Put a Demon carb on my car yesterday. The car idles WAY high now (1,000-1200 RPM), even after backing the primary and secondary idle adjustments all the way out. It's idleing rich, too. It also sort of stumbles/missfires taking from a redlight or just revving it up. Once it gets past the stumble, the car takes off like a rocket and puts you back in the seat like never before. Definately a huge improvement in performance once the car gets rolling. I believe the carb to be a 750. Bought it off my buddy who had it on a 350 Cheby. Any idea how to get this thing idleing lower (would like around 750 RPM) and get rid of the stumble when you first take off? I can tell already this is going to make a huge diffrence, just need to get it tuned in right. Last pic is of the Holley that was on the car when I bought it. Believe it to be from an early 80's Mustang. It's a POS that leaks gas. Whole top end of this motor is edlebrock with 2.02/1.60 stainless valves and Hooker headers going straight to 2 1/2 exaust with glass packs. No way that tiny carb was flowing near enough. Car would fall on it's face above like 4,000.
I don't know a thing about the Demon carbs, but I borrowed a 750 once because a friend couldn't get it to work right on his mav. I adjusted and tweaked, and still got the same things you are talking about, and could never get them to go away. It just ran too rich and tried to drown on takeoff. Once it got going, it ran GREAT, but spit and sputtered when you gunned it. Hope you can figure it out. I just assumed it was too much carb for our 302s...
Adjust the floats. If that doesn't work you may have to re-jet it. Do you know what is in it now? Pack up the Holley and send it to me. I'll take it off your hands and pay shipping. I'll get something going here: I think a 750 is alittle large for a 302. I have a 650 on the racecar and it runs rich too. Gonna have to do all of the above.
Eddie,, power valves blowing out, cause big hesitation and stuff like that. Jerry, I agree 750 is a bit large and have been told all my life a 302 needs no more than a 600 cfm,,,, but my car loves the Holley 700 double pumper, and I was advised not to buy it. Bestest runnin carb I ever had on it. My car is a 306 with 10 sumthin compression and a big lumpy cam that I dont remember the specs due to old age. Dan
The newer Demon's also have a feature called idle eze. It is a screw under the air cleaner stud. Used to compensate for larger cams. http://www.competitionplus.com/04_15_2004/bg_idle_eze.html
Take a look at your spark plugs too. If they're covered in black soot, that could be fouling them causing sputter, etc. Another indication of too rich. Did you change anything else besides the carb? Have you checked the timing? Dan, your carb sounds like it's suited to the combination you have put together.
Easy Carb to adjust really. First Thing I would do is take it back off. You need to set the throttle plate clearances. Hard to tell you how other than there should only be about .020 showing of the transistion slots showing. Second Get the right Base plate gasket. Do not use the open plenum type unless you have single plan intake. Thirdly as mentioned by Alan. Check to see if it has the updated idle system. Bolt back up turn idle screws back in all the way. Then turn 1/2 turn out. Adjust as needed. This carb maybe to big to get rid of the stumble. Demons are built to work with certain comp ratio and cams. I love them. One other thing I see it has the adjustable secondary check to see what spring is in it and also make sure it isn't adjusted all the way out. You have a vacuum leak,or the idle is being bypassed. See above info and you should get it worked out!!!
Need air bleeds to richen the idle circuits. Call Demon and order them. Real cheap and easy to install.
Mine idles like that because i had a bunch of vac leaks doest look like you have any.... ...if your not going to use the holley 4160 i'd like to buy the inlet
I played with it a little this afternoon. I started by adjusting all 4 mixture screws all the way in, then backed them out 1 1/2 times. Was told that was a good starting point. I have the base timing set at 8 degrees BTDC, and about 35 degrees total advance coming in around 2,500 RPM. I've still got some tuning to do on the distributor. The stumble is gone for the most part, but the car seems to be down on power past about 3,500 RPM whereas before it was pulling like a freight train up through 5 grand. The spark plugs are grayish. The intake is an Edlebrock Performer RPM, as are the heads. I'll check on the idle eze. edit: it does not have the idle eze.
I had an off idle stumble when I first put on my 650 speed demon. A quick change to larger squirters and the problem is gone. That is the only thing I have needd to do on this carb, I love it.
I have a 650 road deamon on my 1966 cyclone gt 390 belive it or not that size carb really woke up the 390. If I had a spare cyclone hood I would put my predator on or as some call it the gates of hell
1 1/2 turns is a good starting point, is it still idling high or is it down to a more normal idle speed? The falling flat sounds like it is running out of advance too soon - when you checked for total advance did you have the vacuum hose diconnected? If not then disconnect the vacuum advance and set total timing to 34 at 3000 and try it again.
