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Old 10-11-2011, 10:34 PM
CCK CCK is offline
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Mighty Demon Idle Eze problem & gasket question.

Hi

My mighty demon Idle eze seems to be useless. From snug in, to snug out there is no change in idle or vacuum.
Been running too far into the transfer slots for too long, and need to tear the carb down and see why the idle -eze is not flowing.

My biggest question is: Does anyone know for sure if a Holley 108-7 Throttle Body gasket will work on a 850 Mighty Demon with 4 corner Idle & idle eze.?

So far I have only had the bowls & metering blocks off & have spare gaskets for same.

This car is actually a daily driver, so I don't want to tear it down & find out I have the wrong gaskets.

B.G. Tech seems to be non existent, and parts are hard to find.

Also: Im new to using forums.
I want to put my engine info in with my name so I only have to do it once.
How do I go about this?

Thanks in advance.

C3 Stingray
421 Dart small block. Vic Jr. Mighty demon 850. Big heads.
Ill dig up my cam & head info soon, but its healthy enough to need a little extra air @ idle.

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Old 10-11-2011, 11:51 PM
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From HERE:

Quote:
Tech Tip #1
BG carbs use mostly the same gaskets as a Holley. However, the throttle plate gasket (the gasket between the bottom throttle plate and the upper body of the carb) on a BG has 4 idle fuel transfer holes that are not in the same location as the Holley. If you use a Holley gasket, you will not get any fuel flow through the idle metering circuit on the BG, and the idle mixture screws will not work. You can use the Holley gasket, but you need to slot the idle fuel transfer holes in the gasket to match the holes in the BG carb.
The gasket has to have a hole in the center, obviously. The baseplate has to have the passages that connect to the throttle bores. I take it you've had the base plate off? These passages should have been apparent then. As long as the Idle Eze "jet" isn't stuck in the opening, and the bottom gasket has a hole in it, it should work normally.

If you have the secondary throttle blades too far open, readjust them so that no transfer slot is exposed (as long as the idle speed is below 1000 RPM). Then be sure to set the primary blades so that the transfer slot describes a "square" as viewed from under the carb. This is the baseline for the transfer slots/throttle blades.

Once you have the right base to carb body gasket installed, lightly seat the Idle Eze then back it out about 1-1/2 turns for its baseline and tune from there.

I haven't seen Tech @ BG here in a while, if he's lurking maybe he will chime in.
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Old 10-12-2011, 04:29 AM
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mighty demon

bg closed up his tic guy still around ? i would like to talk to him holley gaskets and jets interchange chris carb shop in dayton oh tolled me what size mine were he is on web site but he dont like demons
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Old 10-12-2011, 04:42 AM
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As soon as I heard heīd packed it in the second time I bought a bunch of rebuild kits for my Speed Demon.

Demon Carburetion and BG Fuel Systems to be Resurrected
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Old 10-12-2011, 07:01 AM
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Barry Grant was purchased by Holley and will be ran as a seperate division. This is why you now see some BG designed parts on the new Holley Ultra HP carburetors.
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Old 10-12-2011, 06:27 PM
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Thanks

Thanks for the info. Thats exactly what I neede to know.

Have not had the carb apart other than having the bowls and metering blocks off.

Have baselined the setup many times making changes one step at a time and everything points to needing to bleed a little more air in at idle.

Ill get a few extra holley gaskets & see if I can get it apart this weekend.
Saw an interesting article on a chevelle site of a guy that had to put a spacer in and line up 4 slots or holes.

Ill find out when I get it open.

Thanks again
Kevin.
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Old 10-12-2011, 07:59 PM
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Manual for your carb- http://www.barrygrant.com/frombarryg...0manual-08.pdf

I see BG recommends 0.020" (approximately) of transfer slot exposed front and rear in this manual. Other info they have published says no exposure on secondary transfer slots w/idle speeds <1000 RPM as baseline- and this is what I said above. If you start it and you know immediately the secondary side needs to be opened more, then do so. Or set the baseline w/both slots exposed the same. In any event, this will likely be changed during the course of tuning it anyway and the manual has all the info needed to adjust it to a baseline.

If you have a vacuum leak- intake or base gaskets bad, vacuum lines bad, or missing, etc. this can negate the effect of the Idle Eze and you will not see any difference between it being open or closed.
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Old 10-12-2011, 11:43 PM
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Big jump in idle speed if I take the cap off the constant distributor vacuum port at the carb base.

Bumped the timing up to 18 initial and 38 total. It didnt make much difference from 14 / 34.

Also: Forgot to mention I can get a low but ok Idle in neutral with all four slots @ .020", but it just won't quite do it in gear.

Almost tempted to put a fuel filter on the vacuum line and run it around a bit just for th heck of it.

The first thing I'll do when I get the carb off is check how far the slots are really open now, just for future refference.

Thanks again.
The responce was much faster And much more in depth than expected.

I'll let you know what I find.

