OK... sorry for not getting back to you guys for so long. Last couple days have been wierd to say the least. Anyways... Got the vacuum guage on the car last night. It started out around 11", but I adjusted the needles per Chris's instructions, and now at idle (900RPM), I can get about 12-13" of vacuum, and I mean anywhere between 12 and 13. It bounces with the lope of the cam. "Hot Start" is definately gone since I messed with the timing and replaced the battery. Starts great now, hot or cold. It's still running rich at idle though. Looks like a power valve check and/or replacement is in order. Whats an easy way to empty the bowl on a carb when you don't have an electric fuel pump?
Rick before you do all that to check the power valve, I also realized that first you should open those sight plugs (you have a demon, but I believe it has 'em) and check the fuel metering block levels. If the fuel spills out the side "holes" then you have to adjust the big screw on front and back top until the fuel just barely trickles out. I might be wrong, but even until it just stops trickling out but gets close. Some mechanic told me that, and hey, it's a lot easier to check than taking the carb off to get to the power valve. It might still be the power valve, but ya never know!o No: ~Mark
Hey Mark, ya I think Rick has checked his float levels already (hopefully on level ground), and you don't HAVE to take the carb off to get to the power valve either. Just drain the float bowls, remove the bowls and the metering blocks. Power valve is right behind that, screwed into the main body. Of course if there are gasket sticking issues, maybe you SHOULD just remove the carb. A LOT easier to work on carb, scraping gaskets on a bench.... than leaning over a fender:grin: Tried that once, boy that was dumb!ou: Back hurt for a long time!!
Thanks! Now you'll save me some time this weekend! I am willing to take the :blast: *~gasket challenge~* :beer
Hopefully you don't have as much fun as I have removing those damn (stock) gaskets. Worst scraping job I've ever had:af: If I ever have to do it again I WILL REMOVE the carb! Either use the non-stick gaskets on reassembly or use lots of Chap-Stick on BOTH SIDES!!ou: Good luck man! make sure NO DEBRIS stays inside that carb....:Smarty:
Yup, BIG, BIG cams do need lots of initial/idle timing to isle correctly, and they don't make enough vacuum to use a vacuum advance, so to get even a mediocre vacuum signal to the carb pull orifaces, the initial timing will need to be quite high for any useable signal at all. The BIG cam will also allow for easy starting with large compression ratio numbers, by blowing the compressable mixture back out the inlet port and back up the intake port, and this is wnat kills both the vacuum and the signal to the carb. LESSER, more moderate cam'd engines will definately profit from a CORRECTLY set up vacuum advance and sensible for them, initial timing with the vacuum advance added with full manifold vacuum. There is a place and time, setup for both ways. Take the eatly Corvette's engines. Some with solod lifters and 2x4 setups used only mechanical advance for thier fairly stoutly cammed 11.00:1 engines, but used a vacuum advance, manifold fed, for their lesser performance engines and low perf stock configutrations. It all depends on the cam and other compression/inlet related factors.
I'm almost embarassed to admit it... but I hadn't thought to check the float levels. ou: I just looked at them (the Demon has sight windows), and the rear bowl has gas just up to the bottom of the window, and the front bowl has gas halfway up the window. Sounds like the front bowl is set too high? I'll try lowering it right now. Thanks! :TU: btw.... I thought the only way to get to the power valve was by removing the front bowl??? You can't get to it from under the carb can you? By reading the posts here, it almost sounds like you're saying I should be able to? It's been awhile since I've monkeyed with carbs, but I was pretty sure you had to remove the bowl. o No: Oh.. and I'll mention it again.... This car has a Mallory Unalite distributer. There is NO vacuum advance for it. It's all machanical. (Springs and weights?)
Lowered the floats, and it didn't help with the "rich idle". I found a pretty decent troubleshooting guide online and I guess I'll have to buy some parts and monkey with the guts of the carb. It also has a very noticable "stutter" at about half throttle. If you mash the pedal to the floor, it's ALL GO, but for putting around town, it sounds terrible.
Might have to change idle air corrector and/or idle jetting oriface in the metering block to get it right, just depends on the vacuum signal at the pull orifices. It's a tinker with it situation, have fun!
bananas I tells ya! alright guys.............I am going nuckin' futs here! :stmad: Here's the situation: 1. The motor has a Lunati cam in it.........here are the specs again...234/244 at .050 with a .491" lift on both sides. Angle of separation is 112* 2. I have my electric fuel pump hooked up correct, and the regulator is set between 6 and 7 psi at idle. 3. The floats are set so that gas just barely trickes out of the sight holes.....barely. 4. Initial timing is at about 25* and it's an HEI with the help of an MSD 6AL 5. Idle is about 800 - 900 rpm. 6. Also the carb is a 750 doublepumper with 4 corner idle system. now...........with this setup, the vacuum gauge reads a measly 2 - 3 hg/in. Whenever I close one of the idle mixture screws completely, the gauge goes up. Oh yeah, each mixture screw is about 1 - 1.25 turns from tightned/closed. What do you guys think? Faulty power valve? Manifold leak? There is no white coolant smoke, and the black smoke has mostly disappeared, so it's not as rich anymore, and my eyes don't really tear up either. Nose doesn't burn as bad either. Spark plugs still look pretty black and have a rich mixture characterisitc to 'em. Does a faulty power valve allow a car to idle with such crappy vacuum readings and such little loosening of the idle mixture screws? Oh yeah...........I had everything going that you guys recommended, but I could only get that 13 hg/in reading on the vacuum gauge when the car was idling at 1300 or so. Now that it's about 850 rpm.........the reading is way too low. Could a non-carb related component such as the brakes or a/c and heating unit give this kinda reading if one of those hoses are leaking? Should I just disconnect everything vacuum related and plug the carb's and manifold's orifices up? Just use one port for the vacuum gauge itself? any help will be greatly appreciated! ~Mark
4 corner idle. I've seen a bunch of these carbs used on tings not radical enough for them, and always, they are rich like a dog on the idle. Most favor turning the rear idle screws all the way off, setting the rear throttle plates to be open 1/8th turn past full closed, and idle the engine off the front circuits, like it should be.
Eureka! Man......that is a great suggestion! :TU: I seriously would never have thought of that 'cuz I'm not a pro at carbs, yet, but it makes sense now. That should explain why things got better as I'd shut one screw off. Thanks a bunch! :beer That is the way a q-jet operates, right? Just off the primary's? Anyways.......I am going to give that a try tomorrow morning. If that doesn't work, I think I'm just gonna rebuild (or try to) my 'ol q-jet and ebay the holley. o No: ~Mark
