kc8oye Posted August 31, 2009 Share Posted August 31, 2009 i Idle around 13-14" of vacuum in gear.. but I cruise around 17-19 depending on my speed.. my carb came with a 6.5 power valve which according to holley is about right (1/2 of idle vac).. but it seems like i have to REALLY bury my foot into it to get the vacum to drop below 6.5 when I'm driving.. well into the secondaries opening up.. I've seen a website or two that suggested the powervalve be set at 1/2 the cruising vac.. as long as it's not more then your idle vac.. would it worth stepping to say an 8.5 power valve? since I idle at 13, that's well clear of 8.5 and would get the powevalve in a little bit sooner and be more useful..... Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted August 31, 2009 Share Posted August 31, 2009 this could turn into a good debate, I'm going to go against everything and try a 10.5" and a 8.5" in mine, and I have a idle in gear vacuum of 8.5-9" when street driving I push the gas just to the secondies, the vacuum doesn't drop below 8", and it falls on its face, get the vacuum to drop to 6" (have a 6.5") its takes off in theory...if you're not pulling fuel from main metering, the power valve should have nothing to do with the idle Quote Link to comment Share on other sites More sharing options...
kc8oye Posted August 31, 2009 Author Share Posted August 31, 2009 well.. if you idle below your powervalve you will have a problem with over rich idle sam.. but using that 8.5 might help you.. the only other option would be to remove the power valve completely... add a plug.. and then go up 3 sizes on the jets to compensate... Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted August 31, 2009 Share Posted August 31, 2009 if you are not pulling fuel from main metering (what the power valve adds fuel to...) how can it effect idle???? and if I plug the PV and jet up...it screws up my cruise fuel ratio don't forget I cruise at 3000 RPM, well into main metering Quote Link to comment Share on other sites More sharing options...
kc8oye Posted August 31, 2009 Author Share Posted August 31, 2009 so do I sam.. I run 3300 rpm @ 70 all the time. the problem is the way the power valve system works.. it actully BYPASSES the main metering system.. so it will flow fuel at idle... same as with a blown powervalve. you may have to put up with cruising a little rich to fix that problem.. btw.. is that on your E85 or racin fuel carb? Quote Link to comment Share on other sites More sharing options...
Heckeng Posted August 31, 2009 Share Posted August 31, 2009 It does bypass it, but it still pulls it through the main boosters, while the idle system is through the idle transfer slot and the idle port. I think Sam may be able to get away with this which could be pretty cool. Quote Link to comment Share on other sites More sharing options...
Crow Posted August 31, 2009 Share Posted August 31, 2009 i Idle around 13-14" of vacuum in gear.. but I cruise around 17-19 depending on my speed.. my carb came with a 6.5 power valve which according to holley is about right (1/2 of idle vac).. but it seems like i have to REALLY bury my foot into it to get the vacum to drop below 6.5 when I'm driving.. well into the secondaries opening up.. I've seen a website or two that suggested the powervalve be set at 1/2 the cruising vac.. as long as it's not more then your idle vac.. would it worth stepping to say an 8.5 power valve? since I idle at 13, that's well clear of 8.5 and would get the powevalve in a little bit sooner and be more useful..... The power valve is simply a 'switch' that opens at a specified vacuum. It does not meter the fuel. Metering is accomplished by the Power-valve channel restrictions. I know you can get staged valves in the Holley, that are designed to open at intermediate vacuum, which will meter the fuel until a low vacuum occurs and the metering is switched back to the PVCR's. Bones: I don't think your valve number should be higher than your idle number. If you remove the valve, you should start by jetting up 6-8 sizes to compensate. Quote Link to comment Share on other sites More sharing options...
CrazyDavey Posted August 31, 2009 Share Posted August 31, 2009 just so I can follow this, what kind of secondaries is everyone using? I thought Tim said his were vaccum, apples and apples otherwise this discussion goes nowhere. Also for my education (it's all about me ya know) where does cam profile and ignition timing and advance curve come into play? Acceleration and response can't be all about the carb. I know Holley warns about the secondaries opening too early as some set them up to do. If they open early and there is not sufficient velocity fuel will not be pulled into the venturi and the motor will lay down until it catches up. This results in the "kick in the pants" feeling you get when everything kicks in...just want to keep up with everybody.... Quote Link to comment Share on other sites More sharing options...
