outboard carbs

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outboard carbs

Postby jus1moore » Tue Mar 30, 2010 9:50 am

whats a good carb to use on the k&b 7.5 outboard? running a stock carb now works well but thinkin about puttin a hotter carb on if there is one. and what is the best carb to use on the 3.5 k&b outboard? red/ gold/ or the stock black one?i noticed the throat size diff on them the larger the better maybe???? no pipes or mufflers on them YET running 25% to 35% fuel. both on tunnel hulls. thanks .
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Postby SteveM » Tue Mar 30, 2010 12:07 pm

The 3.5cc outboard in stock trim, no mods and running 25% to 30% nitro fuel seems to work best with the gold carb. The black carb will give the best throttle response, but has the smallest venturi opening. The red carb is from the older 7.5cc inboards and has a larger venturi but will work with careful tuning. The newer gold carb is in between and seems to be the best compromise. There was also a purple carb at some point and a buddy of mine had one. No idea on the specs and he never did use it so I cannot comment.

I ran either the stock 7.5 carb and eventuallt went to the Prather Mod Engine Kit and ran the exhaust throttle with no carb. Lots of noise and less than ideal throttlr response but I did get lots of power.
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Postby jus1moore » Tue Mar 30, 2010 8:10 pm

steve you are just a wealth of information thank you again. sounds like i might want to try the gold carb .going to run the stock black one this year then see what the gold does next season. if i understand you correctly the red carb would fit the 7.5 and the3.5 ??
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Postby SteveM » Wed Mar 31, 2010 3:29 am

jus1moore wrote:steve you are just a wealth of information thank you again. sounds like i might want to try the gold carb .going to run the stock black one this year then see what the gold does next season. if i understand you correctly the red carb would fit the 7.5 and the3.5 ??


The red carb fits the older 7.5 inboard not the outboard. Some of the guys used to modify an OS carb for the 7.5 outboard to make it fit.
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