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Old 12 July 2008, 11:57   #1
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Uprating Mariner from 25hp to 30hp

Hi - I have a Quicksilver 380HD and a Mariner Marathon 25hp (1 year old). I have been told the 25hp is exactly the same as the 30hp and all you need to do is replace a restrictive gasket that is fitted between the carb and the engine with the one that is used on the 30hp.

Has anyone done this? Is it really this straight forward? Does it need rejetting?

Had 31mph out of it on my gps with 2 people so 5hp should make it even more fun...is a great package! Just need some of those transom wheels now.
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Old 13 July 2008, 03:58   #2
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When you start riding a motorcycle in holland. the first 3 years you got the maximum of 25KW. But most bikes are more. they place another manifold on the bikes, with smaller diameters, so the kw drops. They dont change the fuel settings of the carb. Because the only thing you do with a smaller manifold is let less mixure in the cillinder.
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Old 13 July 2008, 12:23   #3
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think it may need a larger jet size too. i have uprated couple of yamaha models in the past without much trouble .
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Old 14 July 2008, 15:51   #4
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I have the exact same engine and was told that it required the fuel jets to be altered. I haven't done it, due to increased fuel consumption but if it's fairly simple and reversible than I'll give it a go. I shall watch this thread with interest.

Chatts, that engine came with 2 years warranty - check what impact uprating the engine may have on that warranty.
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Old 14 July 2008, 18:14   #5
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Didn't realise was 2 yr warranty, assumed was only 1, will check that!

New gasket thing is ordered and should get it on wednesday so will post the details once I get the spanners out.
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Old 15 July 2008, 07:31   #6
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Don't be surprised if it drops into "limp home mode" - I thought this trick with an aged Suz DT25 was literally a case of removing the "WOT stop" on the throttle shaft. That worked fine and I got 30 horse holeshot.... then 20 seconds later I got the warning blip, 55 seconds later it dropped into limp home mode. One Key off/on later, and the same thing happened. It would run all day at 3/4 throttle......

Still don't know if it was a TPS overshoot or RPM trip, but one (or both) of them sent it into limp home. You may find the mechanical changes are easy, persuading the engine management it's a 30 may be a touch more difficult!

Good luck tho'. Also remember to tell you insurance, coz if you crunch it.......
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Old 15 July 2008, 17:22   #7
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Quote:
Originally Posted by Chatts View Post
Hi - I have a Quicksilver 380HD and a Mariner Marathon 25hp (1 year old). I have been told the 25hp is exactly the same as the 30hp and all you need to do is replace a restrictive gasket that is fitted between the carb and the engine with the one that is used on the 30hp.

Has anyone done this? Is it really this straight forward? Does it need rejetting?

Had 31mph out of it on my gps with 2 people so 5hp should make it even more fun...is a great package! Just need some of those transom wheels now.
If its a twin cylinder, single carb version, that looks just like a Tohatsu, then just take the carb of, remove the gasket that has a small slot in the inlet, buy a gasket for a 30hp and put it in. The carbs are just the same, no need to replace any jets. We do this all the time on some of our test engines, saves having 2 different engines!
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Old 15 July 2008, 17:54   #8
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Thanks. Got the gasket, will try fitting it at the weekend.
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Old 16 July 2008, 06:34   #9
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Where did you get the gasket from Chatts? Let me know how you get on with the fitting and subsequent performance of the engine.
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Old 16 July 2008, 16:36   #10
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Think it was somewhere in Exeter. Will find out and let you know.
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