3406b missing allen screws from pump??

I don't have near the experience working on these that @wore out has, but if it is not connected at the tank end, I would take the line off that is attached to the 90 degree fitting on the injection pump, and then remove that fitting and check it for debris in the little whole. If that is clear, I would re-attach it, unplug the tank end, place it in a container of some sort, and fire it up to make sure that you have a bit of flow coming out. This may well be your problem, as running it without any return cannot be good. I am not sure what would happen running it this way for very long, but it would have to be hard on the transfer pump. As I mentioned before, when mine plugged the fuel pressure went straight to 100 psi, and I only ran it a few miles that way.

Hopefully you are getting closer to the problem.

 

Get you a return rigged up. I think the spec is only 9 gallons an hour or so. I have had the return plug before but it was a constant problem. However I have by no means seen it all or know it all. I do feel like if its blocked off you are on your way to a solution

 

On the b models that return is there for a reason. That reason is just to evacuate any air in the injection pump and it gets carried back to the tank. That special fitting is like a regulator also to keep the fuel pressure correct.
Anybody that plugs it is an idiot.

 

Perhaps the trapped air is causing
the problem?

 

Perhaps yes.

 

No less than 32, but the closer it stays to where it is the better.

 

It sounds like you may be sucking a bit of air in your fuel tank pick up. Does your fuel draw from the bottom of the tank, or do you have a pickup tube within the tank?

In regard to your fuel pressure, at full throttle/load mine also drops to the 30 psi range. I don't understand the 35-38 at the reduced power. It sounds like maybe the rack is sticking, hopefully one of the other more knowledgeable gents like @wore out, @SmokinCAT, or @swaan can help with this.

When mine is at higher RPMs (say 1700) with no load my fuel pressure is usually 42-50 depending on ambient air/fuel temperatures. I have a Teltek electric guage, and I occasionally see the spikes that you mention as well. I assign that to the electric gauge.