Fixed the flooding problem. I have gotten the car (454) to "idle" at 800 rpm, but I have the mixture screws on the primary only open about an 1/8 of a turn out. Any more out and the car runs too rich. I can actually closes the mixture screws all the way and the car keeps running. Pump pressure is 5 lbs and I have set the tranfer slots as stated in LARS's paper...what up with this Might Demon (750)???????

Takes throttle fine. Have not set timing yet ...just advanced it so the car would run (new motor) for breakin.

 

i have a demon 850 on my 383 and it does the exact same thing. it blew my mind that it will keep running. and when turning the mix screws in it supposed to stumble to give you a good idea how to tune, right? mine speeds up!!!!! i hate this carb. its only good when i floor it.

 

where are your floats set????

 

i've got also a 850 on a 406ci application, never gave me (up to now ...) any problem, keeps a good idle and when floor it woooow

 

Bob - float in the front is just above the middle in the sight glass. Float in the rear is in the middle.

 

why don't you try lowering them to just under the middle rib. i have a healthy 350 and i'm just barely at the the lowest rib.... you said timing isn't adjusted yet...i would adjust timing before i tried to fine tune the carb.....


don't be surprised if you have to close those transition slots some as the last part of the final carb tuning to bring the idle down.....just make sure you adjust them evenly.

 

I'll get the timing fixed at about 16-18 degrees tonight...was just bothered that the thing would still run with the primary mixture screws closed.

If I understand all Demon tuning right I should be able to make the engine idle with by using only the mixture screws...the transfer slots need to remain at .020 for primary and secondaries??

 

no....its a multiple step program......the 4 idle screws will get you the best A/F mixture and you can expect the idle to increase as you make these perfect.....you then go back and turn the transition slots (both evenly) to get the final idle speed.....and the floats are integral to this process.....three steps.....float, idle screws, transition slots and don't be surprised if you revisit it 2-3 times to tweak perfectly...use a vacuum gauge and you will know when you hit the proper A/F mixture

my idle screws are 5/8 out

 

Two things:

1.vacuum leak? Is your carb new? If so, there is an option called the idle-eze screw. All it is a glorified vacuum leak. Close it!!!!!

2. I also would do as bob says and lower the float level.
If the float level is too high, it will run rich. I had the same problem out of the box on my demon and after turning the screws all the way in, it still ran rich. I looked at the float level and it was above the third line. I lowered it to in between the lower line and the middle line.

In the end, the screws will probably be 1/2 to 3/4 of a turn out.
Mine are a 1/2 turn out.
Thanks,
Joe

 

hey Joe you guys gonna thaw out today????? mid 50* here today

 

I'll give er a shot tonight and let you know what happens...I just discovered the "idle ease" on the Demon web site and will try adjusting that too.

One last question (for now )... The transition slots will change from the initial .020 setting once I get the idle and mixture set correctly -right? Or does it still need to be .020? Secondaries have to match the fronts too?

 

don't adjust the Idle eze....just close it ...... and yes the the final adjustment of the transition slots will probably be under the .020 original setting and yes they have to be done uniformly to both. this seems like a PITA but once you get the hang of it you will really like it

 

I had to drill the throttle blades with .100's or something close to that to give my idle screws a full range of adjustment. Now mine are out anywhere from 2 full turns to @ 1.5 on the drivers side.

I tuned mine with an exhaust sniffer from each pipe. Apparently my single plane with a spacer doesn't run perfect A/F ratio side to side.

IMO - changing the float level to adjust the idle ratio is a poor practice. The miniscule pressure change of a 1/4 inch of liquid is next to nothing. I also use the biggest titanium needle and seats to maintain the highest unfoamed level of fuel.

The .020 is most important on the primary the secondary may be opened to increase the idle. I have a 900-950 idle.

 

There is a direct relationship between the idle SPEED (not air/fuel) screws and the transfer slots. Mixture screws do not change the amount transition slot exposure, they only change the ratio of air and fuel that comes out of them. Yes, primary and secondary should be set to the same amount.

This is how I would do it:

1. With the carb off the car, close the idle-eze screw.
2. Still with the carb off the car, set the transfer slots on the primary and secondary side to .020 using the idle speed screw.
3. Still with the carb of the car, set the air/fuel mixture screws to 1/2 a turn out.
4. put the carb on car.
5. start car.
6. Check float level. It should be in between the first and second line.
7. Allow the car to fully warm up. This means ATLEAST 160 degrees.
8. Set idle speed by turning the primary and secondary idle screws in or out the same amount. This will change the transition slots.
9. Go to the mixture screws and turn one 1/2 in and see what the car does, it may take a couple of seconds. Then turn it back to the original spot. If when you turned it in, the RPM went down, then turn the screw back to the original spot and then try turning it 1/2out. (Based on your post, I think you will be turning it in.) If when you turned it out, the RPM went up, then turn all 4 screws 1/8 of a turn out. Then adjust the idle speed screw.
10. Once all of the screws have been turn 1/8 of a turn and the idle speed is back to normal, turn one screw in 1/2 a turn and repeat step 8.

Thanks,
Joe

 

, but it is just important that is set correctly. I would not use it as a primary tuning tool, but I would make sure it is set to the correct level.

The top is used for circle track.
The middle is for performance.
The lower is for stock/mild performance.

According to Barry Grant inc.:

Is rich at idle? do the folllowing:

A) Increase initial timing
B) Go in on mixture screws
C) Readjust butterfly positions
D) Lower float level
E) Decrease fuel pressure

http://barrygrant.com/demon/default.aspx?page=28

I would start with the mixture screws......

Thanks,
Joe

 

Yeah, I think so...
I had the car out yesterday. I am trying to install an adjustable pivot ball and it is not going well.

Thanks,
Joe

 

Thanks! I've got some good info to work with tonight...thinking the cam may be making it more difficult than normal...

Not so sure that the butterflys still need to be drilled to steady everything out - comments?


240/246 Dur@ 050

.560/.573 Lift

300/306 Advertised Duration

112 LSA

 

Personally, I do not see a reason to do it right now, and the idle-eze does the same thing as drilling the hole. It just creates a vacuum controlled vacuum leak that allows more air into the carb while the butterflies are close. I use drilling as a last resort.

Thanks,
Joe

 

i wouldn't drill anything until I had many hours of tuning done on this and had exhausted all the normal tuning avenues

 

The Idle - Eze does the same thing as drilling:

"Years ago, some enterprising engineer dreamed up the idea of supplying the plenum and carburetor with a source of air by drilling holes in the carburetor’s butterflies – allowing the atmospheric pressure above them to resolve the problem of poor signal (vacuum). This cleverly adaptive solution allowed engines with modified camshafts to operate at idle as butterflies were returned to their original position and idle-mixture circuits functioned as they were designed. However, given the almost infinite number of engine combinations, how could one decide with any degree of accuracy about the correct drill size? Unfortunately, there was no exact formula, only the educated guess of proportionate size. Further, this sort of change cannot easily be reversed. Once drilled in error the holes can only be plugged – usually less than gracefully. Often the holes would be so detrimental to the carburetor’s condition it would be discarded.

The Idle-Eze™, a new patent-pending concept from Barry Grant’s carburetor manufacturing division, Demon Carburetion of Dahlonega, Georgia, provides the simple solution. It’s a spring-loaded, needle valve and brass seat assembly located in a threaded hole in the center of the baseplate."

Feel free to read the whole article:
http://barrygrant.com/demon/default....id=IdleEZSolve

Thanks,
Joe