Starting problem when gas is low

A

aeromick

New Member
May 16, 2011
11
Dublin Ireland
Boat Info
1996 Sea ray 290 Sundancer. Twin engine4.3 V6 petrol/gas.
Engines
Mercruiser 4.3 V6, Alpha 1 drives
290 Sundancer, 4.3L Mercruiser twin. Port engine is difficult to start when the gas tank drops below half full. It is a fuel starvation issue as I found that pumping the throttle will not result in the acceleration jets sending fuel into the carb. If I pour a little gas into the carb the engine will start and run perfect and will start no problem for the rest of the day. I tested the inline electric fuel pump and it's working fine. Anybody any suggestions where I should look next? :huh:
Thanks in advance.
mick
 
Filter has been replaced a couple of times, this prob is going on for at least a couple of years. I have the boat out for some other work at the moment so I'm trying to get to the bottom of it. When I ran some tests, I get full bore fuel flow from the pump to the carb. It's as if the fuel line goes empty when left for a few days and the pump cannot draw the fuel from the tank because of the air in the line. I always get it started but sometimes it takes 10 minutes.
mick.
 
How is your vent lines? Could there be a spider in your vent line? If you fuel tank vent is clogged you might have these symptoms...
 
Interesting theory, I'll check that out. I presume the idea is that the fuel is been sucked back after I stop the engines. I don't think it will be the problem because I can leave it for 4-5 hours and it will be easy to start, it's when I leave it for 4-5 days I have the problem again. Also when accelerating with full power and cruising I never have a starvation issue, I think if the vent was blocked it would show other symptoms.
 
Check the carb on the port engine. Sounds like the bowls are leaking. 1 dows it start easlily if you pour gas in the carb before starting? 2. Can you swap the carbs to see if the problem moves to the starboard engine? This will narrow it down a bit.
 
Thanks for the replies,
Scoflaw, how can I check this or is it possible to check. When the fuel line leaves the tank it's at the top, it then goes down into the bilge and up again into the filter then up again to the carb. Would it make sense if the line is full when the engine is stopped could it then drain back to the tank because of a hole in the pickup line?
sdarc: I have no fuel in the line to the carb when I'm trying to start it. If I pour gas into the carb, it starts up straight away and once it runs for more than about 3-4 seconds it will keep running and I'm good for the day. I know it's not the carb.
My thoughts are that the fuel line needs a non-return valve, there is a valve where the fuel line come out of the tank with a small rotary knob for open and closed but I don't know if it does anything else. This valve does not show on the Searay parts catalog. Maybe it's a Mercruiser part I'm not sure. Is it possible that the fuel could evaporate from the carb and then the lines to leave them dry over a few days? Is there supposed to be a safety device to stop the fuel flow in case of a leak....is this also a non-return valve. Where is it on the 290, I can't find it.
Thanks to all and keep the ideas coming, we'll figure it out yet.
Mick.
 
Aeromick I think Sdarc had a good idea... swap the carbs what will it hurt? It sounds like an air leak the let's the fuel flow back into the tank and the fuel pump takes so long to get it back over the distance... once ran for a few seconds the vacume will assist the pump and get the fuel to the carb... I am not a carb expert but I've chased these types of problems before...
 
aeromick said:
Thanks for the replies,
Scoflaw, how can I check this or is it possible to check. When the fuel line leaves the tank it's at the top, it then goes down into the bilge and up again into the filter then up again to the carb. Would it make sense if the line is full when the engine is stopped could it then drain back to the tank because of a hole in the pickup line?
sdarc: I have no fuel in the line to the carb when I'm trying to start it. If I pour gas into the carb, it starts up straight away and once it runs for more than about 3-4 seconds it will keep running and I'm good for the day. I know it's not the carb.
My thoughts are that the fuel line needs a non-return valve, there is a valve where the fuel line come out of the tank with a small rotary knob for open and closed but I don't know if it does anything else. This valve does not show on the Searay parts catalog. Maybe it's a Mercruiser part I'm not sure. Is it possible that the fuel could evaporate from the carb and then the lines to leave them dry over a few days? Is there supposed to be a safety device to stop the fuel flow in case of a leak....is this also a non-return valve. Where is it on the 290, I can't find it.
Thanks to all and keep the ideas coming, we'll figure it out yet.
Mick.
Click to expand...

It's part of the fuel pump Mick. There is no safety device incase of a leak. The fuel pump runs when you have ignition and the oil pressure switch (5psi) closes or the alternator has an output.
If the non return valve has failed it makes them hard starting as you need 5psi of oil pressure + the time it takes to fill the line + the time it takes to fill the carb bowl before you get any fuel where it counts.
If the motor stalls out un observed the oil pressure switch will open and shut off the fuel pump.
One of the guys here added a non return valve instead of changing the fuel pump and said this didn't work... the only fix was to change the pump. $280 ouch.
 
Thanks again guys.
Annie I think you might have got it, what I'll do is change over the fuel pumps first and see if the problem jumps to the other side. If that doesn't fix it I'll try what Pyrojodge suggests and switch the carbs. My not so much a problem - problem that I have at the moment is the gas tank is full and the boat is out of the water for other work, so testing will have to wait for a month or two. Thanks to all for their help and I'll get back with the results when available..
Mick.:smt038
 
sdarc said:
Check the carb on the port engine. Sounds like the bowls are leaking. 1 dows it start easlily if you pour gas in the carb before starting? 2. Can you swap the carbs to see if the problem moves to the starboard engine? This will narrow it down a bit.
Click to expand...



+1:thumbsup::thumbsup:
 
For those of you who helped, the end of the story, due to another problem I replaced the two carbs, she now starts first time every time. Thanks all.
Mick.
 
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