Engine Tune Up Question

[thisuldoit]

Ok. I got the new distributor and PROPERLY tightened it this time. The spark plugs are all seated and tightened correctly and are attached to the correct wires. I can now start the boat, but after about 10 seconds it dies in idle. If I start in throttle only it starts up, runs a little rough, then smoothes out, then dies. If I try to give it more throttle, I get a hissing sound from the carburetor and it dies immediately.

 

[Reel Poor]

Re: Engine Tune Up Question

You didn't mention what your working on but it sounds like a fuel issue (lack of) to me.

 

[thisuldoit]

Re: Engine Tune Up Question

Sorry about that. It is a Mercruiser 4.3L, 175 horsepower, V-6, GM engine.

When I pump the throttle with the engine off gas does squirt in the carburetor as it should. Could this be a bad feul pump and if so, how do I test this?

 

[Don S]

Re: Engine Tune Up Question

What year??? Electric or mechanical fuel pump?

 

[thisuldoit]

Re: Engine Tune Up Question

The boat is 1989 and it is a mechanical pump.

Thanks!

 

[Reel Poor]

Re: Engine Tune Up Question

When I pump the throttle with the engine off gas does squirt in the carburetor as it should.

Will it pump gas immediately after it dies?

 

[thisuldoit]

Re: Engine Tune Up Question

I do beleive that it was pumping gas immediately after it shut off.

 

[Reel Poor]

Re: Engine Tune Up Question

Disconnect the throttle linkage from the carb so you can work the throttle at the engine. With the engine running, cautiously look in the carb and see if it's getting fuel (as it bogs down). As you give the carb some gas and it starts to bog try lightly choking it by hand. If it's lean this will enrich it and should help the way it runs (unless you choke too much or not enough, play with it). If it does it's most likely a carb problem.

 

[Coors]

Re: Engine Tune Up Question

Wear protection when looking down the carb; I lost my eyebrows, ONCE.

 

[thisuldoit]

Re: Engine Tune Up Question

Ok. I was incorrect. When I pump the throttle there is no gas squirting into the main chamber. I am assuming that it should be visible squirting through or just beside the Venturi jets. I have tried pumping the throttle (boat off) several times in a row and I am not getting any squirtting. I recenlty rebuilt the carburetor, so I am wondering if I put something together wrong. I did test the functioning of the carburetor by filling the bowl before I put it on the boat, and it was squirting gas into the chamber just fine.

Thanks!

 

[Reel Poor]

Re: Engine Tune Up Question

You need to do this test.

Testing Your Fuel System

 

[Robj]

Re: Engine Tune Up Question

With a fuel pump, I consider it a wear item. On my boat that I am working on, I do not know how old the pump was, but it may have been original, 15 years old. I haven't even run the engine yet, but I already changed the pump, it is a mechanical pump, identical to a GM pump. It cost $60, my logic to change it was it is cheap, and they do wear out, a leaking diaphram can be more serious in a boat than a car. If I were in your shoes, and the pump is old, I would just change it to see if it resolves your problem. Based on your description I think it will.

Have a great day,

Rob.

 

[89Winner]

Re: Engine Tune Up Question

[QUOTE/a leaking diaphram can be more serious in a boat than a car. [/QUOTE]


This is so true. This is why it is important to inspect the fuel pump vent hose that runs to the carburetor. This is to route the fuel and lets it dump into the carburetor instead into the floor of the engine compartment in case of a fuel pump diaphram failure.

 

[thisuldoit]

Re: Engine Tune Up Question

The vent hose is clear of gas. I am going to do a pressure test, and am going to change the pump. It is old and has corrosion all over it.

 

[thisuldoit]

Re: Engine Tune Up Question

Ok, now I don't want everyone to laugh at me at once, but I thought I better own up to it. It seems that the problem was that I put the filter between the fuel inlet nut and the carburtor in backwards. The carb was getting just enough gas to start, but was being starved under load. The old fuel pump was fine, but I bought a new one, as it was only $60.00 and I figure it will go eventually.

Thank you to everyone who helped with this. As of right now my boat is all put back together and appears to be running fine, save a rough idle issue, and I think that is simply an idle mixture screw adjustment.

Thanks,
Luke

 

[njlarry]

Re: Engine Tune Up Question

Hey Luke we can only laugh WITH you. Glad you found the problem and thanks for sharing the outcome with us. I learned a lot following the discussion.