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jsun325
07-25-2013, 10:18 PM
I've got a '89 ProStar 190 with a Holley 4160 carb. I know the carb can be tuned without a vacuum gauge but using one intrigues me. I've watched the video on the Holley website on using the gauge. They talk about hooking up the gauge to a full manifold vacuum port. The only vacuum port that I see on my engine is the one going to the PCV value. Is this the one I use? Is there another port that I am not seeing? Any insight is greatly appreciated.

catamount
07-25-2013, 10:54 PM
This had me confused at first as well. Every automotive tuning video usually shows a port coming off of the throttle body, which none of us with marine carbs should have.

After careful inspection, I found mine... covered in several layers of paint it may be harder to notice. It is a hex head plug located on the back of the intake manifold here:

http://www.correctcraftfan.com/forum/uploads/12957/Manifold_ccf.jpg

(this is not my picture, just something I found on the internet to approximate what you should see)

jsun325
07-26-2013, 04:34 PM
Thanks!

SugarLake
07-26-2013, 04:58 PM
Is it OK to disconnect the PVC and use that one when setting idle mixture? I'm not sure if that matters at idle or not. The oil filler cap has a breather so crankcase pressure shouldn't be an issue right?

j.mccreight@hotmail.com
07-26-2013, 05:25 PM
Yes it is totally okay to connect a vacuum gauge to the pcv port.

SugarLake
07-26-2013, 05:36 PM
Yes it is totally okay to connect a vacuum gauge to the pcv port.

Should I put a tee in the line or is it OK to just connect to the vacum port and leave the PVC line open?

catamount
07-26-2013, 05:46 PM
Just curious, why aren't you guys using the dedicated manifold port?

SugarLake
07-26-2013, 06:00 PM
Just curious, why aren't you guys using the dedicated manifold port?

Just convenience for me. Boats up at the cabin, want to do this tomorrow, and I don't know the thread size of the port to buy a nipple ahead of time. Saves me a 45 minute trip to the hardware store once I'm up there.

I'm assuming it's just a threaded plug in there now. Did yours already have a nipple installed?

thatsmrmastercraft
07-26-2013, 07:11 PM
Anyone with an aftermarket intake manifold needs to Tee into the PCV line. Not a big deal.

j.mccreight@hotmail.com
07-26-2013, 08:21 PM
Should I put a tee in the line or is it OK to just connect to the vacum port and leave the PVC line open?

No need for a tee, just leave the hose off the pcv valve and install vacuum gauge hose into pcv hose.

j.mccreight@hotmail.com
07-26-2013, 08:55 PM
Ok look here's the deal if you have a bone stock intake manifold with the original carburetor spacer you install the vavuum gauge into the port on the spacer, and just leave the PCV valve open for the duration of the test, there is no need to remove the rear port that is plugged with an allen bolt. If you replaced your intake manifold with a edelbrock or weiand you likely installed a port for your pcv already if you didn't reuse the factory carburetor spacer, if the spacer was reused than again use that port. Some later carburetor's had a manifold vacuum port that was plugged if your carburetor has this port use it. Many ways to get manifold vacuum, but by far the easiest way is to go through existing pcv port

jsun325
07-27-2013, 10:36 PM
All good information. Thanks guys!

johnnye23
08-15-2013, 02:47 PM
lots of good info Thanks