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Old 19 November 2012, 12:16   #11
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posted 02-23-2009 07:29 PM ET (US)
I did a thorough investigation of the 75 vs 90 Merc 2-stroke and determined that the only difference is that the 90 has a different high speed jet (carburetor model) and the ignition timing is advanced. Other than that they are identical. Some day I will "upgrade" my 75 to a 90.
Newer models with engine control computers are not that easily modified.

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Old 19 November 2012, 12:25   #12
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Quote:
Originally Posted by Davie
I have a set of 3 here with a venturi at 1.25" what size are the 75's?
Does this help Davie?

75hp uses WME59 carbs with .052/.054 jets
while the 90hp uses WME62 carbs with .062/.064 jets.

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Old 19 November 2012, 14:59   #13
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are the carbs physically different, or do they have different part numbers simply because they are fitted with different jets? is it possible to just change the jets to get the same result?
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Old 22 November 2012, 10:22   #14
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right, ive been doing my own research on this because my carbs have completely different part numbers to what can be found on the schematic pictures. mine just have WME and then 3301-813773, from doodling around on the net it would seem that they are the same as 3301-821946A. ribs marine sell the jets, for each engine you need 2x .062 (#1399-4217) 4.88 each and 1x .064 (#1399-4216) 4.75 each. much cheaper than buying new carbs!
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Old 22 November 2012, 11:59   #15
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Bigger jet on the top carb like the 50/60?
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Old 22 November 2012, 12:18   #16
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yes, though not quite sure why. ive been told that its prob due to the top cylinder needing extra lubrication for some reason rather than performance.
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Old 22 November 2012, 13:00   #17
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Quote:
Originally Posted by Festinghouse
yes, though not quite sure why. ive been told that its prob due to the top cylinder needing extra lubrication for some reason rather than performance.
Top cylinder does run hotter on these triples, more lube may be the reason for larger jet !

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Old 23 November 2012, 09:36   #18
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I have a set of carbs off a clamshell 80hp if they are any use.
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