9.8 Mercury speed prop

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ces308
Posts: 52
Joined: Sun May 02, 2021 8:18 pm
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Location: Houghton Lake, mi

9.8 Mercury speed prop

Post by ces308 »

Hello all. I need some propeller advice. I have a 8’ Mini Most hydroplane , flat bottom boat with a 1964 9.8 Merc and I’m wondering if anyone as played with some speed props for that kind of set up. I just installed a tach and I’m running a 9-9 prop with some cupping on it . It runs 25 mph gps with my big butt in it. Any suggestions? I also have a 1971 110 Merc I’m going to put on after I get some data with the’64.
Thanks for looking!
Chris
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8’ Mini Most.  ‘64  9.8
8’ Mini Most. ‘64 9.8
BE884B8B-338E-4696-AF0D-52151CAA5933.jpeg
SteveC
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Location: Kenosha Wisconsin

Re: 9.8 Mercury speed prop

Post by SteveC »

That's moving right along with a 9p. I have not personally seen any props with a taller pitch than 9 for them. I would bet that you are turning plenty of revs,I don't know if you can add more pitch on a standard prop. Perhaps Dave McKinney will chime in.
2 KD-4s, 2 KE-4's, 4 KE-7's, KF-3, KF-7, KG-7 rat, 4 KG-7's,2 KH-7's, 2 KF-5's, 2 Mk-5's, 4 Mk-20's, 7 Mk-25's, Mk-28.5, 3 Mk-10's , Merc. 450, 10 Merc.110's 62,63,67,68,68,68,69,70, 70,71,14 200's, Merc 60, Merc 800(71), & 1984 "D.U." 7.5
DaytonaJohn
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Re: 9.8 Mercury speed prop

Post by DaytonaJohn »

I have the 10" bronze on mine 48-48924A1 in this picture. Normally I have the Michigan PM-19 2 blade aluminum that is 10" pitch. The Mercury equivalent is 48-47926 A1.

I doubt you will gain 1/2 mph with the 10 inch pitch using a 9.8
Attachments
propeller Mar 18, 2012 002.JPG
dock use #1 May 2, 2012 004.JPG
John Timmins, Ormond -by-the-Sea, Florida. Retired licensed marine engineer from steamship companys under contract with the Marine Engineer's Beneficial Association, a union of merchant marine engineers since 1876. Ship your cargo on U.S. flag ships !
SteveC
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Location: Kenosha Wisconsin

Re: 9.8 Mercury speed prop

Post by SteveC »

Nice prop John, I am usually looking for 7p props as I don't have anything really light enough for the taller pitch props.
2 KD-4s, 2 KE-4's, 4 KE-7's, KF-3, KF-7, KG-7 rat, 4 KG-7's,2 KH-7's, 2 KF-5's, 2 Mk-5's, 4 Mk-20's, 7 Mk-25's, Mk-28.5, 3 Mk-10's , Merc. 450, 10 Merc.110's 62,63,67,68,68,68,69,70, 70,71,14 200's, Merc 60, Merc 800(71), & 1984 "D.U." 7.5
DaytonaJohn
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Re: 9.8 Mercury speed prop

Post by DaytonaJohn »

Thanks!

Maybe somebody familiar with the 10XS or whatever it's called can speak up. I have no further comments to add.
John Timmins, Ormond -by-the-Sea, Florida. Retired licensed marine engineer from steamship companys under contract with the Marine Engineer's Beneficial Association, a union of merchant marine engineers since 1876. Ship your cargo on U.S. flag ships !
ces308
Posts: 52
Joined: Sun May 02, 2021 8:18 pm
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Location: Houghton Lake, mi

Re: 9.8 Mercury speed prop

Post by ces308 »

Thanks for the feedback….I had it in the water today to check the new tachometer I installed out. I am assuming that with the stock prop (9-9) it should be turning 5k . WOT was 2930 on the tach . I forgot to bring some small tie strips with me so I couldn’t adjust the coils on the plug wire to see if I can get a closer rpm reading. Anyone had any luck with these tachs?
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dave bernard
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Re: 9.8 Mercury speed prop

