4020 engine reving at idle

Kemper

Member
My 68 4020 started reving at an idle, if I close throttle lever all the way down and cut off the fuel it will settle down for a bit then slowly rev up again, is there anything I need to check before I have the pump rebuilt? Fuel filters are almost new. .
 
Problem is likely the injection pump (assuming you've got a JDB or DB pump and not a CB). But if the fuel pump is bad - it can also cause that problem. The injection pump has its own fuel pump built into back of it. So the engine has two fuel pumps. If the other pump goes bad (the separate one) and blocks fuel flow, the injection pump will put suction on in, start drawing air, and give the same symptoms.
 
I replaced the fuel pump (with the priming lever) last year but i will investigate it a little further, i did take the timing window off and it is clean in behind it, I also heard that the return line could be plugged, i"ll look at it this morning..

Is there a good way to check the main fuel pump?
 
Best way to check the fuel pump is just crank the engine and check the output. You can't check it by just using the hand-primer.

The injection pump has a pressure-regulator at the outlet with a spring-and-ball in it wih a very small opening. Plugs easy. But if the plastic in the pump has shattered - pieces should be all over the pump. Usually that cavity exposed when you yank off the timing window will be full of the stuff if it's broken.
 
Ok..it seems to have good flow cranking the engine over, I now have the injector pump off and taking it to desmoines diesel today, the seem really nice on the phone, said they could have it done by Friday, the tractor always did smoke black at an idle so I hope I see some improvements!
 

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