Any outboard motor mechanics?

graham

graham

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My Suzuki 4hp 4 stroke outboard has the identical engine to the 6hp version.There is a small metal plate attatched to the carburettor that restricts the throttle opening fully.(mine has a 4 stamped on it)

To increase the power output is it as simple as changing this plate to one with a 6 stamped on it or are other adjustments needed?

The 4 pushes our 22 foot boat along at nearly 5 knots but it could be nice to have a little bit more power on occasions.

I am pleased with the motor as a small yacht auxillary,bit slow to start when cold but grips the water well when manouvering quieter than my old 2 stroke and the icing on the cake is it charges the battery a bit.I wouldnt recommend it for use on a tender,too big and heavy for lifting in and out of cars regullarilly.
 
Sometimes it's even easier than that. You just take the restrictor plate out!

On some engines you may need to alter the carburation by putting new jets in. A friendly dealer may be able to help, but sometimes they get a bit "precious" about giving this kind of information away.
 
Re: Any outboard motor mechanics?re:Joe Cole

"precious ". Wonderful word. Describes that well known dealer attitude completely !
 
Sometimes simple but often not, can be as complex as new camshaft and or valves & head (4st), re porting (2st), Exhaust tube (2st), new carb(s) or re jet (4 & 2st) or just a re jet & ignition timing and or removal of a restrictor either on the intake or exhaust side. On a 4st it would be unlikely that just removing the restrictor would have a real effect unless accompanied by a re jet & ignition timing adjustment to balance the extra combustion air.

David
 
I would also want to check for any difference in gear ratio and prop diameter and pitch.
 
Are you sure about that? I have always been under the impression that manufacturers used restriction plates as an easy and cheap way to modify engines so that they got two different models out of the same engine. If they have to re-port/re-gear etc an engine they are half way towards producing a new engine in it's own right.

Certainly on one of my outboards (8hp Mariner) the 6hp and 8hp models are identical apart from the restrictor plate and possibly the carb jets (My manual is on the boat so I can't check it at the moment)

You may well be right, it's just that what you are saying is very different from what I thought the case to be. Just curious.
 
i have had a look on the Suzuki website.Apart from the revs the only other difference I can see is the price £625 for the 4hp and £889 for the six hp.

Seems a bit of a rip off to me .
 
What's the betting that they would say that doing it this way keeps the price down on both engines? /forums/images/graemlins/mad.gif /forums/images/graemlins/mad.gif /forums/images/graemlins/mad.gif
 
If the only difference is in the paintwork and a restrictor plate in the lower powered motor, surely it is a racket to charge more for the higher powered engine.

As the paintwork would cost the same on both and the resrictor plate cost more on the low powered engine, surely the 4hp should cost more than the 6hp?

Or am I being naive? /forums/images/graemlins/tongue.gif
 
Re: A racket

er no, it's not a "racket". It's not a racket that solicitors etc charge you loads for stuff they could just tell you at zero cost to them, it's not a racket that dsiney charge people lots for allowing them to print mickey mouse on the tshirts....

..and it's not a racket to make an engine that delivers 4hp that is in fact the same as a 6hp, with a restrictor. It's 4hp at the moment, what's the problem? Would it be a problem if there was *nothing* in the engine but it nevertheless worked, somehow? Not really. We just have a psychological problem with peopel not "working hard" to earn money - so we happily pay engine servicing and housecleaning and loads of stuff based on an hourly rate that actually rewards sluggardly slow work, not fast results.

Anyway, back to the issue - I agree with Joe Cole - I'd take the restrictor off- you can aolways put it back if it's rubbish. I reckon the difference in jetting and cams and props etc at these v small power levels will be negligible.

Incidentally, old motorbikes used to be even more of a er "racket" - Sunbeam used to make the same bike and runnem up on a dyno, the gooduns being called "90" and the friday jobs "80".
 
The manual tells you nothing about port timing ect, take a look at the parts fiche and the real story is revealed, but a service manual just shows how to fit an exhaust tube for instance, it does not and needs not tell the level of tune or back pressure, ressonance etc. if I recall correctly the Smaller tohatsu derivatives use jetting and exhaust tube differences, and have you seen the price of an exhaust tube??.

There is a way to get a little more out of any non computer controlled 4stroke o/b or inboard for that matter at no cost all, though that is a secret

Does anybody really think that a couple of £12 jets and 5mins with a screwdriver is going to give an extra 10-25% power and give you a product which you would have to have shelled out a lot more for.

David
 
Re: A racket

<<Sunbeam used to make the same bike and runnem up on a dyno, the gooduns being called "90" and the friday jobs "80".>> That's nothing. I once went through a whole tea chest full of A65 webs until I found one that fitted the bearings that should have fitted all of them (yes, the bearings were the right size). We were an open target for the Japanese motorcycle industry, even if they hadn't employed unfair tactics like inventing a sideways splitting crankcase so your front garden doesn't try to impersonate Saudi Arabia.
 
David,

That's interesting and I am sure that it varies between manufacturers.

However, with my engine I am sure that the only difference is the restrictor plate. My workshop manual gives the part numbers for both engines and the only difference I have found is the restrictor plate and possibly the jets. All other components are identical. I know because bad weather meant I was stuck in harbour for two days last year; it's amazing what you end up doing to kill time! /forums/images/graemlins/wink.gif

So in answer to your question, in the case of the Mariner 6hp, yes, I do think that it is an easy job to get 25% more power!

As I say, I can't talk about other outboards, though I do understand that this is common with motorbikes too.

Out of interest, what do you base your comments on?
 
Restrictor plates on motorcycles to pin them to 33bhp for the new laws are fitted between the carb and the head, so there is no need to change anyhing else. Theyjust restrict the total amount of combustible mixture into the pots.
 
[ QUOTE ]
There is a way to get a little more out of any non computer controlled 4stroke o/b or inboard for that matter at no cost all, though that is a secret


[/ QUOTE ]

Are you going to share the secret with us? /forums/images/graemlins/shocked.gif
 
joe
you are correct, it is a cheap way of adjusting power, the increased flow of air through the venturi picks up more fuel, i suggest that he takes the plate out and tests it.
stu
 
he's having you on, any simple non computerised engine is easy to play with, you cant change the timing because the optimum is used otherwise the engine would not run efficiently, you can take restrictor plates out and get full power, so thats no secret, apart from playing around with port blending any thing else and he's talking twaddle!!
stu
 
Yes, you're right.

To be honest I was beginning to think that he is something to do with the trade; hence all this talk about things being more complex than they really are. If I am right then it just confirms my earlier comments about dealers being "precious" about these things. /forums/images/graemlins/smile.gif

I had hoped he would come back in to support his earlier claims but it seems to have gone quiet. Maybe after the weekend?

Of course, if I am wrong then I'll be eating humble pie. /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif
 
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