Demon troubles!!!!

[ron67fb]

Wounder if I should try a different PV since I'm running the 6.5 that came with the carb and I'm pulling 18" of vacuum at idle in gear. She could be going lean under heavy acceleration?

What kind of vacuum are you getting in cruise? Your PV should be about 2 inches below your lowest vacuum reading under light load. For example if you're going down the highway and your vacuum reads 14 then you want a PV of around 12 to start with. Maybe even a 10 if it kicks in too early, since 14" will drop below 12 really quickly when going up a slight hill. A 6.5 PV is pretty low especially with 18" in gear, and I doubt you get much less than 16" in cruise.

 

[Blown4.6]

Ok i'm not a big fan of any of the Carbs on the market, but for tunability the demon is the best. The problems you are describing a pro carb mechanic can get that thing running like a top in a matter of minutes.
Carb rebuilts are nothing but a bunch of new gaskets and a good cleaning. So The reason they Maybe suggesting a REBUILD is it sounds like you maybe sucking air in somewhere, have a goof'd power valve, or just have the thing over jetted.

The aluminum design does have its drawbacks, mostly heat related.

Edelbrock, are the old Carter carbs, only good thing about them is the fact they don't have large fuel blows to bake the fuel. Tunablity, they are on the bottom end of the list. For a mild build they are fine, but anything that has aggressive cam specs, and high fuel upon throttle demand, they fall flat.

Good luck.

I bought a Demon for this car because I thought it to be the best. That's not to say that the majority aren't great. The problem is, that let's say 1 in 10 don't work out of the box. That's a 10% failure rate. No kidding speed shops want no part of that. Can you imagine 10% of your customers coming back in and bugging you for free work (which takes precident over new work)?

Okay, my 525 Demon has already been to a Pro (old school) tuner. He wasn't able to clear up the problems. Assuming another guy (or maybe me?) can, here's what going on with mine:

1) stumbles under light throttle right at 1400 rpm. Heavy acceleration creates no stumble. Very very gradual acceleration seems to avoid the stumble.

2) While cruising on the highway, it seems to want to get back in that stumble zone, only now it's constant (since I'm cruising). Hit the gas and it clears up.

3) This isn't a problem unless it's causing 1 or 2 or both from above......the front float is always full to the top of the site glass. I mean FULL to the point where you have to shake the car to see the fuel (when is sloshes back and forth). I assume the stumble is from being too lean.....but maybe the high float has something to do with it.

Not to high-jack this thread; but, I think the originator has similar/same troubles with the same 525 Demon?

Rob

 

[06cobra]

What are your cam specs, and what is your timing?


Yes these are very important for tuning a carb.

 

[Blown4.6]

What are your cam specs, and what is your timing?


Yes these are very important for tuning a carb.

Cam specs are like 224/230 @.050 on a 110 lsa. I don't recall how the cam is timed. As for spark, it's 12 degrees initial (or so it says on the vacuum thingy). This is what my mechanic tells me. However, 224/230 seems somewhat agressive for a torque application, as does the 110. I'd like to see the actual cam card to be sure. However, it was a custom grind.

Oh yes, the stumbling was EXACTLY the same before I had the cam installed. The stumbling NEVER happended before I added the Demon, intake manifold and Pertronix.

 

[06cobra]

I'm not sure what you mean the vacuum thingie? do you mean timing light? or he connect a vacuum gauge?

 

[tweet66]

Blown4.6, the problems you described are exactly what I'm fighting with. The only difference is hitting the gas under cruise doesn't necessarily clear it up and real heavy acceleration is better but still not as responsive as I'd expect. I'd put my Autolite 600cfm (1.12 venturies) 4 barrel back on but I sold it I didn't have these problems with it.

ron67fb, I'll hook up a vacuum guage inside and check.

06cobra, if yourtalking about my cam, I have no idea on the specs. It's what ever Ford put in the 69 302 for a Falcon wagon. The engine was rated at 220hp by the factory in 69 (feels more like 150hp ). The cam I have to put in it is a Motorsports cam: 448 int./ 472 exh. gross lift, 204/214 duration at 0.050 lift (280/290) part no. M-6250-A311.

 

[302 coupe]

Tweet, have you tried bigger jets? 52's seem kinda small, my 306 likes 67's up front with the 650 dp. If I were you I would maybe try something in the 60 range. Your stumbles may be the result of a lean condition.

