fuel tanks
 

Okay here's the scoop .. I have two 75 gallon tanks with 3/8" pickups... I am going to run twin150 s on my 23.. My question is can I run both engine on one tank at a time and if so how do I valve them... I have two fuel separators for each engine. I need your input guys.. Thanks Martin
PS there is only one pickup in each tank

I have two pick ups on each tank and two fuel filters. So one line comes from each tank to rack fuel filter. This is my setup. I'm not sure how the best way to set it up with one pickup per tank?

Two pickup from each tank would ideal. But i only have one... I see you have two valves and anothernipple on the top what is that for.. Are you running twins ? Are there two picup tubes or just one with a y manafild

One valve is from each fuel tank and the single nipple goes out to the motor. I have two filters that look like this. I am running twin 150's. I have two pick up tubes in each fuel tank.

this is how I did My 25, I put a shutoff valve on the line from each tank and 1 in between on a cross over line, all on a panel in the rear compartment, I can select which tank I want to run off of , port , stb or both, I put the seperators on the line going to each eng
heres a digram of it{sorry for the crude artwork)

This is the way my set up works...single engine two tanks... you can get the general idea and just adapt for twins.

Attachment 6968

Your bilge is too.....wait, way too clean!!! :)

thanks guys
 

Bilge rat. What size line are you feeding the twin150s.. I was concerned with not being able to feed each engine with the proper amount of fuel... I have twin150 carb..98 model's

Do I understand your proposed filter setup correctly - 2 filters in series between the tank and EACH engine? Seems that is just adding additional restriction on a setup that may already be marginal, trying to suck enough fuel for 300+HP through a single 3/8" line and 4 filters. You're probably OK because they're older carb'd engines that run a fair amount richer than the newer low emission DI 2-strokes and EFI 4-strokes. All the "clean tech" motors are lean enough that there is very little margin for any fuel starvation! Leaning out a cylinder dramatically increases combustion and piston temperatures, leading to scuffed pistons and scored cylinders if not outright piston failure. E-10 gas burns even hotter because of the extra oxygen content of the ethanol, so I'd definitely try to avoid running E-10. Your engine setup is particularly vulnerable to excessively lean operation because you'll have enough power on that rig that you might not notice a slight reduction in output due to a leaned-out engine until it's too late!

You can do several things to minimize fuel restriction and risk with this setup:
1. Use only one Racor type filter per engine. (An additional on-engine filter is OK as long as it's downstream of engine lift pump. You could run a 10 micron filter here and a 30 micron Racor to minimize restriction on suction side of pump.)
2. Carefully check all fittings to make sure the internal passages are drilled out to 3/8". Years ago I heard of a boat that failed a couple of powerheads because one of the 3/8" elbows in fuel system was only drilled out to 1/8" internally!
3. Minimize use of 90* elbows; use 45* fittings or straight fittings and extra hose instead to avoid tight radius turns in the fuel flow path.
4. Tee in a temporary vacuum gauge between last filter and engine, and check vacuum reading at WOT. Also use some clear hose on the fuel side of the "T" to check for air leaks. Don't know how much restriction Merc allows in boat's fuel supply, but BRP specifies a Max Allowable pressure loss of 4"Hg for the E-TEC's, so you should be OK if you don't exceed 4" on a carb'd motor.

3/8 line, haven't tried to run both on 1 tank yet but it should handel it

Thanks

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!!!!

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!

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..