de-rated 6HP Evinrude?

[SnappingTurtle]

I have a de-rated, horse power reduced 1981, 6HP Evinrude made in Belgium according to a search of Evinrude model numbers.

Visually it has the details of the 7.5HP (no 6HP was sold in the US in 1981) sold Stateside for this year, and not the 4.5. In Germany 6HP (where I bought it) is the upper limit for motors not needing a license, so this is done very often here.

When I picked it up the older man I bought it from said it might be a 7.5 and have a restrictor plate but he wasn't sure. I should check. Can you see this plate without taking the carb off.

I can't see anything other than a gasket between the carb and the head, with it mounted. Does this mean, no I don't have one, or do I need to remove the carb to see this. If not would I need to change to a 7.5 carb.

If it does have a restrictor plate, can I simply remove it, or would I also need to adjust the timing, change the jets, new reeds, other plugs, ...

As always, thanks for any response in advance, sorry if this is a dumb question, or has already been asked 100 times before!

 

[CATransplant]

Re: de-rated 6HP Evinrude?

It's tough, over here in the US to find parts lists for outboards like yours. There are several ways to derate an engine. A restrictor plate is one, to reduce the size of the intake manifold opening. The only way to find out for sure would be to remove the carburetor. Another way is to limit throttle butterfly opening. You can see this by looking down the throat of the carburetor with the throttle fully turned open. The butterfly should be perfectly horizontal with reference to the throat of the carburetor.

The exhaust can also be restricted. This could be, again, with a restrictor plate, or with a different part inside the midsection.

Those are the methods that would most likely be used. Others might included lowering compression with a thicker than normal head gasket or a sleeve inside the carburetor venturi to reduce its size. Or a redesigned reed plate with smaller diameter openings.

It's complicated to figure out. I have to say, though, that the difference between a 7.5hp outboard and a 6hp outboard are pretty marginal. Depending on the boat you use it on, you might change top speed by a couple of kilometers or two per hour.

If you can determine where the restriction is on your motor, you may be able to uprate it by simply removing something. It's unlikely, in my opinion, that your engine has a different carburetor, different porting or anything like that. It's probably something very, very simple.

My 1992 6hp Johnson was made in Belgium, too.

You can look at parts for the 7.5 at the site below....just use the menus to get to that motor.
I will note that the engine parts for both the 4.5 and 7.5 are shown on the same page.

http://www.brp.com/en-US/Related.Products/Parts.htm

 

[SnappingTurtle]

Re: de-rated 6HP Evinrude?

Thanks CATransplant!

I really like the motor as it is, but being a old motorcycle and auto racer, I have a real hard time not tuning what can be tuned. It goes against my nature to run a motor at less than it's potential. Sort of reminds me of the old car rides for kids at a theme park.

As long as it doesn't kill the reliability, and it is as simple as removing something or polishing parts the eyes can't see, I am all for it. I thought it would/might make a good winter project if it turns out to be more difficult. If it is as easy as pulling the carb, or adjusting the butterfly I will probably do it this year.

... and yes, I have been known to tune push mowers when I was a bit younger. Don't ask why.

I am really a driver, not a mechanic, in other words I know just enough to be dangerous as my old pit friends would say. Unfortunately the two stroke specialist I know are all in the States. So with this one I am on my own.

The boat it going on is a 9ft by 3ft fiberglass I am rebuilding at the moment. It has no information plate stating it's maximum HP, but it used to have a 20 on it. I know that for many it is just easier to buy a bigger engine than to tweak a smaller one but I don't want the added weight that comes with this option. I am a “less is more” person. Less weight means more fun, less gas.

With the Coast Guard formula I come up with 2-3HP max for the boat. That is about what is needed WOT to set in one place on the Main (where it will be used) river if you are fighting the current.

This is what I share the waterway & locks with (look close and you will see that there is a SUV on the back for size comparison) and it is sometimes nice to have the little extra power to get out of their way when two at once decide to pass.

 

[CATransplant]

Re: de-rated 6HP Evinrude?

I understand. I boat on the Mississippi river and have to dodge barge tows of up to 15 barges at times. I also go through locks, but I do pick my times and contact the lock operator on my VHF handheld. If there's a barge in the queue, I go somewhere else.

I'm saying this because I use a 12' aluminum boat that is 54" wide. I have a Johnson 6hp outboard on it. It's plenty for the river, even upstream in the typical current. I do tend to stay completely out of the main channel, though and well away from the barges, huge cruisers, and others who populate the river.

I understand the need to tune, though. I used to race 50cc and 125cc class road racing motorcyles. Those classes are gone now, but it was always fun to see if you could tweak another half a horsepower out of the bike.

