Need info on my new purchase OMC 4.3L Cobra

[BoatingTimbo]

I've recently bought a new boat and can't find much by way of detail on the engine specs etc. so hoping you guys can help me fill in some gaps. The boat is an 1989 17' marlin open bow with OMC 4.3L cobra.

Can you guys help me with some details/specs:
Horsepower:
WOT RPM: 4200-4600? with 19 prop?
Engine Block: GM or Ford (i've had different people say Ford and GM)
Max Speed: I've read about guys here getting up to 50mph (i'm not)

Where's the best place to find parts on-line for this engine?

Need to know the appropriate fuel pump which my mechanic at the marina tells me is too small and the engine is starving for fuel. He's trying to source a pump but having problems!? Boat will get to about 3/4 throttle then die out until i throttle back to neutral. runs perfectly at 50-75% throttle approx. 30mph... but i want to go faster! I can't believe that it would have the wrong pump on it? Carb was rebuilt so not sure what else could cause fuel starving?

Any help would be much appreciated.

 

[IVAZ]

Re: Need info on my new purchase OMC 4.3L Cobra

Well mine is a 1988 Merc 4.3 so I cant tell you for sure what your specs are.
The Merc 4.3 with a two barrel carb is 175 hp(you did not say if you had 4 or 2 barrel). It seems OMC had higher HP in their 4.3's but Im not really certain.
Wot RPM is 4400 to 4800. I can get up to 46mph pretty easy but I never hold WOT for very long to see if it has more speed but I bet its not much more than that.
Parts can be found at the iboats store or ebay. OMC has been out of business for over 10 years and the parts are not as easy to get but, lots of guys here have them and get parts to them.
The 4.3 is a chevy engine.
Water separator should not be difficult to find.

 

[BoatingTimbo]

Re: Need info on my new purchase OMC 4.3L Cobra

thanks for that info. Doesn't seem many people run the OMC or buy boats with the OMC since they've been out of business for so long! Will be curious to hear from anyone who's got this identical motor.

 

[bruceb58]

Re: Need info on my new purchase OMC 4.3L Cobra

Your engine is a GM.

When I buy parts for OMC or Volvo I buy from these guys:
http://www.fasteddiesmarineparts.com/

read this guys site...you will definitely need it some day:
http://www.hastings.org/~stuart/cobra/

 

[Diggerpine]

Re: Need info on my new purchase OMC 4.3L Cobra

thanks for that info. Doesn't seem many people run the OMC or buy boats with the OMC since they've been out of business for so long! Will be curious to hear from anyone who's got this identical motor.

According to my Spec. Sheet, the 4.3L I have is 47 mph @WOT and 160 HP at the propshaft. I usually run my engine by RPM and not MPH.

 

[bruceb58]

Re: Need info on my new purchase OMC 4.3L Cobra

Have you replaced your fuel filter?

Could be the anti siphon valve at your tank is restrictive. You could try running the boat on a small portable tank to see if its a fuel tank related problem. Try running with the gas cap off to make sure its not a tank venting problem too.

Who rebuilt the carb? If it was something the previous owner told you I would consider ignoring that statement becuase who knows if it was done correctly or not.

 

[BoatingTimbo]

Re: Need info on my new purchase OMC 4.3L Cobra

I've replaced the fuel filter... it was bad! I didn't try running with gas cap off... that would have been good to try. My old porsche 944 had a similar problem that was solved doing this!

I've left it at the local marina shop now... problem is they don't deal in OMC much so not sure about them working on it? They told me yesterday they feel at some point someone put the wrong size fuel pump on (too small so it's starving for fuel at 75% throttle)... i find that hard to believe!? Could that be possible? Would a past mechanic be that dumb to do something like this??

 

[danond]

Re: Need info on my new purchase OMC 4.3L Cobra

What? Take your boat somewhere else. You don't want your mechanic guessing at what's wrong then spending your money to diddle around.

There's no way for them to diagnose your boat as having a "small fuel pump" by looking at it or listening to you. That's just dumb of them to even speculate. Does he even know what that means? I sure don't.

Did he check timing? Distributor cap/rotor/plugs? Carb adjusted properly? Throttle adjusted properly? Is the prop the right size/pitch? Is it bent? Is the boat full of water (under-sole foam can definitely absorb water)? Plugs OK? Compression OK? on and on.

I have an OMC Cobra, I can speak from experience I think. Here are your steps:

1) get an original OMC service manual. Find them on ebay.
2) read it, cover to cover, repeatedly
3) learn to service your own drive and engine.

If you plan on keeping this boat, 1, 2 and 3 are a MUST. If you want a "take it to the mechanic and they'll know what to do" boat, sell this one and get one with a Mercruiser drive.

