omc3.8 1985 46 mph, then 52mph once never again

[ossi93]

I purchased boat new. first summer it ran 46mph.Next summer after a few outings it ran up to 52mph felt like it was running free. rpms were within limits.Took it out later that day back down to 46mph never did go back up to 52.10 years later froze block replaced engine with 5.0 ran about the same 44-46mph after a few outings it broke free again 54mph never did it again.Have replaced distributer plugs wires fuel pump filter etc. Can't figure it out not sure if carb was replaced with new engine or not.Thinking maybe trim unit not functioning properly? carb? Help

 

[waterone1@aol.com]

Re: omc3.8 1985 46 mph, then 52mph once never again

First question, what are you using as a speedometer ? If you are expecting the boat speedometer to always be accurate....forget about it. Second question, are you on a body of water that has a current ? Next, was the water more calm on your "high speed runs" ? was the load in the boat always the same (same number of people and gear, fuel tanks at similar level, etc.) ?<br />There are so many more variables that could cause this (clean boat bottom, wind direction, trim/tilt of engine, trim tab position, etc.). The main thing is that the engine is achieving the correct rpm's at wide open throttle.

 

[SeattleMatt]

Re: omc3.8 1985 46 mph, then 52mph once never again

is there a noticeable change in sound and rpm's ? waterone1 is right about the gauges, in a boat they are hit or miss, i usually hit mine alot <br /><br />all of the other items he mentioned should also be checked.

 

[ossi93]

Re: omc3.8 1985 46 mph, then 52mph once never again

The speedo is just the standard type nothing fancy I could tell it was much faster,water was the same just a ripple,on a lake no current. Boat bottom clean and waxed.Weight the same. Noticeble change in sound engine not working as hard 52mph like not dragging. seems like trim is'nt enough but why would it be good twice in over 800 hours running time.wondering if trim unit is faulty or needs fluid, air in lines? Or does the engine need to be leveled (shimed)rear or front.It is 1985 OMC 800 stringer

 

[trog100]

Re: omc3.8 1985 46 mph, then 52mph once never again

"but why would it be good twice in over 800 hours running"<br /><br />that is the interesting question.. why would any of the many possibilities change only twice in over 800 hours running.. one assumes u have tried to reproduce these rare burst of extra speed and failed.. ??..<br /><br />any idea of the speed your boat should go.. ??<br /><br />trog100

 

[Bondo]

Re: omc3.8 1985 46 mph, then 52mph once never again

I've had My boat do that Several Times.............<br /><br />In Freshwater, it'll run a good 43/44gpsmph.......<br />Every year or so, I get to drag it up to Maine,+ Splash it in the Salt......<br />It'll run a Solid 52/53 Then.........<br /><br />The Only other time was on a small lake,.. Late December,.... <br />The water was So Cold, the lake Froze Over the Next Day/That Night........<br />Dense Water,....... Pull 51gpsmph that day..........<br /><br />Only taken Me 687hrs in 5 years to figure that out.................

 

[trog100]

Re: omc3.8 1985 46 mph, then 52mph once never again

praps it didnt like the salt bondo and just went a bit faster thinking it might shorten its time in it... he he<br /><br />same with the cold stuff.. it just wanted to get out of that icy lake as quick as it could.. he he he<br /><br />trog100

 

[TwoBallScrewBall]

Re: omc3.8 1985 46 mph, then 52mph once never again

Yeah if I had my dangley bits in water that cold like your boat did I'd be moving out of it pretty fast too.

 

[Bondo]

Re: omc3.8 1985 46 mph, then 52mph once never again

You Guys Might be Right............<br /><br />Water Density makes Much More Sense thou......<br /><br />The Hull sits Higher,...... And,.. The Prop Bites Better...........<br /><br />Simple Physics.......................

 

[KaGee]

Re: omc3.8 1985 46 mph, then 52mph once never again

"Dangley bits"...... ROFL!

 

[ossi93]

Re: omc3.8 1985 46 mph, then 52mph once never again

It's in fresh water, same day it ran 44-46 then later that day, ran 52. Later yet, it ran back down to 44 to 46. It can't be water density or water temperture or current (it's on the same lake, everything was the same - I mean the conditions). It's a ponderable. <br />Anyone know anything about trim pumps? Any input would be great - thanks for all the replies!!

 

[tommays]

Re: omc3.8 1985 46 mph, then 52mph once never again

i have made several 8500 mile tours around the good old USA on motorcycles with good old carbs non of that EFI stuff<br /><br />and you would be amazed at the difference in power even during the same day with just different temps and humidity you get that just right temp and air and its got to make a 20 HP difference <br /><br />and boy when your going up pikes peak or some other crazy 12000 ft pass its so damm rich your luckey you made it<br /><br />tommays

 

[Bondo]

Re: omc3.8 1985 46 mph, then 52mph once never again

What are your rpms doing when this happens ???<br /><br />Changing Trim could Easily cause an 8mph difference......<br /><br />Don't know a Thing about Your trim pump......

 

[vipzach]

Re: omc3.8 1985 46 mph, then 52mph once never again

"Anyone know anything about trim pumps? Any input would be great"<br />sure we know about trim pumps. Do you have a reservoir? If so see how much fluid is in it. Is the fluid clean? A good quick test to see if you have air in your lines is to walk around to the back of boat and give your drive a good push down. If it goes down and sponges back up, the you have air or nasty fluid in it.

 

[ossi93]

Re: omc3.8 1985 46 mph, then 52mph once never again

yes i have a reservoir. it's an Omc 800 outdrive trim raises and lowers engine

 

[ossi93]

Re: omc3.8 1985 46 mph, then 52mph once never again

how do I fill or change fluid in reservoir