help with a 8hp mercury question please

[up the creek]

hey gang i am looking at a 8hp jap made 2003 mercury tomorow to possibly buy..
has anyone owned one and do you know if they can be tuned to a 9.8 or 9.9hp as i think tell me if im wrong that the 8 9.8 and 9.9 are the same cubes so is it just a carby tweak etc to get a little more out of the 8hp?? 8hp may be enough but if i can get more it would be good..
thanks..;D

[aussiebasser]

No, different valves as well apparently.

[Noelm]

Lots of motors share a common basic engine, most however are too costly (or near impossible) to make them into the next HP up, lots will tell you things like "it's just the carby jets" but in reality, lots can be different.

[fishwpa]

What happened to the 18hp you have? Why are you now looking at an 8hp? Have l missed something? Thought you were looking at a tinny 3.5 to 4.0 for your 18?

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[TheRealPoMo]

Yeah you lost me too Creeky...Wots going on ?

[up the creek]

What happened to the 18hp you have? Why are you now looking at an 8hp? Have l missed something? Thought you were looking at a tinny 3.5 to 4.0 for your 18?

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lol fishwpa andmopo you 2 dont miss a trick i cant do amnything without being audited... but yes i do have the 18hp brand new not even broken in yet.. to get a tinnie and trailer for it i want brand new and i have to pay my c/card out before i can chock it up again for around 4.500 sooooo i got a little $50.00 tinnie sittin around and i was gonna get a little motor and play and get out there until i can get my 18hp set up going which may take until summer to pay off so i was just gettin sumthin i can afford in the mean time... :-?

[ericcs]

pretty sure the 8 is a de tuned 9,8hp(169cc), while the 9,9 is a de tuned 15hp(262cc)!

[up the creek]

pretty sure the 8 is a de tuned 9,8hp(169cc), while the 9,9 is a de tuned 15hp(262cc)!

they do look online specs as the 6 8 and 9.8 being same cubes same everything and only difference being a slightly bigger carby jet..
thats why i asked if it can be tuned up.. may be silly buying and 8 and wanting to tune it up .. why not get a 9.8 and be done with it.. but it was just a good cheap little engine and i of course will squeeze every ponyy out of it.. ultimately i will try find a 9.8 and be done with it.. thanks for your replies..

[scottar]

Just whack the 18 on it.☺

[up the creek]

Just whack the 18 on it.☺

lol scottar i just had 2 scotches dont tempt me...but here comes another paragraph... i got my 1st new motor ever.. i intend soon to move to anywhere along the murray river and make it my happy hunting ground for fishing, boating, and playing.. i do if i can want to save the 18hp for fresh water so it lasts longer and dont want to wack it on a shitty tinnie.. but i cant afford new tinnie atm.. so im lookin for a old tinnie and an old little motor to play with in the mean time..:P

[Noelm]

Just putting a bigger jet in a smaller HP motor will just make it run rich, it will not increase the HP by 25%, more fuel in requires more air, and a way to get it all out the exhaust, and timing to suit.

[TheRealPoMo]

My American 9.9 Mercury was a 15 with a restrictor plate fitted. No carb changes required - just toss the plate between carb and motor in the bin....not sure about smaller Jap ones.
Honda did similar with my XR400 to get through ADRs....didn't last long or take up too much room in the bin.

[up the creek]

Just putting a bigger jet in a smaller HP motor will just make it run rich, it will not increase the HP by 25%, more fuel in requires more air, and a way to get it all out the exhaust, and timing to suit.

the jet was like .02 of a difference in size so maybe you could just tune the air fuel carby mix screw.. all other specs were the same.. could be wrong i just read a website briefly i would just buy a 9.9 and be done it was just the motor i found was the right money and i was just askin if i could then id get the few extra ponies.. motor fell through anyways..

[up the creek]

My American 9.9 Mercury was a 15 with a restrictor plate fitted. No carb changes required - just toss the plate between carb and motor in the bin....not sure about smaller Jap ones.
Honda did similar with my XR400 to get through ADRs....didn't last long or take up too much room in the bin.

yup some are that easy as we know my 18 tohatsu and a 15 jap super are just the throttle cam shaft opening a bit wider..