Hey there. Do any of you know the original power valve size for a Holley 1904 carburetor on a 223 truck motor? (mine has no numbers on it) I replaced jets from a 64 to a 59 and it winds up quicker at WOT in 3rd, but with cruising at lower constant throttle it’s a bit too lean. Thinking of getting a valve that opens with less vacuum. (20min hard run around town with old NGKRs) Thanks
I'd rethink that. A power valve open at cruise will be a gas hog and way too rich. Cruise A/F ratio is controlled by the main jet. You probably need to hit somewhere in the middle of what you had and now have.
Not sure why you made such a change in main jet size, but you may have gone too far. As noted above, the power valve is for temporary enrichment. Ideally you could hook up a manifold vac gauge and see what your reading is at steady state cruise and get a power valve that would open at a value below that.
It's OK to jet down (or up) within reason, but this does alter the wide open throttle air fuel ratio. This is why drag racers at the track are interested in altitude and humidity and all that stuff before deciding on jet. They aren't ever doing any cruising, but it has a direct effect. Keep in mind the power valve determines when the extra fuel comes in on demand, not how much. That is governed by the power valve channel restrictors underneath the power valve. Basically the PVCRs are just fixed jets. Unless you live at a high altitude or have a performance camshaft a 6.5" or 7.5" is going to be more than close enough. It is a good idea to see what the steady cruise vacuum for your particular engine is if you're picky. If it isn't misfiring or surging while at cruise your jetting isn't too lean, but, if the wide open throttle air fuel ratio ever goes too lean, then stuff will start roasting. Think of what happens when you crack open the O2 on a lit acetylene torch. Point being be careful with jetting if you don't know what you're looking at. Old spark plugs are useless for any serious work. If you want to dial it in close it may be necessary to slightly open up the power valve channels with a pin vise drill set. The flip side of this is a power valve that is dribbling fuel on flat ground cruise. This will burn lots and lots of gas and foul up the plugs, plus you'll need a fuel tanker to follow you around.
Thanks, what’s weird is that 59 jet is what was originally in the carburetor. But I’ll stick with the 64 for now.
sorry, I forgot to mention that the 59 was what it had originally came with but I put a 64 from my spare carburetor in 5 months backs. It was a bit too much for when it was warmer outside.
The plugs have a few hundred miles and with the richer jet they were a darker brown while now they’re a bit more lighter brown and cleared up around the porcelain and ground strap. When it was warmer out I could tell it was a bit too rich, I’m just looking for a middle ground jet. Sorry I forgot to mention the 59 came with the carb and the 64 was one I put in 5 months back from a parts carb when I rebuilt the one I had just to see. Isn’t the main jet functioning throughout all throttle positions though? Or was the richer jet maybe compensating for another issue that’s prevalent at low throttle cruising. This carburetor also has a economizer valve that acts like another power valve, maybe it’s opening too late?
It is really tough to read spark plugs with modern gasoline. They are going to look pretty lean even when running fat. It's a lot better though to run a little bit on the rich side of the air fuel ratio as it is safer. There's a lot of variables to consider when tuning. A factory stock engine with restrictive exhaust versus say headers, a different performance intake design, stock or factory camshaft, everything will tend to change the operating points of a carburetor. You tune or calibrate a carburetor one circuit at a time. Before getting serious about it, everything else has to be squared away, especially the ignition, and ignition timing. Start with checking the fuel pump output pressure, and setup the float carefully and make sure that's within spec. If the fuel pump is wonky or the fuel height in the bowl is out of spec it will throw everything off. If the ignition or ignition timing is buggered it won't get the correct vacuum signal through the venturi, it and it won't be able to reliably light off lean fuel mixtures if the igntion is weak.
It is coming back to me....I had 3x1's on my 170 in college. The power valve is adjustable using little plastic "C'" clips under the spring. Make sure it is moving smoothly, don not pinch the diaphragm.
If I remember right the 1904 power valve is an "atmopheric", having said that I don't know how they work or are adjustable (thanks Rick).
I appreciate the help. I think I figured it out. I went back through and realized the bottom of the choke plate acts as a separator/atomizer for the nozzle the fuel exists, and it wasn’t aligned properly. I re aligned it and now it runs really well at WOT and doesn’t do lean hesitations at part throttle. Basically, the fuel wasn’t being evenly distributed for each cylinder and at low vacuum some cylinders were way too lean while others weren’t.
You really want the fucking manual. Read it, study it, and it will go much better. I'm sure it's available online. Regardless of how the power circuit works we don't want it to open, even a little bit, when steady cruising on flat ground. This is why measuring stuff is so important, instead of guessing or asking random imternet people, because if the engine is modified or out of spec in some way, then things like the manifold signal vacuum changes along with it. I bet that system on the 1904 works pretty good when setup. The power valves in other models don't seem to handle modern gasoline very well, at least the el-cheapo generics.
If your 1904 has a valve that looks like a normal Holley power valve, that’s not a power valve. It is the spark control valve. Only used on Ford apps.
For most of us the fuel we use today is not what our carbs and distributors where set up for when they were built 5 to 10% corn makes a differance. I end up raising 2to4 jet sizes and adding a couple of degree of timming and droping a couple in the vacuum advance.