OMC 5.0L question (1988)

[0aj0]

Hey all,
I recently bought a 88 bayliner Capri 1950 with a 5.0L cobra motor. The boat runs great but I found a problem that I cannot narrow down a fix for. The engine has plenty of power in the lower rpms, I can go WOT from a standstill without any engine hesitation. Problem is when I get the boat up to around 4500rpm, it starts to bogg like it's getting starved for fuel or something. I had adjusted trim while it boggs and no change. I pulled the fuel filter and it was NASTY, so I put a new one on an it seemed to fix the issue at the time (I only had boat out for a few hours just to test). This weekend at the lake I could tell the problem was slowly coming back... Here is the tricky part, it only seems to do this after several hours of use. Not constant wot, just using it to move around lake for 5 to 10 minute spurts then letting it sit for 30 minutes or so while we swim.

Do you think the fuel filter is shot again, or do I have other problems?

Thanks!

 

[superbenk]

Re: OMC 5.0L question (1988)

I would certainly check the filter again. You may also have water in your tank and/or bad gas. Might also want to check/replace the anti-siphon valve at the tank, it could be sticking. Perhaps the screen on the pickup line inside the tank is gummed up too. Finally, you might be developing a vacuum in the tank which could explain why it only happens after running for awhile. If it does it again, you might want to simply crack the filler cap open while it's happening to see if it relieves the pressure and fixes the problem - if it does, you might want to check that your vent line or fitting isn't plugged.

 

[0aj0]

Re: OMC 5.0L question (1988)

Thanks for the info, I will check those things next. Do you think it could be fuel pump and or carb issues? I know the boat sat for about 3 years winterized in storage before I purchased it, do you think a carb cleaning would help out any?

Thanks again
AJ

 

[airdvr1227]

Re: OMC 5.0L question (1988)

How much higher are you expecting it will go? I think 4500 is really spinning for that motor.

 

[sethjon]

Re: OMC 5.0L question (1988)

After 3 yrs a carb clean would definitely help. Doubt if its fuel pump issues. After 3 yrs I would clean out the entire fuel system.

 

[0aj0]

Re: OMC 5.0L question (1988)

Well this is my first boat, so I am not exactly sure. My throttle handle will keep going down and the motor will run up to about 5k... I read somewhere online that the 5.0 maxes out at 4600-4800rpm WOT. Either my rpm gauge is a little off or the motor will run higher then 4800rpm at WOT. It was my understanding that you could push the throttle handle all the way down and it would run WOT... is this not correct? The boat is 19.5' and with two people WOT before it starts bogging it will run about 46-50mph on smooth water... but the rpm gauge shows like 4800-5000rpm.

 

[haulnazz15]

Re: OMC 5.0L question (1988)

You should probably be maxing out around 4200rpm or so. Either way, I'd pull the fuel tank and flush the old fuel out and clean it with some Chem-tool.

 

[airdvr1227]

Re: OMC 5.0L question (1988)

Well this is my first boat, so I am not exactly sure. My throttle handle will keep going down and the motor will run up to about 5k... I read somewhere online that the 5.0 maxes out at 4600-4800rpm WOT. Either my rpm gauge is a little off or the motor will run higher then 4800rpm at WOT. It was my understanding that you could push the throttle handle all the way down and it would run WOT... is this not correct? The boat is 19.5' and with two people WOT before it starts bogging it will run about 46-50mph on smooth water... but the rpm gauge shows like 4800-5000rpm.

WOT is a function of Horsepower and prop pitch. It just seems like 4500 on the 5.0 is enough. I know that 4400 on my 5.8L is maxxed out for the most part. I'd be afraid that I'd find out the hard way that my max is 4200 right as the engine gives way at 4600. I'm not one to run at the limits on any equipment.

 

[haulnazz15]

Re: OMC 5.0L question (1988)

WOT is a function of Horsepower and prop pitch. It just seems like 4500 on the 5.0 is enough. I know that 4400 on my 5.8L is maxxed out for the most part. I'd be afraid that I'd find out the hard way that my max is 4200 right as the engine gives way at 4600. I'm not one to run at the limits on any equipment.

While that's all true, I wonder why the RPM range differs for some engines. Like 350 vs 351 WOT ranges seem to be a few hundred higher for the SBC. I figured the outdrive was the limiting factor in regards to rpms, not the engine. That being said, I still think he should prop back down to 4200.

 

[0aj0]

Re: OMC 5.0L question (1988)

Luckily, the previous owner has all the books for this boat and motor. I just checked and the 5.0L "Full Throttle Operation" is between 4200-4600rpms.

With that being said, my boat will run 5K WOT with its current setup... so do I need to try and find a new prop with a higher pitch?? Currently, I feel noticeable power gains even in the 4600-4800rpm range, but if that is not safe on the motor then I definitely will not run it that high again.

So, with all this being said, do you think there is a chance that I am experiencing the "bogging" because I am exhausting the engine by running it above the WOT range specified by OMC? If so, would the higher pitch prop allow the boat to maintain the 45-50mph speed - but at the safe WOT range?

Currently I have a 14.5x19 aluminum prop.

If you think a new prop is in order, how high would I go in the pitch? Are stainless props going to give me any noticeable difference vs aluminum?

Thanks much everyone, you have been a great help so far!

 

[Bondo]

Re: OMC 5.0L question (1988)

So, with all this being said, do you think there is a chance that I am experiencing the "bogging" because I am exhausting the engine by running it above the WOT range specified by OMC?

Nope,... You need to prop Up, to get the rpms at wot down to 4600rpms...
You Also have to clean the ship outa the fuel tank,+ the rest of the fuel system...
2 issues...

 

[0aj0]

Re: OMC 5.0L question (1988)

Nope,... You need to prop Up, to get the rpms at wot down to 4600rpms...
You Also have to clean the ship outa the fuel tank,+ the rest of the fuel system...
2 issues...

Ok, so what type of prop would you recommend to decrease RMP's approx 400-500rpms if my current prop is 14 1/2 x 19? Also, will this have any effect on my WOT speed?


Thanks

 

[airdvr1227]

Re: OMC 5.0L question (1988)

20 or 21? It should lower your WOT RPM. It might increase your speed also. Over in the prop forum you'll get better answers.

 

[Sparkinator]

Re: OMC 5.0L question (1988)

Ok, so what type of prop would you recommend to decrease RMP's approx 400-500rpms if my current prop is 14 1/2 x 19? Also, will this have any effect on my WOT speed?


Thanks

You will lose low end torque by increasing the prop to a 20-21, but you will gain some top end speed. If you are pulling skiers, that 19 may be your ideal prop, you just need to watch your rpms and keep them below 4600.

It all depends on what performance you want from your boat.

I've got a Ford 302 on a SX Cobra and if pulling skiers, my 19 aluminum is ideal, but, like you, I can run over recommended rpms if I'm not careful.

I've got a 17 pitch prop I'm itching to try. I figure I can 4 skiers up with it, but I just won't be able to run over about half throttle though.

My 21 pitch stainless allows wide open throttle and does not exceed recommended RPMs. The problem is that, it doesn't pull as good, and when pulling skiers, low end pulling power is what counts.

YMMV

 

[full stringer]

Re: OMC 5.0L question (1988)

go with a four blade 20 inch pitch and youll be impressed sold on iboats store around 130 bucks for aluminum free shipping too, now to pull skiers and just want hole shot averege daily cruising and your rpms under control put a 3 blade 21 inch prop on the four blade 20 or the 3 blade 21 will lower wot rpms down 350-400 good luck