287B air in fuel runs rough above idle

I have replaced the electronic pump/filter assembly, blew out my fuel lines to the tank, then bypassed the tank to a jerry can with clear lines. still had the same problem- starts up and runs at idle fine but when you pour the coal to it, it smokes and bogs down. I installed a clear line from the filter housing to the injector pump and was amazed to see at least a quarter of the line is being fed air! all clamps are tight- new o-rings on the barbs for the supply and return to the tank, even put Mylar washers on the two plugged ports- where is the air coming from. at least half the line is air when you hit the throttle. There is absolutely no air in the supply and return lines to the tank.

I figured it out- hooked an in line fuel pump directly to the injector pump- no more air and it runs great. I still do not know why the brand new assembly (600 bucks) from cat is introducing air to the system- must have a crack in it somewhere

Is that the transfer pump built into the top of the water separator housing.?
If so pull the bowl (#4) off the bottom of it and make sure that the O-Ring that seals the bowl is located correctly - or even is there at all.........
While you're at it pull the water separator element (#1) off and do the same.

The O-ring Nige speaks of (letter "E"). And, did you verify no clogging in the fittings you swapped to the new filter head?
I've had to add an inline screen before that filter assembly to prevent restrictions from occurring.

This thread is a Kubota, but, same concept.
https://www.heavyequipmentforums.co...r-revs-up-and-down-bogging.80284/#post-983399

There is nothing in your machine currently to stop debris from reaching that new pump/ filter assembly.

it's not that- i put a wix filter on that doesn't have the separate bowl- no change. I ordered a new assembly from cat. there's got to be a crack in the housing or something wierd. there are no clogs in the fittings- that would not create air even if there were. This is not a problem of it not getting fuel, it's a problem of it getting 75% fuel and 25% air to the injector pump as i stated before. I have an in line filter for debris in my line- I added one.

Since there are 3 lines to the primer head, are you sure that you didn't transpose 34 and the one next to it?

i put both of those in a jerry can- that means it can supply and return freely. If you were to mix those two lines, then the filter would not get any fuel. Those lines are clear lines, they are full of pure fuel- the electric pump is working great, the filter is full of fuel, when the machine is fired up, the short line going to the injector pump is being filled with air bubbles.

Fuel systems can be fickle ... it is often not the obvious solution that fixes these problems.
Perhaps post a photo or two showing how your fuel system is plumbed.
A serial number for your 287B would be helpful for troubleshooting too.

How much fuel is being delivered in the line to the injection pump ... a measurement of open flow rate and pressure would be helpful in troubleshooting.

Perhaps it is not air that is getting in your system but it is vaporized diesel ... possibly from a fuel system restriction. I had a similar situation to yours on my 242B where idle was good but stalling at higher demand ... and eventually it would not even idle. When troubleshooting using my primer pump, I noted only foamed diesel being pumped ... yet no air leak was obvious. It turned out that I had a plugged basket strainer on my mechanical fuel pump ... I cleaned that up and the primer pump pumped only fully fluid diesel ... no more foam ... so in my case I don't think the foamed diesel came from an air leak ... it came from the primer pump sucking hard enough on the diesel to vaporize and foam it.

Checking the fuel delivery (rate and pressure) going to your injection pump will helpful to determine if the above foaming fuel problem that I experienced is similar to your issue.

Here is a thread that might also assist you in your troubleshooting: https://www.heavyequipmentforums.com/threads/cat-226-fuel-problem.78929/