OMC V-8 Loss of Top Speed

[xudustin]

Hi all, hoping you can help me. I have a 1994 Four Winns 19' Horizon with the OMC Cobra V-8 I/O in it. It's a great boat and when we moved to TN from OH its top speed was about 47-48 when te trim was just right. However after having it docked for 2-weeks we took it out and now at 4000 RPMs, its top speed is now 30-32 tops!

Quick question for the forum is, when I put it into gear in idle speed then pull it back to neutral, it does tend to stay in forward gear unless I slide the shifter into reverse then back to neutral. Knowing on the OMC, its default is to drop some cylinders (instead of on the Mercruiser when it shuts it off) could the cylinders remain "dropped" at full speed? RPM levels and everything else seems normal just no speed or power.

I have also checked to bilge pump but no water, just looking for answers

PLEASE HELP and thanks in advance!

Dustin

 

[fordplayin']

Re: OMC V-8 Loss of Top Speed

ok i'm totally new to this site or any site for that matter so if i'm rude for jumping in on this please forgive me but... i have the same problem and have been reading through here for two days!
We have a 1995 Four Winns 19' horizon. 5.0 ford engine omc cobra outdrive two barrel. we have had the boat for 11 years. usually ran about 49-51 it has not been used much in the last few years, busy having babies, but we've been out a couple times this year, with kids, how fun!!! however our boat barely goes 38-40 top end trim up where it usually runs best, even with only the two of us and no extra weight.
We did drain gas before beginning of this season and changed our water fuel separator, as it did sit two years. boat runs great very smooth, i didn't notice rpm's when we were out, obviously i'm not a guy huh?
we are planning to check screens in fuel tank and carb line. not holding onto any water that i can tell. oil seems a little overfull, not sure why. but is nice color not milky? any other ideas would be a huge help.
like i said runs great but ten mph seems like a whole lot to be no big deal. thanks
sorry again for jumping in if i'm being rude, i just read this and thought thats us.. almost same boat and all except no throttle problems thanks again, Melanie

 

[Howard Sterndrive]

Re: OMC V-8 Loss of Top Speed

Hi all, hoping you can help me. I have a 1994 Four Winns 19' Horizon with the OMC Cobra V-8 I/O in it. It's a great boat and when we moved to TN from OH its top speed was about 47-48 when te trim was just right. However after having it docked for 2-weeks we took it out and now at 4000 RPMs, its top speed is now 30-32 tops!

Quick question for the forum is, when I put it into gear in idle speed then pull it back to neutral, it does tend to stay in forward gear unless I slide the shifter into reverse then back to neutral. Knowing on the OMC, its default is to drop some cylinders (instead of on the Mercruiser when it shuts it off) could the cylinders remain "dropped" at full speed? RPM levels and everything else seems normal just no speed or power.

I have also checked to bilge pump but no water, just looking for answers

PLEASE HELP and thanks in advance!

Dustin

sounds like the ESA (if equipped - is your drive a dog clutch cobra?) is malfunctioning due to a lower shift cable issue.
The ESA (Electronic Shift Assist) is employed when shifting out of gear - it stumbles the engine via the ignition to allow the dog clutch in the lower unit to disengage.
Don't keep operating it like that - the lower shift cable will just keep stretching worse and worse.
Out of whack, the ESA may be robbing you of power by stumbling the ignition when you don't want it to. i.e. cruising

other possible reasons for low rpm/power here:
http://forums.iboats.com/showthread.php?t=295070

 

[Howard Sterndrive]

Re: OMC V-8 Loss of Top Speed

almost same boat

a 1995 is quite possibly an almost entirely different drive system with cone clutch Volvo SX style shifting rather than ESA/dog clutch shifting

 

[fordplayin']

Re: OMC V-8 Loss of Top Speed

yeah i have read there is a difference in the dog and cone however i don't think we have the sx. can't find anything in manual like that anyway. also i really don't think i have a problem with that. i guess i should have read Dustin's post more carefully seems that may be his primary problem. mine is the loss of ten plus mph. maybe i should open my own question, i've never done this so if i should please tell me. i don't want dustin to not get his answers. i just saw omc 5.0 loss of top end speed and got excited.
I also would have a question about the carb screen at top of fuel line. ours nut is stripped on the outside so wont take standard wrentch. if i use a vise on this will i hurt anything or make it worse? because the exact part is obsolete and at least now i can run boat all be it slower and would hate to mess that up and not have a boat for the rest of season. if i shoud post this somewhere seperate i will. thanks again, sorry Dustin....although cool boat you got!!

