Engine vaccuum port location on 1978 Mercruiser 228

[THenning]

HI All,


Where is the location where I can hook up my vacuum gauge to? Lost a power piston spring and need to find vacuum at idle so I can get the carb tuned.

Running a 1978 Merceuiser 228 with a Quadrajet Carb.


Best,

Tim

 

[Bondo]

Ayuh,.... I doubt there is a vacuum port on that motor,..... unless there's 1 on the carb,...

 

[THenning]

I know the 6 cyl had one on the manifold. Was hoping the 8 did too. Shoot.

 

[Bt Doctur]

nope, sure its a Q-Jet 4bbl? see no mention of a spring

 

[THenning]

No Title

It's the power valve spring for the rods on the main jets.

 

[THenning]

From the Mercury Marine Parts catalog: 38 N.S.S. 1 SPRING, POWER PISTON (ROCHESTER #7029529)...Page 21 item 38 for the 228 Carb on the 1978 Motor. Problem is that part number was taken over by AC delco and then delco stopped making these springs a little after 2008. Reason I need engine vacuum is because I need to know what spring strength I need to replace it with because my only options for getting the boat back in the water are replacing it with hot rodder springs and those are all categorized by inches of vacuum puled by the engine.

 

[Bt Doctur]

unplug the black hose and plug a vac gage there. why not just replace the choke pull off
In the second pic, there throttle return springs . the secondary jet needles are raised by the upper plate as the air is sucked into the secondary openings

http://c777913.r13.cf2.rackcdn.com/quadrajet_carburetor_manual.pdf

 

[THenning]

OK, So I can get an accurate vac reading from the choke pulloff vac port? I thought I might have needed a larger port on the manifold somewhere. To give you an idea on the missing spring it's item # 38 in the attached diagram. It isn't for the metering rods, but the needles for the jets.