Kevin.
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Old 10-13-2011, 12:21 AM
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You haven't said which MD 850 you have. Ever find the cam specs? Do you have an idle vacuum reading, both in and out of gear? Is there a vacuum advance being used? Hooked to ported or manifold?
Quote:
Originally Posted by CCK
Big jump in idle speed if I take the cap off the constant distributor vacuum port at the carb base.
That is saying the air/fuel mixture is rich at idle, as you know. Have you looked down the throat to see if the booster nozzles were dripping any fuel? This will often happen if the transfer slots are open too much along w/the idle being too rich. It's a lot better to fix it and not drive around w/an open vacuum port- I think you were mostly kidding anyway.

Another area to check is the power valve. Be sure to check to see that it's not perforated and that the rating is at least a couple numbers lower than the idle vacuum in gear.

Also check the air bleeds to see that they're not blocked- that will make it run rich. The idle and high speed air bleeds are described in the manual. I know you've baselined it already, but if you didn't buy this carb new, check the air bleeds to see if they've been changed by a po. If so go back to baseline w/them. The metering block orifices can also be blown out real good while it's apart along w/the main body, etc.

I checked and Tech @ BG hasn't been here since 07-16-2011. I was hoping he'd have something to add...

Last edited by cobalt327; 10-13-2011 at 12:27 AM.
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Old 10-13-2011, 03:37 AM
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I checked and Tech @ BG hasn't been here since 07-16-2011. I was hoping he'd have something to add...

Didīnt it come out that Tech @ BG was more than one person at Barry Grant ?
I assume as they lost their jobs any responsibilty to any BG product went with them.
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Old 10-15-2011, 09:53 AM
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Wow! It's like you guys are here as my pit crew!

Ok just off the top of my head the cam is like a 254 deg @ .050" Hyd Roller.
i'll get more later, but it gives you a bit of an idea of the breed of animal we are working with.

Running mech advance only. 18 -38 at the moment.
Timed vac. port capped off.
Constant vac port has a vac. gage attached.

Engine is only 9.5-1 comp. which of coarse is a small part of the problem, but this is trully my daily driver. Any weather, any temp, any distance, and sometimes not the best gas when thats all I can find..

Alum big port heads (More info coming). Dart block. 421 CI.

Carb is a mighty demon 850 with drop leg? boosters, & four corner idle.
stock power valve 3.5 LB. (front bowel only) & jets.

Victor Jr, No spacer, (Vette hood clearence).

MSD street HEI. Dont have a 6AL yet.

If I remember, I think the torque converter is a 3500 Stall witch might be a little too tight, but the carb feels like it is so close to working as it is, if it could just get a tad more air @ idle.


With front & back slots @ .020 I get about 6 lbs vac. @ idle in newt.
Wont pull Idle in gear with the slots in this location and with the stock 3.5 power valve will have a flat spot as I gently speed up.
I changed the power valve to a 4.5 which helped the flat spot but of coarse didn't help the orig. problem.

With the slots open more (which of coarse is wrong) it idles @ about 7.5 in newt. and 6.5 in gear.
This is with the stock 3.5 LB. power valve back in.
I always check the power valves for leaks before installing.


When I get all my info, is there a way I can add it to my profile so it will automatically post on this site when I comunicate?

Thanks
Kev.
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Old 10-15-2011, 11:50 AM
CCK CCK is offline
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Dart little m block. 9.025 / 4.125

Crank 2.448 / 2.100 / 6.000
H-Beam Con Rods 6.000 / 2.100 .927 / .940

SRS Pistons Chevy 400-FT 1.062 / 4.155 /.927 /-4.0cc

220cc x 76cc AFR Heads. FelPro 1205 Intake gasket.
Hooker super comps FelPro 1406 Exhaust gaskets.

Victor JR 2975

BG Mighty demon 850 Drop leg boosters.
Stock jets.
Stock 3.5 LB power valve in Primary metering block only.
Rear metering block power valve port plugged from factoy.

Primary jets: 80, 80.
Secondary Jets: 88, 88.


CAM: Comp Cams Small base circle Hyd Roller.
Grind # CS3113S / 317 OS HR110+3

GROSS VALVE LIFT:
INTAKE: .550 EXHAUST .541

DURATION @ .006 TAPPET LIFT:
INTAKE: .304 EXHAUST .315

VALVE TIMING@ .050":
OPEN: INT: 14 BTDC EXHAUST 57 BBDC
CLOSE: INT: 48 ABDC EXHAUST 11 ATDC

INSTALLED @ 107.0 INTAKE CENTER LINE.

DURATION @ .050: (OOPS WAS WRONG ABOUT THIS ONE)
INTAKE: .242
EXHAUST: .248

lOBE SEPERATION: 110.0

(And yes I degreed it when I intalled it.)


Lifters: Comp Cams High Energy Hydraulic Rollers .842 DIA.

Crane Shaft mount rockers. 220-1.6

Fuel pump Aeromotive 11101
Aeromotive 16302 pump speed controller
Aeromotive 13204 Press regulator.
Mechanical pressure gage @ the windshield runs @ about 4.5 lbs @ street legal speeds.

MSD Street fire 8362 distributer with vacuum advance removed.
18 - 38 mech advance

Canton 15-250 Oil Pan.


