Offshoreonly.com - More air through carb = less power. What does this mean for jetting?

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I've never even owned the same boat that long so I wouldn't know. I will say I've always ran the gafrig or comparable SS flame arrestors and never had an issue nor seen any gains with just the non coastguard approved single outside screen.

Currently posting from the boat.

Rigged up the vacuum gauge to a vacuum port below the carb, getting vacuum around 2.5 at WOT. Hard to tell exactly as I’m ripping across the water.

Ran the gauge to the flame arrestor nipple, needle did not move at all at WOT and stayed 0.

I assume this is telling me my 800cfm carbs are too small.

Quote:

Originally Posted by SB (Post 4747197)

Yes. We are a boating community on dirt and gravel roads. Most boats on trailers as we have close to 20 yr waiting list for docks that have max 26’ rule. Sand dust all summer, especially when dry. Abrasive Grit gets in house and boats and every thing else.

It’s a big country. Not every area is the same.

Sorry to hear about your dust and abrasive gritt on the water , you probably have to wear a mask and aviator goggles , that sucks. but on the bright side you get your face exfoliated . 26' boat length limit too.. Thats a place I would definitely avoid

Quote:

Originally Posted by getrdunn (Post 4747639)

It's not so much the screen that's the issue. It's the sharp turns into the carb that restrict flow and create turbulence that also interferes with booster performance as well. The only reason I went to the K&N filter is that I could get velocity stack style hardware to use with it and stay legal. I'm pushing the limits of the 4150 platform with a custom 1000cfm version and I need to make sure I am getting every CFM I can get. I had a very large Gafrig spark arrestor, but it was a flat plate bolted to the carb. The other problem I have is that because I have such a big cam my in gear idle vacuum is 2.5". If I start to pull vacuum at full throttle my power valves will close and lean out the motor. When you push the limits, you have to walk a fine line. Everything matters!

Quote:

Originally Posted by AWOL (Post 4748222)

Yup. 2.5" is huge. 4bl carb's are rated at 1.5"Hg (unless the carb cfm is a marketing lie), so you are pulling much more than 800cfm thru that carb and losing power. How much ? Dunno, but did I mention 2.5HG is a bunch ? :)

Quote:

Originally Posted by AWOL (Post 4748222)

If your flow is restricted due to turbulence of the air entering the carb it will look like the carb is too small as well. Check the manifold vacuum with the spark arrestor off and see if there is a difference. Preferably you would run this with a velocity stack on the carb to smooth the airflow into the carb to maximize it's capability.