[sherr20]

I am getting my car running again after almost 2 years in mothballs. I checked all gaskets etc...

But, it has never run right with this 650 mighty demon. It was recommended by Barry Grant Techline when I bought it due to my camshaft. The cam is just barely over 240 duration. The problem is I just cannot get this to lean out, it runs extremely rich, I have lowered the PV, adjusted the floats many many times, the throttle blades are set as per BG. I am thinking of going with a Speed Demon vacuum secondary, or a Holley Avenger.

What do you think? It never ran right out of the box, I re-tuned many times with BG tech, I have done everything but the lo idle bleeds and jets. All my problems are at idle.

[pro1]

Have You Checked Fuel Pressure.........is It High

[sherr20]

That I do need to check.

[sherr20]

That I do need to check.

[Drag Fabricator]

how about the idle screws? have you ever set them, and by what method?

[Eric68]

The Demon carb is not just another Holley . . . they have some unique things about them. 1st -- the Mighty Demon has a 4 corner idle circuit. You need to set the idle screws for the front and back exactly the same, and the mixture screws exactly the same. Use a vacuum gauge to set the idle mixture.

[Chris88Z]

I had to drill out the idle air bleeds on mine it helped a lot but its still rich and stinky at idle... Best of luck to ya on this one cause if this carb didnt run so good everywhere else I'd be buying a Holley right about now.

[sherr20]

Yes I have adjusted the 4 corners many times with a vacuum guage. Previous to this I have tried different initial timing, running as much as I could. I believe I am at 18* initial right now, and my smallest spring in my MSD pro-billet is 18, so I have a total of 36*.

It was so bad at first that I couldnt even get it to idle without opening up the transfer slot more. Somthing BG says absolutely not to do. After this I added an Idle-eze base plate (so that I could keep the transfer slots at their .020" if I remember correctly) and use the 4 corner to adjust mixture, well my idle-eze adjustment does absolutely nothing, close it no change, open it, no change. I have been on the phone a lot with BG tech support prior to me going away. Now I am trying to re-do the tuning, I just feel like it is not working as it should.

[camaro_fever68]

Are you pulling enough vacuum to keep your PV shut at idle? Seems like a relatively small carb if it goes on the engine in the description under your post. The problem may be that you have to run too big of a jetting for the air bleeds to handle. The techs at BG should pick up on that though. If you can't get anywhere with them, demand they take it back and calibrate it.

Have you tried shutting off the back bleeds altogether? I think the BG works like the Holley in that the screws govern how much emulsified air/fuel goes out the idle ports. It pulls through the mains, goes to the emulsion tubes and mixes with air from the bleeds in the top of the carb, and then screws control how much to let go into the engine. I've had to drill small holes in the butterflies to allow more air into the intake and no uncover the transfer slots. I wouldn't recommend this though unless you have some extra butterflies because it can hurt sometimes more than help. You must start off very very small also.

[Eric68]

A non-blown power valve will not add gas to the engine at idle. Its impossible because the power valve merely acts like a switch adding extra fuel (amount is controlled by the PVCR) through the main metering circuit. The main metering circuit is not active at idle.

[Silver69Camaro]

Boy, I've been through this a number of times.

1. Pull carb off. Make sure .020" of transfer slot is showing on BOTH sides
2. Lightly seat idle mix screws and back out 1/2 turn.
3. Start motor, set initial timing to anything more than 15. 16-18 works best, just make sure you recurve for the proper amount of total timing.
4. Allow motor to warm up somewhat and turn idle mix screws 1/16 turn at a time until the highest vacuum is reached. Then lean it by 1/16 turn.

It's a pain in the butt, but I believe this is one of the few ways there are to do it with a Demon. Eric is totally right, you cannot treat them like a Holley.

I couldn't ever get the idle mix totally tuned until I bought my wideband sensor. 1/8 of a turn out of ONE mix screw will throw your idle mixture off by about 1 point (say from 14.5:1 down to 13.5:1).

Once it's tuned, the results are worth it.

[camaro_fever68]

The main metering is NOT active at idle, but idle fuel is picked up through the main jets and circuit. I went through the BG diagram and it will pull too much if the valve is not closed/blown. The idle air bleeds can only pull so much air to mix with the fuel. You have idle bleeds and hi-speed bleeds. These must be calibrated to match the fuel curve of your engine. Drilling is not recommended but if you have removable jets like mine, they're easy to swap out till the mixture gets right. I tuned mine with an air/fuel ratio meter and a vacuum gauge to set my idle mixture screws.

[NER perf]

obvious quest but do you have a vacuum leak anywhere ?

[sherr20]

No vacuum leak. I did lower my power valve to a 5.5 from the original 6.5, it actually did help a little i was able to lean out a bit.

Camarofever, the idle-eze baseplate is suppose to do the same thing as drilling the butterflies and completely adjustable, mine just doesnt seem to work.

I have a lot of catching up to do again, setting my project aside for 2 years I have forgotten a lot of where and what I was doing and where I had things set up. Pretty much learning it all again.

Thanks, Im going to pull off again and inspect everything

[camaro_fever68]

I for some reason, have not had much luck with the idle eze system. Maybe others have. What is your vacuum reading at idle? If dropping the PV helped some, maybe it's still too high. I had to run a 3.5 in mine to keep it from opening at part throttle, but unless you have a monster cam, that's probably not the problem. I think your air-bleeds need calibrating but unless you have removable air bleed jets installed, I would send it to get calibrated. Drilling them is the easiest way to turn a good carb to junk.

I still think the carb is too small for the application, but then again, it's what the tech line recommended. IMO, that engine could easily handle a 750 vacuum secondary.