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Author Topic:   Honda Outboard Question
fester posted 08-14-2001 08:00 PM ET (US)   Profile for fester   Send Email to fester  
In the process of buying a 15 horsepower honda outboard and I found a dealer who said he has a year 2000 9.9 horsepower honda. The dealer indicated that in year 2000 the 9.9 and the 15 horsepower were the same moter with the exception that the 9.9 had a restriction screw which limited the opening of the throttle. He also indicated that I could buy a 9.9 and remove the restriction screw and the motor would be the same as a 15 horsepower. Is this true? If it is, I will buy the 9.9 because he is going to sell it to me for $1900.


dgp posted 08-14-2001 10:04 PM ET (US)     Profile for dgp  Send Email to dgp     
While I can't speak specifically about this make and model, it's standard practice in the outboard industry to derate horsepower by installing restriction devices in either the intake or exhaust. If the number of cylinders and displacement is the same on both ratings it's highly likely the 9.9 is a derated 15.
On my own Mercury 50HP Four Stroke, the only difference between it and the 60HP model is an "isolator plate" between the carbs and the intake ports. When my 3 year warranty is up I'll change the plate.
Clark Roberts posted 08-15-2001 06:58 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Generally speaking there are several differences in "same block" engines with different hp ratings, among which are compression ratio, reed valve lift, timing, carb jetting, carb venturi size, intake and exhaust porting, exhaust tuning etc.. it's a good idea to have part numbers checked and compare before beginning in order to determine the exact extent and $ and therefore the feasibility of such a modification! Been there, done that! Happy Whalin'... Clark.... Spruce Creek Navy

Bigshot posted 08-15-2001 09:09 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Clark that is true on 2 strokes, not sure about 4's. Supposably the only difference between the 60hp Suzuki 4 and the 70 is the computer($1000+) which determines most of what Clark said(sans reeds,etc). With a cruder design like the small Honda it might be something as stupid as a governor. I would find out for sure.
dgp posted 08-15-2001 10:45 AM ET (US)     Profile for dgp  Send Email to dgp     
According to the Honda website, the 15HP has the same bore size as the 9.9 but different stroke, so you would have to change pistons or connecting rods or both to upgrade from 9.9 to 15.
I doubt Honda would go to the expense and complexity of an engine governor.
Clark Roberts posted 08-15-2001 10:49 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
To specifically address 4 strokers (which I should have done) differences in "same block" engines of different hp ratings can be combinations of: compression ratio, engine control module (ECM)programming , valve lift and duration (cam specifics), valve number and size, other head and piston dome (combustion chamber) specifics, exhaust tuning, intake tuning (critical on electronic fuel injected - EFI - models), etc... there must be more but that's all this feeble old brain can think of ! Happy Whalin'... Clark... Spruce Creek Navy
SuburbanBoy posted 08-15-2001 01:08 PM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     

In any case, if the stroke is different (9.9 to 15), chances are the dealer lied about the restriction screw upgrade. Imagine that, a dealer lying! There is no free lunch, and there is no magic 5.1 hp restriction screw. Find a new dealer. Try an internet purchase. The urban legend about ensuring prompt service if you purchase your outboard locally is big BS. If the outboard fails the chances are pretty high that you will suffer no matter who sells the engine.


dgp posted 08-15-2001 01:37 PM ET (US)     Profile for dgp  Send Email to dgp     
The only caveat to all of this is that the info I got from the web site is either 2001 or '02 model year data. The dealer maybe completely correct in what he's telling you about the 2000 model year.
fester posted 08-15-2001 03:36 PM ET (US)     Profile for fester  Send Email to fester     
I appreciate your comments. In talking to the dealer where I am considering purchasing the outboard, he has both a year 2000 9.9 and 15 horsepower. He tells me they are the same motor and the 9.9 is $400 less. The dealer went on to say that in 2001 Honda redesigned the motors and the current year 9.9 and 15 are different. I call Honda directly and spoke to a customer service representative about this. It was obvious he was not very knowledgeable but he indicated that he thought in year 2000 the 9.9 and 15 had the same block but the stroke and cam were different. I do not know whether this is true or whether Honda just wants to sell more expensive 15 horsepower engines. Given the unknowns with all of this, I think I am going to get the 15.

Whaletosh posted 08-15-2001 03:52 PM ET (US)     Profile for Whaletosh    
As an example of what Clark is stating. I talked with my dealer today about my impending engine swap from a carbed 60 HP Mercury 4-stroke to an EFI Mercury 60 HP 4-stroke. According to him another dealer tried a comparison test of these same motors on a Montauk. The EFI was 4 MPH faster. He didn't give specifics, but I suspect that the EFI engine allowed a larger prop to be used due to greater low RPM torque.

Another example, the new Honda 225/200 four strokes a very close to being the same motor. The big difference is wether the Variable Valve Timing is enabled or not.


jimh posted 08-15-2001 10:33 PM ET (US)     Profile for jimh  Send Email to jimh     
There may be some other differences between 9.9 and 15 horsepower engines which share common blocks and displacements.

I had a friend whose sailboat was powered by an auxillary outboard on a bracket. He bought the 15-HP model, thinking it would be better, but the engine turned out to be terrible in that application. It was tuned/tweaked for more horsepower at higher RPM. Chugging along trying to push the 25-foot sailboat it was always fouling the plugs, coughing, sputtering, etc. My friend thought the 9.9 would probably have been a much better choice.

The engines might be geared differently and have different pitch props, too.

SuburbanBoy posted 08-15-2001 11:00 PM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
Honda direct says it has different cams and displacement. Don't believe the dealer, he wants to sell you his left over 9.9. If you want/need 15 hp, pay for it. The dealer is full of fertilizer.


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