84 720 fuel issue

[B.clair54]

I picked up a cheap 720 a few months ago and I’m slow

[datzenmike]

Maybe a few clues about your fuel issue??? Mind reading hurts my head.

[B.clair54]

Picked up a cheap 720 from a buddy and have slowly been fixing it up, the stock carb was junk so I put a Weber 32/36 on it and have been issues trying to make it run right. I’m pretty sure from what I’ve been reading this morning that it has a clogged fuel filter but one thing that doesn’t make sense to me is that the truck diesels sometimes even with a fuel cutoff solenoid??

 

This is what I posted earlier don’t exactly know the other got there

[datzenmike]

The fuel filter is in the base of the electric fuel pump just forward of the rear right wheel. Possibly it's been replaced but should have a filter between it and the tank. A clogged or part clogged fuel filter will mean reduced output. This means the truck's speed and power is limited by how much gas is in the carb and how much the pump can keep it filled before running out. Speed can be limited on the highway and the truck will lose power climbing hills.

 

 

Causes of 'run on' or dieseling.

 

Idle speed way too high for the idle cut to have any effect.

Idle cut not working.

Secondary throttle plate not closing fully.

 

Flooding or running too rich causing carbon build up that glows red hot causing dieseling....

Fuel pressure too high

Float set too high

Inlet needle obstructed and can't close when the float chamber is full

Idle mix way too rich

 

Engine running too hot

Poor quality octane gas

Compression too high for the gas used

Wrong heat range plugs

[B.clair54]

It has an airtex replacement fuel pump on it so I don’t think it has an integral filter but I’ll double check, I did see a filter mounted on the frame rail which I’ll replace though. Once you get into the rpms it’s fine but coming off idle if you have to take off quickly it will hesitate. The idle speed is set at 750 and I’ve leaned out the carb as much as l could just by following Weber’s tuning guide but haven’t messed with the floats because honestly I don’t know where they need to be set at.

[datzenmike]

Filter should be before the pump to protect it from trash that will harm it.

 

That won't be the filter. The carb is full of gas or contains half a cup so you should be able to take off and go down the block on that before needing more from the pump

 

Could be the accelerator pump. Look down the carb primary and pump the gas pedal. You should see a strong squirt of fuel into the barrel. 

[B.clair54]

Fixed it, previous owner had gotten rid of the factory fuel pump and had run an in-line filter right before the pump, the filter was clogged and oriented the wrong way. Put a new one on retuned the carb and it’s much better.