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Author Topic:   How fast can I run my older engine?
CFCAJUN posted 09-23-2004 09:08 PM ET (US)   Profile for CFCAJUN   Send Email to CFCAJUN  
My boat came with a 1976 Evinrude 85hp. When I got the boat a couple months back, she looked in good shape. The motor started easily, was clean, seems maintained, doesn't leak.

I generally run her around 3200 - 4200 rpm max. I have at times bumped her up to around 4500 (35 MPH-ish), which I might call 85-90% WOT.

I have no need to run WOT, but because of the age of my engine, should I keep the RPMs around where I do now, and never run WOT, or is it OK to run WOT on occasion?

There is no "redline" on my tach and I don't know if outboards even have a redline.

brisboats posted 09-23-2004 09:23 PM ET (US)     Profile for brisboats  Send Email to brisboats     
Not only is it OK it is a good idea. Blow the carbon out of her every now and then that old crossflow will love ya for it.


CFCAJUN posted 09-23-2004 09:29 PM ET (US)     Profile for CFCAJUN  Send Email to CFCAJUN     
She has been a little harder to start these days. Maybe a good idea if not taken too far???

Nausiat posted 09-24-2004 02:53 PM ET (US)     Profile for Nausiat  Send Email to Nausiat     
Without knowing your compression etc can't say this for certain, but one of the main things that causes hard starting is carbon deposits, especially on the plugs and rings. If you never wind it out, this may be as simple as your problem..

If you choose to not run it through its entire working range, then I would suggest a high end synthetic oil and regular plug changes..


CFCAJUN posted 09-24-2004 03:45 PM ET (US)     Profile for CFCAJUN  Send Email to CFCAJUN     
I would like to do a compression check. It's now on the list.

When I bought the boat, she started before the key was even completely turned. Fired up nicely.

Now granted, I use the boat only on weekends, so when Saturday comes, I plug in the fuel line (I keep it unplugged from the motor), pump the ball and crank her. I choke her till she pops then crank from there. Sometimes she takes 3 or 4 attempts to get her going. Once she's warm, she starts very easily every time. So, I think this is just a case of getting the fuel into the system after sitting.

As for oil, I use the Evinrude brand and also Quicksilver. I read Evinrude uses something that does something with newer motors (forgot what I read), and since my motor was older I didn't think it would apply -- so I alternate.

Haven't looked at the plugs and need to inspect the lower unit oil.

Thanks again.

2manyboats posted 09-24-2004 05:27 PM ET (US)     Profile for 2manyboats  Send Email to 2manyboats     
New plugs and at least look at lower unit oil for water.

Get some of the de-carb spray, use it, then add some of the additaves to keep the carbon from building up.

Every trip if you can, run wot. for at least a little while, your motor should run close to 5500 rpms. Best speed for cruise should be 3500 to 3800.

CFCAJUN posted 09-27-2004 05:59 PM ET (US)     Profile for CFCAJUN  Send Email to CFCAJUN     
OK, worst case scenario. Let's assume I have a good oil/fuel mix. Assume my lower unit has proper oil. Just based on the age of my boat, what is the most likely damage that could occur at WOT?

I guess I am trying to compare to a car, where you throw a rod, crack a head, burn a head gasket.

Just trying to imagine what would go first.


PS: Does anyone like to run the older engines rich?

2manyboats posted 09-27-2004 06:35 PM ET (US)     Profile for 2manyboats  Send Email to 2manyboats     
Engine age may not mean high hours. Very few outboards fail because they are worn out. If you are going to not run at higher rpms ,use a spark plug rated for low speed operation, make sure you have thermosats installed and don't over oil.

But if it was mine I would maintain it like I love it and run it like I hate it. Those old 90 degree v-4 s will run and run.

CFCAJUN posted 09-27-2004 08:29 PM ET (US)     Profile for CFCAJUN  Send Email to CFCAJUN     
I think I am going to inspect her, then let her run like a racehorse. We'll see how she feels.

Thanks all!