You say, "If I turn the mixture screws all the way in the idle gets crappy but it never shuts off. If I run with them turned in any less than 1 full turn it is down on power and will surge under any throttle. I'm runing the supplied 52 primary jets and it doesn't have a secondary metering block. "

Note that the idle mixture screws you adjusted only affect idle. They do nothing when driving down the road, at part throttle, cruise, WOT, ever. Fuel supply when crusing and lightly/heavily accelerating is supplied by the jets, pump/s, and power valve.

 

[tweet66]

302coupe, wouldn't the idle mixture setting affect the initial transition from idle to metering circuit? In other words, if turned in too far it will run even more lean until the metering circuit takes over.
I didn't changes the jetting mainly because the engine is bonestock, no headers,exhaust, or cam YET

 

[302 coupe]

302coupe, wouldn't the idle mixture setting affect the initial transition from idle to metering circuit? In other words, if turned in too far it will run even more lean until the metering circuit takes over.

nope, thats what the accel pump is for, along with the PV and secondaries if you're really getting on it. If you want, remove the carb and look at it from the bottom. You'll see 2 narrow slots(1 for each bore) just above the primary throttle blades. When idling, these slots are all but covered by the throttle blades. Once you crack open the throttle, even a little, and the slots are uncovered, well, thats when the idle mixture screws no longer have any effect on tuning or performance. Additional fuel for the transition from the idle circuit to the main circuit is provided by the accel pumps, this fuel is what comes out of the squirters (or shooters) when you give it a bit of throttle.

I still think you need bigger jets. I don't know if your Demon has a 30 cc pump or not, I would imagine it does, you said you had changed pump cams. I'm assuming this was to remedy the transitional stumbling problem. Did the different cams have any effect on it? If the different cams had little or no effect, I would definately try some bigger jetting.

 

[Blown4.6]

My BG is still running like crap. Stumble.....you know the drill.

Here's something though. I called an old timer carb guy today. Carbs are all he does (well, plus ignition). He asked me about my setup. When I got the 2" open spacer, he stopped me and said "that's causing your stumble.....take it off" I said "but I thought a spacer would only help things?" He said, "nope, 100% trash. Take it off because it's killing the signal at certain points and therefore it's trying to die and probably flooding a little" BINGO.

He didn't say maybe or "it could be" or "try....." He was all over the fact I had a spacer with that carb. ?? Well, it remains to be seen if he's right or not. I'll take it off when I get back home.

Anyone else with stumble problems running a spacer, particularly an open one??

 

[06cobra]

I'm not sure what you mean the vacuum thingie? do you mean timing light? or he connect a vacuum gauge?

You never answered this question.

Maybe in that 2" space of yours.

 

[Blown4.6]

No, I meant the vacuum advance "thing" that's attached to the distributor and to which you attach a vacuum hose. What the heck is that thing called?

 

[Gud T.B. Blown]

My BG is still running like crap. Stumble.....you know the drill.

Here's something though. I called an old timer carb guy today. Carbs are all he does (well, plus ignition). He asked me about my setup. When I got the 2" open spacer, he stopped me and said "that's causing your stumble.....take it off" I said "but I thought a spacer would only help things?" He said, "nope, 100% trash. Take it off because it's killing the signal at certain points and therefore it's trying to die and probably flooding a little" BINGO.

He didn't say maybe or "it could be" or "try....." He was all over the fact I had a spacer with that carb. ?? Well, it remains to be seen if he's right or not. I'll take it off when I get back home.

Anyone else with stumble problems running a spacer, particularly an open one??

FWIW i had no spacer on my edelbrock performer manifold and i still had the same stumbling problems with my 750 demon.

 

[66HertzClone]

No, I meant the vacuum advance "thing" that's attached to the distributor and to which you attach a vacuum hose. What the heck is that thing called?

That is called a vacuum chamber.

 

[tweet66]

302coupe, I'll try some bigger jets and I'm going to replace the PV while I'm at it. I've been noticing alot of surging at all types of throttle application. Last time I had that on my 74 Bronco with a 1850 Holley the PV went a day later.

 

[ron67fb]

302coupe, I'll try some bigger jets and I'm going to replace the PV while I'm at it. I've been noticing alot of surging at all types of throttle application. Last time I had that on my 74 Bronco with a 1850 Holley the PV went a day later.

