CC247

Anyone ever watch a vacuum gauge while running? What rpm and vacuum do you see? If my boat was a car I'd say I've got a plugged up converter. Only 3" at cruise to Wot, what gives?

oldandtired

Ideally, you should see 0 at WOT. I have never put a vacuum gauge on a boat, but high vacuum=idle/low throttle position, low vacuum=power/high throttle position. Try measuring the vaccum at your cruise rpm with the boat in neutral and you'll see plenty of vacuum. I haven't hooked up a vacuum guage in many years, but I don't remember using one for anything other than diagnosing at idle/very low throttle positions.

Rene

CC247

I see 11" at idle, 14" at 2500 in neutral. As soon as I drop it in gear I see 5-6" at 800 rpm. Then 3" at cruise 3000rpm.

madbouyz

My old 351W had one and it was a great tool to let you know if you needed a tune-up . There was other things they are good at warning about but I guess you have to know what the signs are. A friend tried to install one on his 289 Holman Moody but the cam selection resulted in a gauge that constantly jumped all over at idle.

If I remember correctly mine would pull 20" at idle rock steady.
Of course, the more the butterflies open up , the lower the gauge goes !

kennyo

Your gauge might be bad.

CC247

blown head gasket