OMC Cobra Information

[elizenby]

Hello,
I recently acquired a 98 Four Winns 225, also first time owning a larger sized boat. I am for sure new to the inboard/sterndrive type boats. (Had a small stratos outboard fishing boat). Anyways just trying to get some information on the engine and drive.

Engine:
OMC Cobra
Model - 502BPBYC
Hour Meter says 790.9
My guess is a GM since Distributor is in the rear of the engine
Does appear that the intake manifold has been changed at some point. Appears to be a newer Edelbrock of some kind.

Drive:
Volvo Penta
Model - 3868856
(From what I can tell appears to be an SX-C2)

Boat runs great after warming up a bit, seems to have good power. Took it to a local shop and they did a tune up (new plugs, cap, etc..) and checked compression. Had 6 people in it last weekend and it seemed to get out of the water ok and go on plane. Honestly for the little I paid if the boat last me three of four years I'll be happy.

My Questions:
Is this a 5.0 or 5.7 liter engine. Im guessing 5.0 with the model number beginning in 50.
Is it actually TBI or are they carbs
Any chance they still have owners manuals for these somewhere haha?
Is there any common knowledge about these engines I should know about?

Sorry for all the questions. Just trying to get a good understanding of what I got.

Thanks in advance!

 

[Lou C]

That's a Chevrolet 5.0 with a Holley 2bbl carb, nothing out of the ordinary about them, but if you anticipate freezing temps you must manually drain all the water out of the engine and exhaust system. There are two drains on the engine block, one on each side, lower midsection area, and each exhaust manifold has a drain, it could be on the end of it where you can't see but you can feel it, or you can disconnect the hoses at the connection at the front of the manifold. Someone added a throttle return spring that is not used on boats, not sure why but I noticed that. I'm thinking someone has been inside that engine before since the intake was replaced and there is some writing on the front of the block "bore...." not sure what to make of that but if it runs well, doesn't burn oil and there is no water in the oil it may be just fine.

 

[elizenby]

That's a Chevrolet 5.0 with a Holley 2bbl carb, nothing out of the ordinary about them, but if you anticipate freezing temps you must manually drain all the water out of the engine and exhaust system. There are two drains on the engine block, one on each side, lower midsection area, and each exhaust manifold has a drain, it could be on the end of it where you can't see but you can feel it, or you can disconnect the hoses at the connection at the front of the manifold. Someone added a throttle return spring that is not used on boats, not sure why but I noticed that. I'm thinking someone has been inside that engine before since the intake was replaced and there is some writing on the front of the block "bore...." not sure what to make of that but if it runs well, doesn't burn oil and there is no water in the oil it may be just fine.

Thank you for the information! I took it again this last weekend, and the only thing I noticed was that it doesn't really like to idle without stalling unless it's warmed up, but after that it runs like a champ. My shop did say they would like to "deal" with the manifold since its not what they recommend. Im going to take it back here in the next couple of days to get winterized so ill probably just have them take care of it (after I figure out what "deal with it" means.

Thanks again for the information you provided!

 

[Lou C]

well what did they mean by that? I'm just wondering why the original cast iron unit was changed since unless you are in salt water they last nearly indefinitely unless the engine wasn't winterized. There is nothing wrong with an aluminum intake as long as it is a marine unit that has brass lining for the water ports that connect the cyl heads with the thermostat housing. If it isn't and is corroding internally then yes it should be changed to either a cast iron unit or a correct marine aluminum intake. I prefer cast iron because they are more durable in some ways, but aluminm can work just fine, many muscle cars and hot rods using Chevy small block power have Edelbrock alumium intakes but these all run antifreeze with corrosion inhibitors not raw water cooling as in most boats.

Your Holley carb has an electrically heated choke valve. The way it works is that there is a bimetal spring inside the round black cover you see on the left hand side of the engine as you face it looking toward the stern of the boat. The spring contracts with a cold engine and that closes the choke valve. Then when the engine starts a vacuum operated linkage pulls the choke open a fraction of an inch so it gets enough air to keep running. Then the electric heater gradually heats the spring and it unwinds making the choke plate fully open, usually within 3-5 min of engine operation. So if its stalling cold it may not be closing all the way, or the vacuum pull off may not be opening the choke slightly right after the engine starts.
A lot of people who did not grow up with cars that had carbs have a hard time understanding old style carbs with chokes. EFI does all the work for you!
One big difference between an auto and a marine carb set up as far as the choke goes:
auto choke on a car, has a fast idle cam, so you floor the gas pedal all the way before starting, this allows the choke to close and also sets the fast idle via the fast idle cam/linkage because a cold engine needs a fast idle when running with the choke partially closed (like 1500 rpm).
on a boat this would be a safety hazard so there is the same auto choke but no auto engaging fast idle cam. So the user must set the fast idle manually by either pulling the throttle lever out to dis-engage the shift system (older OMC and Volvo controls) or pushing the button in the middle (newer Volvo and Merc controls). You then open the throttle all the way 1-3 times depends on the engine then set it at about 1/3 advanced, this will set the fast idle so the cold engine can stay running. Let it warm up about 5 min and then reduce your idle to normal by bringing the control to the idle (center) position.