One thing at a time, otherwise you'll have a hard time learning anything about your carb. Change the PV to something closer to your cruise vacuum readings since you're already way off. You mentioned that it accelerates fine under light throttle, that means the jets are doing their job. Once you get into it, the vacuum signal drops, and the PV should open, letting in the extra fuel it needs. If your signal drops but your PV doesn't open then you get a lean condition, which is felt with a stumble.

Surging at cruise can actually mean that your jets are too big, and your engine is loading up with the extra fuel until it is burned up.

Do one test at a time when reading plugs. To check jetting, drive at steady-state throttle for as long as you can before pulling them. Stay off the power circuit as much as possible or this will foul up your readings. This way your plugs will tell you if your jets are too rich/lean.

You mentioned your plugs read a little lean, but was that from light acceleration testing, steady-state driving, or full throttle? Or all of the above? One test at a time, especially if you're going by smell, your butt-dyno, and plug readings.

I'd suggest for anyone with a carb to invest in an air/fuel ratio (AF) meter. You will learn tons of things about your carb with an AF meter installed, and just carbs in general. The guys with "perfectly tuned carbs" will be surprised on how far off they are with an AF meter installed. Not to mention the time you save from constantly pulling plugs and playing guesstimate with a box full of jets.

 

[302 coupe]

or you can tune it at the track, lots cheaper and way more fun!!

I def. agree about only changing one thing at a time. If you change mulitple things you'll ed up chasing your tail and getting nowhere.

 

[Blown4.6]

Okay, it had nothing to do with the spacer......same thing as before. It has zero power below 1500 rpm. Runs like crap to about 1400 then actually stumbles and drops back to 1200 rpm before "catching" and then takes off nicely all the way to 6000. I'm inclined to believe it's too little fuel now. In fact, the other morning it was trying to die. I had to keep it reved to keep it lit. Every time I'd put it in gear it would die. I even did a 4000 rpm tranny drop. Nothing really happened. The engine was just producing ZERO torque and so it jus stalled instantly. Something's seriously goofy when the engine instantly dies when doing a 4000 rpm tranny drop!!!! It's got to be too lean...?? maybe??

The plugs are tan with a LOT of white. I'll replace all the fuel lines (which are truly Mickey Moused and spliced like 6 times). From there, I'll just have it re-jetted and maybe a bigger squirter.

Now, on the freeway, it still surges/dies at cruise. I used to think it was flooding; but, I have a hard time thinking there are two, opposite problems at different times (light acceleration vs. cruise). It's probably all related to being too lean. But then, this is the 99th time I've "figured it out."

 

[Blown4.6]

To all who are having stumbling problems with their BG 525.....Mine is now fixed!!! It runs like a champ....smooooooooth!

Here's what I did:

1) Get a 1/2" socket and unbolt the BG 525 Road Demon.....remove linkage and hoses.
2) Set the now removed BG on the ground
3) Take a mini-sledge hammer and bash the piece of s*#t into several pieces
4) Buy a new BG 650 CFM SPEED DEMON
5) Bolt it on, connect linkage and enjoy.

Guys, that's all I did and it worked perfectly almost right out of the box. It's a little rich right now (blows some black smoke when you hit it);but, that can be tweeked. Plus, the 4-corner idle adjustment is great.

This came with a price. The 525 Demon was brand new and ran $300 or so. The new 650 Speed Demon was nearly $550 with the fuel log. What the hell. What's your time and aggrevation worth to you??

 

[tweet66]

The 650 on my stang is the only BG carb I haven't had problems with. It runs smooth, reacts quickly to adjustment, and the driveability is great. I've been on the phone with BG again and they ant me to send the carb back to them for a "checkup". That's great but this is my daily driverand I can't be with out it. NOT that i wouldn't mind driving the Stang but it's apart for a T-5 conversion. I've actually been driving my 62 Falcon van for the past two days because my problems with the BG 525 got worse on Tuesday. I couldn't get it to idle below 2500 rpm without surging from 100rpm to 1200rpm at random. One "good point" was the stumble was gone and she'd haul azz when punched but where can you drive a wagon at full throttle all the time????? The problem cleared up, by itself , later in the day and I'm back to the stumble.