Here is some info that may help you change the fuel pump button (I think its actually called an 'idle plunger' or something). What this does is increase the fuel rail pressure.
(Cummins calls this pump/injector system the 'pt' this stands for 'pressure-time' Really the external pump is just a big ,fancy pressure regulator ) More fuel pressure = more fuel.
Turning up the pump is not that hard to do but I can't recall the specifics because its been over a decade since I did this. A few hand tools are all thats required to pop the cap off the end of the pump then a socket and needle nose pliers to pull the stuff out. The 'buttons' are stamped with a number on the groove where it is narrower and the lower the number, the more fuel pressure. The numbers go up in a weird sequence if I can recall --> alternating between the increase of 2, then 3, then repeat --> like 5, 7, 10, 12, 15, etc. Depending on how far you want to go,On the big motors, 350's, and 400's guys used to take whatever they had and drop the number by 10 or 15 and it was pretty safe, I'd just drop one size on a 250.
If the exhaust temp stays low on a hard pull, then maybe I' drop another size.
Just be sure to have a pyro , be sure to warm it up properly because that extra fuel will score a liner much quicker when not warmed. Do not lug the engine - drop a gear soon as there is enough rpm room to do so.
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