monte70car Posted August 31, 2009 Share Posted August 31, 2009 My understanding of the power valve is it enrich the main circuit. I had some information on the power valve and either it got deleted or its in a old post here. I believe I run a 7.5 power valve in my 750 dual feed Holley. I know my doubler pumper has a 6.5 power valve in it, same with the one in the 750 on the Nomad. The power valve is like the pump cams its a guessing game. I know you take your vacuum number at idle and and you need a power valve half the size. And if you have a back fire though the carb. the power valve will need to be replace. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted September 1, 2009 Share Posted September 1, 2009 yes the power valve jet controls the amount of fuel, but as Scott said, it still flows through the boosters (main metering) unless you have a very old holley, they have a power valve blow-out protection staged power valves are for vacuum secondary carbs, I run a double pumper, and need a high flow power valve because I run E85 using the "recommended" way to choose the PV, it only opens when your open the throttle completely, that's the only way you'll getting the vacuum to drop enough to open the PV if this works, it's like adding another circuit, I'm trying to add more fuel without getting into my secondaries, when street driving my car...hitting the secondaries can be hazardous (Tim understands what I mean here ) watch my burnout video, you can here when I hit the secondaries, and it jumps to 7000 rpm in a blink of an eye Quote Link to comment Share on other sites More sharing options...
kc8oye Posted September 1, 2009 Author Share Posted September 1, 2009 yeah I heard you left some pinch marks in your seat sam ~ Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted September 14, 2009 Share Posted September 14, 2009 a little update here I put a 8.5 in mine, with 8.5" of in gear idle vacuum no issues sure helped my flat spot, I'm going to throw the 10.5 in it just for an experiment Quote Link to comment Share on other sites More sharing options...
kc8oye Posted September 14, 2009 Author Share Posted September 14, 2009 i finally put a narrow band o2 sensor on mine.. can't afford a wideband system (about $400) vs the $30 for the narrow gauge and $0 for the spare 02 sensor I had for the car that just got wrecked ~ I'm off the scale rich on the primary side.. and nearly off the scale lean on the secondaries... hrrrm ~ Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted September 15, 2009 Share Posted September 15, 2009 i finally put a narrow band o2 sensor on mine.. can't afford a wideband system (about $400) vs the $30 for the narrow gauge and $0 for the spare 02 sensor I had for the car that just got wrecked ~ I'm off the scale rich on the primary side.. and nearly off the scale lean on the secondaries... hrrrm ~ what's that have to do with power valves???? Quote Link to comment Share on other sites More sharing options...
Heckeng Posted September 15, 2009 Share Posted September 15, 2009 Tim, this could mean that your PV isn't opening up when your secondaries are open, or your secondary metering is not rich enough obviously. Also, make sure that your secondary air bleeds (on top of the carb on the outside of each venturi) are clear of debris. Quote Link to comment Share on other sites More sharing options...
kc8oye Posted September 15, 2009 Author Share Posted September 15, 2009 it's a brand new carb outta the box scott.. i've suspected that that 6.5 pv is just too small for my application. even tho I idle on 13" of vac in gear... I pull almost 20" cruising.. and I'm well into the secondaries before I drop below 6.5".. so this weekend I'm gonna go down one jetsize in the primaries (it's all I have here, I know it should be two) and swap the 6.5 powervalve for an 8.5 and see how it drives. when I meet up with my club at the track saturday.. I'm gonna borrow a jet kit and go up 4 sizes on the secondaries and see if I can find that 0.5 second I LOST going to the new carb.. Quote Link to comment Share on other sites More sharing options...
wallaby Posted September 15, 2009 Share Posted September 15, 2009 If you are like me. you're going to love & hate that narrow band AF guage. It will probably have you doing carb adjustments until the cows come home, even when you know the car is running good. I know I can't get you to ignore the gauge; it just seems like it should be SO helpful. But there are some things to remember about using those narrow sensors: 1. Their idea of "perfect" combustion seldom (if ever) exists in our carbureted engines. The engine runs on the rich side most of the time, and sometimes at cruise you will see it run a bit on the lean side. Most of the time however, the mixture fluxuates back & forth depending on RPM, engine load, and ignition timing. It's a rare day when you see the guage running in the middle...and if it does, you're probably running too lean. 2. The narrow band sensor is focused only on that one magic,"perfect" mixture. It looks straight ahead with blinders on and waits for that ideal mixture to happen so it can tell you about it. If the mixture is lean or rich it really isn't concerned, and has no idea how far lean or rich. Imagine you are looking at a tachometer through a piece of pipe. You can't see the entire face of the gauge, so you aim the pipe at the number 6 and you wait. As your engine speed goes up & down, all you know is whether the needle is to the left or right of that number 6000 you are focused on. And you don't have any idea how far left or right, and you don't care. Now imagine installing the pipe & tachometer in your car, and the view is focused on the 4000 position. That's how the narrow band works. You don't idle at 4000 You don't cruise at 4000 You don't over rev at 4000 You don't even make best power at 4000, but darn it, you have a gauge that indictes when you are at 4000! Quote Link to comment Share on other sites More sharing options...
