4520 compact tractor engine surges when put in forward or reverse

[Crankygranke]

Engine surging up and down like governor kicking in and out. when put in gear forward or reverse. also when operating loader. when increasing rpm surges for a couple minutes then stops and becomes stable. I have replaced fuel lines, filter, air filters. transfer pump,cleaned tank and screen. I'm at a loss, please help

 

[Jerry/MT]

Engine surging up and down like governor kicking in and out. when put in gear forward or reverse. also when operating loader. when increasing rpm surges for a couple minutes then stops and becomes stable. I have replaced fuel lines, filter, air filters. transfer pump,cleaned tank and screen. I'm at a loss, please help

fuel injection pump metering valve sticking?

 

[Crankygranke]

fuel injection pump metering valve sticking?

it has a pump for each injector. not the regular setup.