Mercruiser 4.3 fuel isues-gctid806151

[Trophy_25]

Hi , I have a bay liner Trophy with a 4.3 Mercruiser engine aproximitly1995.

The engine starts fine and ticks over no problem will even run the boat fine up the river (tidal) until you want to bring the boat onto the plain. 9 times out of ten it will run fine for a few mins then the engine revs just drop off and the engine dies. I then leave it for a minuet and it starts straight up again.

I have replaced the old carb with a brand new one, check the anti siphon valve check the tank pipe. fitted new fuel filter/ :evil: Ht leads new distributor starter motor oil pressure switch. The only thing I haven't replaced is the electric Fuel Pump.

I was going to try running it next from a separate fuel Tank.

Any Suggestion would be great and most appreciated as its driving me insane.

[GearGuts]

Sounds like your fuel system cant supply enough fuel for high load. Can be caused by a few different things such as , Fuel filter partially clogged, fuel lines collapsing internally, faulty or dirty tank check valve, random debris inside tank getting stuck in pick up tube or a partially blocked tank vent line. A boat over 20 years old should have the fuel system updated anyway so If I was you I would install new filter fuel lines and tank vent, then remove pickup assembly from tank and clean or replace check valve. If your fuel sender is near the pickup you can remove it and look inside the tank where the pickup goes and see i theres and debris in there. You might need to clean your tank.

[Pcpete]

Welcome Trophy 25! You have done a great job of chasing a frustrating problem. I do agree with gearguts that the problem is in your fuel system. Having had a similar problem, and assuming your 4.3 has an electric fuel pump, do you have more than the on engine fuel filter in the system? That's a no-no according to the installation instructions for the engine as Merc says it is hard on the electric fuel pumps. Is your in line fuel shut off valve fully open? That may sound silly but I've failed on that one. Did you replace yor fuel tank vent on the side of the boat? I've found that while the stainless steel vents last longer the screens can still clog. It usually showed up as giving me difficulty fueling, but occasionally it was like a one way valve. Air out while filling, very little air in while running. Frustrating? You bet!

The next test I would try would be to disconnect the fuel line at the carb, connect a hose to the fuel line and pump a bunch of fuel into something like a clear gallon or more plastic water jug. Doing that I'm not just looking at flow from the pump but water in the fuel. It could be that your new carb has nearly a bowl full of water causing too little room for fuel while on a plane. That would act similar to a clogged fuel filter. So, if you see water in the fuel, problem identified. If you have a flow problem from the tank, and your fuel lines are original, it could be they are not ethanol resistant. I think the E85 fuel started in the late '90's and those of us who were dilligent and with boats older than that had to replace all of their fuel lines. The older type lines, as I understand it, get eaten and softened from the inside and bad thing happen. Or so we were told at the time.

If it turns out you need to have your tank cleaned, you will be money ahead if the tank is low on fuel. The cost of polishing was more per gallon for me than the cost of the fuel, but the disposal would have been more yet.

Let us know how it's going, and please add some information like where you are and like to use your boat. There may be a BOC member nearby.

[Trophy_25]

Thanks Guys for all you help /suggestions I will get back to you when i have tried these out. The boat is on a mariner near the entrance to the wash in Lincolnshire its a tidal river so I have to wait for slack water each time to test the engine,I just get the feeling its the electric pump which doesn't make sense because the boat revs like hell when its out of gear.

[Pcpete]

I too doubt it's the pump itself. That's why I suggested running the flow into an open container. In my experience the flow required for an engine under load is exponentially greater than at no or very little load. I don't know about the fuel additives used in the UK, but in the US our land based fuel stations have up to 10% ethanol. On Puget Sound, around Seattle, most marina fuel is ethanol free. However, some is and our water stored boats need to have the same protection as their trailered cousins.

[Nickdixon]

Not saying this is it, but my mechanic went through a lot of the suggestions here and this is what it was:

http://www.baylinerownersclub.org/index.php/forum/bowridersskifishcuddiesdeckboats/81024-call-from-the-service-department

Don't know enough about the carbureted version myself. Just something easy to look at...engine temp.

[Ruffryder]

Nick, carbureted version does not have that feature.

T25, that electric fuel pump is fed through the Oil Pressure Switch...was that the OPS has been replaced?

Try running her with the fuel cap open,

Try running her from a separate fuel tank,

[Chief_Alen]

Vent clogged, agree with Joon ...

However I would dump the fuel,filter contents into a clear clear glass jar let sit see if you have water in the fuel.