Compression / decompressor

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pritch
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Compression / decompressor

Post by pritch » 10 Mar 2018, 09:29

Hi
I just carried out a compression test on my 2010 Tohatsu 20hp ( I wished I didn't)
I'm only getting 90psi but after looking at the service manual( see pic) there seems to be mention of a decompressor that makes the outboard easier to pull start.
It looks like 73 psi is normal when tested with the decompressor engaged.
Do I take it that my decompressor is engaged so my readings are good ?
Thanks
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Andy B
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Re: Compression / decompressor

Post by Andy B » 10 Mar 2018, 12:10

Are you getting the same reading on both bores?
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pritch
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Posts: 224
Joined: 10 Aug 2017, 21:51
Boat Make: BISON 390
Outboard: Tohatsu 20hp
MMSI Number: 10
Location: Staffordshire
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Re: Compression / decompressor

Post by pritch » 10 Mar 2018, 12:44

Yes the same on both.

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Andy B
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Re: Compression / decompressor

Post by Andy B » 10 Mar 2018, 16:29

I wouldn't worry then.
Very doubtful that you'd have problems on both bores.
Sounds to me like you have a very tight motor if you're getting 90psi with the decompressor engaged.
If memory serves me right the decompressor doesn't disengage until the engine exceeds 500rpm.
I doubt you'll be achieving that on the pull start... Unless you're Popeye :o
Needs a good thrashing to loosen it up a bit :D
SOLENT
Waveline 2.3m/3.3hp Mariner
Zodiac 380/ Mariner 9.9hp

pritch
Advanced Member
Posts: 224
Joined: 10 Aug 2017, 21:51
Boat Make: BISON 390
Outboard: Tohatsu 20hp
MMSI Number: 10
Location: Staffordshire
Has thanked: 56 times
Been thanked: 26 times

Re: Compression / decompressor

Post by pritch » 10 Mar 2018, 16:37

Thanks Andy :thumbsup

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