Nausiat posted 09-27-2004 08:47 PM ET (US)     Profile for Nausiat  Send Email to Nausiat     
A decent outboard mechanic can tell you the only 2 real concerns about full throttle running, bearings and mixture. If the bearings are worn/loose, full throttle won't help them at all, however they will eventually fail regardless.

The more critical one is mixture and/or timing. Take a 5 min full blast run, then bring it down to idle and shut it off (don't putt for a while). Check the plugs, if they are tan to dark, things are good. If they turned white on the tips, then either the carbs are leaning out or the timing is advanced (assuming correct plugs). Either condition can cause a melted piston at full.

Flip side is, excessive carbon build up from constant trolling and slow running will jam the rings, this in turn causes excessive wear and scratching on the cylinders. I think as many or more engines are damage by fishermen trolling all the time then by hot dogs running them hard...


brisboats posted 09-27-2004 09:05 PM ET (US)     Profile for brisboats  Send Email to brisboats     
Give her a check over and then go run it like you stole it. Crabbed (trolled) all weekend with my 18hp 2 stroke on my 13 and just had to take a 1/2 hour blast around the river this morning to clear her carbon and my cobwebbs, she never idled better as I putted back to the ramp. You have one of the most durable engines ever made, no need to baby it. Look at it this way your 1976 outboard is almost dead even with a 1976 Porsche 911 in the horsepower per liter comparision. Run for awhile like the high output machine it is.


CFCAJUN posted 09-27-2004 09:21 PM ET (US)     Profile for CFCAJUN  Send Email to CFCAJUN     
Guys, ya'll are hurting me!
I can't even think about running until Sunday. I GOT THE NEED FOR SPEED!!!!!!



Binkie posted 10-01-2004 05:16 PM ET (US)     Profile for Binkie  Send Email to Binkie     
Make sure your running a prop that won`t rev the motor higher than recomended at WOT. Most failures occur from over-reving, and running to lean. But if you blow the motor, it should be cheap to replace, and will make a swell mooring anchor
CFCAJUN posted 10-01-2004 05:19 PM ET (US)     Profile for CFCAJUN  Send Email to CFCAJUN     
Binkie -
Now those are encouraging words. :-)

Good thing I have a 2hp kicker. Bad thing is I usually leave it at home.

Prop I think is original.


CFCAJUN posted 10-02-2004 08:36 PM ET (US)     Profile for CFCAJUN  Send Email to CFCAJUN     
Update : Saturday 10/2

GREAT afternoon run today. I hauled the Katama out to Lake Pontchartrain and launched around 5pm. Lake was near glass, with a light breeze from the North.

I keep the fuel line unplugged from the motor, so I launch, plug it in, pump the ball once or twice until it's firm and turn the key unchoked. She doesn't fire, so I choke and try again, doesn't fire. I fast idle her, no choke, turn the key, she fires but doesn't start. I start as normal, bump the choke she fires and is running. So, about 4 attempts and she starts easily.

I don't think I have any problems so far, I just think I need to get fuel into the system.

So I head out into the Lake, Northbound in beautiful conditions. I run at about 3800 RPMs and about 32MPH for about 5 minutes, then I opened her up, WOT.

WOT per the gauges was 5200 RPM and 43MPH. I am in my 16' 7" 1971 Katama with a 1976 Evinrude 85HP 4 cylinder. I was running solo with 12 gals of gas and no cargo.

Now, I do know that I need to replace my throttle cables because reverse only goes up to 1500 RPM and the cable casing is cracked open at the engine. I have noticed no problems with forward. My only curiousity at this point is that the engine does not sound like she is whining like I am used to hearing a WOT engine do.

Instead, she sounds to be at what I would call about 90%, maybe 95%. Maybe the V 4 engine just doesn't do that.

Anyway, I ran WOT at 5000 - 5200 RPM and 40 - 43MPH for about 30 minutes. Every 5 or 10 minutes I would come down to 40 MPH or about 4800 - 5000 RPM. She showed no signs of problems.

I stopped because I wanted to adjust the pin that controls the fixed motor trim position (I have no power trim, only tilt) It is in the 2nd hole from the top. So I move the pin to the #1 top position to see what happens.

