HICKL Posted November 13, 2006 Share Posted November 13, 2006 I just need a consistent answer. I have 2 Holley 450's on my tunnel ram, to adjust the "fuel mixture" or "idle mixture" or whatever you want to call it, (the two screws at the bottom of the primaries), if you back out the screws, is it richer of leaner? I keep getting conflicting info, if it is an air screw, then to me backing out would make it leaner but the holley web site itself says backing out is richer. (I just read on a random holley as I can't remember my part number). Someone please explain. thanks! Jeff Quote Link to comment Share on other sites More sharing options...
Just Jim Posted November 13, 2006 Share Posted November 13, 2006 Turning the idle mixture screws on the side of the metering block, out,counterclokwise,will richen the mixture.Turning them in will restrict the flow of fuel to the idle circuit and lean the mixture.Only the odd ball Holleys made for fuel economy work by turning in to richen. I don't think your tunnel ram was made for economy. Quote Link to comment Share on other sites More sharing options...
LeeMS Posted November 13, 2006 Share Posted November 13, 2006 Correct, FUEL is meterd by turning in the mixture screws. A blown power valve will allow fuel to enter through the enrichment circuit thus the meter screw will have little effect. With two carbs and eight idle circuits (the rears are fixed and are used to consume rear bowl fuel if you never get into the secondaries thus keeping fresh fuel in the bowl) you may not get much idke variation when turning them in or out. An infared machine would be helpful. Lee Quote Link to comment Share on other sites More sharing options...
HICKL Posted November 13, 2006 Author Share Posted November 13, 2006 I was wondering if you could close off one carb and adjust the other, if I screw any one of the 4 all the way in, it does start to sound like it will die, but once I back it out a turn or so, I can't really hear any more change. The car run's pretty rich at idle or cruising rpm's, at WOT the plugs look great (like after a 1/4 mile pass) but after a month of cruising, they are pretty black. Quote Link to comment Share on other sites More sharing options...
jimszx Posted November 13, 2006 Share Posted November 13, 2006 1. Hook a vaccume gauge to a good vaccume sorce 2. Warm up engine to operating temperature and turn off. 3. Set all idle mixture screws on both carburetors, turn clockwise until seated then turn counter clockwise 2 1/2 turns. 4. Start engine, turn all 4 screws 1/8 turn counterclockwise and check vaccume gauge, reading should increase. 5. Repeat screw adjustment sequence until the vaccume drops. Turn all 4 screws 1/8 turn clockwise 6. Adjust idle speed to desired RPM Done. Quote Link to comment Share on other sites More sharing options...
HICKL Posted November 13, 2006 Author Share Posted November 13, 2006 So if Understand you correctly, my base is 2 1/2 out and I will go further out (richer) from there? I figured my starting point would be out 1 turn or so. So the bottom line is I am looking for max Vacuum pull? Thanks a bunch. Jeff Quote Link to comment Share on other sites More sharing options...
jimszx Posted November 13, 2006 Share Posted November 13, 2006 Usually you will go richer but each engine intake combination is different and you might have to go leaner but I doubt it. Just follow the vaccume gauge and you can't miss. Good luck, Jim Quote Link to comment Share on other sites More sharing options...
HICKL Posted November 13, 2006 Author Share Posted November 13, 2006 Thanks, I'll give it a shot. My plugs may be a bit fouled so I may probably need to replace them to get a good read, will play around with it anyway. Jeff Quote Link to comment Share on other sites More sharing options...
jt1 Posted November 13, 2006 Share Posted November 13, 2006 Good advice from jimszx. One thing I'll add, while you've got the vacumn guage on it, note the reading, and be sure the power valves are lower than the idle vacumn. You want them closed at idle, not open. jt Quote Link to comment Share on other sites More sharing options...
blueovalz Posted November 14, 2006 Share Posted November 14, 2006 I had to eventually go with a 2.5 power valve in order to keep it closed during idle. Camming and many other parameters will require different valves. Quote Link to comment Share on other sites More sharing options...
HICKL Posted November 14, 2006 Author Share Posted November 14, 2006 What do you guys think I'm some kind of an idiot? Everybody knows to make sure you have the right power valve! OK, here's where I laugh at myself. Months ago, when I set this thing up, I checked the power valves under advice form this board and was satisfied that it was correct. I guess I had my wires crossed because I re-checked it last night and I have 8.5's in there and am pulling 7 lbs max. What a bonehead, I can't tell you hom many people have mentioned this to me and I have responed "yah yah, I already checked that". Will try some 5's in it tonight and start over with the idle circuit tuning. Man I'm stupid. Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted November 14, 2006 Share Posted November 14, 2006 ...what's a power valve:confused: Quote Link to comment Share on other sites More sharing options...
HICKL Posted November 14, 2006 Author Share Posted November 14, 2006 Question guys, I have read to go 2 lbs less on the power valve then my intake vacuum. The Holley web site says to go 1/2 of your intake vacuum. I am at 7 lbs of vacuum, should I buy a 5.0 or 3.5? Quote Link to comment Share on other sites More sharing options...
jt1 Posted November 14, 2006 Share Posted November 14, 2006 There are a lot of theories on power valve selection. My somewhat goofy method, which has worked well for me, is to tape the vacumn guage to the windshield where you can see it, then take a drive. Watch the vacumn at steady state cruise, then select a PV 0.5 to 1.0 below the cruise vacumn. The goal is to get the PV to open as the vacumn drops when you get on the gas, and to be open before you use up the pump shot. jt Quote Link to comment Share on other sites More sharing options...
HICKL Posted November 14, 2006 Author Share Posted November 14, 2006 sounds logical, I wish I would have done that before I tore both carbs down. I may just split the difference and go with a 4.5 or something. I can always check it later and change them again. Quote Link to comment Share on other sites More sharing options...
HICKL Posted November 15, 2006 Author Share Posted November 15, 2006 I went with 4.5's, one of my 8.5's was blown, seems to be running much better (go figure). I set my idle screws per the instructions below and it seemed the happiest at about 1 1/4 turns out. Does this seem right? I also drove it a little with the vacuum gage stuck to the windsheild and while it idles at 7 to 8 lbs, it cruises at 15lbs. I have never watched vacuum except at idle so was wondering if this made sense. Thanks Jeff Quote Link to comment Share on other sites More sharing options...
Just Jim Posted November 15, 2006 Share Posted November 15, 2006 Yeah,those numbers seem about right. The base setting for the idle mixture screws is 1.5 turns out so 1 1/4 is good. The 4.5 PVs are a good choice also based on using about 1/2 the idle vacuum. 15lbs seems a bit low for cruise but may be normal for a tunnel ram. I bet it runs better now,right? Quote Link to comment Share on other sites More sharing options...
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