Post by dave bernard »

should be about 5500 RPM
Tom Brockmeyer
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Re: 9.8 Mercury speed prop

Post by Tom Brockmeyer »

DaytonaJohn wrote: Mon Aug 22, 2022 11:12 pmMaybe somebody familiar with the 10XS or whatever it's called can speak up. I have no further comments to add.
This isn't a 10XS powerhead... Or anything else in common for that matter.
Lake Lanier, 30miles North of Atlanta, GA
Old Mercury outboard fan... Especially the fast ones!
Mercury/MerCruiser, Evinrude/Johnson & VolvoPenta Technician (After my suit & tie wearing career was done!)
DaytonaJohn
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Re: 9.8 Mercury speed prop

Post by DaytonaJohn »

I know a guy who had to wrap the transducer wire around both spark plug wires on his Mark 25 to get his Tiny Tach to read correctly.
John Timmins, Ormond -by-the-Sea, Florida. Retired licensed marine engineer from steamship companys under contract with the Marine Engineer's Beneficial Association, a union of merchant marine engineers since 1876. Ship your cargo on U.S. flag ships !
bobvdinghyracer
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Re: 9.8 Mercury speed prop

Post by bobvdinghyracer »

Set to 2stroke 1 cyl
7.5 9.8 s ke7 kf7 kg7 kh7 wiz10,wiz10q wiz12,mk15 mk20s mk25s mk30,50,55,58,10a,15a,28a,200s,35twin,300,350,400,450,500,650/4,
650/3,kg4q,kg7h kg7q ,wiz12h,wiz12q, mk25pop,30h,450q,25ss, 25xsmodh, 650/3cyl mod h, 35twin mod.16/21 25xd mod-16/21h
AllanF
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Re: 9.8 Mercury speed prop

Post by AllanF »

I have a 1964 Merc 110 (9.8hp) bought new by my Dad. This motor came with a 2 blade aluminum prop 9" dia. x 10" pitch.
It easily pushed a heavy home - built wooden boat - or my 8' 3 point hydroplane. A GlenL Tiny Titan. It ran 29 mph - uncorrected speedo.
It would scream at full throttle.
My friend had a Minimost? - his was heavier. The Merc did not rev as high on it.

Check the rpm's now and get a 10" pitch bronze and cup it or maybe the aluminum 10" can be cupped.
Your 9" cupped is about equivalent to a 10-11" pitch.

I tried a newer 9.8 on it once. It came with a 3 blader. My impression was with all the silencing done - it did not breathe/wind up as freely as the '64!

You could also try raising the motor - although not much.
On the Hydro - I went from 25 mph to 29 just by tilting the motor out to the 2nd or 3rd tilt pin hole.
For some reason - it does not look like a Minimost? I thought they had enclosed sides/air chambers????

Have fun - a great motor!!!

Allan
ces308
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Location: Houghton Lake, mi

Re: 9.8 Mercury speed prop

Post by ces308 »

This summer I bought a 1971 Merc 110 from this guy for $50. Bucks… he said he couldn’t get it running and thought the coils were bad. When I got it home I pulled the pugs and pulled it through and it had a great spark in both plugs! I removed the carb, cleaned it and tried it in the tank and she ran like a million bucks! So I put it on the MINI Most to compare and it would not get me on plane where the ‘64 did without leaning over the bow. Tried moving the pin , but unless I put my weight to the front it wouldn’t do it.
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AllanF
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Re: 9.8 Mercury speed prop

Post by AllanF »

I believe the 1971 Merc 110 had the infamous Thunderbolt ignition system?? Maybe needs a good tuneup and wiring check?? Also check ignition coils with an ohmmeter - only way to be sure they are good.
The powerhead is essentially the same on the '64 and '71 models - just brackets for the recoil and different throttle linkages, remote fuel pump etc.
It should easily plane the boat.

Allan
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