Not familiar with your carburetor but are the floats set too low?

 

Not to but, what brand FP gauge did you use and, where did you place it? I'm thinking post filter.
Sequence : Manual fuel pump -> Fuel filter -> Pressure gauge -> Carb.
Again, sorry if I jacked the thread.

 

When I had the carb. off for cleaning, I checked the float level and it seemed close.

 

When you had the carb off for cleaning, was it just to dip it, or did you tear it down for a rebuild ? Just curious on how far you went with it.

 

That is how it should be run just before the carb so you know how the full system acts.


There should be a volume level posted some where on the web for your pump and thinking 5-7 psi for the pump pressure.
as someone posted you need to do a volume & psi test on your fuel pump to rule that out.


Dave ----

 

Details here in a new thread:

https://www.ford-trucks.com/forums/1...ure-gauge.html

 

The carb had very few miles on a complete rebuild. Since it sat for a while during the engine transplant and not always in the best of conditions, I suspected it may have collected some dirt in the fuel bowl, causing my issue. I removed the carb. & just pulled the top off, removed the float, needle and seat and cleaned the fuel bowl well. Replaced everything, roughly checked the float level and reinstalled.

 

All right, you're making progress. You've ruled out a tank vent problem.

I'm not sure I agree fully with your logic that the tank pickup is okay. Let's say for reasons unknown, the tank/lines/pump can only deliver to the carb 80% of the fuel flow needed at full throttle. Since the carb float bowl also acts as a small reservoir, this shortfall may not be apparent for short bursts of power, such as doing donuts in the DQ parking lot. But for a prolonged period of high demand, such as climbing a long hill, the shortfall in fuel delivery catches up and the float bowl level drops too low, resulting in rough running and long, run-on sentences with questionable grammar structure.

Can you duplicate the problem by revving the engine while parked? If so, get the engine to act up, don't let off the gas, and then switch off the ignition immediately. The idea is if the engine is running out of fuel, get it shut down in the same fuel-starved condition and then check the carb for fuel.

Take off the air cleaner cover and look down the carb throat. Cycle the throttle and watch the accel pump discharge nozzles. If the float bowl is empty, you might get one or two shots and then nothing. If the float bowl is still full, you should get fuel for many cycles. This should give you an idea of how full the float chamber was when the engine acted up.

 

The much easier solution is to just unhook the fuel line post pump and add a length of hose and feed it in to a container. Then have some one start the vehicle. It will run for a min or 2 on the fuel in the bowl. This will let you know right away if you are getting adequate fuel flow no questions no guessing.

Then the only other potential restrictions are the fuel filter and or a piece of garbage partially blocking the needle inlet on the carb. I've Seen this happen before on the 4100/2100 Series carbs with the fuel inlet on the bottom of the bowl. (unlikely but possible)


If you have a piece of garbage between the filter and and the carbs inlet seat ,when fuel flow demand increases you get enough flow that it pushes the garbage to the seat inlet blocking or reducing flow, as soon as the flow reduces or stops the junk falls back away form the seat allowing full flow.

If all that checks out you can rule out fuel flow issues.
And look at the carb and or ignition problems.

The next thing I would check is for Power valve function to insure you are getting the full enrichment needed at WOT and low manifold vacuum.

This will require pulling the carb and checking to insure the PV is working not stuck or has a leaking diaphragm and that the PV circuit passages are not full of gunk.

If that checks out then time to pull the carb apart and blow compressed air through all the passages to insure they are clear.

If all of this is good then you need to consider ignition or vapour lock.

 

Revving the engine in the driveway uses very little fuel compared to pulling a hill out on the road.

The bucket test while cranking may show the problem if you had a good one to compare it to.

 

Actually the bucket test is pretty definitive you will pump more fuel than the carb could ever hope to digest. If you do not have a good jet/ stream of fuel there is an issue. Also the residual fuel in a 2100 will allow the engine to idle up to a minute. More than enough time to check flow rate.

 

From the FSM the spec for your pump is 1 pint in 20 seconds. Crank for 10 seconds and you should have a cup (8oz) of fuel in your container.

What I am confused about is my 1986 460 specs the same but the pump has a capacity of 40 GPH, while that pump you have is 25 GPH the same as what came on the 460 and 351 in 1984. Why did Ford increase the pump capacity?

 

All good suggestions. I'm not sure I can get it to act up in the driveway because of lack of load, but I will give it a try.

After I found that it wasn't a vent issue, my next thought was that my new pump was failing, but it only acts up under high load. Can a mechanical pump function well enough at normal load and still fail at heavy load? I've never encountered that but I've never done much racing either so my experience is limited. Most failures I have see have involved leaking pumps.

I will try the flow test and then maybe swap to the old pump and try it again for comparison. If they are both the same and the old pump encounters the same problem, then I will pull the carb. completely down.

This will take a few days but I will report back. Any other thoughts you have just let me know.

Thanks.

 

In short yes they can. Mech fuel pump problems can drive you bats***.
The mech fuel pump is actually a pretty complicated little piece of kit. There are 2 one way valves and 2 diaphragms several springs etc.

If either of the valves goes bad it will affect fuel flow and pressure.
Additionally if the pre screen in the tank goes for crap there is nothing stopping the pump from picking up garbage and plugging or partially plugging it's self up. This will not affect pressure capabilities of the pump but will affect the over all flow rate and will be noticeable at periods of high fuel demand.


Since you have no sock on your pick up a jammed up fuel pump is a very real possibility.

See below pic of a cutaway mech pump for reference.

 

The 460 had a return system didn't it? With 3 lines on the mechanical pump. Or it had electric pumps in the tanks with a return system also.