I'm just saying that you're not likely to notice the difference on your outboard between 6 and 7.5 hp. The OMC's of that size are pretty nice outboards, and plane my little boat, loaded with tackle, etc. at about 15 mph. I think you'll do fine.

 

[SnappingTurtle]

Re: de-rated 6HP Evinrude?

Hello CATransplant.

Thanks once again for your informative response. I think I will probably leave it as it is, at least for this season.

I am always amazed at the common points (other than a love for boating) you find among the members in this forum, and the quality of the responses given.

I have a few friends here running in Historic Motorcycle & Auto Racing and it is always a blast to climb on/in and run a few laps around the “N?rnbergring”. The bikes and cars from the 30's to the early 70's were those that my idols rode and it is really something to be able to ride/drive the same machines they road for the factory teams at the time. I have always had a soft spot in my heart for the smaller end of the race spectrum. For many years the manufactures have concentrated on the upper power ranges, this being where they have the biggest profit margins.

With the gas prices being what they are, and America & Europe now competing with the former states of the Soviet Union, China, and India for this gas, I don't think prices will every go back to what they once were. That being said, I think we will see a return to smaller and lighter, and as such perhaps the big manufactures will start promoting the lower end of their products range again as sales of the "big (and ever growing) toys" continue to drop.

These classes of motorcycles & boats are still being raced in Asia and maybe, just maybe ...

 

[CATransplant]

Re: de-rated 6HP Evinrude?

Yes, the smaller classes were, in my opinion, the most fun in road racing. My favorite was a little Benelli 50cc bike that I bought from another racer. It wasn't the fastest bike on the straightaways, but cornered beautifully. This was back in the early 1960s.

It had a paper-thin fiberglass fairing and a tunable expansion chamber that I constructed. With me at 6' 1" and weighing about 140 lb., it wasn't really competitive, but it was really fun, even if I always finished back in the pack. I think its top speed ever was somewhere around 65mph. I lived in a rural area, so I could do testing right on the roads near my home, but always with an eye out for the local sheriff.

My 125cc bike was a Yamaha twin that I had modified. Also not particularly competitive, and a lot more dangerous, due to much higher speeds on the track.

Fun times, those were. Being in my late teens and early 20s and fearless helped. Today, I'd be scared to death of such racing. I'm too old and fragile now.

 

[iwombat]

Re: de-rated 6HP Evinrude?

I really liked my 250 ducati desmo. It had the worm-driven overhead cam with the inspection glass. You could watch that little worm gear all day.

Of course, the manx norton w/ the tappets external to the heads was pretty cool too. Dunno if the valve clacking or the thump-thump-thump was niftier sounding.

 

[SnappingTurtle]

Re: de-rated 6HP Evinrude?

I too remember keeping an eye out for the local sheriff and the city police. I grew up in north Texas and it was a long drive to the closest tracks, too long for training and testing.

We had a lot of desolate roads though, and they would look the other way at the time, as long as we stayed out of town and didn't make a nuisance of our selfs. That has all change now.

I did get 12 tickets once (all at once) from a rookie cop from out of town, who showed up and started running around playing “Barney Fife”. The local judge thew them all out, but I had to perform a little community service, which I already did anyway just for fun. So basically nothing came of it.

My new friend Barney got arrested shortly thereafter by the FBI, for trafficking drugs & stolen guns over the state line. He didn't get to perform community service.

I really enjoy watching the little 50 and 125cc classes race at the vintage races over here. They are still relative cheap to buy and easy to work on. Although parts are now very hard to come by, and must be all custom manufactured by hand.

There are a lot of Italian made Harley Davidson's mixing it up with names like Benelli, Bianchi, Garelli, Gilera, MV Agusta, Morini and Ducati. Then there are the early Japanese contingent screaming aroud the tracks.

I came along after these bikes ruled, and ran mostly Yamaha's in the stock classes as a privateer.

Here are a few old photos ...

Sorry to those not interested in bikes and for getting off topic.

 

[SnappingTurtle]

Re: de-rated 6HP Evinrude?

Well something definitely needs to be done to increase my performance a little. Had it out for the first, finished boat, and new/old motor test run on the Main river in Germany. Motor purred like a fat & happy cat, but ...

... the boat plows through the water at a standstill when fighting the current. Gets kind of scary when the barges are bearing down on you. It was so slow I don't think it will ever plane, even with one person and no gear with this motor as it is. It gets close, but will never come out of the water, even with just me.

It sets so low in the water with two on board, I would really worry about adding a heavier motor.

Now to tune this one to it's “potential” of 7.5hp is another subject.

Are there any good books on the subject of tuning older, small outboards?

 

[Sandhammaren05]

Re: de-rated 6HP Evinrude?

