Help! OMC 3.0, won't go under load

BoatinJeepr

Cadet
Joined
Jul 28, 2001
Messages
8
Newbie on this forum, hoping for some clues.<br />My brother and I have an 85 or 86 Cobia Sportster with an OMC 3.0 (GM) The boat has run great for the past few months and just up and quit on us. Originally thinking we ran out of gas, we thought some goo was sucked from the bottom of the tank. I removed the last 4 gals of gas from tank, changed all the filters, the H2O Separator, and cleaned the carb. <br /><br />The motor seems fine when there is no load placed on it, Revs and idles decent (not like it had before though). Put into gear and it craps out. It will accelerate, then bog, then accelerate, then bog. I thought it was a fuel related prob. After dealing with everthing in the fuel delivery system (Except pump) And tinkering w/ the timeing. I am at a stand still. I have experience with engines, but none with points. Every engine I've ever owned has had electronic ignition, even my dirt bikes! Could the points be causing this flux in power? Is there a way to test an engine under load with out taking it out? (Boat is in driveway, river is 30 min away). Any help is welcomed. Money is very limited so a shop is out of the question for now. <br /><br />TIA
 

prplhze65

Seaman Apprentice
Joined
Jul 9, 2001
Messages
33
Re: Help! OMC 3.0, won't go under load

DOES THAT MOTOR HAVE A CLEAR TUBE THAT RUNS FROM THE CARB TO THE FUEL PUMP? IF THERE IS FUEL IN THAT HOSE THEN THE FUEL PUMP NEEDS REPLACING. THAT IS WHAT IVE LEARNED ABOUT MY3.0. GOOD LUCK. P
 

BoatinJeepr

Cadet
Joined
Jul 28, 2001
Messages
8
Re: Help! OMC 3.0, won't go under load

yes it does have a clear tube, never really looked at it though, I think i did notice a small amount in it once, didn't think anything of it. hmm thanks. Any other possibilities?
 

skiJay

Recruit
Joined
Jul 26, 2001
Messages
4
Re: Help! OMC 3.0, won't go under load

Hey, let me know what you find out! I am just purchasing a 1988 with a 3.0 gm/cobra outdrive, so any knowledge of her would be greatly appreciated. How is it for power otherwise? You guys ski a little?<br />Thanks! <br />Jason
 

BoatinJeepr

Cadet
Joined
Jul 28, 2001
Messages
8
Re: Help! OMC 3.0, won't go under load

Power wise it was decent, I have nothing to compare it to. Other than the fact we can hear a V8 over ours at WOT. It pulled myself and my dad out of the water (not same time) and we weigh over 220# (individually). I think we have an 11/17 prop have to check to make sure. We are devestated that Pittsburgh is having once of it's nicest summers and the boat is sitting in the driveway
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. Any more suggestions are welcome. <br /><br />Thanks
 

BoatinJeepr

Cadet
Joined
Jul 28, 2001
Messages
8
Re: Help! OMC 3.0, won't go under load

anybody else have any ideas? Getting anxious to get her back out in the green wet stuff. Hey it's a river! i'm going to try changing the points and checking output of the fuel pump. (Clear filter?)<br /><br />thanks again
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MarkC

Seaman
Joined
Jun 26, 2001
Messages
52
Re: Help! OMC 3.0, won't go under load

Could be electrical: When it's boggy, and you shift it to neutral, can you rev it out of gear? <br /><br />WHen it's boggy, pull one plug wire at a time and see if it makes it run worse---you might have a cylinder missing. If so, try swapping plug wires (both ends!) and plugs to see you can make the problem move to another cylinder. Get a manual, and do the tests it recommends for the ignition system (you may have a bad coil, or bad wiring somewhere reducing your ignition voltage).<br /><br />Check compression if you can, too.
 

BoatinJeepr

Cadet
Joined
Jul 28, 2001
Messages
8
Re: Help! OMC 3.0, won't go under load

yeah, it'll rev in neutral, not as well as it used too and it seems to have a miss. I'll check what you suggested and do some other trouble shooting. thanks<br /><br />I like the fiberglass hole in the water where you throw money, line I've read on the board. It goes with our Jeep moto<br /><br />Just<br />Empty<br />Every<br />Pocket
 

mrtim1

Cadet
Joined
Jul 28, 2001
Messages
19
Re: Help! OMC 3.0, won't go under load

you may have droped a flapper down the exhaust, you will get the revs with no load but underway there is to much back pressure.You will have to pull of the riser and look down the exhaust , if the flapper is gone and you can't see it you still might have to pull the leg and it might be in the exhaust bellows.
 