IMHO you are better off with a simple carb engine on an older boat because while throttle body or MPI fuel injection has some advantages (mainly better cold starting/running) when they act up the parts are expensive and sometimes get discontinued for boats more than 15 years old. Simple Holley carb and Edelbrock carb parts are eveywhere in the aftermarket.
I have a Rochester Quadrajet 4bbl on my boat and it performs very well, I have rebuilt it a few times over the years and have all the parts needed on hand, all from aftermarket suppliers. Big market for these in the aftermarket because they were original equipment on many GM cars from 1966-1986 or so. More complex in some ways than a Holley 4bbl but once you've done one they are pretty easy to rebuild.

 

[Lou C]

PS looking closely, I think this engine has been replaced because by '98 it should have been a Vortec engine with updated cyl heads, but I see the old style 12 bolt intake vs the 8 bolt Vortec one. Not that it matters much, but the Vortec puts out about 25 more HP. As long as it has good compression, doesn't burn oil and there's no water in the oil its all good!

 

[elizenby]

well what did they mean by that? I'm just wondering why the original cast iron unit was changed since unless you are in salt water they last nearly indefinitely unless the engine wasn't winterized. There is nothing wrong with an aluminum intake as long as it is a marine unit that has brass lining for the water ports that connect the cyl heads with the thermostat housing. If it isn't and is corroding internally then yes it should be changed to either a cast iron unit or a correct marine aluminum intake. I prefer cast iron because they are more durable in some ways, but aluminm can work just fine, many muscle cars and hot rods using Chevy small block power have Edelbrock alumium intakes but these all run antifreeze with corrosion inhibitors not raw water cooling as in most boats.

Your Holley carb has an electrically heated choke valve. The way it works is that there is a bimetal spring inside the round black cover you see on the left hand side of the engine as you face it looking toward the stern of the boat. The spring contracts with a cold engine and that closes the choke valve. Then when the engine starts a vacuum operated linkage pulls the choke open a fraction of an inch so it gets enough air to keep running. Then the electric heater gradually heats the spring and it unwinds making the choke plate fully open, usually within 3-5 min of engine operation. So if its stalling cold it may not be closing all the way, or the vacuum pull off may not be opening the choke slightly right after the engine starts.
A lot of people who did not grow up with cars that had carbs have a hard time understanding old style carbs with chokes. EFI does all the work for you!
One big difference between an auto and a marine carb set up as far as the choke goes:
auto choke on a car, has a fast idle cam, so you floor the gas pedal all the way before starting, this allows the choke to close and also sets the fast idle via the fast idle cam/linkage because a cold engine needs a fast idle when running with the choke partially closed (like 1500 rpm).
on a boat this would be a safety hazard so there is the same auto choke but no auto engaging fast idle cam. So the user must set the fast idle manually by either pulling the throttle lever out to dis-engage the shift system (older OMC and Volvo controls) or pushing the button in the middle (newer Volvo and Merc controls). You then open the throttle all the way 1-3 times depends on the engine then set it at about 1/3 advanced, this will set the fast idle so the cold engine can stay running. Let it warm up about 5 min and then reduce your idle to normal by bringing the control to the idle (center) position.

IMHO you are better off with a simple carb engine on an older boat because while throttle body or MPI fuel injection has some advantages (mainly better cold starting/running) when they act up the parts are expensive and sometimes get discontinued for boats more than 15 years old. Simple Holley carb and Edelbrock carb parts are eveywhere in the aftermarket.
I have a Rochester Quadrajet 4bbl on my boat and it performs very well, I have rebuilt it a few times over the years and have all the parts needed on hand, all from aftermarket suppliers. Big market for these in the aftermarket because they were original equipment on many GM cars from 1966-1986 or so. More complex in some ways than a Holley 4bbl but once you've done one they are pretty easy to rebuild.

Thanks again Lou, very informative information. To be totally honest I don't know a whole lot about engines but I'm researching like crazy haha so I can avoid being taken by a shop and at least know somewhat about what they are talking about.

After I did a little more research it appears that I have the 305 5.0GL model of the cobra. I haven't pulled the flame arrestor off but according to what I found it should be a 2bbl carb and was the limited output model.

As far as the intake goes, I didn't catch it when I looked over the boat originally. The number on the back of the manifold is 2101 and says "Performer". (attached a couple more close up pictures of the engine)

To be honest I got it for a few thousand dollars, and figured at worst I would get my money back on parts or even the trailer which is a nice 2014 shorelandr. I did try and message the gentleman I bought it from to see if he knew why it was changed but no luck there.

I figured at worst I would have to put 3 or 4K into it which overall is still within the ball park of what Ive seen them sell for.

 

[elizenby]

PS looking closely, I think this engine has been replaced because by '98 it should have been a Vortec engine with updated cyl heads, but I see the old style 12 bolt intake vs the 8 bolt Vortec one. Not that it matters much, but the Vortec puts out about 25 more HP. As long as it has good compression, doesn't burn oil and there's no water in the oil its all good!

Actually that makes a lot of sense. The engine mounts look pretty new and not at all like the ones that Ive seen came with the boat originally.

