fuel flow all over the place

[big al 08]

the rear eng fuel flow goes all over the place for 30 sec then the engine wants to quit. has happened four time from san felipe to la paz always within 45min to an hour. have gone from mmsf to kyum 40mims in between thes time with no problem. had all the pressures reset so all go to red line wot and in the green at cruise. flying between 9.5 to 13.5 depending on winds. all temps okie dokie.
it is not vapor locking. put it on low boost first time & finally settled down this last time needed to go to high boost for it settle down, if the boost are turned off after 1/2 eng quits. on final with mp at low end of the green eng quits every time. i do not believe running a long periods of time are good for the boost pumps. have an annual in ten days however need to go north and not really thrilled running the boost for four hours. any suggestions

[Mitch Taylor]

When you say fuel flow is all over the place, does it go above and below what's set, or just below? Sounds like it could be a vent problem if it's just dropping off.

[big al 08]

goes up and down quite rapidly. up to 16gph and back down to 5gph, surging up and down. happens very rapidly then eng quits i think due to fuel starvation. reading is off a shdin digaflow not the orginal fuel flow meters, but both agree.
rick

[Francisco]

Have your Mechanic check your mechanical fuel pump you may need to replace it.


Francisco

[big al 08]

okie dokie found the problem. the rear fuel screen/bowl "o" ring became hard and started to leak after 30 yrs. so in normal cruise setting the eng fuel pump pumps less/less pressure which allowed air to be sucked in via the top "o" ring that connect to the shaft that hooks to the sump drain cable. at t/o and climp setting it still sucked air; however the air leak is minor with the high pressure the pump is generating.

today nice tailwind prc-blh-yum 250mph