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Old 09 March 2013, 20:02   #21
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Now there's a thought - what thread is the spark plug on those engines? The tester you refer to seems to come with metric adapters, will those work?

Mind you I have vague memories of a compression tester which just had a big rubber bung in the end which you pushed manfully into the plug hole while turning the starter ...
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Old 10 March 2013, 09:17   #22
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Ok this is what ive done, removed the prop and tested the engine in gear. At full throttle she revs fine close to 6,000 revs 2,000 more than with the prop on.

i think this points to the prop. the numbers on it are very faded but look like 48 //// 44 445 17R ? i cant make anything else out?
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Old 10 March 2013, 09:32   #23
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17R should be 17P, which is 17" pitch.
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Old 10 March 2013, 10:45   #24
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I believe for every inch of pitch you drop down, you gain around 250rpm?
So if you do have a 17inch pitch prop at the moment, you may need something around the 13inch pitch mark to gain another 1000 revs!
Thats if the plugs etc are ok?
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Old 10 March 2013, 13:03   #25
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I run a 75 mainer 3 cyl 1996 , with a 21p stainless on my 5.3 humber 2 people on board 80 litre of fuel it will quite happily rev to 6000rpm plus @ 36knots ,I have tried 17p and 19p previously, as stated about a 250rpm decrease per pitch size.

from experience I'd check for crud the jets or the carbs for blockages or the fuel system , just from experience.

good luck.
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Old 10 March 2013, 13:20   #26
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Quote:
Originally Posted by jethro110 View Post
Ok this is what ive done, removed the prop and tested the engine in gear. At full throttle she revs fine close to 6,000 revs 2,000 more than with the prop on.

i think this points to the prop. the numbers on it are very faded but look like 48 //// 44 445 17R ? i cant make anything else out?
All that points to is that you've probably done more damage than any already there by revving it at full throttle without load. It tells you nothing apart from that there's at least 2 cylinders running.

It doesn't point to the prop.

Start with the basics. Compression, spark at each plug and fuel to each plug.
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Old 10 March 2013, 15:47   #27
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+ 1 .......
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Old 10 March 2013, 18:57   #28
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yeah, the fault is with engine not prop. 17inch is the smallest i would go as mine will over rev with a 17.
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