Heckeng Posted September 15, 2009 Share Posted September 15, 2009 I didn't realize it was a brand new carb Tim, that is weird. Usually they are pretty dead nutz on in my experience, at least close enough to run without worrying. Try that 8.5 and see if it helps, that may be the trick. Also check your float levels. Does your carb have sight glasses or plugs? With plugs, with the engine running and the plug out, the gas should dribble out slowly. Mark, you are 100% correct. Quote Link to comment Share on other sites More sharing options...
kc8oye Posted September 16, 2009 Author Share Posted September 16, 2009 I'm well aware of the limitations of narrow band 02.. but since it's 1/10 the cost of wide band.. I'll live with it. I figure if I'm showing rich.. I'll keep going down on jet sizes till I run into either 'ideal' or 'lean' mixture.. then go back up one and leave it there. same with teh secondary side.. if it's showing lean when I'm in the secondaries, I know I'm WAY WAY lean, since the gauge only shows me 14.7:1 or just a little bit either side.. it should at least be pegged to rich when I'm in the secondaries.. Quote Link to comment Share on other sites More sharing options...
CrazyDavey Posted September 16, 2009 Share Posted September 16, 2009 Tim I know you would like to get answers from the narrow sensor but I think Mark is right, you're going to be chasing rainbows, there's too many variables. I know it's not hi tech but the best way to see where you are is read the plugs after a couple of runs this weekend. For your application that Holley should be spot on if not too rich out of the box. I would say if your going to play do one at a time, PV or Jets or you won't know what did what...JMO Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted September 17, 2009 Share Posted September 17, 2009 Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted September 17, 2009 Share Posted September 17, 2009 Good call Dave Quote Link to comment Share on other sites More sharing options...
Crow Posted September 17, 2009 Share Posted September 17, 2009 Tim I know you would like to get answers from the narrow sensor but I think Mark is right, you're going to be chasing rainbows, there's too many variables. I know it's not hi tech but the best way to see where you are is read the plugs after a couple of runs this weekend. For your application that Holley should be spot on if not too rich out of the box. I would say if your going to play do one at a time, PV or Jets or you won't know what did what...JMO No school like old school. Quote Link to comment Share on other sites More sharing options...
kc8oye Posted September 18, 2009 Author Share Posted September 18, 2009 i got the metering block off today.. looks like holley's documentation was wrong... the paperwork said my carb had a 6.5 powervalve... it actully has an 8.5. so I'm going to leave that alone for now.. and re-evaulate things with the vac. guage. i am gonna drop from the 67 to 66 jets and see what happens.. i'll take a drive up to the speed shop and get some 65 or 64 jets if it still needs to go further.. I figure what I'll do is keep going down on jet sizes until either a) the cruise mixture is dancing around inside the narrow band's range.. and leave it there.. or if I cross over onto the lean side.. then I'll go back one setting... then tomorrow I'm going to go up probably 4 jet sizes on the secondary side and see if I Can get the a/f to stay on the rich side while I'm WOT Quote Link to comment Share on other sites More sharing options...
kc8oye Posted September 20, 2009 Author Share Posted September 20, 2009 o.k.... quick update.. after I made that post.. I realized I was reading the #'s on the powervalve wrong.. the carb *DID* have a 6.5 PV in it.. I took the 8.5 out of my old 600, and put it in the new 650 along with dropping the primary jets one size... it has _NO_ trouble with burnouts now.. lights 'em up with just a touch of the throttle... it drives AMAZING.. SUPER responsive.. amazingly torquey.. and that peculiar bog just as it shifted is gone too I'm not sure if I wanna try a 10.5 just for grins and giggles or not just yet and while cruizing on the freeway it hangs out on the rich side , but in-range of the narrow band sensor so I think that's good.. and in the cold night air it actully reads up in the 'ideal' area. also got to the track today.. went up 3 more jet sizes.. (total of 5 over stock) due to a really stupid mistake on my part i never made a good pass on the bigger jets.. but now the 02 meter was staying in the green zone (slightly rich side of 14.7) so I think I wanna go two more jets just to make sure I'm deep into the rich side and close to 12:1 thats gonna leave me with 66's in the front, and 80's in the back.. seems like a big spread.. but that appears to be what it wants.. Quote Link to comment Share on other sites More sharing options...
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