Saw it!
You can start by moving the throttle lever on the side of the IP.
If it is frozen, then do not rotate the motor at all!
Go to the TM section of this forum and locate the MEP-003A info.
In it you will find tons of additional info about the IP.
Determine if you have an Ambac M-50 or an American Bosch pump ( identified by the large flat head screw on the bottom of a Bosch pump and no screw on the Ambac M-50.
I'd suggest reviewing the IP data so you get familiar with the parts etc.
If you have a Bosch do not try to free it up, remove it , disassemble and clean it. If you break it using the procedure below, the Bosch is not repairable.
If you have an Ambac M-50 Continue reading:
Remove the 1" cap in the center of the IP, then remove the 5/8" 12 point cap under it, and remove the small spring and delivery valve/holder under it.
Disconnect the fuel line from the last filter and raise it up as high as possible.
Pour acetone into the line and eventually it should come out of the "open" IP pump.
Put the 5/8" 12 point cap and the 1" cap back on loosely.
keep filling the hose with acetone and let it sit for a good 4 days or more. add acetone if needed to keep it full.
If you have an air hose handy you can blow air in behind the acetone to help force it through the pump.
The refill.
after sitting, see if the linkage has freed up yet.
If so, remove the a caps on the IP again and put a 5/8" socket on the bolt on the blower wheel.
If not keep it full of acetone and wait a few more days.
Once the linkage is moving,
Get a bright light and shine it in the center of the IP so you can see the plunger.
Rock the engine back and forth slightly while looking for rotational movement of the plunger.
Note: it will rotate at 1/2 the speed you are rocking the crankshaft.
If movement is seen, rotate the crank further, back and forth.
The plunger will also be pumping in and out as well as rotating.
If it rotates but does not move in and out, tap it lightly with a brass punch and see if it will move inward until hitting against the camshaft.
Rotate again and see if it sticks again, if so continue tapping lightly after rotating until you can get it freed up.
You can also spray carb cleaner in the end of the IP while you are do this to help free things up.
On an Ambac M-50 if the plunger is frozen and the engine is rotated more than a small amount the plunger guide is designed to split in half, disconnecting the pump from the engine.
If you can rotate the engine but the plunger is not rotating, then you plunger guide is split and the pump needs to come apart to replace it.