1988 Force 85hp Top end rpm loss troubleshooting help.

[DunbarLtd]

I did some poking around and that value looks to be the same as I found. I think the engine is like 225lbs so anything over 1700lbs most likely means im tugging around some extra weight.

I do however have a question that Ive pondered. Im not sure if anyone has done this or if it would help troubleshoot anything.

But I was thinking taking the boat down to the launch ramp while still on the trailer and back in enough to get it underwater and run the motor WOT for a few seconds just to see what the rpms would be.

Im thinking with no weight or water resistance on the motor it should spin to its full potential if its trailered on a boat. And would tell me if the motor is the problem or the weight of the boat is holding it down.

Im sure someone will correct me on why its pointless to do such a thing but Im trying to think outside the box here.

I could just pay a guy $150+ to diagnose it but if I can figure it out myself then why not.

 

[jerryjerry05]

Won't work.
You won't rev up to the max on the trailer at the ramp.

Now if you had a test wheel you could do something like that.

The extra water soaked in the foam?
There ain't enough foam in there to soak up enough water to make a difference.

 

[The Force power]

Im thinking with no weight or water resistance on the motor it should spin to its full potential if its trailered on a boat. And would tell me if the motor is the problem or the weight of the boat is holding it down.

Jerry is(always) right!

you DO have resistance, the boat is on the trailer connected to a vehicle that your trying the push forward. For the motor to come to WOT the boat would need to plane (reduced resistance)

If you alone in the boat & no extra's on board, the water soaked foam can then count for a passenger

I have a 1990 bayliner capri bowrider with a 90hp so fur sure I have soaked foam and I can ref. mine to the max fully loaded or alone.
I think that it's engine related & not the boat

 

[racerone]

Perhaps find a shop with a ---" marine dynamometer "----To test actual condition / power output of the motor.----Have one myself.-----That is the next step to determine if problem is the motor or the boat that is the issue here.

 

[The Force power]

Perhaps find a shop with a ---" marine dynamometer "----To test actual condition / power output of the motor.----Have one myself.-----That is the next step to determine if problem is the motor or the boat that is the issue here.

Hi Racerone I have a question for you;

would an under seized Prop. work as a dynaometer? or is it the weight of the dynamo resembling the resistance of a prop.?

 

[racerone]

Perhaps google ----marine dynomometer----Mine is the blue cabinet K&O model.-------It is an oil pump mounted on the propshaft.------Oil is then pumped through a control valve.-----You raise RPM of the motor.------Close control valve more.----Open throttle more.--------Until you reach full throttle RPM for the motor.-----Refer to a chart to evaluate.-------This tool ( $ 4000 + ) is used in the shop yard to save trip after trip of launching the boat..-----Like all good tools it is a " time saver / money maker " so to speak.

 

[The Force power]

I know they used them on (diesel) engines for break-in, but our shop did not have one (we kept them running in low speed) with a Refrigeration-compressor hooked to them

 

[DunbarLtd]

Perhaps find a shop with a ---" marine dynamometer "----To test actual condition / power output of the motor.----Have one myself.-----That is the next step to determine if problem is the motor or the boat that is the issue here.

You mean this right? https://www.youtube.com/watch?v=zWL0yWvYlJM

And theres maybe one guy willing to work on this motor around me and by the sound of it after talking to him i dont feel comfortable giving him my boat to test on the water. Which is what he does. He said nobody works on the old motors (in my area) anymore because customers never want to pay the money to fix them and parts are so hard to find. Whatever i guess i understand.

So thats not an option for me right now and im stuck trying to solve the problem on my own. Which has me getting to the point of just dealing with it until Im too tired and then sell the boat. I just dont know what else to test. It has spark fuel, etc ,etc.

Tach "could" be wrong but i really dont think it is. Doesnt sound like the boat is the issue so i dont know. Ill probably just run it until something obvious happens and if that means i seize the damn thing then so be it. I barely paid anything for the boat and put a grand or so into it to fix it up somewhat and ive gotten 4 years out of it so if it goes to crap its not a huge loss.

But for my own curiosity and to learn something, not to mention help someone else out there with similar issues, Id love to find out why it wont rev over 4200+ with 17P prop and the power trim working.

Thanks for all the kind advice but I am at my wits end with this thing.

 

[racerone]

Correct-----That is what testing is all about.-----Proper tools and " know how " counts for a lot.-------Simple testing is the key.-----Yes boat shops deal with people that can afford the service / repairs.-----Some folks relate repair costs to what they paid for the old boat / motor / trailer.-----But the time / shop overhead / mechanics wages are all " brand new " so to speak.

 

[jerryjerry05]

Different tach or the tiny tach might give you the answer??
You sure the props a 17p ??

 

[DunbarLtd]

Prop stainless?
A stainless 17p is equal to an alum 19p

Maybe drop to a 15p

Just wanted to update this problem I was having. I finally switched to a 15P prop and have now been able to get to 5100 rpms WOT. Overall speed hasnt changed. Still 32mph tops. It does get on pad quicker.

I also found an official document from bayliner that lists performance numbers and it says @ 5k rpm this boat with 85hp should hit 34mph.

so I have to assume either my boat is water logged/overloaded or I have a worn out engine???

It may be ok for most people because it runs and starts and has decent speed but I would like to get this thing running as good as i can.

So just thought I would update. Im not sure what to make of it though. The stock setup is 17P 13" 3 blade from the documents i found online. Which was an official bayliner pamphlet.

I know this is an old boat and all and most people should just be happy to have it running but if I can do anything to figure out why Im only getting 4200 with a 17p, which is designed for the boat, then why not???

One thing I have been thinking about is the fuel tank pickup. That I havent checked yet. Just wondering if its clogged just enough to limit the max rpm. I dont know just speculating here.

Anyone have any other ideas?

 

[jerryjerry05]

If the fuel was restricted?? It probably wouldn't get the rpm's your getting.
It would fall flat once the flows restricted.

32 GPS or speedo?

Your change to a 15p shows the motors capable of getting the rpm's up.
Do you have Trim and Tilt?
You have a whale tale?
What boat? 17ft. 19ft?
Check the weight of the boat.? but it would have to carry about 700-1000# of water to be affected.
I've seen under the deck on a 17 and there's NO WAY the foam will hold that much water.

I drove a 17 with an 85 and it got over 40mph???