'88 Force 125hp - How fast should I be able to go?

[On a boat]

This is the first large-ish boat I've owned so I'm not sure how fast I should really be able to go. I have an 1977 18' Cobia Centaur. With just myself in the boat, on calm water I can get 26-27 MPH according to my GPS. I know there are problems causing slowness that I'm trying to work through one at a time, I just want to know how fast I should be able to go so I can tell if I'm really making progress with the repairs/maintenance.

Additionally, I just replaced the fuel/water separator. I've had the boat for 2 years and only used it about 20 hours and didn't even think about changing it. Looks like it hasn't been changed much, much longer than that. I won't be taking the boat out for another week or so, but should I expect this to have any noticeable affect on performance?

 

[bman1bpm]

Re: '88 Force 125hp - How fast should I be able to go?

Knowing nothing about the weight of that boat, I still would say you should be able to get into the mid 30's at least. Does your boat have a tach? Knowing how many RPM's your hitting at WOT would help determine your speed problems. I wouldn't be surprised if your fuel system wasn't in bad shape. If it were my boat, I'd replace all the rubber fuel lines and replace the fuel pump diaphragms, its cheap, easy, and old rubber doesn't hold up to new ethanol gas very well.

 

[foodfisher]

Re: '88 Force 125hp - How fast should I be able to go?

^^+1 My '86 pushes me to 35+ then I back off. Don't know your hull.

 

[On a boat]

Re: '88 Force 125hp - How fast should I be able to go?

From http://boatspecs.iboats.com/Cobia_Boats__C18V_Centaur__1977/bp/66b21297
"The boat weighs approximately 1300 pounds with an empty fuel tank and without any gear or passengers."

The tach, speedometer and other dash components were cut by one of the previous owners. They are, however, on my long todo list for this boat.

Curiously, what is 'cheap' ballpark for replacing the fuel lines and pump diaphragms? I like the idea and will get it done as I'm sure it needs it, but my budget lets me fix only so much at a time and I want to prioritize.

 

[foodfisher]

Re: '88 Force 125hp - How fast should I be able to go?

$50 bucks max. including new primer bulb.

 

[Justinde]

Re: '88 Force 125hp - How fast should I be able to go?

I get 45mph out of my 1988/125hp.

 

[On a boat]

Re: '88 Force 125hp - How fast should I be able to go?

$50 bucks max. including new primer bulb.

Awesome. That's near the top of my agenda.

I get 45mph out of my 1988/125hp.

On what hull? Similar in weight to mine at 1300lbs? Thanks for the feedback.

Oh, and I'm sure my prop is not the ideal one for the job as it's just one that I got for free from someone. I'll also be taking care of that going for more ideal one in the near future.

 

[bman1bpm]

Re: '88 Force 125hp - How fast should I be able to go?

If your budget is super tight skip the hoses for now, and just replace the pump, don't forget to clean the little screen under the black plastic piece that the fuel hose connects to, might be full of crud. Don't buy a rebuild kit (comes with all kinds of gaskets you don't need) just go to your merc dealer and get part numbers:

F438760-Diaphragm Gasket
F438617-Gasket for the black plastic piece the hose hooks to on the pump
F438747-Pump Diaphragm
Should run less than $10

Dump a can o' seafoam in the gas, I think its great stuff, but who really knows. You should be able to grab a used tach for a $10-20 bucks on craigslist or ebay.

 

[Justinde]

Re: '88 Force 125hp - How fast should I be able to go?

On what hull? Similar in weight to mine at 1300lbs? Thanks for the feedback.

Oh, and I'm sure my prop is not the ideal one for the job as it's just one that I got for free from someone. I'll also be taking care of that going for more ideal one in the near future.[/QUOTE]

I am unsure the weight of my hull in total, however its a 17foot Force Custom Bowrider ( look at Flightcraft 1600 bowriders). Actual weight would be close to 800kilo's, plus fuel/kids etc. I have a 17" Stainless Steel prop. Because its 20 odd years old- I CHOOSE to cruise at a little more than 3/4 throttle, and still get a respectable 38MPH.

There are so many variables, but if you do a youtube search on 'force custom bowrider', thats me and the kids on Botany Bay, Sydney, at 44MPH.

Cheers

 

[jerryjerry05]

Re: '88 Force 125hp - How fast should I be able to go?

First do a compression/spark test.
No spark or low comp on one cylinder will kill top end.
A clogged vent on the fuel tank will slow you down too.
Then what prop?Get a tach hooked up.
Mercury sells a Tiny Tach works great.
With out a tach and prop size we're only guessing.
But you should be doing at least 30????

 

[On a boat]

Re: '88 Force 125hp - How fast should I be able to go?

