no fuel in lin after sitting 30 minutes

1988 Mercury classic 50 45 HP
complete rebuilt 1 year ago. has 25 hours on rebuilt by certified mercury techs
carbs recently rebuilt by certified mercury techs, cause: needle valve sticking closed and were replaced and carbs cleaned. They advised to run the fuel out after using by unplugging the fuel line and run till it dies.
Problem:
Runs great but when it sits for approx 30 minutes will not start. Fuel line has no fuel and the bulb takes a long time to pump up. The fuel tank fitting was replaced with a moeller anti siphon valve and a new fuel line and bulb were replaced. This has been an on going problem. To restart I switch to another tank and pump up the bulb. It has the same problem after 30 minutes of non use.
Any clues?
Hud

Sounds like original problem is still there,Seats in carb could have damage that cant be seen with the ***** eye. Just because he's certified doesn't mean the rebuild is perfect.we are all human.

Agree, the carbs might be leaking out after 30 minutes; the fuel literally could boil away inside the hot powerhead.

I've had trouble with the spring-loaded float needles and there is an upgrade you can try if your carbs still have those:

http://www.marineengine.com/newparts/part_details.php?pnum=SIE18-7062

The Sierra needles are cheaper but they do sell the Merc part here if you prefer:

http://www.marineengine.com/newparts/part_details.php?pnum=MER1395-879194011

HTH & G'luck..........ed

THanks for the replys.
If the seats are bad, what can fix it?
The needle have both been replaced.

Hud said:

THanks for the replys.
If the seats are bad, what can fix it?
The needle have both been replaced.

Click to expand...

But if the mechanic used the older-style spring-loaded needles, you still might have a problem. They just don't work as well as the newer-style parts.

It would be extremely unlikely that the seats themselves were bad, since the float needles are rubber-tipped and there would be virtually no wear on the seat itself. Of course, anything is possible and if you're going to take the carbs apart again, the seats should be carefully inspected.

One thing you could do is run the motor until it's at normal operating temperature, unplug the fuel line, wait 30 minutes and then see if the carbs are emptying themselves. If so, you've got a leakage problem between the needles and the floats. Or something else strange going on.

Is it possible for fuel to drain back to tank,bad check ball in primer bulb, faulty new aftermarket parts.

I've had similar problems due to micro-cracks in fuel lines. I recently replace all fuel lines and the increased performance was astounding.

Thanks for everyone that replied. I'm going to try the new needles and go from there.