2 stage power valve?
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=49667
Printed Date: November-26-2024 at 7:40pm
Topic: 2 stage power valve?
Posted By: rebel skier
Subject: 2 stage power valve?
Date Posted: March-14-2021 at 10:50am
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I am rebuilding my carb (4160 - 85 SN2001). From the records I have the prior owner had it rebuilt in 2005 from National Carburetors. What I have found in the primary metering block is a 2 stage power valve that looks much more restrictive than either the 2.5 or 6.5 that is in my rebuilt kit. I have searched here and can find no reference to a 2 stage power valve. All I find suggests that the single stage power valve is exactly what I want. So I am going with the 6.5. If I am missing something about why my boat would have a 2 stage power valve in it, will someone please let me know. Thanks, Richard ------------- Hotty Toddy lets go skiing! |
Replies:
Posted By: Jonny Quest
Date Posted: March-14-2021 at 11:23am
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From the Holley website: "The purpose of the power valve is to improve part-throttle drivability, air-fuel ratio, and fuel mileage. With high manifold vacuum in a part-throttle situation, this low pressure “pulls” on the valve keeping it closed. As the throttle opens and the load increases, the manifold vacuum will drop. At a calibrated point, a spring inside the power valve will overcome the low manifold vacuum and open the valve. When the power valve opens, it directs fuel from the float bowl into the main well in the metering block. The main well is the circuit that directs fuel into the primary boosters in the venturi of the carburetor. This power enrichment circuit is completely separate from fuel delivered by the main jets and is used to supplement the amount of fuel supplied by the primary jets. Each power valve is rated to open at a given manifold vacuum level. Intake manifold vacuum for carbureted engines is generally expressed in inches of mercury, or “Hg. For example, the most commonly used Holley power valve is rated at 6.5 “Hg, which means the valve will open when manifold vacuum drops to 6.5 “Hg or lower. Idle vacuum can be anywhere from 9.0 “Hg to 16 “Hg, based on engine build, camshaft, etc." If you were to put a vacuum gauge on your stock PCM 351W engine (full manifold vacuum) you would most likely be in the 12 to 14 inches Hg. That would indicate a 6.5 power valve. JQ ------------- Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
Posted By: KENO
Date Posted: March-14-2021 at 12:15pm
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You could probably look at the list number on the air horn and use that to figure out what the original power valve was that the carburetor came with and use that one. Or post the list number for some help  Over the years lots of the marine Holley 600's went to a 2.5 power valve as their their factory calibrations changed. The 2 stage were for better fuel economy You never know what National Carburetor might do on a rebuild |
Posted By: rebel skier
Date Posted: March-14-2021 at 12:30pm
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Thanks. So its list is R-9392, so I see from Holley it should have a 125-25. I will put in the new 2.5 power valve. May darn kit only came with 6 fuel bowl gaskets. Can I re-use the 2 best ones? ------------- Hotty Toddy lets go skiing! |
Posted By: KENO
Date Posted: March-14-2021 at 12:43pm
| Use the 2 best old ones on the top on the front bowl where they're not submerged in fuel, just air to minimize chances of a leak |