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Old 11-11-2019, 10:51   #1
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Mariner Outboard 2.5 & 3.3 difference?



Hi,
I have a Mariner 2.5 hp 2 stroke outboard, and would like to upgrade it to the 3.3....the only difference I can find is the throttle valve in the parts breakdown (the carb' body would appear to be the same, so it can't be a different diameter).
However, I have just taken off the carb' to have a look at it and found a restrictor plate (not shown on any of the parts breakdowns I have found) between the carb' and the inlet spigot on the crankshaft base.
Anyone have any experience of removing this restrictor plate please?
I have yet to test the outboard on the dingy, so can't tell if there is any difference in hp.
Thanks,
Neil




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Old 16-11-2019, 10:02   #2
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Re: Mariner Outboard 2.5 & 3.3 difference?

Found this:



So it looks like removing the restrictor is the way ahead.....I have yet to check if the throttle slide goes all the way to the top....if I remember correctly it does.

Jets are the same.

Just awaiting a new fuel tank (thread has gone on the filler cap) to test it....oh, and a nice day of course!
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Old 16-11-2019, 10:44   #3
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Re: Mariner Outboard 2.5 & 3.3 difference?

Never seen a restrictor plate on those just the length of the plunger. Can probably cut it down carefully with a hacksaw
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Old 18-02-2020, 05:48   #4
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Re: Mariner Outboard 2.5 & 3.3 difference?

Restrictor removed, the throttle slide is not restricted (the slide when fully open clears the throat completely) more performance.....job done!
2.5 to 3.3 hp just by removing the restrictor.
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Old 18-02-2020, 18:26   #5
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Re: Mariner Outboard 2.5 & 3.3 difference?

Interesting.

Had a Nissan 2.5 and a Mercury 3.3 concurrently, and sincerely believed that the 3.3 lower unit was geared lower (slower) than the 2.5 based on counting revolutions. Seemed odd to me. Some time after I sold the 2.5 I recounted this, and someone who said they were a Tohatsu (or clone) mechanic stated that this was wrong, that they were identical. I still think I was right, but it didn't make sense for Tohatsu to slow the prop with more horsepower available. All I know is that the 3.3 burned noticeably more fuel, same inflatable.

If you can, could you count engine revolutions per propellor rotation? That would be interesting to compare to my 3.3. I'll have to do this again, myself.

One other oddity about these motors (maybe just those with neutral shifters) was discussed in a previous thread which I will soon post. Several of us have had trouble being able to inject lower unit oil as is typically done. There seems to a blockage that can occur.
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Old 18-02-2020, 19:00   #6
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Re: Mariner Outboard 2.5 & 3.3 difference?

Here is the post:

https://www.cruisersforum.com/forums...de-158524.html
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Old 19-02-2020, 02:19   #7
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Re: Mariner Outboard 2.5 & 3.3 difference?

....the part numbers are the same on the gears for the 2.0/2.2/3.3hp models. I would not expect them to change ratios on the models for many reasons.
1-No need
2-Cost
The reason you will see higher fuel burn is that you are using 50% more power: 50% more fuel burn.....or any % more than the 2.2hp output v fuel burn.
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Old 19-02-2020, 04:02   #8
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Re: Mariner Outboard 2.5 & 3.3 difference?

So removing the restrictor plate results in more fuel burned at same rpm?My dinghy use didn't change, just had a neutral shift for my kids with the 3.3.

I'm skeptical. I would think that the restrictor plate was there to limit maximum fuel mix flow, thus slower top rpm (which I believe the specs show), thus lower hp.

As far as the part numbers being the same, are you sure that this is true across all brand labels? Not that I conducted a complete study, but the only 3.3 I recall seeing at the time was the Mercury. With all other brands it was 3.5. Perhaps Mercury (and Mariner) for some reason spec'ed something different from Tohatsu?

FWIW, this weekend I will determine the gear ratio that my 3.3 has.
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Old 19-02-2020, 06:39   #9
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Re: Mariner Outboard 2.5 & 3.3 difference?

Let us know. The gearbox is different with one having the clutch. Also the different water pumps. Certainly the 3.3 or 3.5 will use more has due to the carb difference at higher throttles.
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Old 23-02-2020, 08:32   #10
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Re: Mariner Outboard 2.5 & 3.3 difference?

My Mercury 3.3 has a final ratio of 2.15 to 1, which is what the specs call for.

So I must have miscounted years ago as I was certain it was different from the Nissan 2.5.

Unless the Nissan was different....
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