 

[mcleaves]

Re: OMC V-8 Loss of Top Speed

It's not going to say SX in that vintage, but Four Winns were putting the joint venture drive on their boats in 94/95. Mine said nothing more than Cobra on the side, but it was an SX. Every OMC 5.0 I have come across in a Four Winns from then was an SX drive with OMC stickers. I will caveat that and say they have all been the fuel injected models though so there may be a difference with the carbed versions. Can you post a picture of the drive?

 

[ddbaran]

Re: OMC V-8 Loss of Top Speed

I am having the same problem on my 1994 OMC 5.8L EFI with the Cobra SX drive. I've owned it since new and I have never had any problems with it until now. I have been checking everything out and I am down to R&R one thing at a time until I find it.

I have it down to the fuel system; possibly the fuel pickup screen being clogged up right now. Next steps are to pull the fuel pickup tube out and also completely siphon out all the old gas. I have a suspicion that the old gas (with ethanol) is causing alot of my issues.

Thanks everyone for bringing your ideas out here. It is helping out alot!

 

[aldena]

Re: OMC V-8 Loss of Top Speed

Is there an easy way to tell if it's the Cobra SX drive? I too have a 1994 OMC with 5.8 EFI. The raw water pump is belt driven off the engine. There's Cobra stickers on the outdrive, but not a Cobra "badge" like on the outdrive of the neighbor's 1990 four winns with 5.0L.

 

[ddbaran]

Re: OMC V-8 Loss of Top Speed

The Cobra SX did not come out until 1994MY. There may be a few 1993's that had it.

OMC used the Cobra name on earlier models as well before they did the JV with Volvo.

I would say your neighbors drive is probably an older Cobra model.

 

[hellepa]

Re: OMC V-8 Loss of Top Speed

I have a '95 FourWinns 245 Sundowner w/ a 5.8 Cobra SX. For a few years, I had problems with intermittent takeoff speed, top end speed loss, etc and had 3 different mechanics troubleshooting everything from fuel filters to fuel rails, main computer, injectors etc.

Turns out it was an exhaust issue - like a banana or potato in a tailpipe. With this particular configuration, there was a bad exhaust design. If you can find a picture of the exhaust system it will make sense. Just below the elbows beyond the exhaust manifolds, the exhaust converges into a Y-pipe where the exhaust gasses head out to the thru-hull exhaust. In the top of those pipes, there are oval flapper valves meant to prevent hydrolocing the motor by keeping water from rushing back up from the prop. The valves have a swivel pin offset in the pipe. The pipe material wears over time and the hole becomes oblong. If the pin moves in the oblong hole, the flapper valve can become lodged in the pipe and cause some restricted exhaust. Eventually one of my valves melted and fell into the Y pipe and caused enough blockage that it was audible when running on land and the diagnosis changed from intake (fuel/air/computer) to exhaust. There was a tech bulletin we found years back but that's been 4 or 5 years now for me. You can raise the exhaust elbows to see if the pin holes are elongated or the valves are lodged/burned to see if this may be your gremlin. I know I was relieved when we finally figured our issue out!

 

[dbaran]

Re: OMC V-8 Loss of Top Speed

Volvo had a service bulletin to completely remove the flapper valves back around 2000. You have to make sure to plug the holes with silicon so the water doesn't leak back into the boat. I had the same issue and I finally removed mine. I mostly boat on inland lakes and don't have this concern. I know there is some risk in doing this, but this boat is 20 yrs old anyways; its going to need a complete rebuild soon if I decide to keep it.

 

[sw33ttooth]

Re: OMC V-8 Loss of Top Speed

i can almost certainly say its not your esa, huge relief? the way i know its not your esa is mine came out of wack going down a dirt road and it would stumble my motor when i tried to accelerate and some times stall. took me forever to diagnois this and now i have loss of speed and popping over 4k rpm thinking its either carb or exhust both getting worked on in winter.

if your motor is injected i cant help you much since my knowledge there is lacking, however if its carbed you may need a rebuild, clean the spark arestor. also if it has a carb it may be elevation differnces from your move from TN to OH that would just need minor adjustments. i've yet to mess with my exhust but i am half way thinking thats my problem and it may be in your best intrest to look there as well.