fuel tanks

[martin]

Thanks

[wattaway2]

Bushwacker you got me thinking -- haven't run it yet but in setting my tanks up (2)each tank has two pickups. I felt that by putting a "T" between the two pickups and running one line from each to one filter with selector valves I would reduce the chance of one of the pickups getting clogged and at least one would continue to flow. Had a problem with a 69 chargers tank pickup when someone slipped a paper towel used to clean the windows down the tank fill ! It would get sucked up shut the car off and then float away after the vacuumed realeased it might be days before it acted up again! Drove me nuts finding it!!!!

[martin]

my tanks have 1/2 inch suction lines. I was going to have custom suction tubes made for 1/2 " then reduce to 3/8 at water seperators .. you think that is over kill

[Bushwacker]

Originally Posted by martin

my tanks have 1/2 inch suction lines. I was going to have custom suction tubes made for 1/2 " then reduce to 3/8 at water seperators .. you think that is over kill

The 1/2" lines are UNDERKILL! They'll give you about 78% more flow area than the 3/8" line, but by feeding 2 engines from 1 tank you're increasing the fuel flow by 100%, so you'll still have more restriction between tank and selector valve than you'd have if you ran each engine off a separate tank with 3/8" lines! 5/8" lines (178% flow area increase!) would have been overkill! I'd check to see what size fuel lines they recommend for a 300 HP Verado. If they can feed them with a 3/8" line, you still might be ok, but the typical 2-stroke outboard lift pump, which operates off pressure pulses from the crankcase, isn't that strong, so they're pretty sensitive to flow restrictions on the suction side. I'd still recommend putting a vacuum gage between Racor exit and engine to determine how much restriction you have, and also I'd try to find out what the allowable restriction is from Mercury. The DI E-TEC motors are totally different animals from carb'd motors, so their 4" Hg limit on suction side pressure loss might not be applicable to your motors.

Wattaway - at least a total fuel blockage won't destroy your engine because it just shuts down completely. A PARTIAL blockage is more sinister because the resulting power loss is less obvious, especially on a high powered rig, where you might not even notice it until it's too late!

[martin]

Originally Posted by Bushwacker

The 1/2" lines are UNDERKILL! They'll give you about 78% more flow area than the 3/8" line, but by feeding 2 engines from 1 tank you're increasing the fuel flow by 100%, so you'll still have more restriction between tank and selector valve than you'd have if you ran each engine off a separate tank with 3/8" lines! 5/8" lines (178% flow area increase!) would have been overkill! I'd check to see what size fuel lines they recommend for a 300 HP Verado. If they can feed them with a 3/8" line, you still might be ok, but the typical 2-stroke outboard lift pump, which operates off pressure pulses from the crankcase, isn't that strong, so they're pretty sensitive to flow restrictions on the suction side. I'd still recommend putting a vacuum gage between Racor exit and engine to determine how much restriction you have, and also I'd try to find out what the allowable restriction is from Mercury. The DI E-TEC motors are totally different animals from carb'd motors, so their 4" Hg limit on suction side pressure loss might not be applicable to your motors.

Wattaway - at least a total fuel blockage won't destroy your engine because it just shuts down completely. A PARTIAL blockage is more sinister because the resulting power loss is less obvious, especially on a high powered rig, where you might not even notice it until it's too late!

Thanks Bushwacker..
I will call Mercury Guys Tomorrow. They are now in Pc doing there Testing on there motors. I have a friend who works there.. Maybe they can tell me the specs.. I will definitely put a gauge on the load side and see what i get.. I am in the process of mounting my bracket now. and then the engines that way I can see how much weight I need to move around.. Thanks again..