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  #16 (permalink)  
Old 07-18-2006, 05:58 AM
Technical Support Barry Grant
 
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Mad Maggot,

I'm not wanting you to change the bleeds just yet, just to see if we can make a difference to the problem you're having. From there we can work with you to help dial the carburetor in.
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  #17 (permalink)  
Old 07-18-2006, 09:51 PM
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Ok I checked for vacuum leaks with the carb cleaner, and there are no problems to be found. So now that that is rectified, I went ahead and performed those diagnostics you mentioned. First I set the idle so it was stable and not too rich, then pulled on the throttle until it went lean and wanted to die. Pumping the accelerator pump while not moving the throttle at this point definitely made a huge difference, it increased the RPM substantially and eliminated the sputtering, then after a couple seconds it returned to the dead lean state again. I also tried this starting from a higher RPM point and dropping the throttle to the lean condition, and it basically did the same thing. The wierd part is that plugging the air bleeds (the bigger ones on the outside) didn't really do too much to help the problem, although the best I could do plugging it was two small hex keys, so I doubt if I sealed the bleeds off entirely. The choke horn was in the way and I couldn't get my fingers to cover the holes too well. If I need to totally seal the bleeds to have an effect, I will come up with a better way to do this next time.

Also, I fixed the old 650 Holley that this Demon is replacing, and I put it back on for a bit and it worked great - so no vacuum leaks for sure. If for some reason I really need to get deep into the Demon to find the problem at least I have a backup so I can drive my car I bought a rebuild kit for the Holley and I still have two bowl gaskets and two metering block gaskets left over so if I need to tear into the Demon repeatedly I at least have backup gaskets.

Thanks for the help so far, and if there's any other suggestions please let me know.
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  #18 (permalink)  
Old 07-23-2006, 02:28 PM
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BUMP!

I'm still hoping there's a way to fix this bugger, I'm not quite ready to give up on it yet
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  #19 (permalink)  
Old 07-24-2006, 10:55 AM
Technical Support Barry Grant
 
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Mad Maggot,

Sorry about that, I've been out of town. You've got a PM.
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  #20 (permalink)  
Old 07-25-2006, 10:30 PM
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Well, curiosity got the best of me, and I decided to take the carb apart and do a more thorough check of all the parts - against my better judgement seeing as how this carb is still under warranty. It's a damn good thing I did, Once I took off the metering blocks, I found metal shavings embedded in the metering block gasket where it mates to the main body, and some of those shavings came loose once the gasket was removed. The same thing happened to the secondary side as well. Come on, Barry Grant. I know you can do better than this - better give the quality control guys a smack upside the head. What if one of those shavings found it's way into a main bearing? ... ... It looks to me like they came from where the entrances to the main passages to the boosters in the main body were reamed out to make the funnel shape, as there was still some small shavings still not quite detached from there.

I had some time today so I got a hold of an air compressor and an air nozzle with a fine rubber tip, and went to work blasting all the passages with 120 PSI of compressed air, to make sure none of the metal shavings made it into any of the orifices. Once I was sure the metering blocks and main body were free from debris, I decided to have a look at the idle circuits to see if I could find anything that might be causing me trouble. At first I did not see anything wrong, so I decided to blow air through the jets to see where the fuel was able to go. It turns out after some deductive reasoning and some time blowing air and blocking various orifices with my finger that I could not get any air to come out of the orifice leading to the transfer slot or idle discharge port (the part that is regulated with the idle screw). I tried blowing air backward through this orifice and it would not go anywhere. This led me to believe there was no way for the fuel to get to the transfer slot or idle discharge port. I didn't seem to have this problem with the secondary side. After some looking, I discovered a potential problem with the primary metering block, as shown in the pictures I have attached.

The secondary metering block has a hole drilled in the orifice shown in the red circle, while the primary metering block does not. My guess is that the hole is supposed to be where the fuel goes from the main well into the idle circuit, and if that is the case, the entire fuel supply of the primary idle circuit is cut off. This would certainly explain my dead lean problems. I would appreciate it if you would confirm if this is in fact what is causing the problem. If so, I'm going to need a replacement metering block under warranty, unless there is some way I can drill the holes myself (though I don't have much confidence in my ability to be that intricate with a drill). I would also need a precision drill bit set to have the proper size hole, and that could be costly. Please inform me on how I should proceed.
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  #21 (permalink)  
Old 08-11-2006, 04:38 PM
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Hello hello out there.

