350 Chev fuel pump stopping

[FleetwoodMac]

Hey can any tell me why my  LT1 350 Chev with 80 gal per hr mechanical  Holley fuel pump stops pumping after 15 minutes, I thought diaphram must be stuffed or crack in housing couldnt find any so bought a new one ,this does same thing ,the push rod from cam moves easily ,fuel tank clean,fuel line clear, intake clean. I by passed mechanical pump and plumbed in an electric pump - motor run perfectly with mechanical pump sucking and blowing air perfectly but after a while mech pump stops ,the diaphram is good ,the valves both good in both mechanical pumps. I am putting in an electric pump to cure the issue but would love to know whats going on has any one got any ideas, thanks , the eccentric on cam appears to be OK

[swifty]

If the tank vent isnt venting the pump will starve after a few minutes of pumping,either that or air leaks around hoses,fittings or filters. I dont think the electric pump will fix the issue. You need to find the cause and its most likely not the mechanic pump.

[Paul]

I by passed mechanical pump and plumbed in an electric pump - motor run perfectly with mechanical pump sucking and blowing air perfectly but after a while mech pump stops ,the diaphram is good ,the valves both good in both mechanical pumps.

If the mechanical pump still stops pumping after being taken out of the fuel loop, then it cannot be tank vacuum, it must be a mechanical issue.

It sounds like you've already swapped in another mechanical pump with the same results, so this only leaves the a sticking push-rod when engine/oil is warm.

The push rod is only splash lubricated from the crank/cam.  How's your oil level - high enough?  What grade oil?  When was the last time the oil was changed?  What sort of angle does the engine sit at - higher angles means less oil splash at front.

You haven't got some of that 'moreys oil stabiliser' crap or similar in there have you?  It just tends to glue everything together in my experience.

Maybe take the push rod out and polish it up with some oiled 800-1200 wet and dry paper for a few minutes.  Just trying to get a few more microns clearance, so it keeps moving when warm.  Maybe also check the end of the lever in the pump to make sure it's all smooth.

[FleetwoodMac]

Thanks alot for replies , I will check for rod clearances, this pump is a bugger to take off and on (69 Corvette ) no room , oil is new , no additives, level good ,  I had a hard time keeping rod from sliding down but used a blob of grease frozen for sticking . The electric pump will be mounted at the rear near fuel tank so will be pushing rather than sucking

[yjet]

I'd be looking elsewhere, if the fuel pump pushrod slides free then thats an end to your problem, in all my years of jetboating  (incl commercial) have never seen a problem with the fuel pump pushrod. look for a vacuum lock at tank?

[spud]

put a longer 3/8 bolt finger tight in from front to hold push rod,