Re: Help out a new boat owner
That diaphragm (not diagram) does 2 things. It pulls open the choke if you apply power while the choke is not all the way open. And it restricts the rate of the opening of the secondary air flaps. Otherwise when you snap the throttle to wide open it would bog.
You can get manifold vacuum in a few places on my 5.7. Doesn't your intake have any plugged ports?
Your carb # is 17084516. 1708 is a Q jet from the 80's or later, 5th digit is application year, which means nothing, they probably didn't change them since 84. The 6th digit "5" indicates California application for some reason. I think they all have that. Mine does. 7th digit "1" is Chevrolet. Last digit is a transmission code so it's moot. The line below that is a Julian date with the first field being day of the year and the second field is the year, 1988.
Go to cliffshighperformance.com and get the phone number for Cliff, he'll talk with you and get you the right stuff. Very good guy, dependable, professional, and reasonably priced. I wish I had called him first. By the time I found him I had a Mercruiser kit that was missing a lot of the stuff I needed. It was cheaper to get one of Cliff's kits and add a couple of things than it was to add stuff onto the Mercruiser carb kit. His stuff works. He will do your carb (kinda costly for my wallet) or send you the stuff to do it yourself.
My boat absolutely leaps onto plane even though it has a high pitch propeller. It's due to Cliff's book and parts.
