Power Valve on a Holley 4160

My last time out, had some small backfires. After discussing with several people, said the "power valve" has "ruptured and is leaking fuel into the engine. I went to an auto zone close by my house, and talk with someone and want to make sure this is the proper procedure on changing the power valve out.

First, he explained that you will remove the "front" fuel bowl to the carb. There are four screws to do so. You will spill fuel out so be careful.
Once you pull the bowl out, there are (2)sets of gaskets. One too the carb, and one to the fuel bowl. Blue gaskets. The power valve will be in the middle part of the carb, comes out with cresent wrench, and then put new one in. Replace gaskets if needed, and attach everything back. He said the tricky part is making sure you put eveerything back "in line" where it needs to go.

Parts:

(1) 6.5 power valve
(1) blue gasket
(1) Mentioned I need these clear o rings type gaskets that go on the screws. Is this right?
He also tried to sell me (2) different types of gaskets. One was more open, and the other was more closed in. If that makes since... Also explained does not change your settings on air/fuel mixtures or even idle. Sounds pretty easy to do. Is this correct? Or am I missing something. I am always "grateful" for the help...

Can not wait one day to be able to do everything myself.

Lee, Tom got you covered here
About power valve size I have my doubts on wich is the "correct" one, my carb came with a 4.5 PV, the kit I bought had 6.5 PV, and skidim only sells 2.5...so lots to choose from..I replaced the 4.5 in mine, runs fine.
Tim (TRbenj) is running a 6.5 or higher and he states better throttle response...

How old is the carb,is it pre '92? I blew mine out a couple of years ago after a masive backfire.My back fire was due to miss adjusted points,I don't think it actually causes the backfire,but it is a symptom of one occuring.You will know it by the way it runs,poor idle, black exhaust.I replaced it with a 6.5 and this runs fine now

Gary S wrote: How old is the carb,is it pre '92? I blew mine out a couple of years ago after a masive backfire.My back fire was due to miss adjusted points,I don't think it actually causes the backfire,but it is a symptom of one occuring.You will know it by the way it runs,poor idle, black exhaust.I replaced it with a 6.5 and this runs fine now

Hello Gary,
I do not know how old the carb is? Good question? If I had to guess, probally the orginal one, just been fixed if ever had probs. I had the boat since 05, and had a rebuild last summer. All new guts, and was soaked real good. It sure looks like the orginal carb... But I have had probs on cold starts since the rebuild, never have, and she backfired a couple times between 2300rpm's,-2700's rpms. They where not "wake the neighborhood" backfires, just loss of power and a blup, blup...During the rebuild of my carb, my mechanic said my points where bad also, so re-did those and re-set the timing too. I sent him a email on what was happening, he thinks power valve has rupterd, and has caused the backfires.(Leaking Fuel into motor)
I am putting the boat in the water one more time, to see if it occurs again, but I am thinking it needs to be replaced. One thing I have learned over the last 5 years these Holley carbs are tempermental, and if not one turn of a screw or mixture is not correct that run like "Horse manour"... But they are fun... My boat has always run real good, just since this rebuild on the carb these little problems have occured. I have a mechanic which is cool by me, but thinks of "If it aint broke, dont fix it"! I love that motto, but I always over the last few years point the "Finger" at him when *************** goes wrong.
So my points, timing, and all other stuff has been done, but I cant have my 85 barking at people on the water.... Please help!!

Lee If your going to take it off to replace the valve might as well put in the check valve if you dont have one.Here are the instructions

Steve gave me a pump for the horns I got from work but it would not power them,so after realizing all the parts needed to get them to work and the fact they would need a rechrome I bought these.They look really nice and are LOUD! Oh and don't forget my new wheel. Thanks for asking Pete and sorry for the hijack Lee.

I used a 2.5PV in my rebuild becasue that was what came in it.(89 SN) I talked at length with guys here and elsewhere about swapping ot the 6.5 but in the end decided to stay with the 2.5. Still have the 6.5 in the garage.

According to the Holley book I have, you can test to see if your PV is busted by tightening the fuel mixture screws on the side of the metering block all the way in with the engine running. If it dies, PV is good. If it continues running, PV is busted. go slowly and count the number of turns it takes to tighten them so you can put them back to the correct location afterwards.

skicat2001 wrote: I think my settings are set for a 6.5 power valve.