Pull the carb and you'll see that the intake hole is about 1/3 the size of the carb throat. Whether filing it out is enough, I don't know: high speed jet may need to be changed. We have one on Hiddensee, I can let you know next summer .... . But I though that OMC made a 6 h.p. in 1981?!

Is that a Quincy Merc in your photo?

Texas/Austria

 

[SnappingTurtle]

Re: de-rated 6HP Evinrude?

Pull the carb and you'll see that the intake hole is about 1/3 the size of the carb throat. Whether filing it out is enough, I don't know: high speed jet may need to be changed. We have one on Hiddensee, I can let you know next summer .... . But I though that OMC made a 6 h.p. in 1981?!

Is that a Quincy Merc in your photo?

Texas/Austria

Servus Gristi Sandhammaren05!

Evinrude did build the 6HP in 1981, but only in Belgium. It came as 7.5 and the 6HP. In the States there was a 4.5 and the 7.5HP version, but no 6HP. Where as the 4.5 is a different older build style. The Stateside 7.5 is from a optical point identical.

The more I look at it the more I am sure that there is a plate about 3/8 of an inch thick between the piece that the carb & the recoil start rope assemble mounts to and the powerhead. I suspect that this maybe the restricter plate. But I haven't had the time to pull it all apart to check. If it is so I will do a little polishing to it this fall.

The next problem would be finding the right jets. Parts seem to be a real problem at the moment. The older OMC dealers have changed over to the big Japanese brands and are only interested in selling new motors. The new BRP dealers are only interested in selling PWC, and their new three wheel motorcycle. They treat the outboards like unwanted step children.

Hiddensee, would that be the island on the north coast in the Ostsee?

Where in ?sterreich & Texas are you? Send me Personal Message if you don't want publicize it, or if you would prefer not to say that is also OK.

 

[SnappingTurtle]

Re: de-rated 6HP Evinrude?

Is that a Quincy Merc in your photo?

Sorry forgot this part.

Yea, preaty lil? girl, or?

Check out the center folds here: http://quincylooperracing.us

 

[Sandhammaren05]

Re: de-rated 6HP Evinrude?

Sagmal, perfekt Tirolerisch! Wo bist du dann? Wir sind in Ehrwald, Hiddensee ist doch Ostsee, parallel zum R?gen. Where you from in Tx? Unfortunately, I'm in ehrwald, the motor's on Hiddensee. When I (too hastily) pulled carb I saw the restriction, and my memory is that it must be an additional plate, because photos of the 7.5 show the rewind mount as integral part of the intake mfld, and that plate was detached from the mfld. Actually, it would help me if you'll take a look at yours and tell me if there's a plate behind the carb NOT attached to the rewind mount. I can tell you that the jet size is nr. 35 in both motors, but I don't know yet is the carb throat is smaller on the 6.

Joe McCauley
jmccauley@uh.edu
photo from Lake Dallas race, 1977, EP Class. Raced and won for 9 years, also drove JP and Mod VP.

Servus Gristi Sandhammaren05!

Evinrude did build the 6HP in 1981, but only in Belgium. It came as 7.5 and the 6HP. In the States there was a 4.5 and the 7.5HP version, but no 6HP. Where as the 4.5 is a different older build style. The Stateside 7.5 is from a optical point identical.

The more I look at it the more I am sure that there is a plate about 3/8 of an inch thick between the piece that the carb & the recoil start rope assemble mounts to and the powerhead. I suspect that this maybe the restricter plate. But I haven't had the time to pull it all apart to check. If it is so I will do a little polishing to it this fall.

The next problem would be finding the right jets. Parts seem to be a real problem at the moment. The older OMC dealers have changed over to the big Japanese brands and are only interested in selling new motors. The new BRP dealers are only interested in selling PWC, and their new three wheel motorcycle. They treat the outboards like unwanted step children.

Hiddensee, would that be the island on the north coast in the Ostsee?

Where in ?sterreich & Texas are you? Send me Personal Message if you don't want publicize it, or if you would prefer not to say that is also OK.

 

[Sandhammaren05]

Re: de-rated 6HP Evinrude?

Did you race Quincy Mercs? My parents were Mercuty dealer 1957-'61, O.F. Christner was one of my heroes, defending the faith against Dieter K?nig and Anzani, although we raced NOA Pleasure Craft where the competition was first McCulloch, then OMC, then by 1961 it was Mercury all the way but I missed it all, was in the Uni..

Sorry forgot this part.

Yea, preaty lil? girl, or?

Check out the center folds here: http://quincylooperracing.us

 

[Sandhammaren05]

Re: de-rated 6HP Evinrude?

A closeup photo of the starboard side of the 6 hp powerhead might let me see if there's an extra rstrictor plate. It looks like there is one, from your starboard side photo, but I need to see a photo taken from perpendicular, the existing ones are from a rear angle and obscure the required view.

