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Elgallo
03-09-2010, 02:51 PM
If I were to buy a brandy new 4160 for me PCM 351 powered PH, would I have to change anything internal to it such as the power valve ect? Or would it be just bolt on and go?

I'm getting tired of some of the minor problems I'm having with getting the idle right so it stays where it should, xtra cold blooded nature of late ect. and not give me fits at the worst time e.g. recovery onto my trailer.

SCOOTER
03-09-2010, 03:12 PM
The two Holley 4160 marine versions that are available for the 351, both have a 2.5" Hg power valve in them.

Elgallo
03-09-2010, 03:34 PM
Scooter:

Can I intrepret your responce to mean NO mods on my part would be necessary?

SCOOTER
03-09-2010, 03:39 PM
No, you may need to change it, many here use a 6.5" Hg power valve.

Elgallo
03-09-2010, 05:17 PM
No, you may need to change it, many here use a 6.5" Hg power valve.

Thanks Scooter. I will keep that in mind.

Kurt
03-09-2010, 06:02 PM
The lower the number of the power valve, the further open the throttle has to be for it to open (to enrich the mixture under load). The number of the PV indicates the manifold vacuum at which it opens. This means that a 2.5 should give you better fuel economy than a 6.5, BUT, you may be running lean under load in the mid-range (2500 - 3000 RPM).

It seems as though both PCM and Indmar chose to use 6.5 PVs in the carbs they put on their 351's. This actually follows the guidelines that Holley outlines in their tech bulletin on selecting a PV. They say to measure the manifold vacuum under normal idle conditions (in the case of a boat, in gear and moving unrestrained in the water) and then divide that number by 2 to get the PV number. If the idle vacuum measures 13 in Hg or greater, they say to use a 6.5 PV.

The idle vacuum on mine runs around 15 - 16 so it would seem that a 6.5 is the ticket. Why Holley installs a 2.5 in their stock marine carbs, calibrated for a 351, I don't understand.

One of the advantages of recently built (past 5 - 6 years) carbs or renew kits is that they use non-stick bowl gaskets which means that you can open the carb up, a couple times, and change the PV without having to buy new gaskets. Opening older carbs usually meant destroying the gaskets and having to install new ones. If the gaskets are blue or black and feel a little slippery, they are the later gaskets. Older gaskets are tan and feel more like normal paper/fiber.