Edelbrock 8825 Water pump

Be cool radiator

Whew! I need a nap!!!
Kev.
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Old 10-16-2011, 10:50 AM
CCK CCK is offline
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Got it!!! Running good now! Fully adjustable.

5 Main things I Noticed:

#1. In its fully assembled state the adjustment screw would back out 5 1/2 turns before stopping. (Keep this in mind)

#2. After taking it apart I first noticed the 4 small holes around the circumference had burrs inside that cut their inside diameter aprox in half.

#3. The holes did not line up with the slots and they look very shrouded by sitting down in a counter bore.

#4. The intake slots use the body gasket as the roof of the slot.
When the gasket gets compressed it embosses the gasket into the slot choking it off. This I didn't alter, leaving it for later if needed. My thinking was that making the slot any bigger would cause turbulance in the venturi.

#5. And this is the big one... The location of the 4 holes was too far up from the screw seat.
The screw had to be turned out 5 1/2 turnes before it would even start to pass air being blew through it.
Even out of the body the screw would disingage the threads @ 6 1/2 turns.
It remains engaged in the carb by backing out till the head hits the body.
I opened the 4 holes first to lower the point that the screw would start to work. (The radius of the bigger drill dropping the opening point that much).
After opening the holes I took a needle file & opened the hole into a window like a power valve, thinkin more flow & also lining the new windows up with the slots in the base plate.

I tapered the transition from the base plate slot floor into the counter bore that the jet sits in. The orig design looks like the 4 jet holes are very shrouded down in the counter bore they are in.
Also turned a taper on the jet O.D. from the top of the holes to 1/2 way up the nut. Again to help unshroud the four holes.

It now starts to flow at 2 turns out. Have pics and dimentions if any one needs them.

Kev.
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Old 01-05-2012, 03:30 PM
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This thread seems very close to what I'm dealing with on my Mighty Demon. Rather than start a whole new thread, I thought it might be more efficient to tag onto this one. If it should be its own thread, mods please feel free to move this to its own thread.

Engine Specs:
A lot of the specs I won't know, because the engine was built for the car's previous owner. Most of these are going to be guesses.
383 stroker
Brodix heads
Radical cam, but no idea what lift or duration. Extreme lope at idle.
Hooker 4:1 headers, 3" dual exhaust
Mighty Demon 650 CFM carb
MSD 6AL
There are no vacuum accessories at all running off the engine

First, I have a leak on the front bowl which appears to be coming from where the accellerator pump rod enters the bottom of the bowl. I haven't removed the bowl yet to check this, so let me know if this isn't possible. I need to fix this leak and have no idea at this point where to start. If I need gaskets, are they even available anymore?

Next, I have a horrible stumble off-idle, no matter whether it's a modest stab at the accellerator or a full-on mash. I'm guessing either the butterflies are not set right (I do understand how to do it, but haven't pulled the carb yet), the power valve is wrong, or both. I pull about 8 inches of vacuum at idle, about 6 in gear. The carb still has the stock 6.5 power valve. I'm guessing I should be more down into the 3.5 size? Is the power valve for the Demon the same as a Holley, or do I need a Demon specific part?

As stated in this thread, my Idle eZe does nothing.

The engine is running really rich as well, but I believe if I can solve the adjustment problem, the rich running will go away.

I feel like I'm forgetting something, so please ask away if you need more info.


Last edited by RobbieH; 01-05-2012 at 03:55 PM.
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Old 01-06-2012, 06:50 AM
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I don't know everything about demon carbs but the majority of the parts are the same as holley such as the bowl gaskets accelerator pump diaphragm etc. As far as your power valve goes since your running only 6 inches at idle your power valve is open at that point if its a 6.5 which is causing your engine to be very rich and that could be your problem with your stumble.

Also on your transfer slot make sure no more then about.020 to .030 is exposed as too much will make it very rich as well as it will be pulling from the transfer slot and not the idle discharge ports. Also make sure your secondary's are open enough to about the same amount so you have equal air flow and since your's is a double pumper it will work like that.


Rule of thumb is what your vacuum is at idle divide that by half which would be 3 and since holley does not have a 3 power valve you would want a 2.5 power valve. The demon carbs take the same power valve as a holley does. But you need to check one thing at a time as making to many changes at once can make it even worse and you might loose track what you have already done.

Trust me been there and done that and have learned to do one thing at a time. Also if you do need a rebuild kit summit just put in there new catalog rebuild kits for all the brands of demon carbs but also quick fuel makes rebuild kits that cover many holleys as well as the demons.

Most parts are the same gasket wise and needle and seat assemblies etc.
First change out your power valve before you do anything else to a 2.5 then take your accelerator pump housing off and check the diaphragm to see if its torn or not and also the check valve underneath it make sure its tight.

Then reset your butterflies as you stated you know how to equal points in the front and rear and then reset your idle mixture screws starting them at 1.5 turns out from seated position.

Also make sure your timing is up there too at least around 16 degrees initial with vacuum advance unhooked and you might want to run your vacuum advance to full manifold if your not already doing that will help as well cause if you don't have enough timing it can cause issues as well. Hope that helps

Eric
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