Come on Lee, what the heck settings are you talking about. That doesn't make any sense. Go online and do some reading to get up to speed on the Carb's components and their functions and then we might be able to help you. Didn't I send you a link a while ago with Holley basics, it's a good basic info read and worth your time.

81nautique wrote: skicat2001 wrote: I think my settings are set for a 6.5 power valve. Come on Lee, what the heck settings are you talking about. That doesn't make any sense. Go online and do some reading to get up to speed on the Carb's components and their functions and then we might be able to help you. Didn't I send you a link a while ago with Holley basics, it's a good basic info read and worth your time.

Alan,
Love those pics of the boat at the renunion.. After reading up on the power valve,does it not depend on vacum to the carb. When the carb is set at a certain level of vacum, then the power valve kicks in and allows enough fuel to pump in gives power to the accerlator pump. If you have a low power valve, it has to go below that point of vacum load and then the power valve kicks in. If I decide to put in a 2.5, my vacaum load my be different than others. What do you think?

skicat2001 wrote:     When the carb is set at a certain level of vacum, then the power valve kicks in and allows enough fuel to pump in gives power to the accerlator pump.

So how do you set the carb at a certain level of vacuum? You don't. Also the power valve has nothing to do with the accerator pump.

I'll try very briefly to explain.

The acel pump is only one short squirt of gas immediatley at throttle up, picture hitting the throttle real hard, what happens? The butterfly opens and your air fuel mix goes incredibly lean and the boat stumbles. To counter that carbs incorporate an accelerator pump which gives a short burst of fuel to offset the additonal air and create a mix that can be burned. Your power valve hasn't even come into the picture yet.

Your accel pump is used to adjust mixture at the low rpm of operation and the power valve is used to adjust mixture at the higher end of rpm. Power valve is probably not the correct term for what it actually does. It's function is to enrich the fuel mixture from approx 14:1 at normal running down to approx 12.5:1 at WOT throttle. This is done for a couple of reasons, one to make power but most importantly to protect the engine from running too lean at high rpms and burning a piston. The added gas actually cools the combustion chamber. That along with the correct heat range spark plug can save a high performance engine from self destruction.

The power valve rating is just as waterdog stated. it is the vacuum at which the valve will open. The lower 2.5 number will open later and the 6.5 will open slightly sooner or at a lower rpm. As your engine gets put under a load and rpm increases the vacuum drops and your secondaries and power valve are actuated.

I would say that a stock 240 hp 351 will be fine with a 2.5 PV. IF you stray from stock and more importantly increase your compression ratio and or max rpm range then you should perform plug chops and determine which power valve is correct for your application.

Hope that helps a little but find a minute and pick up a holley tuning book, it will be money well spent.

81nautique wrote: I would say that a stock 240 hp 351 will be fine with a 2.5 PV.

While this statement is completely true, Im not sure you (Lee) understand why. A stock engine, with its (relatively speaking) restrictive intake, heads and cam, will have no problem pulling a lot of vaccuum- and thus, no problem opening a 2.5 PV in a timely manner. Furthermore, stock carbs are generally on the rich side, so you stand little chance of leaning out the A/F ratio and causing damage.

Thats not to say that if you were to install a 6.5 PV in a stock engine, that you wouldn't notice a slight increase in throttle response (and possibly a corresponding decrease in fuel economy).

In a modified motor that breathes better (due to improved heads/intake/cam), you wont pull as much vacuum- and thus, might benefit from a higher PV that will open more easily. Personally, Im running a 7.5 in my 351w.

Hey TR,
That makes since. In that 351 you are running, do you have big time specs in that motor? Myself, I have always had good throttle repsonce so wondering what is in mine. My fuel economy has always been awful. The 351 or 350's are quite thirsty on gas. I can easily burn a 1/2 tank of gas if I put a couple hrs on it in a afternoon. But I guess I wont know until I pull it. I like better throttle reponce on the low end. Long as if I put a 6.5 in there and dont damage anything else.

After reading more tonight, what causes this? A lean postion, bad fuel pump, or just a bad power valve? I seem to can not find a real answer...

Any holley made since the early eighties do not need the PV check valve kit . Some models have it already, others have the throttle plate orifice resized smaller so that the pressure from a pop doesn't rupture the diaphram.
The problem of the PV rupturing every time the engine pops died with disco, unfortunately the myth lives on.

GottaSki wrote: Any holley made since the early eighties do not need the PV check valve kit .

Holley's web site says anything before 1992