'85 OMC 3.0L not running right past half throttle

[F14CRAZY]

Hi guys, first time poster

I recently purchased a 1985 19' Bayliner Capri cuddy cabin with the 3.0L OMC. It was running great until a couple weeks ago...

It seems to be okay when cold but it's hard for me to say because I don't like to run engines at higher RPM when not at operating temp (I wish my tach was working BTW). But when warm it runs fine until you run it to about half throttle. Above that, the engine will miss/sputter with little increase in power/speed/RPM. If you leave it there for a moment, which can be a few seconds or like a minute, it'll suddenly clear itself up and run great. You can vary the throttle and it'll be fine unless you get it below about half throttle, and from there you have to let it miss for a moment and wait until it "clears itself up" again.

I haven't changed anything for this to happen.

My spark plugs are in great shape. I've replaced the wires. Distributor cap and rotor are in good shape (I had my dad check too cuz he worked on vehicles with distributors back in the day, all my vehicles have had coil packs). I've cleaned the terminals at the big relay/solenoid on the dipstick side of the engine. Battery, terminals, and cables aren't old and are in good shape. I've run a bottle of fuel system cleaner through it. Gas is fresh. I tested the fuel pump according to the Clymer manual and it's pumping above spec (which is 1/2 quart within 45 seconds while cranking the engine with the starter). I've cleaned and rebuilt the carb (what an awful puzzle). I've replaced the filter in the fuel/water separator. Choke is not sticking. Cleaned the air filter/spark arrestor and also ran the engine without it (engine cover off)

lol sorry to go on but I wanted to mention all the things I've done so far, and NONE of these things have really had a change. On the car message board I frequent someone mentioned that the advance weights in the distributor could be sticking, so I removed it from the engine and sprayed the internals of it with electrical terminal cleaner (what I had around) and Liquid Wrench. I'll have to try it on the water, probably tomorrow along with resetting the position of the distributor.

What's wrong with my engine? Thanks in advance...seems like this is a nice message board community

 

[chiefalen]

Re: '85 OMC 3.0L not running right past half throttle

There is a fuel screen in the fitting that goes into the carb. I would clean it.

There is a fuel screen in the fuel pump.

There is a fuel fitting in the pickup in the gas tank.

There is a one way valve called a anti-siphon valve on top of the fuel pickup.

Check if it's working or sticking.

And the fuel tank vent check if it is clear.

 

[F14CRAZY]

Re: '85 OMC 3.0L not running right past half throttle

There is a fuel screen in the fitting that goes into the carb. I would clean it.

There is a fuel screen in the fuel pump.

There is a fuel fitting in the pickup in the gas tank.

There is a one way valve called a anti-siphon valve on top of the fuel pickup.

Check if it's working or sticking.

And the fuel tank vent check if it is clear.

I will check the fuel pump screen along with the check valve on the fuel pickup...is there a screen/filter in the tank? I did clean the screen on the inlet of the carb and the vent is clear...I accidentally had some overflow come out of it the other day. Thanks for the suggestions, I'll report back

 

[F14CRAZY]

Re: '85 OMC 3.0L not running right past half throttle

Hey guys...

I removed the dip tube that goes down into the fuel tank and runs to the fuel pump...the check valve is working fine (tested with compressed air). No filter or screen there.

I opened up the fuel pump...no filter or screen there.

Tried it at the river anyway...no change. I did get the timing advance set again though.

A gentleman working on a Volvo Penta powered Bayliner of similar vintage suggested that I check the gap of my ignition points (I think I've got the terms right). I'm going to check the gap and probably try it again this afternoon

 

[Uraijit]

Re: '85 OMC 3.0L not running right past half throttle

It's probably "dwell" that he was suggesting you test.

Also, is your timing advancing as the engine's speed increases?

This sounds like a fuel delivery issue to me, but if your dwell isn't set properly, or the timing isn't advancing, that could bog you down as well...

Have you tried running the engine directly off of a gas can?

 

[chiefalen]

Re: '85 OMC 3.0L not running right past half throttle

Someone removed the screen on the bottom of the fuel pickup? I wrote fitting.

Someone took out the screen in the fuel pump?

How mush pressure the fuel pump giving you?

How about the carb you rebuild it?

 

[Uraijit]

Re: '85 OMC 3.0L not running right past half throttle

He did state that he cleaned and rebuilt the carb.

His method of testing the fuel pump seems suspect to me though...

This is why you don't use a Clymer manual...

 

[chiefalen]

Re: '85 OMC 3.0L not running right past half throttle

Maybe not fuel related. Gonna sound crazy disconnect the esa, just unplug the 2 plugs.

If a fix you can change out the esa module. Or Don s posted a wiring diagram that will make it shift like a merc.

And he did say he rebuilt the carb. I missed it got more trouble with my boat .

 

[F14CRAZY]

Re: '85 OMC 3.0L not running right past half throttle

Thanks for all the replies guys...after a chat with a fellow boater at the ramp and a mechanic down the street the problem was that the point gap of my distributor was too large. I borrowed a feeler gauge and set it to 0.018'' (Clymer says .016-.019). I ran the boat for a long while after that and its doing great.

If I have any other trouble I'll keep all the things mentioned in mind...the things you suggested may not have fixed it but that doesn't mean they won't someday