Don't get me wrong, OMC Cobra drives are fine to run if you can service them yourself or have a local marine mechanic who knows and enjoys OMC. If not, you're screwed. Your mechanic is going to break your stuff and you'll be left with the bill.

 

[bruceb58]

Re: Need info on my new purchase OMC 4.3L Cobra

i find that hard to believe!?

Me too!

You need to systematically test out what you have. First step would be to run on a small portable tank.

What do you mean the filter was bad? Was it full of water or other junk? If so, it is very possible your tank is still full of the junk that caused the filter to get clogged in the first place.

 

[bruceb58]

Re: Need info on my new purchase OMC 4.3L Cobra

2) read it, cover to cover, repeatedly

LOL

I am curious...how long does it take to read the OMC manual cover to cover? Maybe Oprah should assign it to the book of the month club!

 

[danond]

Re: Need info on my new purchase OMC 4.3L Cobra

About a week of evenings. Yes, I've read mine. I can't stand not knowing what I'm dealing with.

If someone died in the manual, anywhere, or got cancer, I think it'd be up there! NYT best sellers list, either way.

 

[Schmoe]

Re: Need info on my new purchase OMC 4.3L Cobra

If your engine is dying out, then it's an engine problem. You have a 4.3L engine, you have a GM engine. Find a good GM mechanic......

 

[bruceb58]

Re: Need info on my new purchase OMC 4.3L Cobra

You don't need a GM mechanic. You need someone with basic troubleshooting skills.

 

[BoatingTimbo]

Re: Need info on my new purchase OMC 4.3L Cobra

Ya, I need to get much more informed when it comes to this engine.

the fuel filter had a lot of **** in it. when i dumped out the fuel the top was fuel colored then it got pretty slimy and very brown with small junks. I'll pull it off again and drain to see how bad it is.

the motor runs like a top, idles cold perfectly, shifts like a dream... just bogs down at 75% throttle. I'd like to see if i can get it working but a little sketched out by a non-standard set-up that my local marina and shops in my local vicinity don't often work on!

 

[danond]

Re: Need info on my new purchase OMC 4.3L Cobra

Another note - Bombardier owns OMC parts now. Find a Bombardier dealer and you'll be able to walk up to the counter and order parts.

 

[bruceb58]

Re: Need info on my new purchase OMC 4.3L Cobra

The fact that this is an OMC is not going to be your problem here. What you are having problems with is common to all type of engines.

Your big clue was the condition of the fuel filter. When you take it off again, dump its contents into a glass jar and see what you have in there.

 

[BoatingTimbo]

Re: Need info on my new purchase OMC 4.3L Cobra

i definitely will check out the filter again.

I've done the plugs, rebuilt the carb completely, replaced fuel filter. Didn't feel timing needed adjusting, or distributor or wires replacing but i'm no mechanic??

 

[BoatingTimbo]

Re: Need info on my new purchase OMC 4.3L Cobra

so i'm more informed when I head down to the shop this evening can someone fire me a link to the appropriate fuel pump so i can see the size of it and know how much i can get one for on-line.

Just got off the phone with them and they've put a bigger fuel pump on that they had in the shop (from what i don't know but not OMC) and will be putting in the water to take for a rip and test if that solved the problem. they said it was starving for fuel b/c someone put the wrong size pump on...

if the correct pump was actually on it i don't want to be charged for something i don't need -- and want to find the real cause of the problem.

thanks so much for your help on this guys and educating me on this set-up.

 

[BoatingTimbo]

Re: Need info on my new purchase OMC 4.3L Cobra

After ruling out possible causes by checking/replacing/rebuilding (below list) the stall out problem from fuel starvation is still happening!

have:
- rebuilt carb (double)
- replaced fuel filter and cleaned out twice... more junk coming through.
- replaced all plugs
- hooked up external fuel tank, tested, still same problem
- ran with fuel cap off
- checked for vacuum leak in/around carb
- put larger fuel pump in

Talking to the mechanic he feels he's ruled everything out and replaced/tuned to a point the only remaining thing is replacing the carb all together.

What do you guys think. Is it worth upgrading to a 4 barrel and this being the excuse. Will that solve my problem (boat stalling out at 75% rpm)??
how much for a 2 or 4 barrel carb? can i find a good one used somewhere or better just to buy new? Does it need to be OMC or could it be GM?

 

[bruceb58]

Re: Need info on my new purchase OMC 4.3L Cobra

I know its been a few days since you posted but you definitely need to check your timign next. Not only do you need to check to see where it is at idle but also what its complete advance is. If your distributor is not advancing completely(stuck weights), this could also be your problem.