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1987 OMC Seadrive 150hp crossflow v6 fuel probl;ems

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MikeSnider

New member
I have a 1987 OMC Seadrive 150hp 90 degree crossflow V6 I've been having problems at low idle or speed keeping fuel pressure, have been through all the carbs and manual fuel pumps cant find any pin holes in diaphragms, screens are clean and no leaks visible after putting all new fuel lines on motor. also has a new primer bulb, but every time I stop the boat I have to pump the ball again. So I've decided to put an electric inline fuel pump in, with a fuel pressure regulator and gauge. I've found 1 forum that says the carbs need 2.5 psi fuel pressure I just wanted to check on that pressure and get other suggestions or advise, thanks Mike.
 
(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

NOTE: There has been cases when the output valve in the fuel primer bulb would come apart, and the inner portion of the valve would actually reverse itself and be drawn back into the primer bulb's output valve body. This in effect would create a shut off valve and result in a fuel restriction. If this is the case, you should be able to feel something laying in the bottom of the primer bulb when held horizontally.

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no this power head doesn't have that valve, I'm new to boat motors, but have been a mechanic for 30 yrs so I got the basics. this motor the fuel line comes up through the cowling straight to twin fuel pumps which are pulse driven from the block, I have taken both apart and cleaned them, the diaphragms both look good held up to the light and no pin holes can be seen. So I reassembled everything put a new primer bulb, and fuel filter in, it ran better this time but at lower speeds I lose fuel pressure, so I'm thinking the impulse from the block is possibly not strong enough for the pumps at low rpm, or the pumps are getting worn out. So I'm wanting to just put an electric in line fuel pump on it with a fuel pressure regulator and gauge. Will that work? and if so what pressure is needed at the fuel rail/tube?
 
I'm well aware of the design of that powerhead. I was working with OMC before they were even thought of and have rebuilt two or three of them since their manufacture. Why are you talking about the powerhead?

Re-read my reply above... two very short paragraphs, then a statement in the 3rd paragraph states "Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve." This is where I'm telling you that the Anti Siphon Valve would be... NOT at the powerhead area but rather at the built in fuel tank!

We're taking the time to give you advice, knowledge that we've obtained over the years in the marine line, in particular the OMC Evinrude and Johnson engines and you're simply skimming through it, then going off on your own thoughts of what it might be.

Think about it..... If you need to refuel your engine every time you shut it down, where is the fuel going that was there a such a short time ago ago? It didn't evaporate or dump itself into the water so where did it go? The logical explanation is that it siphoned back into the tank.

You state in the second line of your explanation... "every time I stop the boat I have to pump the ball again.". That pretty well spells it out. Why are you re-working the fuel pumps? If the engine runs, obviously the fuel pumps are doing their job.
 
There is not a fuel tank built into this motor it has a fuel line coming from the main tank primer bulb, fuel filter then straight through the cowling into the manual fuel pumps. has brand new lines, new primer bulb with anti siphon valve built in and new fuel filters. so back to my simple question of i want to put in an electric fuel pump with pressure regulator, will it work and what pressure should it be set at? I read and re-read the entire response the first time but my motor does not have the parts you are referring to. Thanks mike
 
sorry just read again unless you mean the anti siphon valve is at the Main fuel tank connection, which in this case i can't get to without removing my T top and center console then removing the floor panel, which is a big pain in the ass, so once again back to my original thought of just installing an electric pump so when i turn the key on i have automatic fuel pressure.
 
My question would be where is the fuel going that is in the float bowls at shutdown? Would it siphon from the carbs, thru the pumps, thru the bulb, all the way back to the tank? I don't have a primer bulb on my V8, the tank fitting is just a straight thru connection, but I have enough gas left in a small coil of gas line that the pumps will pick it up and start the motor. That's even after tilting the motor for trailering and emptying the float bowls by tilting the motor.
 
What brand primer bulb? Don't buy WalMart fuel lines/bulbs (not saying you did). "New" doesn't always mean "good". Put a quality primer bulb on it (new Merc style), you may have a bad check valve in your bulb.
 
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