View Full Version : Carb power valve
07-18-2006, 10:17 PM
On a previous thread it was mentioned that if your carbed engine backfired you would need to change the power valve. It seems like the power valve in the carb kits for the 4160 are all different, do I need to be careful or will any 4160 carb power valve suffice?
07-18-2006, 10:53 PM
I would not assume just because you got a backfire that it is the power valve. I thought the power valve circuit was mainly used to richen the mixture during speed changes. If your boat is backfiring from a stop it could be your pump. Have someone pump the carb once or twice while you are looking down into the carb. If the pump works you will see the streams of fuel(engine off). Check the cleanliness of the carb and clean with carb cleaner. Run some good carb cleaner through the tank and see if it clears up. The pump streams should be clean and solid shots of fuel. If this is happenning from a drop of the throttle at 20 mph it may be your power valve. Hopefully someone who knows carbs will be along shortly as I am mostly working on M-Cycle carbs. I do work on my 93 dominator knock off one time use by MasterCraft carb often! Early every year I get the startoff hesitation backfire. I clean with carb cleaner and run additional Gumout through the tank. I then change my plugs for the season and have at it!:twocents: On a previous thread it was mentioned that if your carbed engine backfired you would need to change the power valve. It seems like the power valve in the carb kits for the 4160 are all different, do I need to be careful or will any 4160 carb power valve suffice?
07-19-2006, 08:52 AM
A lot of times a backfire will blow out your power valve. But, your power valve can sometimes survive a backfire depending on how big the backfire was, mine has. If you power valve is blown, it’s usually rather obvious; bogs on holeshot, runs fine as high speeds, smells very rich at idle, possibly black smoke at idle as well.
Backfire is either caused by too rich or too lean, could just need a carb fuel/air adjustment. Mine started to get some small sputtering and backfires last year, converted the distributor to electronic ignition and readjusted the carb and it runs much better now.
On my 4160, I've been using the 6.5" power valve. The renew kits sold by Skidim have the 2.5" in the kit, but the ones sold separate are 6.5". Here's the email response I received from Skidim regarding which they offer.
"The Holley Power Valve we sell separately is a 6.5. That will work on the 351 in that Master Craft. The 351 HO and standard engine will run ok with the 6.5. The new 300 horsepower GM Engines use a 66 main jet with a 2.5 valve. You won't see a difference in gas mileage with either valve.
The Official Engine Parts Supplier of USA Water Ski
07-19-2006, 01:24 PM
My carb backfired a couple of times earlier. It was me that started the thread you mentioned that talked about backfires blowing the power valves in the 4160 carb's. Mine survived the backfires I had luckily. I fixed the problem by adjusting the idle mixture. It was a bit lean. I have the 6.5 valve in my carb and it seems to work fine. I think if your valve is blown you will have all kinds of trouble coming out of the hole, particularly under heavy load. If you're in doubt you can buy a renew kit for about thirty dollars and they come with a new valve and they are easy to install.
07-19-2006, 02:15 PM
I have played with the powervalve size on my 4160 and I can tell you this.I ran an 8.5 ,6.5 and now running a 2.5. Top end was the best with the 8.5 4600 rpms. 6.5 was about the same just not as much top end punch. I lost 400 rpms down to 4200-4300,and some of the punch with the 2.5.It's just a seat of the pants observation to many variables to know for sure,every time I go out it seems I have a different amout of people in the boat.Also fuel usage seems to be better with the 2.5.I could be just hoping that I'm using less fuel.Been paying 3.39 a gal.
07-19-2006, 02:18 PM
It does kind of make sense that the 2.5 could get slightly better gas mileage because it's harder for the secondaries to open on the carb. The less time those things are open the better for a gas mileage standpoint I guessing.
07-19-2006, 09:23 PM
So all of the power valves that come in the kits will suffice!
Thanks that is what I needed to know!
07-20-2006, 11:10 AM
To pick out the proper size power valve you really need a vacuum gauge and check vacuum under load. Remember all these size power valves all meter the same amout of fuel,they just open at different times.All that said I had all three so I just played with the different sizes just for the fun of it.
08-12-2006, 02:46 PM
i've changed the power valve & it seemed to make a difference until I went @ 20 mph for 10 minutes .after stopping for a bit ,I gave it gas & it started backfiring again for a few minutes until what seem like excess fuel was burned off. Do I need to replace the power valve again . I'm getting really thrustrated!
87 PS 190 Ford 351 4160 carb
I did the timing & the wires at the start of the season & also installed the pointless ignition!
08-12-2006, 03:07 PM
Dont be too concerned about popping power valves. Holley has been useing a ball and spring check in the P valve circuit for years. Look on your exploded veiw on the part sheet in your kit, it will show it. You do need to get to the bottom of the backfire problem. Sound like you have fooled with a lot of stuff already. I hope it has not added problems on top of the original problem.
08-12-2006, 03:22 PM
There ya go bro right from there website....
Check out there site. Lots of info
08-12-2006, 06:00 PM
Thanks,:o I'll check it out!