4.3 fuel starvation

[Estarnes67]

My buddy has a bayliner 4.3 merc carbureted. Boat starts up and runs great. About a minute of wide open throttle the fuel filter runs dry and will stall. Can keep it running if he pulls back on the throttle to neutral so the filter fills back up. I can see it happen cause he installed a clear inline filter. What's going on here? Bad anti syphon vavle? Not really sure. Only thing he has done is bypassed the oil pressure switch because it would stall with it even though it has good oil pressure. Any help is appreciated as we have a trip coming up this weekend. Thanks

 

[achris]

Merc have been using the 4.3 since 1983, so WHICH 4.3? Serial number at this point would be the most helpful... Now, because you said the oil pressure switch was bypassed (and not a good idea BTW), that indicates it's an electric fuel pump.... Also, clear plastic filter in the engine bay.... Seriously bad idea. :boom: GET IT OUT OF THERE! Illegal, because they blow up boats!

Ok, After you remove that bomb from the engine bay, I would start with disconnecting the main fuel tank from the engine right at the fuel pump (does this engine have an engine mounted spin-on water separating filter?) and connecting a remote fuel tank, like those used on outboards. That will tell you if the problem is engine bound or on the fuel tank and supply lines side.

The problem with the oil pressure switch it corroded terminals, just clean them and it should be good. If not, replace it, but you really shouldn't be running with it bypassed.

But please, get that plastic filter out of there....

Chris.......

 

[Estarnes67]

I'll tell him about the filter first thing in the am. I think he did it just to see what's going on. And today we hooked the supply line to an external tank before the original hardline filter to see if the tank was the problem and the same thing happened ran the filter dry. And no fuel water separator

 

[achris]

The filter running dry indicates an air leak somewhere. Including in that filter...

Once he has the plastic filter out, get a proper water separating fuel filter kit put on. Merc do a good one.

Chris.........