 

[Lou C]

Ok what I saw that I don't like was that someone cobbled up the throttle bracket/cable and connection to the carb. What they did was used the later style bracket (to hold throttle cable retainer) that is for the Vortec intakes where the bolts go straight up and down with the old style intake where the bolts go in at an angle. Probably because the original engine WAS a Vortec and they could not find the older style bracket. Just to be on the safe side you should check to make sure the carb is really a marine unit, there are a few differences between marine and auto carbs of the same carb model. Take a pic with the flame arrestor off and I can probably easily tell. Marine carbs have a curved vent tube and a nipple on the air horn for the overflow hose if the engine has a mechanical pump. Yours should have the "J" tube for the bowl vent but does not need the overflow connection because you have an electric pump.
On marine inboard engines the following must be marine rated:
carb
distributor
alternator
starter
and any fuses in the engine compartment should be closed fuses (ATC, not ATO)
all of this is because an explosive atomsphere can exist in the engine compartment because fuel vapors are heavier than air. So I'd check ALL of that and get that cobbled up throttle cable set up fixed in the off season. Make sure your engine compartment blower works and use it. Check all fuel lines for leaks.

 

[Lou C]

Holley 0-80402-1 500 CFM Marine Carburetor

All Holley Marine Carburetors are designed to meet Coast Guard specifications. A marine carburetors fuel metering system is calibrated to compensate for unique engine loads found on boats. The J-style vent tubes direct fuel/fumes back into the carburetor for safe operation while on rough...

www.holley.com

see the curved tube above the choke plate? Yours should look like that.
Now I think VP used an adapter to use the 2bbl carb on the standard 4bbl intake. If that's how yours is and that's not a marine carb, I'd upgrade to a Holley 4bbl to really wake up that 5.0. You may need to find the proper throttle valve bracket on the carb and for the engine to get rid of the set up you have there.

 

[elizenby]

Holley 0-80402-1 500 CFM Marine Carburetor

All Holley Marine Carburetors are designed to meet Coast Guard specifications. A marine carburetors fuel metering system is calibrated to compensate for unique engine loads found on boats. The J-style vent tubes direct fuel/fumes back into the carburetor for safe operation while on rough...

www.holley.com

see the curved tube above the choke plate? Yours should look like that.
Now I think VP used an adapter to use the 2bbl carb on the standard 4bbl intake. If that's how yours is and that's not a marine carb, I'd upgrade to a Holley 4bbl to really wake up that 5.0. You may need to find the proper throttle valve bracket on the carb and for the engine to get rid of the set up you have there.

When I bought it I immediately took it to a shop to have it inspected. I knew of the dangers of fuel leaks and fumes and wanted to make sure it was safe before I put people on it. The shop gave me the all clear, (other than the note about the manifold) so I'm really hoping I don't have an auto carb. haha. Im on my way down to the boat now to check and get some pictures.

By the way thank you again for your help and information you have provided thus far. Really appreciate folks such as yourself.

 

[Lou C]

You're welcome! The Four Winns Horizons are nice boats, we have an old H-200 and while it needed a lot of repairs due to prior neglect its in good shape now and still runs well with the original Cobra drive and 4.3 V6. I did replace the cyl heads 4 years ago due to the originals being cracked from a bad overheat, not too bad of a job for me, parts were inexpensive and easy to find.

 

[elizenby]

Here are some more pics of the carb.

 

[Scott Danforth]

nothing special about the carb. Holley 2300 series marine carb. its either a 350 CFM or a 500 CFM (would need numbers off the air horn)

 

[elizenby]

nothing special about the carb. Holley 2300 series marine carb. its either a 350 CFM or a 500 CFM (would need numbers off the air horn)

I think this is what you need.

 

[Lou C]

That # you can look up on Holley.com
the carb looks like a marine unit, it has the J tube, the throttle lever does have the bracket used by VP, so that's good, that spring, not needed, just make sure that the end where the cable is anchored to the intake is not boogered up too much so the cable is secure but does not bind. You do have a 2 to 4 bbl adapter on that 4bbl manifold so you could drop a 600 cfm 4 bbl on it if you wanted to get some extra top end power.

 

[Scott Danforth]

I think this is what you need.

Just needed the numbers. Its a 500 cfm

 

[elizenby]

That # you can look up on Holley.com
the carb looks like a marine unit, it has the J tube, the throttle lever does have the bracket used by VP, so that's good, that spring, not needed, just make sure that the end where the cable is anchored to the intake is not boogered up too much so the cable is secure but does not bind. You do have a 2 to 4 bbl adapter on that 4bbl manifold so you could drop a 600 cfm 4 bbl on it if you wanted to get some extra top end power.

Thanks Lou! Really appreciate all the information. Once I get back to the shop to winterize ill post back here about the intake. Again thanks!

 

[elizenby]

Just needed the numbers. Its a 500 cfm

Thanks Scott. Im new to all of this so getting all this info helps for sure! Appreciate it.

 

[bruceb58]

You can buy Volvo Penta manuals. Your model is a "BY" so look for them when you are looking for manuals and for buying parts.