I barely touch the key and the motor fires effortlessly.
She cavitates when I engage forward, so I ease her up to speed and find she porpoises and hits high RPMS at lower speeds.

I kill the engine, move the pin down to #3 hole, bump the key, fires right up. Engage forward, bows riding lower, max speed is 40MPH at 5000 RPM. So, I kill the engine, put the pin where it originally was, #2 hole from the top. I bump the key, she fires right up. This position keeps the boat on a good plane, with no plow.

Engine runs perfectly and I think the WOT really cleaned her out.

Headed in before sunset as I watched mullet feeding topside and numerous fins break the surface. Wonderful afternoon ride in the Whaler.

Got to the launch, stepped onto the wharf and I hear at the next pier over, "Good old Boston Whaler!"

That made a perfect end to the day.

Barney posted 10-02-2004 09:01 PM ET (US)     Profile for Barney  Send Email to Barney     
CF, Today was great huh! We were at Ship Island today, great calm day. No fishing tackle onboard, so saw two redfish at the island and a cobia at a marker. If we had been fishing there would have been nothing. Jim
CFCAJUN posted 10-02-2004 10:41 PM ET (US)     Profile for CFCAJUN  Send Email to CFCAJUN     
I had 2 rods on board, 1 gold spoon and one Plastic. Forgot the tackle box. I thought about stopping to wet a hook, but didn't want to spoil the day. If I caught fish, I had no ice. If I did not catch fish, I would have been a little sad. Today was the first time I really just had a great boat ride.

It was short, it was different, but it was really great!

I want to see Ship Island. We picked up a brochure at a rest stop one day, I hope to make that run in the near future.

Better luck next time!

WSTEFFENS posted 10-03-2004 04:00 PM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     

All engines have a "red line", Most domestic engines fall (2 stroke) in the 5000-6000 RPM range. Engine speed isn't a factor with a 2 stroke OB. It is designed to run at full throttle without harm. That is why they are needle and roller bearing crank and rods! The highest wear is on cyl bores as the cyl blocks are aluminum, and relatively soft. By the way you can't run an engine rich as all domestic OB engines have had fixed jet carbs since the early 60,s. Actually if you don't run an OB hard you might dammage it. This is based on the experience of 356 Porsche "carria" engines of the late 50's & 60's who had engine failures due to flatting of the crank and rod jornals (roller & needle) due to lack of engine speed! Great high performance engins, just didn't like city driving!

Run it you won't hurt it! Meatalurgy doesn't change with time!



brisboats posted 10-04-2004 09:01 PM ET (US)     Profile for brisboats  Send Email to brisboats     
CFCAJUN glad you finally got to wring her out. When you say the motor does not sound like it is running 100% at WOT. I am curious what you are comparing it to. The V-4 you have is a cross flow and does have a much different tone when compared to a looper. You are on the right track by tuning your ear to your motor.


CFCAJUN posted 10-04-2004 09:23 PM ET (US)     Profile for CFCAJUN  Send Email to CFCAJUN     
Thanks for the great feedback.

When I am running WOT, and I say it doesn't sound 100%, here is what I mean. My only comparison might not be an accurate comparison but it is all I have to go by. My dad runs a 50HP Mariner on the back of a 16' aluminum Duracraft (I think it's 16 feet, not sure) Everything 1989.

I have run that boat since 1989 and know how to trim her just right, I know the sound of that engine like my heartbeat. When I run with a load and the wind changes or the waves, I constantly trim and tweak the motor to get the maximum speed from the lowest RPM. Always trying to keep as much boat out of the water as I can just before she porpoises.

Anyway, with his engine, she maxes out WOT I think at about 5500 RPMs. When I hit about 4900 - 5200 rpms, she maxes out on speed. If I WOT her, the RPMs go up but no speed is gained. Also, when she is WOT, this 50 HP 3 cylinder Mariner is whining and you hear the difference between 5200 and 5500 RPMS. It almost sounds like if you add another 500 rpms the motor would explode. You can tell she's maxed out.