 

[SnappingTurtle]

Re: de-rated 6HP Evinrude?

Sagmal, perfekt Tirolerisch! Wo bist du dann? Wir sind in Ehrwald, Hiddensee ist doch Ostsee, parallel zum R?gen. Where you from in Tx? Unfortunately, I'm in ehrwald, the motor's on Hiddensee. When I (too hastily) pulled carb I saw the restriction, and my memory is that it must be an additional plate, because photos of the 7.5 show the rewind mount as integral part of the intake mfld, and that plate was detached from the mfld. Actually, it would help me if you'll take a look at yours and tell me if there's a plate behind the carb NOT attached to the rewind mount. I can tell you that the jet size is nr. 35 in both motors, but I don't know yet is the carb throat is smaller on the 6.

Joe McCauley
jmccauley@uh.edu
photo from Lake Dallas race, 1977, EP Class. Raced and won for 9 years, also drove JP and Mod VP.

Ja freilig! Was glabsch du den, wenn die Freiden a halbe Tirolerin isch!

We are in Offenbach/Frankfurt now. Girl friends mom is from Innsbruck, dad is from the States. I was born in Dallas, and grew up on Texoma.

She said Ehrwald was a beautiful little town, ein typisches “Tiroler Gebirgsdorf”.

Here are some photos I uploaded from the manifold. Your right about the intake and rewind being integrated in one piece, and directly between that and the head is this plate.

In the second Photo (port side), you can see, but not read a stamp that says, 6 horsepower. So I don't know if the manifold is different than that of the 7.5, therefore needing a little polishing itself, or if the small plate (seen in the photo) is in fact a restrictor plate that could be removed.

 

[SnappingTurtle]

Re: de-rated 6HP Evinrude?

Did you race Quincy Mercs? My parents were Mercuty dealer 1957-'61, O.F. Christner was one of my heroes, defending the faith against Dieter K?nig and Anzani, although we raced NOA Pleasure Craft where the competition was first McCulloch, then OMC, then by 1961 it was Mercury all the way but I missed it all, was in the Uni..

No they came along a little before my time. I remember them being scattered around the little marine shops when I was a kid on the lake and I always wanted one. At that time I was in Junior/High School and had little money for such things. Girls, my Pickup & motorcycle, and gas money for boats took every penny I could earn.

After the Uni, I ran small “Road Race Bikes” when I could raise the money to fund myself as a privateer, there was generally little left for other activities other than paying the rent and eating. I was at the mercy of friends when it came to race boats, and then they were generally no longer competitive & we did it just for fun.

I found two Konig motors on EBay last week for sale. One, a race version, missing a lot of critical parts. The other, one of their production motors, looked very complete, nice and original. I lost the auction.

 

[SnappingTurtle]

Re: de-rated 6HP Evinrude?

photo from Lake Dallas race, 1977, EP Class. Raced and won for 9 years, also drove JP and Mod VP.

Hey we have a celebrity among us!

I wonder if you were one of the guys we used to watch, that I dreamed of being.

 

[Sandhammaren05]

Re: de-rated 6HP Evinrude?

The world is indeed small. I raced the boat shown in the photo several times on Lake Texoma. I just now saw your response with the very helpful photos because Iboats didn't email me about your new posting last summer. I'll be able to take a look at the motor in Jan.

Actually, Ehrwald isn't that pretty (too many new buildings), but the air is always good here and I sit with a view of the Zugspitzbahnliftstation. however, I'm now suffering under the ban on outyboards in Tirol and Bayern! Where can I find a parts list for our 6 on the web?

Ja freilig! Was glabsch du den, wenn die Freiden a halbe Tirolerin isch!

We are in Offenbach/Frankfurt now. Girl friends mom is from Innsbruck, dad is from the States. I was born in Dallas, and grew up on Texoma.

She said Ehrwald was a beautiful little town, ein typisches ?Tiroler Gebirgsdorf?.

Here are some photos I uploaded from the manifold. Your right about the intake and rewind being integrated in one piece, and directly between that and the head is this plate.

In the second Photo (port side), you can see, but not read a stamp that says, 6 horsepower. So I don't know if the manifold is different than that of the 7.5, therefore needing a little polishing itself, or if the small plate (seen in the photo) is in fact a restrictor plate that could be removed.

 

[Sandhammaren05]

Re: de-rated 6HP Evinrude?

Your photos show carburetor-intake manifold-leaf plate, so there's no restrictor plate behind the carb. One must remove the intake manifold and file or grind out the intake hole to match the outlet side of the carb to boost from 6 to 7.5hp. The shape of your intake manifold looks like it matches that of a U.S. made 1981 7.5, not a 1979 6. Question is where to find a parts catalog online for the Belgian made motors.

Thanks again!