1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

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4Wins

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I have a 1995 Four Winns 195 Sundowner. It has a 5.0 V8 and Cobra OMC drive. This is my first boat and the performance of the boat has me really frustrated. When I bought it I test drove it on a lake nearby and it ran good. The water was very choppy and I did not get to open it up fully. After a few months of owning it and feeeling it out the boat seems to be very SLOW and getting more slow. It has gone from going about 40 mph (which seems weak) to down to 30 mph with a full tank and me being the only passenger. I had my wife and two small children on the boat this past weekend and could only get it up to 25 mph. Other than being SLOW it runs fine. Starts fine. Idles smooth. No funky noises. At full open on the water it gets to about 4000 or 4200 RPM and 30 MPH with just me on the boat. When i'm sitting stopped on the water and push the throttle fully open it responds sluggishly and even back fired once yesterday. If I baby the throttle open on a still start it accelerates moderately to top speed. This boat SHOULD be capapble of much more and ever since I've owned it I have't seen it at its best. It has a 2 barrel carb and distributor.
 
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HT32BSX115

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

4Wins said:
How can I find out the year/model/serial numbers of my engine and drive? Is it stamped somewhere?
Click to expand...

It should be on the engine on top someplace. Valve cover etc.

If you do infact have a 1995 engine it'll look like the following 4 1995 models.

502APHUB 1995
502APHUE 1995
50FAPHUB 1995
50FAPHUE 1995

You may also have a 1994 model engine,

502ACPMDA 1994
502AGPMDA 1994
50FACPMDA 1994
50FACPMDM 1994
50FAGPMDA 1994
50FAGPMDM 1994

Boat builders frequently use last years model engine in this years boats.....
(My 1997 Mercruiser 454/Bravo came out of a 1998 Bayliner)


By the way, that sticky message link I sent you to also has a list of things to check when unable to reach MAX WOT RPM etc.


Cheers,

Rick
 
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HT32BSX115

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

At full open on the water it gets to about 4000 or 4200 RPM and 30 MPH with just me on the boat. When i'm sitting stopped on the water and push the throttle fully open it responds sluggishly and even back fired once yesterday. If I baby the throttle open on a still start it accelerates moderately to top speed.
Click to expand...

Now that we know what you have, here's a few things to check.

1. Make sure your tach is accurate. They're FREQUENTLY WAY off especially at the higher RPM. (as much as 500 RPM OFF)

2. Use GPS to determine speed. Pitot type boat speedo's are also frequently off.

3. drive trim. Use trim to make small adjustments in drive angle. small up/down settings from optimum will slow you down considerably.

4. The list of other things. fuel,timing, carburetion, engine just flat worn out, boat water logged, too much weight in the boat, dirty bottom, damaged prop, dragging an anchor, trailer, etc etc, etc!

By the way,

drive trim is determined experimentally and changes with speed load etc....., the gage is only good to tell you that the drive is either all the way up or down.
 
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4Wins

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

In this video below. I noticed there is a small amount of water leaking from my exhaust. Could this be an issue?

1995 OMC 5.0 - YouTube
 
bruceb58

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

That is not normal. You need to figure out where that is coming from.

And by the way, you have a Cobra SX which is basically the Volvo SX drive.

I agree with Rick on using a GPS to calculate your speed. You also may want to check your RPM with another tach(shop tach).

Pushing your throttle very fast on a carb'd engine will cause a lean condition and may cause back firing through your carb especially if the accelerator jets are clogged. You can verify those by pumping your carb throttle and looking into the carb and looking for fuel stream/s. Do this with the engine OFF so you don't get singed eyebrows.
 
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4Wins

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

Thanks to Bruce and Rick! I am working thru all of the things you have suggested. My biggest concern is where this water came from. I did tightens the clamps to my exhaust. They were very loose and the water stream seemed to slow a lot. Would this leakage cause any further damage?
 
