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Old 03-29-2006, 07:01 PM
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mighty demon horror!!

Hi, and thanks for reading this. I am at my wits end and ready to give up. I hope you all can help me. I am having a rich idling problem with my car. The engine is a 434 cubic inch stroker smallblock chevy and has 10.7 to 1 compression. Heads are Brodix Track 1 with the intake runners cnc ported, think they are 227cc, 208 int and 160 exh valves with 64 cc chambers. The cam is a comp cams mechanical roller 12-900-9 which duration is 254 258 @50, with 630 inch lift and 106 lsa, small circle base. Had to use the 106 lsa to fit everything for the stroker kit. I have 1.6 roller rockers so a total of 680 lift. The intake is a port matcher victor jr with a 1/2 inch nitrous plate under the carb.



The car has a 6 speed manual trans and headers and dual exhaust. Ignition system is a mallory unilite dist, msd blaster 3 coil and 11mm wires. The timing is set at 20 degrees initial and 18 dist for a total of 38 all in at 3000 rpm. Fuel pressure is 6lbs with an holley blue fuel pump and regulator. I called Barry Grant and they recommended a 750 mighty demon. I installed it and have nothing but bad luck. So far I have done the following. With a vacuum gauge installed I have 9 inches of vacuum so BG told me divide in half and change the powervalve, I did it had a 4.5 in it. Didnt help. BG told me to lower the float level, now its on the lowest line in the sight glass, didnt help. I found that the jets were wrong from BG they said numbers are small and they make mistakes, so I rejetted factoring in my altitude (1 jet smaller than stock front and back) didnt help. The transfer slots look like small squares so they are correct. The car likes to idle around 800 rpm very very rich.



Idle screws are 1/2 turn out any more out and car fouls plugs. Any more in and the car dies. Idle eaze is 4 turns out. At 2 and 1/2 the idle eaze the car wont idle clean. Not sure what to do. Have no vacuum leaks, timing is set right, tranfer slots are set right, fuel pressure is set right, floats are set right, carb is clean no dirt in it, powervalve is right, cant get the idle screw to respond well. Even tried to bump timing to 24 degrees all it did was brought the idle up, didnt help with the richness very much. Idle burns your eyes and smells very rich. I know the car will idle around 1000 rpm with such a big cam, but with the idle mixture screw not responding it not easy getting the idle up without opening the butterflies. Tempted to turn it up to 1300 with the butterflies and say forget em!!! Thanks for reading and HELP!!

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Old 03-30-2006, 12:50 AM
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I'd crack the secondary throttle plates open a hair further then what they came with and see if it starts to clean up and idle faster. I would leave the primary throttle plates and idle circuit slot alone where it is at. If it does clean up, you'll have to go back and confirm that the PV is still what the carb wants. If this dont work, call BG back and ask if they are still having problems with quality control and those pesky metal shavings.

Don't give up and dont get mad, it sounds like a fluke or something stupid that you'll be laugin about later.

That BG tech guy hangs here also and can probably talk you through it pretty good.

Does that NOS plate interfere with the carb anywhere? On a side note, I dont know anything about NOS except that plentiful and reliable fuel delivery is the only thing between you and some expensive replacement parts. In reviewing the available information describing your fuel system, I'd recommend gettin clarification from some NOS parts supplier about that blue pump you are intending to use. In my estimation, I'd guess that the blue pump would be marginal even without the nitrous on a 434.

Last edited by 56Maynard; 03-30-2006 at 01:22 AM.
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Old 03-30-2006, 05:03 AM
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nitrous not hooked up

The nitrous plate has no interference with the carb what so ever. I also do not have the fuel line hooked up to the silenoid. I wanted to make sure the carb ran good before i hooked up the nitrous. So I really dont think it is the plate. Thanks for the suggestion.

When I was jetting the carb I came across a long thin metal shaving and pulled it out now that I think of it. Tonight I will rip the carb off and totally clean it since alot fo people are having shaving issues in their Demons. Had the same problem with my Brodix heads out of the box. had to be disassembled and cleaned. What is going on with quality. Makes you want to puke. As far as drivability issues the car runs fine. No hesitation, no bog, no backfires. Just idles rich. So I think my powervavle is correct. The car did seem to like the stock one better than the 4.5. but BG said thats the one the car needs.

Last edited by 91vette; 03-30-2006 at 05:14 AM. Reason: new information
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Old 03-30-2006, 06:33 AM
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hi everyone, ive been lurking around here for a while now, but this post hit a nerve with me because im having the same problems with my 750 speed demon(vac sec). i went through everything you did and am still having the problem of running rich at idle. i can actually see gas sitting in the bottom of my manifold. now, when i pulled my carb apart when i first bought it (purchased 9 months ago), it was covered in metal shavings(the gaskets were filled with them) which i promptly removed, but who knows how many noseeums were tucked away in the idle circuits or someplace else that i couldnt get to....... another thing that i noticed just recently when i pulled the carb off was that the base plate was loose, this may be my fault, i didnt put any kind of thread sealant on the bolts for the base plate after i pulled it apart. anyway, i pulled the carb off because i noticed gas residue accumulating on the outside of the base plate, this may be something you should check. time for work, john
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Old 03-30-2006, 07:41 AM
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Something else you could try. The mighty demon i believe has changeable IFR's. If you are running too rich at idle with almost no adjustability on the idle screws (you did try all four???) I would either get a smaller set of IFR's and try that, or as I have done in the past you can put a small piece of wire in the hole to make the orifice effectively smaller. That will allow less gas into the circuit, possibily allowing the idle needles to have better control. It does work, you might try it if you can't figure anything else out. I have never messed with the idle eze but I thought that was supposed to take the place of drilling small holes in the butterflys on the holley. Should be a slick setup.