Unfortunately I don't have to right equipment for a compression test but will hopefully be able to take it somewhere this weekend to a friend that does.

The fuel filter was gunky so I cleaned that up until I can get to Napa for new filter, diaphragm and hoses.

I found that one wires connecting to the spark plug thing (yes, thing, as I don't know a better word for it) was almost completely corroded/melted off another was pretty bad. I re-did both. These were both positive leads on small odd shaped boxes that say 'made in USA' that the spark plug wires attach to on the starboard side of the engine. Hooked up some muffs and started it up and it sounded pretty good and accelerated faster that I recall it ever doing. I'll take it out to the lake this week/weekend to see if there's any noticeable gains between this, the fuel pump diaphragm replacement and the fuel/water separator.

Also, I should have the tach hooked up tomorrow to get an idea of the RPM's I'm getting. Gatta redo the wires for it but it looks simple enough.

 

[foodfisher]

Re: '88 Force 125hp - How fast should I be able to go?

About the tach. Should have should be changed to "will" have. Without those numbers it's a guessing game.

 

[On a boat]

Re: '88 Force 125hp - How fast should I be able to go?

Well, I *should* have it hooked up tomorrow and when I do I *will* let you guys know. It just may not be tomorrow, depending on if I can fix another issue first. I just didn't know if there was a good estimate for the motor/boat in general, not how fast mine in particular should be going.

 

[Justinde]

Re: '88 Force 125hp - How fast should I be able to go?

If it starts, runs, goes, is reliable, takes you to your spot, keeps your kids safe, and you take care of it, who cares if you get 38MPH,40MPH, or 45 ( like me....). I back off to take it easy on the old girl, and usually run at about 4500-5000 RPM rather than flat stick.

My 2 cents

Cheers

 

[On a boat]

Re: '88 Force 125hp - How fast should I be able to go?

If it starts, runs, goes, is reliable, takes you to your spot, keeps your kids safe, and you take care of it, who cares if you get 38MPH,40MPH, or 45 ( like me....). I back off to take it easy on the old girl, and usually run at about 4500-5000 RPM rather than flat stick.

My 2 cents

Cheers

While going 40 mph would be entertaining to me, and those in the innertube when doing that, that is not my primary concern. Slower than normal speeds indicate a problem all too often problems become worse. If I can get the motor running how it's supposed to be running and maintain that, I can drive it leisurely or fast as I want without worrying that it's going slow because it's got a problem that could leave me stranded.

And about the tach: looks like it's shot. I'm getting a new steering cable tomorrow and apparently will another tach as well. Hope to do some test rides this weekend to see how things are going and will let you guys know that kind of RPMs I'm getting.

 

[bman1bpm]

Re: '88 Force 125hp - How fast should I be able to go?

If it starts, runs, goes, is reliable, takes you to your spot, keeps your kids safe, and you take care of it, who cares if you get 38MPH,40MPH, or 45 ( like me....). I back off to take it easy on the old girl, and usually run at about 4500-5000 RPM rather than flat stick.

My 2 cents

Cheers

+1 my boat has had the wrong prop for years butttttttt it goes fast enough for me and runs great. on a boat's boat sounds like its got some deeper issues that need to be addressed to keep it reliable!

 

[jerryjerry05]

Re: '88 Force 125hp - How fast should I be able to go?

Wrong prop can cause overheating and worst it can realllllly hurt the pocket.
My boat came with 17p I thought I wanted to go faster.I put 19's on it.It went 3-4 mph faster and consumed about 20-25% more fuel.

 

[On a boat]

Re: '88 Force 125hp - How fast should I be able to go?

mmk. So, I'm guessing this isn't a good thing. Hooked up my tach and with WOT with muffs it's maxing out the tach at 6k. With neutral WOT it sits at 4.5k but after a minute it goes up to max as well. Manual states 4.5-5.5k as the recommended operating range but that's like half throttle and I get very low speed at that level.

Prop: I can't find any markings/etching on it, but with a tape measure it looks like 12-13" across. I have attached a pic if that helps at all determining rough size.

Any suggestions?

 

[foodfisher]

Re: '88 Force 125hp - How fast should I be able to go?

WOT measurements is "IN" the water! Doing that on muffs is asking for trouble. Honestly! Are you doing this with the prop spinning out in the open???

 

[riptorn]

Re: '88 Force 125hp - How fast should I be able to go?

WOT measurements is "IN" the water! Doing that on muffs is asking for trouble. Honestly! Are you doing this with the prop spinning out in the open???

Agree foodfisher
Good way to blow up an older motor.
You have to to have a torque behind.Would you take your car and do that in park?