Small 4 stroke sound question
#1
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Small 4 stroke sound question
Hi all,
I just bought a 20hp Merc 4 stroke to replace my 15hp 2 stroke Yamaha. I have had small 2 strokes in the past and all would make a sound like marbles bouncing around in the upper rpm range. The 4 stroke also makes the marble sound. I was very surprised. Is this normal for 4 strokes as well? Is not detonation. Engine calls for 87 octane and I'm running 91 non ethanol fuel.
I just bought a 20hp Merc 4 stroke to replace my 15hp 2 stroke Yamaha. I have had small 2 strokes in the past and all would make a sound like marbles bouncing around in the upper rpm range. The 4 stroke also makes the marble sound. I was very surprised. Is this normal for 4 strokes as well? Is not detonation. Engine calls for 87 octane and I'm running 91 non ethanol fuel.
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The following 2 users liked this post by BillK:
oconnor marine (08-16-2020), SB (08-15-2020)
#4
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Only reason I put the 91 octane in we were tubing and figured the engine would be loaded. I can't get ethanol fuel by my house and seen it at the pump and said what the heck. I knew it could hamper performance a touch but figured it would be safer with the engine loaded. Don't want to damage it the first few trips out. The fuel economy is great. This is a fuel injected engine. Definitely better then the 15hp 2 stroke It replaced. Probably burned 3 1/2 gallons of fuel with 3 trips out. Drove 50 plus miles with one day of tubing. Engine came with a 10 pitch prop. With 2 on board it runs 27mph over the max rpm. 4 adults runs 24 at a safe rpm. Hooked up a tack to verify. Have a 11pitch stainless prop on order. Should run 30ish mph. If it still over revving they sell a 12 pitch. With 4 adults on board the 10 is perfect. Might but a 9 for tubing. Still have more testing.
I know this is a performance boat web site, but I enjoy my inflatable for exploring. Well enough of my rambling. Back to the lake now to enjoy my vacation.
That's for the help guys!!!