Good luck.
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Old 03-30-2006, 09:23 AM
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i have a road demon 725 and having problems with it as well. the tech on here told me i have to much cam and the carb is to big for the engine. its a 383 with a mild roller and air gap.

it runs very rich at idle, gets about 5 mpg and back fires thru the carb. the company that built my engine is sending out a tried and tru holley 750 double pumper. they turn ouit 8-9 of these 383's every day and every time they try to run the BG stuff they just cant get them dialed in with out allot of work. this is a nascar engine builder so i think they know what they are doing.

they did say the BG made about 10 more hp over the holley though. i like the looks and the thoughts behind the grant stuff but have been hearing from many people on here and around town from mechanics is that finding a BG that runs good out of the box is like winning the lottery.


its sad that you have to take a brand new carb and take it all apart to clean it before use.
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Old 03-30-2006, 10:31 AM
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You don't have enough compression for that cam. That's one of the reason you have to crutch the idle to make it work.


Now why would a Nascar builder be building 9 or 10 383's per day for street use? What sorta NASCAR engine are they building?
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Old 03-30-2006, 11:48 AM
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just a follow up...... like your demon my mixture screws are out 1/2 turn also and after i tightened the baseplate screws it still ran rich at idle. also, i had the idle ease closed all the way and when i opened it up all the way it did make a difference, but it still isnt enough. demon dissapointed me here, i called and talked to tech when i first got my carb and they suggested the 750 speed demon for my 383 246/248 @.50 with 15 in/hg at idle in park and the other day i called again to talk to em about the ongoing problem and the guy i talked to (eric, i think) thought that the carb shoulda been bigger(like a mighty demon 825). whatever, i think the idea with the wire blocking the idle bleeds is a good idea and i will try it. i wish i woulda gone with my gut instinct and gotten the mighty demon because i like the idea of changing air bleeds.
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Old 03-30-2006, 11:57 AM
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john i dont know,but here is there web site http://tandlengines.com

and here is the link to my post about my engines problems backfire thru carb

so do you think the road demon 725 isnt right for my engine? like the tech said.
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Old 03-30-2006, 02:09 PM
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The web site says the yare supplier for Nascar engines. I've never heard of any Cup teams farming out engines to someone else. They are only about 10 cup engine buillders and none that I know of are building for street use. Some will do do BGN or small time ASA but nothing smaller. In fact the cup teams don't allow anything newer than 5 to 7 years to be released to the public so if there were actually building SB2 or SB2.2 stuff they are at least 5 to 7 years behind on technology compared to the Cup stuff now. In fact, the lastest doesn't share much of anything wht the SB2.2 stuff. I think they are just name dropping. I think they are just a High Volume Shop. No one builds High Volume $50,000 engines.
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Old 03-30-2006, 02:59 PM
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john so dont like T&L engines but what about my question on by other thread about demon carb? should i go with a 650 speed demon or just get the 750 double that he wants for his engines.
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Old 03-30-2006, 03:34 PM
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I do'nt wanna prottrasy they are a good shop, IN nfact I woudlnt have a clue, I never heard of em till today. I just see the marketing in the web site I guess.

For street use a daily work to back home I would use the 650cfm. Anything else you can sacrifice a little slow speed response.
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Old 03-30-2006, 04:00 PM
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thanks maybe latter i will get one because they already sent the 750 double pumper with choke. hopefully it will run better andthen i can work on gas mileage
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Old 03-30-2006, 04:16 PM
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Quote:
Originally Posted by johnsongrass1
I do'nt wanna prottrasy they are a good shop, IN nfact I woudlnt have a clue, I never heard of em till today. I just see the marketing in the web site I guess.

For street use a daily work to back home I would use the 650cfm. Anything else you can sacrifice a little slow speed response.
Not to hijack the thread, but I've seen these guys on Ebay, and I was wondering why a high end "Nascar" shop would be peddling cheap engines on Ebay. Their stuff is cheap, so cheap it makes me wonder who is actually building the engines.

I think it's smoke and mirrors.

Brian
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Old 03-30-2006, 04:36 PM
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not trying to defend them because i was wondering the same thing. i didnt see them on ebay though.

i was kinda leary when they couldnt take visa payments but i was over in IRAQ at the time so maybe thats why. anyway. for what they was offering was saving me about 400 dollars over most other shops that were dynoing there engines. i did look up some "nascar" stuff and there name did appear on some of the winning cars. they were sponsers and engine builder/supplier stuff. so once i saw that they maybe have been involved with some of nascar and have seen some mag's talking about them then to me them seem good enough to send money to. i really wanted a engine ready to go and wasabout to get a chevy 383 with iron vortech head from chevy but they were cheaper.

a local builder would have been first choice but i am leaving my area soon going to cali and wanted a engine ready to go.


so by thoughts as to why they are getting into the crate engine stuff is maybe they are not getting as much "nascar" stuff as they used to and to make some more money they are getting into the crate engine stuff.

sorry to hijack your thread.
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