Just curious if this problem was ever fixed for you! I am having the same issues with a demon I just acquired from my neighbor. He was having an off idle stumble really bad like you've described.

He never did get it to work again on his car. Originally, the carb he worked well for him. THen I think he put new gaskets in and it has never been the same since. I did notice that the new gaskets are blue. Does this mean they are HOlley gaskets??? Will they work??

Any more help from BG TECH would be much appreciated.

THanks in advance for any help you can give!

jer
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  #22 (permalink)  
Old 08-12-2006, 03:17 PM
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Yes I managed to fix the problem by drilling out the two holes that should have been drilled from the factory. (Shown in the pictures above) It idles great and light acceleration is responsive but I still seem to have a hesitation when I punch it off the line. I haven't played with the squirters yet so I suspect that this should fix the problem, though I will probably need to go with the big 50cc pump. As for the problem you described, I noticed that when I put the metering block gaskets from a Holley and Demon together they don't always have the same hole alignment. I'm not sure if I mismatched models when I did this, but it wouldn't hurt to check if all the holes in your gaskets line up with the holes in your carb. Also don't forget to check if there are holes that are completely covered by the gasket. It's possible that something is blocked off and you are not getting the right amount of fuel.

Another thing to try is adjusting the butterfly positions on both the primary and secondary side. My experience with Demons has taught me they can be very finicky if they are not set just right.
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Old 08-12-2006, 03:46 PM
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Thanks for the info.

Good to hear that your demon has cast away it's demons. he he.

Mine is still possesed. I did check the new gaskets visually, and I can't see anything at all wrong with them. I have even seen where Tech@BG has posted that the gaskets are interchangeable. A smart forethought in the design no doubt.

Maybe I'm going to the wrong people. I need an exorcist.
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  #24 (permalink)  
Old 08-13-2006, 02:59 PM
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LOL @ the religious metaphor

There's quite a few reasons why you could be getting an off-idle stumble, Demons seem to be more prone to this. It's probably in need of some tuning. What engine/tranny/carb size/gear ratio do you have? I know that a heavy car with an auto tranny and highway gears can have a stumble with just about any carb, sometimes the squirters and pump cam need to be adjusted to cover this up.

Does the car idle well? Does it run smoothly at 1200-1500 RPM, or is there a constant lean condition (white smoke, choppy sound) at these RPM? Are your butterflies set to the proper positions? If it idles well, and runs well at a constant RPM, but hesitates or stumbles only when accelerating, then it's likely in need of some squirter/pump cam tuning.

I don't claim to be a carb wizard, but I've tuned my fair share. Here's a few great guides that can help with further tuning (written by experts, of course). They talk about tuning Holleys, but Demons work in pretty much the same way.

http://www.bob2000.com/carb.htm
http://www.jason.fletcher.net/tech/c...carbtuning.htm
http://www.holley.com/data/TechServi...ech%20Info.pdf - This one needs Adobe Acrobat
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  #25 (permalink)  
Old 04-02-2007, 05:08 PM
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yup

I had the same problems tuning my carb...one question I have is...what type of intake is it?...and are you running a spacer and what type if you are?...I was running a single-plane intake and an open spacer...this made the demon run like *** when my 650 dp holley ran ****...so these are key questions in the tuning process of the carb for sure...good luck...ps when I took the thing apart...I had all kinds of flashing and metal in the circuitry...so I would def. rip it down and look for that type of stuff too...once we put a "cloverleaf" spacer in and cleaned all the metal out of it...we vaccum tuned it and it ran mint ever since!!!
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Old 04-02-2007, 06:23 PM
Drive it Like u Stole it!
 
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in the past 7 years, and 7 demon carbs purchased, 6 of the 7 have had issues (debris inside, idle feed circuits too big, etc) and 1, the ONLY road demon i bought, worked out of the box (minor tuning, of course). all in all, once all of the issues are worked out, the carb ran very good, if not, better than most holleys i've ever dealt with. there's a lot of information about people's findings with barry grant's carbs on this forum... all you need to do is search for it!

my 0.02
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