Twin 38 carbs vs. single 40 mm Which is better

[ejc]

Im running a 717 with twin 38s from my old 657 motor. I'm wondering if it would be faster If i changed to a single 40mm I have the intake for a single carb in my tool box. Any opinions?

[quickSX/XP]

Re: Twin 38 carbs vs. single 40 mm Which is better

No, the dual carbs accelerate harder and are faster on top than the single. If you have stock boat you wont notice much difference. Although the singles perform well and are better on gas

[JustplainKevin]

Re: Twin 38 carbs vs. single 40 mm Which is better

No, the dual carbs accelerate harder and are faster on top than the single. If you have stock boat you wont notice much difference. Although the singles perform well and are better on gas

Not doubting you but I have often wondered why? Both cylinders are never drawing air at the same time, right?

[1fastski.com]

Re: Twin 38 carbs vs. single 40 mm Which is better

just do the math :-) single 40 is easy to tune .

[Flyin Fil]

Re: Twin 38 carbs vs. single 40 mm Which is better

I would not switch to a single 40. Twin carbs are better suited to tune each cylinder individually.

Due to numerous reasons each cylinder could and usually does require slightly different jet sizes and or adjustments.

If I remember correctly... If you tune both carbs 100% identically, a 657 is prone to a front cylinder seize, on a 787 it's the back, I don't remember which one on 717 but I think it's the front.

It may be harder to tune two, but, you can tune each cylinder to "its" greatest potential.

[Bill O'Neal2]

Re: Twin 38 carbs vs. single 40 mm Which is better

A stock 587-657-717 upright engine's front clyinder runs hotter than the rear clyinder because of heat transfer from the magneto.

With proper jetting, a single carb can work very well ( just look at all the single carb models that SD has sold).

There is a slight performance gain when using two carbs on any of those motors.