[DAVID GAGNARD]

Well, I now have a lotta things to double check thanks to all the suggestions here....Let me back track and answer some questions....

The motor is my 331 cu in race motor, the carb is a 650 Speed Demon DP.I've been running this set-up for 4 or 5 years now ( no problems). Took the motor out to freshen it up and it's on a run-in stand now, getting broken-in and tuned before going back in the race car.

The last 2 races before pulling the motor is when this "problem" developed. It wasn't that much of a problem cause once I get it warmed up and I'm on the track and the motor probably doesn't go below 3000 rpms while "on track".

I bet you developed a vacume (air) leak in one of your intake ports where the manifold mates to the heads. That will cause exactly what you are experiencing.

I don't think it is a manifold air leak cause it was doing this before I tore the motor down and doing the exact same thing afterwards, but I'll check that anyway.

Make sure the throttle is returning all the way. When the idle is up, pull the linkage on the carb and see if it closes, returning back to your normal idle. I had a Demon carb that would do this unless I kept the throttle shaft and linkage well lubed, or put a really strong return spring on it.

Once started and idling correctly,everything seems to be fine, rev it a time or two and the idle rpm stays high, first thing I do is push back on the throttle linkage thinking it is not returning all the way, it does move, but only a very,very tiny amount, maybe a few thousands, I have the double throttle return springs on it, same as I always have had on it. I don't think the springs are the problem as they are very stiff..When the carb was off the motor, I turned it upside down and slowly worked the linkage from closed to wide open and watched all four butterflys to make sire they were not "rubbing" on anything or touching anything causing them to hang up,there was no problems there, all worked freely as they should.

or, at some point did you turn the idle adj. screw and open the butterflies uncovering the transition slot which means the idle circuit can not be used to tune the idle a/f mixture? there should be only about .040 opening at the primary butterflies.

When I had the carb apart for cleaning as I re-assembled it, I checked and double checked that and set it as per the directions from the Demon tuning papers that came with the carb.I have not touched the secondary idle adjustment, only adjusting the primary. Sometimes I have to turn that screw 1 to 1.5 rounds open to keep the motor running and then I think I'm out of the idle circuit by then....

pcv valve?

No pcv valve, each valve cover has a large clear plastic line going to a vented catch can. the large pcv port on the rear is blocked, one of the two small vacum ports on the side is also, the other vacum port goes to a vacum gauge on the dash.

i'm thinking maybe at some time the idle circuit got gunked up and you opened the butterflies?

Probably right, but since then I have had the carb apart twice to clean it out, I thought I did a good job of cleaning everything out and blowing it out, but that didn't cure the problem.

the no adjustment at idle would indicate fuel is somehow getting into the intake via the secondary circuit.

and you could have two problems here, in searching for one you've created another, or fixed one and created another.

I'm thinking the same thing, when it is idling fast, it should be out of the idle circuit, looking into the carb, there is some fuel "dribble" from the primary boosters, but that is at at least 1500prms, when back to normal idle speed there is no dribble of fuel from the boosters....

Dave what about wear in the baseplate with the throttle shafts? Sometimes I have seen the return spring on the bottom of the pivot linkage with the accelerator attached at the top. This put the shaft in a situation where the tension of the return spring is pulling the shaft foreward into the baseplate.

Back to the Demon-- I have found several where the throttle shaft is 'loose' where fitted to the linkage arm. Since the arm has the idle speed adjustment, the shaft & throttle blades have a mind of their own with a random idle speed resulting.

This is about the only thing I DID NOT really check!!!!!!!! guess what I'll be checking now?????I didn't give this part any thought since the carb is on my race car and doesn't have that much running time on it, never thought the throttle shaft or baseplate could be that worn in that short of time!!!!!!! but I'll defiently be checking this out later today.
I've got to re-jet the carb up a notch or two, plugs looked a little too lean for me.Once it is off and apart, first thing I'll do is check the throttle shafts for "play" and where the linkage arm attaches to the shaft, never thought to even check this before....
The return springs are on the bottom of the linkage and the accelerator linkage is connected at the top, so that makes sense.

sometimes you need to take the shafts apart to oil them---it isn't the weights hanging up but the shaft assy

definetly will do this today!!!!!!!!!!!

At times like this, I kinda wish I had a Holley, been running the same old 20+ year old Holley 600 DP on my street car for over ten years now and I don't think I have had to touch it in the last 5 or 6 years!!!!!!!!!!!!!!!!!!

Thanks for all the responces, I'll be in the shop later today working on that and a few other things, hopefully later this afternoon, it'll all be back together and running "properly"........

David