Ideas?

[Windsor]

So, finally got everything together and got my engine running. I am having a couple issues though.
1: it is running rich. I mean burn your eyes, black plugs, see the unburnt gas rich. To try to fix, I adjusted all 4 corners of my demon 750 to 1/2 turn from bottom out. Also, I set both floats dead smack in the middle of the adjustment markings. That is where it runs "best".
2: it runs rough and low at idle. ~500 rpm and it would be a nice lope if it wasn't a rough one. I adjusted the base timing (with vacuum plugged) and it runs "best" at ~10*btdc at idle.

I had to pull the radiator to fix a hole that the shop missed, but when I get it back, I will adjust the idle speed to bring it up to ~750/800 to see how it does. There is no backfire or noticeable stumble when I rocked the throttle by hand, but it still was noticeably rich.
Any ideas would be appreciated, I'd love to get the engine running right.

[John_Kunkel]

If it's a Holley check for a blown power valve.

[BSB67]

Could be a lot of things  What intake?

[Windsor]

It is a Demon 750 on top of a Mopar aluminum single plane. I adjusted the butterflies to .020 at idle and all 4 corners to 1/2 turn out from bottom. I tweaked with it a bit today and got the idle to 900 and smoother but still a little rough. I picked up a new vacuum gauge to tune with, but as soon as the engine got warm, the radiator started pissing out a pinhole right smack in the middle. So I will get that fixed tomorrow at the local radiator shop before I get it running again.
I did try it with no spacer, 1" spacer, and 2" spacer. The 2" gave the best throttle response and a slightly smoother idle. 

[Cooter]

All Holleys beginning around 1999, and subsequent carbs sold have built in power valve protection from factory.

[c00nhunterjoe]

If the idle mixture screws have an effect on the car then odds are the power valve is functioning. If it were blown or open (wrong size for vaccum reading) then the idle screws set all the way in wont effect the car.
   Another thing that can cause that is the bjtterflies open too far at idle, making the primaries control idle instead of the idle circuit. 900rpm should be closed still. A simple peak down the carb will tell.

    Single plane intakes typically give poor signals for the carb to operate on and can complicate idle mixtures. Your demon may have adjustable air bleeds. If not, and you have verified base timing, float levels, fuel pressure, no fuel dribbling from boosters, then drill a 1/16 hole in the primary butterfly to allow more air through.

[Windsor]

Yeah, the mixture screws did have an effect. I found out that the carb has the Idle-Eze setup just for this reason. I decided to hop on the website for the Demon carbs and that's where I found the info. There is a screw valve down the hole for the air cleaner stud that is there to adjust extra air that is coming in. Turn out the previous owner had closed it so tight that it broke my screw driver getting it loose. But now that I know a bout it and it is loose, I can adjust it to lean out the idle a little bit. I had to yank the intake and valley plate to fix a leak, but I will start it back up tomorrow and see how it works out.

For base timing. With it running rich, it ran best at about 10* BTDC. I did a bunch of searching on here and saw that people were saying around 18* is what these motors like. You guys think it will like a little more once I get it leaned out at idle? Also, any suggestions for timing markers since mine only goes TDC to 10* BTDC?

[Cooter]

18* is fine as long as you know what total timing is. 18*+ another 20-25* mechanical+another 10-15* vacuum advance can spell problems. May run ok at idle, but once you hit total advance, it might be too much depending on what weights you got in the distributor.

[Windsor]

Yeah, I was just wondering. I have no clue how the dist is set up. I assume stock since I haven't touched it as far as changing parts.

[Cooter]

Yeah, I was just wondering. I have no clue how the dist is set up. I assume stock since I haven't touched it as far as changing parts.

still depends. Mid 70's distributors have as much as 30* mechanical alone. So 18* +30* is like 48* total.

[Windsor]

Well, went out there today to run her up and try to get everything tuned.
First thing she did was complain about starting. Took me 3 tries to get her to run. Then she was running on maybe 6 cylinders. In a state of clear mind, I put my hammer away and started another project on the car that I had been meaning to do, so I built some ground straps out of some stainless ground strap that are from surplus military radio equipment (3/4" wide by 1/4" thick tight weave stainless wire). I built a strap for each head to the brake then use a piece that is a little heavier to go from the block to the frame.
Anyways that's for my other thread. A I was tightening a bolt, I saw a gas streak on my intake and right as I said WTF, it dripped again. Turns out, the damned carb has a couple bad gaskets. So I ordered a rebuild kit for it. I did check the power valve also. It is still good. Clean and the diaphragm was good, but I will still replace it with the one in the kit.

[Kern Dog]

A "dial back" timing light is a great way to read the timing in a performance engine. Explaining its full function....its easier to refer you to google.
The initial ignition timing should be higher than 10 degrees if the motor has any increase in cam specs over stock. I have mine set to 20 initial with an additional 14 degrees of mechanical. 34 degrees total. The older Mopar distributors are not adjustable like the newer electronic ones. The older ones require disassembly and welding to limit the total amount of advance. Again, google or a search here will display how to modify a distributor.
I have a Demon 850 in my Charger. It runs rich according to the Air/Fuel guage I have in the car. I reduced the primary jets to lean it out. It did run cleaner but also lost power. I'm going to have to drill out the PVCR in the primary metering block. This will allow me to reduce the jet size while still providing additional fuel on demand.

