Perkins 4.154 starts immediately, runs great, then knocks off once put into gear. Af

[a64pilot]

Whats your idle RPM?

It's normal to not show vacuum at very low fuel flow rates, reason is there is essentially no vacuum required to pull very little fuel through a clean filter.

a section of clear line after the lift pump as suggested earlier will rule out or prove the existence of an air leak, but if it starts again easily, I don't think it's sucking air

[starfish62]

Thanks all for giving some time & thought to my problem. It turned out that the large inlet (banjo type) bolt on the injector pump had "failed." It's a sleeved fitting and it was junked up, I guess just due to old age.