Iron Duke not running right

[F14CRAZY]

Hey guys it's actually the engine in my boat but since it's pretty much just a big GM 2.5L I4 (in OMC 3.0L form) I thought I'd post here before a boat message board...

I wish my tach was working but the engine starts and runs great from idle to about half throttle. Above that you can set the throttle anywhere and it'll "stumble" or "miss" for a while with little gain in power/RPM. After a moment, which can be a couple seconds to a few minutes, it'll suddenly "kick in" and accelerate appropriately to where the throttle is set and it'll run great. Spark plugs are good, wires are new (no change) and I've cleaned the screen in the carb inlet and the filter in the fuel pump. It's carb-ed with a distributor ignition. I pulled the cap off and my dad inspected the contacts, rotor, etc and from his old school experience it all looked fine in there.

Thanks guys

[KillerMRK]

Well the issue is here is that it's an old OMC motor. Get rid of that thing before it costs you any more than it has. :P

[bouda]

Wouldn't hurt to check out the carb.

[Smaart Aas Saabr]

sounds like she's starving for fuel, how is the fuel pump on that? (electric?)

[F14CRAZY]

That's what I'm thinking too. I picked up a carb rebuild kit today and will work on that this weekend. The fuel pump is mechanical/vacuum from what I know

Well hey at least it's kind of a GM motor

[Dave B]

That 3.0L marine motor is a real good bulletproof motor and good on fuel (for a boat).

I'm guessing you checked/changed the fuel water seperator.

One other thing to check is the selonoid for tight and clean connections. It should be mounted on a bracket on the spark plug side of the motor towards the left rear looking at the motor from inside the boat. If it went totally bad then it wouldn't start, but if there is a bad or rusty connection, it might be acting up under a load.

[GMCSonoma]

Originally Posted by KillerMRK

Well the issue is here is that it's an old OMC motor. Get rid of that thing before it costs you any more than it has. :P

What???

Originally Posted by Dave B

That 3.0L marine motor is a real good bulletproof motor and good on fuel (for a boat).

I'm guessing you checked/changed the fuel water seperator.

One other thing to check is the selonoid for tight and clean connections. It should be mounted on a bracket on the spark plug side of the motor towards the left rear looking at the motor from inside the boat. If it went totally bad then it wouldn't start, but if there is a bad or rusty connection, it might be acting up under a load.

This is excellent advice...thanks for posting such...

[doh]

I would also check the exhaust flappers.

And there is a fuel filter at the carb as well as one in the water seperator.

[F14CRAZY]

Thanks again guys. I did clean the little filter on the inlet of the carb but I'll check the one in the water separator again...I was in a bit of a hurry when I did it and it was almost midnight (lol)

I think I know the big solenoid you guys are talking about, looks a lot like a typical Ford starter solenoid. Is it for the main power?

deh, exhaust flappers? I'll have to check my Clymer's manual on those...

[doh]

They are flaps on the exhaust riser, to prevent the back wash of water up the exhaust manifold, into the engine.

They can stick causing excessive exhaust back pressure.

It sounds like the Fuel/water separator though, if your Dad did check the spark advance weights in the distributor.

I have seen hole in the fuel pickup line in the tank cause all sorts of problems before though, the engine would run fine until it got to about 1/2 tank then run horrible.

[F14CRAZY]

thanks doh, I'll look into that too. I think I know you you mean...on the right rear of the engine there's like a 3'' pipe running down with a rubber Fernco coupler below a double 90. I have a tiny seep at that gasket anyway so it wouldn't be a bad thing to take it off and take a look in there at these flaps you speak of if it isn't the carb, fuel filter/separator, or connections at the solenoid

[doh]

It looks something like so.

http://www.anthonybradley.plus.com/IMG_3463.JPG

But the picture is from a Merc Cruiser

[F14CRAZY]

aye thanks for the pic

[F14CRAZY]

Hey guys...

Last weekend I installed a new filter in the water/fuel separator and tested the fuel pump in accordance to the Clymer manual and the fuel pump is working fine.

I decided to go ahead and use the carb rebuild kit I picked up and whipped it in a couple hours...what an awful puzzle to put together but I did get it back together and tried it out on the water again...NO CHANGE at all.

I read through my Clymer manual and can't find any info on the so called exhaust flappers...do OMC's not have them? I removed the big water cooler exhaust elbow on the right rear of the engine that sends exhaust to the sterndrive but I didn't see any flappers in there either.

I brought up the potential problem with the spark advance weights not operating as they should with my dad and he though it would be good to check into them...I opened up the distributor (something we had not checked into before) and saw them in there. They seem free but I sprayed the heck out of them with electrical contact cleaner and then Liquid Wrench. On the inside it appears that at least at some point the weights had come in contact with the inside wall of the distributor housing...is that bad? I couldn't tell if the weights that were present had caused the wear. It wasn't severe or anything and my dad thought it was okay but at any rate that's what I saw.

I guess I'll have to adjust the timing when I get it back on the water and see if the weights freed up or not. Any other ideas guys?

[doh]

Nope you have pretty much checked everything I can think of.

The weights were the first thing I thought of, but in the "Land of the Marine" there are many things that are abnormal, from auto tech.

E10 dislodging "Tank Varnish" for 1