Ever hear a motocross dirt bike max out in a low gear, you know you've reached the limit and you better shift because the engines screaming? That's what I mean.

Now, with the Evinrude, I don't get that maxed out WOT, engine screaming sound. It's more like a car, you punch the gas to the floor, the engine revs as high as she will, but that's all it will rev and it doesn't sound like she'll blow.

So, I suppose my bottom line is that WOT I don't feel as if the engine is whining or screaming or being over revved. I can tell she is nearly maxed out on speed at 5000 RPM and I may barely gain anything at 5200. I thought maybe if I had bad throttle cables, she was not actually WOT, and being "governed" accidently.

Hope that helped.

grandpas68 posted 10-04-2004 10:34 PM ET (US)     Profile for grandpas68  Send Email to grandpas68     
i didnt see anyone answer his question about running the motors a little rich, and im curious to see what yalls opinions are. We run a bored out 1977 Johnson, based on a 70 horse block and i usually mix the fuel slightly rich. I have not noticed any negative effects, but i could see where it might possible lead to inefficient combustion and carbon build ups. Anyone want to attack this one?
nFL_Bosn69 posted 10-05-2004 11:15 AM ET (US)     Profile for nFL_Bosn69  Send Email to nFL_Bosn69     
While not much of a comparison, I've got a 1969 20HP Johnson that I don't think gets to WOT either, though I also have yet to do a compression check. It winds up to its full speed, but doesn't sound like it's about to blow to pieces(not that I want it to), though when I hit some chop, it will rev and can fell the boat pick up speed. I always just assumed this was because of water friction against the hull decreasing because of the bouncing. It's to the point where it seems to perform better in a light chop with a light headwind.

When I first rebuilt the motor, I ran it a bit rich, but only because it hadn't been run in 20 some odd years. I've started running closer to 50:1 as the year has advanced, since I've noticed carbon building up. So far this year, I think I've put more hours on her than she's had in 35 years. Pappaw would be proud.


WSTEFFENS posted 10-05-2004 11:29 AM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     

Your observations are valid. Based on old "marine archtetecture" base line. Once the hull design speed is reached, speed goes up with the cube (#3) of the Hp applied. That is why a hull will start to "porpose", it wants to fly but falls back into the water. This is different from "chine" walk which is side for side. Both are typical of hulls over their speed limit.

As for running rich. I was under the impression it was fuel, in the question. Rich oil will just get you carbon on the ports and ring lands. That is why they went to 50:1 back in the '60's. With synthetic, (somithing on the line of Amsoil) you could probibly pre mix and go even leaner!

Would I run a large block OB at WOT all day, no I would most likely use the aircraft rule of about 75% power for max all day running. It keeps the stress's low. The difference in sound you describe is most likely due to the reed valves in the induction system (behind the carbs). They "humm" at various levels based on engine speed they would have a "harmonic" sound level a some speed depending on the length of the reed valve and how far it is allowed to flex (depending on the retainer plate).



gcl posted 10-05-2004 03:36 PM ET (US)     Profile for gcl  Send Email to gcl     
Try not disconnecting the fuel line from the outboard when not in use. I find I have much better luck starting a cold engine if the fuel line had remained connected. Give it a shot.
nFL_Bosn69 posted 10-05-2004 04:13 PM ET (US)     Profile for nFL_Bosn69  Send Email to nFL_Bosn69     
I always disconnect my fuel lines, since I store the motor in the house. When I reconnect, I prime until I can hear gas coming through the jet. This is on a one carb system though, not sure how the pressure is distributed on multicarb setups, so may not be the same. Once I hear gas, I choke it completely, pull the rope until it cranks and dies(1-2 times), unchoke, pull once more, blap,blap,blap, smoke,smoke,smoke blap, purrrrrrrrrrrrrrrr. lol. Well as much purring as a 35 year old motor can purr.

As I was sitting at the dock idling the other day, some guy came by with a 40 Merc, I guess 4 stroke. As he approached I could see him talking to his old lady in a normal tone of voice, but when he pulled along side and commented on my boat, he had to yell at me. I felt like some kind of endangered Spotted Owl murderer.


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