[Windsor]

When I pulled the primary metering block off, this fell out of one of the passages. I am assuming it is from a vibrating cleaning tub.

[Windsor]

Rebuilding the carb seemed to do the trick. She now runs smooth, starts super fast, and aside from a small exhaust leak (on a spot I missed) she sounds pretty good. Definately can't sneak up on anyone, but I can drive her through town without getting a noise violation ticket.

[Ghoste]

Thats a nasty little dude to drop out of your carb.  I've heard some similar tales with the Demon quality in more recent years but you always hear when someone is unhappy I guess.
Nice to hear its running good now.

[Windsor]

Yeah, that and a couple shavings. I'm not gonna bash them too bad, I like the carb. Especially at the price I got it for.

[Windsor]

Ok, so I am still having issues. I rebuilt the carb and put in a new power valve (35 based on the lowest vacuum reading I got). The car is running noticeably cleaner, but still slightly rich. I got it to idle somewhat smoothly at 950rpms but there is still a noticeable roughness to it.
When I yanked the distributor to prime the oil pump (did some work on the oil hoses), a small pin/rivet dropped out. It is only about 1/8" long, tapered with some threads/grooves on it. Anyone have an idea of what it is suppose to hold?
I'm thinking that once my VA disability starts, I will buy a new dist and msd ign system along with taking the heat range on the plugs up a step. Until then, I need to get it running the best I can before I go under the knife and won't be able to do anything for a month+. 

[Ghoste]

The pin dropped out of the distrbutor?

[Windsor]

Yeah. Kind of like this, but tapered and the splines are more vertical with a slight twist.
It ran smoother before I pulled the dist out and the rivet/pin fell out. Now I can't figure out where it goes and can't get it to smooth out like it was.

[Windsor]

Figured out what the pin was when I pulled the dizzy apart and found a rotor tip stuck in the grease below the weights. I guess a rotor came apart at one point in time in the engines life.
Looks like the internals are original. Spring on only one weight. It was either white or light blue at one point in time.

[Windsor]

Ok, so still fighting my motor.  All plugs are tan and clean except 6 & 8. Cyl 8 plug is black on 3/4 of the insulation and tan on 1/4 opposite of the ground (where you would expect the plug to fire), number 6 is fuel fouled and completely black. I rechecked the resistance of the wires. While they are a little high ~300 per foot, they are the same in respect to their length. Before it is asked, yes, the wires were in the correct order.
I did a compression check. Though unable to get cyl 1 and 2 due to clearance (would have to take fenders back off).
Cyl 3: 128
Cyl 4: 131
Cyl 5: 135
Cyl 6: 132
Cyl 7: 132
Cyl 8: 130

[firefighter3931]

The compression looks fine and the resistance on those wires is a bit high but won't cause the issues you are experiencing.

What plugs are you using ?
What is the engine combination ?
What distributor ?

Couple of thoughts ;

-it will want more than 10* at idle....most do.
-if electronic distributor check the reluctor gap on 6 & 8....check all of them for that matter and compare. A variation in gap will cause poor ignition to specific cylinders
-possibly two defective sparkplugs



Ron

[Windsor]

Plugs are NGK XR5, wires are JEGS 8.5mm, electronic dizzy with new reluctor and gap set at .008 and new cap and rotor (brass terminal cap).
Engine is a B383, MP intake with Mighty Demon 750 leaned down, 35PV and 2" 4hole spacer.
Heads were shaved down .008 (previous owner used a flapper disk to try to clean them), hardened seat, new valves, springs.
Unknown specs on cam (I know, I know, I need to get a new cam). I guess it is stock, the guy I purchased the motor from said it had been rebuilt with a performance cam, but he was full of ..it.
Ignition system used is a Jegs module wired up with a MSD Blaster (GM dual connector e-core). Or atleast that's what I was using until the coil melted, now I'm waiting for MSD to send the replacement.

It isn't bad plugs, same two fouled with two sets of Autolite plugs that were in there before. I will be buying a Firecore dizzy and coil once I get my VA pay.

[Windsor]

Update. Changed the reluctor and pickup again, disconnected the vac advance. Now it starts up fast (about a second), idles steady at 1k, and no longer bogs under throttle while rolling. However, it still has a very slight miss,  is a little rich, and bogs at WOT from a stop.
I went ahead and ordered a firecore R2R dizzy and coil (sorry Ron, got em both at a good price when getting other parts), so I will put those in next week after they get here.

[firefighter3931]

Cool....you're going to really like the FireCore RTR ! 

If you have any questions feel free to ask. I do tech for all Firecore sales....not just the stuff i sell. If you call them with a problem....they will give you my number   

Looking forward to your results 


Ron