BoatinJeepr

Cadet
Joined
Jul 28, 2001
Messages
8
Re: Help! OMC 3.0, won't go under load

Thanks for the suggestions. The exhaust flapper, exhaust bellows? Marine engines are new to me and these are obviously new terms too. I look in the manual to see if these parts are listed with a picture and I'll figure it from there. <br /><br />The intake and exhaust manifold are one on this engine and the exhaust from what I can see comes out in a large tube up then down into the outdrive. would the tube be where the flapper be located? and down from there into the outdrive the bellows? The 180° tube has 4 bolts to the manifold, but a rubber section and heavy hose clamps to the drive. I imagine this is for flex.<br /><br />Thanks for the help
 

mrtim1

Cadet
Joined
Jul 28, 2001
Messages
19
Re: Help! OMC 3.0, won't go under load

Sorry about that, the riser comes off the intake/exhaust manifold and joins onto the exhaust pipe via that big hose with the 4 hose clamps on it . The flapper is a oval piece stainless steel coated in rubber held in place by a pin that goes through the exhaust pipe at the same level as the two lower hose clamps on the big hose.You see the hose and clamps keep the pin in place. Now what happens sometimes due to the constant flow of exhaust and water the pin rattles around in the aluminum pipe and the flapper falls down the pipe and blocks the flow of exhaust(like the banana in the cops tail pipe prank).By the way the flapper is there stop water flowing back into the engine when you slow the boat quickly.If the the flapper restricts the flow of exhaust the engine will bog down and have no power when under load , but when not under load it will seem fine.I hope this helps and sorry about the late response I don't get in till 8:00 pm and live on the west coast.<br />Good luck.
 

BoatinJeepr

Cadet
Joined
Jul 28, 2001
Messages
8
Re: Help! OMC 3.0, won't go under load

thanks very much, going down to work on it today, wish us luck! will keep posted the progress or backwards progress (congress?)
 

Liam

Petty Officer 3rd Class
Joined
Jul 8, 2001
Messages
86
Re: Help! OMC 3.0, won't go under load

Had a similar problem with my Johnson 60. Just took it out for a test last night and everything is goooooooooood! The problem was with the power pack (coil). I could go out for 15 - 20 mins and then it would bog down but never cut out. <br /><br />Hope this helps,<br /><br />Liam
 

BoatinJeepr

Cadet
Joined
Jul 28, 2001
Messages
8
Re: Help! OMC 3.0, won't go under load

I think we have it figured out Houston. after farting around with it in 90+° and 90% humidity on the front street flooding everyone out with our hose for 3 hrs. We think we've beat it. While it was running I started pulling wires from the distro cap. #2 and #4 cyl weren't firing at all. We had ourselves a 2 cyl! I tinkered with the points and got 3 to fire then all 4, but was still running like crud. Yanked the exhuast apart only to find the flapper flapping away like its supposed to. Put that back together and went got new points. We checked compression just for ****s and giggles, #1-135psi, #2-135psi, #3-140psi, #4-130psi, Manual claims 130 PSI, I figured we were close enough. and hey it wasn't low. <br /><br />I was educated that our points were burnt beyond service. Put the new set in w/ a new condensor and still ran crappy, but all 4 cyl had strong sparks. Did some quick reading in the handy manual and point gap is .019, ours was more like 1/8" I closed the gap and viola! we have ignition. Last test was to run down to the river.<br /><br />stuck her in and prayed just for luck and we took off like a banshee. We have a slight tick that may have evolved from a small section of manifold gasket that parted way during a back fire episode. that was cool at night. any way it's running like she was and a new gasket is in the works. <br /><br />Thanks for all the help and I'll recommend this forum to anybody who asks me a boat question. <br /><br />Once again thanks! BoatinJeepr °| || ||°
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mrtim1

Cadet
Joined
Jul 28, 2001
Messages
19
Re: Help! OMC 3.0, won't go under load

good to here you got it licked , happy boating.
 
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