level in the emulsion tubes. I've had them over fill and drip into the primary so if somewhat over full it may slosh over going around corners.

[Brandon.fair]

Datzenmike I saw you post awhile back about the computer under the driver seat. You mentioned what the computer controls. I was wondering what those things were. I can't seem to find your post about it. If I buy an aftermarket carb with no feedback system to the computer, will the truck run reliably? If so what would you recommend? I'm not going to buy one right away as I want to try to get this one running properly. Honestly I just want something that is incredibly easy to work on.

[datzenmike]

Yes an older Z24 carb would work just fine. All you would need is the Red and Blue wire for idle cut solenoid and auto choke.

 

Or a Weber, about $300 but includes everything.

[Brandon.fair]

Do you know where I could find a older z24 carb. Also can you tell me what the computer controls?

[captain720]

The Weber is a super simple aftermarket carb that everybody runs. It is the easiest thing ever to work on. The only wire is for the electric choke.

There are two options the 32/36 and the 38/38. I am running a 32/36 on both of my 720s, the 38/38 is bigger and synchronized so both barrels open simultaneously, the 33/36 is a two stage so you run on the primaries most of the time, but when you hammer it the big one opens too.

The 32/36 is know to be a little more drive able while the 38/38 has a better top end. (Correct me if I'm wrong guys)

You can clog your jets or lose power to the choke relay, every one's in five million years somebody says something got stuck or whatever. Super reliable and a Weber isn't really gonna break and leave you with something you can't zip tie together on the side of the road in the middle of Kansas.

Sometimes they show up in Craigslist.

[Brandon.fair]

33 or 32? And what do you mean by "more drivable"

[captain720]

Oops 32, my bad. Better low end torque.

[datzenmike]

Yeah sorry not an 'older' Z24 carb but the 'non California' carb. Has only two wires.

[Brandon.fair]

Thanks guys If I get a weber can I delete the computer?

[datzenmike]

Yes an older non California emissions Z24 carb would work just fine. All you would need is the Red and Blue wire for idle cut solenoid and auto choke.

 

Or a Weber, about $300 but includes everything.

 

You don't have to delete anything just connect those two wires to it. The ECU is under the seat, no one will see it and there is risk of disconnecting something important.

[Brandon.fair]

What does the computer control? 

[Beaver_shots]

This is exactly like what I just went though with my 86. Same carb very similar issues, bad wiring to carb and in my case the carb itself had some issues. I just put on a weber last night and it runs much better. The computer controlled carb seems to be a bit touchy. Mike told me and I'm sure he is correct that having everything factory and working properly will be the most reliable configuration. Originally that is what I wanted to do, but once I started finding so much tampered with wiring I caved and just put on the after market carb.   

[datzenmike]

The ECU controls only the solenoid in the carb. The solenoid opens and closes the primary jet many times a second and using feedback from the O₂ sensor tailoring the mixture closer to stoichiometric. It is over ridden during warm up and at full throttle. If removing the carb there is no need for it at all. However I caution removing anything (wiring) as it may disconnect something vital. Just unplug the electrical connector at the back of the carb and connect the idle cut and the choke.

[Brandon.fair]

Truck will idle now but it's back to the original issue of bogging down/loss of power past 3k RPM. It will rev up to redline in neutral or with the Clutch pressed in. Any ideas? I was thinking possibly a mixture issue? It was reving fine when it was stalling at idle (no bogging). I'm at a loss.

[datzenmike]

Primary jet part plugged.

 

Secondary jet completely plugged so when the secondary opens only air and no fuel. Mixture goes very lean and engine falls on it's face.

 

 

There's an old saying that 80% of carb problems are ignition. And 80% of ignition problems are carb related. Have a good look at your cap rotor and wires. Start it up at night and look for any blue flashes.

[Brandon.fair]

Do you have any pictures of the primary and secondary jets? Best way to clean them? 

[Brandon.fair]

While trying to find the secondary jet I stumbled on to this diagram.

 

 

I have sprayed out the secondary as well as the primary. I will do it again soon to double check.

 

While looking at the diagram I noticed that the float bowl level viewing window appears to be on top of the float bowl.

 

 

When I got the truck the window was on the bottom side. Like this.

 

 

Can someone confirm if it is supposed to be on the top or bottom please? I'm leaning toward the top because when I adjusted the float bowl level to the dot on bottom I think the level it lower than the top hole. Seen here below. I don't know what this is but it's my best guess 

 

 

Yes I cleaned that stuff out. (Does anybody know what it is?)

 

thanks again everybody for the help I'm not familiar with carbs so forgive me if I seem awful needy haha

[datzenmike]

Yes up to top. If at bottom it's been off before and put back wrongly.

[Brandon.fair]

FML  I just adjusted the float level to the window on the bottom ugh!!! Guess I'll fix my fix.

[datzenmike]

It should still run, but under high demand (climbing a hill) it may empty the bowl and act like it's running out of fuel. When you stop it will refill and act normal again.

[Brandon.fair]

What are the two holes for on the vertical brass tube in the picture a few post up?