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HT32BSX115

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

4Wins said:
Thanks to Bruce and Rick! I am working thru all of the things you have suggested. My biggest concern is where this water came from. I did tightens the clamps to my exhaust. They were very loose and the water stream seemed to slow a lot. Would this leakage cause any further damage?
Click to expand...

It really wouldn't hurt much. ALL the raw water from the engine cooling system exits through the exhaust.

A leak at the rubber connections wouldn't be ahuge problem unless it was leaking a LOT more. There'd be water in the bilge, exhaust gasses in there too. but it wouldn't really affect much unless there wasn't enough going out the exhaust. The ex tubes might overheat if you didn't have enough water in there.


If there was a leak in the aluminum y-tube far enough below the water line, you could sink the boat..........Make sure your bilge pump is working!
 
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4Wins

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

The bilge pump works good.
 
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4Wins

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

I'm going to change out plugs tomorrow. Hope that does something.
 
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4Wins

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

Could this be prop related? My prop has 3 blades. 14 3/4 x 21 "Viper"
The prop has one ding in one of the blades but nothing too major.
 
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HT32BSX115

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

4Wins said:
Could this be prop related? My prop has 3 blades. 14 3/4 x 21 "Viper"
The prop has one ding in one of the blades but nothing too major.
Click to expand...

Maybe if there's a blade missing..... but you'd know it..

Earlier you said:

After a few months of owning it and feeeling it out the boat seems to be very SLOW and getting more slow. It has gone from going about 40 mph (which seems weak)
Click to expand...

And

At full open on the water it gets to about 4000 or 4200 RPM and 30 MPH with just me on the boat.
Click to expand...

If your drive is of the correct ratio, you would get approx 40 mph at 4000 RPM with that prop (using a prop slip calculator to estimate)
Prop Slip Calculator

Your engine *should* be capable of turning at rated RPM which is probably 4400-4800 (check your manual if you have one) And you should be "propped" to allow the engine to turn at MAX RPM 4800 when lightly loaded.

If it's not turning at least 4400 RPM, you either have a defective tach, the wrong pitch prop, the wrong ratio drive, a water-logged boat, or you're dragging the anchor. (Assuming your engine is "healthy" and otherwise running correctly)

You MUST determine that your tach is accurate BEFORE anything else. (also, use GPS to determine speed. Boat speedo's are almost always suspect)


Once you determine the tach and speed are correct, you can troubleshoot everything else.


By the way go to http://boatinfo.no/lib/library.html for manual info etc
 
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Gangly

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

Yes, prop damage can affect your rpm's.

On the flame arrestor cover should be a sticker that shows maximum operating RPM range so check to see what it should be then compare you dash tach RPM's with a shop tach to verify accuracy and to see what the differential value is if any.

Also, if it has been sitting up for a while, check for dirt dobber nests behind the prop. I couldnt get a lot of RPM out of my motor and when I pulled the prop there was a huge soggy mesh that was at one time a dirt dibbers nest. After spending 10 minutes to clean it out my engine started gaining its RPM's like usual. You would think the water and exhaust would blow it out but it doesnt. Just check to make sure no restrictions are found in the exhaust pathway.

Get a timing light and check your timing, sometimes the timing can advance or retard slightly over time.
 
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4Wins

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

Over the weekend I had a friend come and help me out. We looked at a lot. Changed out plugs and wires. Cleaned a ton of corrsion and build up. Carb and fuel system look good. My speedo my be a indicationg about 5 MPH slow. Prop is GTG. We got it on the water and I drove him around the lake. After lunch I let him drive and almost immediately said that my throttle cable was way out of rig. And my shift cable was all jacked up too. So thats where I am headed. Is this a tough job? I have found kits online to diy. Are there two seperate cables? Throttle and shift?
 
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4Wins

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

Does anyone have a good link where I can buy spark plug wires? Or a manufacturer part number? I have been trying to find some and havent had any luck.
 
bruceb58

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

Did you end up checking your RPM with a shop tach?
 
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4Wins

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Re: 1995 OMC 5.0 only gets to 30 MPH at 4000 RPM

Bruce,
I never did a check that. I had no capability of doing that.
 
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