Merc 3.0 litre 4 cyl. I/O runs rough

Chiefalen,
To answer your questions in order:

The centrifical weights do move freely.

The engine never really did run perfect. To get it to run as good as it did everything had to be just right -- the ponts, plugs, carb mixture, timing, etc. Even not to get it to start sometimes i have to run a matchbook striker between the points. Or maybe just a fluke?

I didn't use new fuel. Just filled the bowl with new fuel to start it. I used startron in the tank last year and added a 10-micron water seperator because everyone was talking about ethenol problems.

The engine runs at normal temp. last year overheated maybe because of low hose water pressure. Was running worse last year.

I will try the micro switch. I wanted to disconnect the tach wire too.

Thanks -- and you are right you never know unless someone points things out to you.

...one more thing -- I replaced the fuel pump last year thinking it might be a cause, and didn't want to go out on the water with a 20+ year old pump.

And you tested it correct ? Cause it's new don't mean chit. 4-7 psi no less no more.

I didn't test it. Not really sure how to. I did adjust the carb float out of spec so that it's not flooding.

What can be done if it's too high or low?

if you bought the wrong one nothing but replace it.

Did you re-install the old pump see how it runs

No, did not install the old fuel pump. Bought it because I thought it was one of the reasons it wasn't running right.

And now your stopped throwing parts at it and want to know the real reason it isn't running right.

Smart move.

You install a gauge crank it a few times over and the psi of the pump will reveal itself.

I know guys who installed the gauge at the helm.

Ok i will re-read this whole thread again, rack my brain and try to think something up and post it, after i talk to a few guys here that have yours and my setup, i have the same motor.

Ok where in the real world are you generally ?

It's no secret i live in Manalapan NJ want the exact street and number of the house ?

I think ether you need to borrow, steal, or rent a dist. Then you need to borrow steal, or rent a carb.

Both known good working units.

See some carbs just can't be rebuilt.

I didn't see if anyone asked you if the choke is opening all the way ?

But i did see you posting that your running on old gas.

Me i would be running it on a external tank of clean fresh gas.

I would then make sure the fuel filter in the fitting that enters the carb is clean.clean, clean.

And i would make sure the filter in the fuel pump is clean,clean, clean.

No inline filter straight from the external tank of fresh clean gas right to the fuel pump. After cleaning the above mentioned filters.

Good new rubber fuel lines.

See how it runs then. Before any change up to the dist. and carb.

And make sure the external tanks vent is open.

one more trick, in pitch black darkness on the external tank of gas and of course water going to the drive, run the motor and see what sparks in the engine bay you see.

You see a spark you see a problem understand ?

Not one spark, cause that's a problem.

Located in Seaford, LI, NY.

The pressure gauge goes between the carb and the pump. Have to by pass the existing line i guess.

Coke is opening all the way.

I was always told that ethanol is a problem...

I do see a kind of dark red sediment in the filter occasionally and in the bowl. Tank filter, 10-micron water sep filter, fuel pump filter and carb screen filter and still see it! Could this be the fiberglass tank deteriorating?

Haven't tried the spark at night thing yet.

Not one spark...?

... dark red sediment in the filter occasionally and in the bowl.

Click to expand...

Varnish from old fuel; it begins to deteriorate after about 30 days. A filter only removes sediment before it in the fuel system. Use a stabilizer w/each fill up to reduce fuel degradation.

rust in the tank.

Crank the bow up on the trailer. Remove the fuel pickup tube. It unscrews from the tank. check to see if the one way valve is working good and not clogged up. It is the fitting that enters the tank. The fuel pickup tube might have a screen on the bottom, it clear the tube and screen?

Stick a hose into the back bottom corner of the tank and suck all the gunk and junk and water off the bottom of the tank maybe a soda bottle full.

When you leave that soda bottle sit for a while you will see all the chit on the bottom of the bottle.

Very best friend of mine lives near you.

All you need to do is hook the gauge with a short hose to the fuel pump and crank for a few second will give u the pressure.

Also check the clear return line to the carb it maybe yellow now, it have fuel in it ?

Last year I did suck the last few gallons out of the tank with a hand pump thu the hose to the fuel pump. I'll try tilting it back, check the valve, etc.

One side to the fuel pump and the other side of the hose open?

There is no gas in the yellow hose. I guess that's an overflow to the carb?

With new carb parts and after cleaning, adjusting and installing the carb, I put clean fresh gas into the bowl to get it to start right away and it doesn't. When it finally does it runs like crap and SOMETIMES I can screw the mixture adjustment in all the way and it still runs -- bad of course. Can this be anything but the Merc-Crap itself?

yep my guess the carb.

Do you or anyone out there think it might be the venturi assembly that may be bad or clogged (that's the 4 brass tubes that are pressed into a die cast aluminum base; fastens with 3 screws)? I put a fine wire thru the holes but may be varnish instide. That would be a last resort 'cause everything else on the carb gets replaced with the carb kit parts.

The venturi needs to be clean. Soak it in carb cleaner and blow out the passages w/compressed air.

In the past I have spayed it with carb cleaner and have blowned it out with compressed air, to no avail. Have to get non-aresol can of carb cleaner to poure and soak it I guess.

There's not much else in the Merc-carb to replace, other than what's supplied in the carb kit -- just 3 castings.

Anyone know where to buy the venturi ass'y?

VENTURI 3302-9810

It's sold here for $40. Put the part # in above.

I would put it in a 1/2 pint jelly jar filled w/lacquer thinner, cover w/a lid and soak it overnight, blow it out and repeat if necessary.

I bought a venturi ass'y on the internet for $10.50 in the Mercruiser box with the right number. It looks okay. I will try it this weekend and see if it works. It looks new with a few minor burrs on the surface.