Alright, Last year I put my 383 togather, ran it on the dyno, and they tuned it for me. Motor ran fine, thing ran real good actally. 6 months after (about) it starting running rich. I didnt care, I was putting away for winter. This season, it has been nothing but problems. I foul out plugs all the times. I resealed the carb, and put a .45 power valve in it, because i had 10 Lbs of vacuum in drive. It ran okay for a little while, but still ran rich. Now its running insanly rich again. Fuel pressure is 7 PSI, and the mixture screws are 1 1/2 turns out. Everyone is saying change the jets, but my whole thing is if it ran fine when the carb was new, why should I change it when it ran fine all the time when it was new?

Ive heard you pretty much get a crappy demon, or a good one. I ready to buy a holley...... Its a 750 might demon... Help!

 

pay to have a wideband tune done and that'll explain your problems. Running too rich at idle or at cruise? Did you test for vacuum leaks all around?

 

Yes, it runs rish all around. I did check for vaccum leaks, there are none. I tryed paying for a tune, but the only place that does it keeps putting me off. So id thought id try to figure out what was wrong with it myself.

 

Check your float levels and check if there's any junk stuck in the needle and seat. New Demons sometimes have metal chips in them (my brand new 850 did). Even the act of taking one of the fuel bowl bolts out could introduce a metal bit.

My used 750 Mighty was lean out of the box (I had put it to stock specs). Think it's pulling 12 inches at idle and still have the 6.5 PV in it. Don't remember what the jetting is at the moment but the 4 mixture screws I don't think are out 1 turn, close to it though. Whenever something goes really wierd I put it back to factory specs and start from there again. That's taking the carb off and resetting the throttle blades to get the transition slots right, possibly changing jets back to stock and so on.

 

there has to be a bunch of speed shops in the area that could point you in the right direction to have it tuned. Any local dyno shop, etc etc.

 

cam specs and initial timing?

 

cam specs are: Lift .540 intake .560 exhaust
Duration .294 intake 300 exhaust

i dont remember what my base timeing is, but my total timing is 36*, and my dist. hasnt moved since.

 

so it's rich allt he way through? does messing with the idle mixture screws do absolutely nothing? after the basics like float level and psi id check ur initial timing. Probably need a lot more, guessing @ .050 you have about 250-260ish duration which is a healthy amount...specially with out a lot of cubes.

 

well its a 530 HP 383 stroker, so I would say its were its sopposed to be. I dont want to mess with the timeing because when it was dyno'ed last year, the timing was set, and the carb was tuned, and nothing has changed, its still the same engine set up. Its rich all the way except WOT I think. I dont know about the mixture screws, I always thought you screw them in all the way, and then screw them out 1 1/2 turns.

 

oh really it made 530 horse power at idle huh

sigh, enjoy

 

no, it makes it at 6100rpm. But thanks for the sarcasim.

 

The 1 1/2 turns out is a starting point not always the final adjustment.

 

you have the msd pro billet? pull the cap/rotor and tell us what limit advance bushing you're running. may be possible to limit your mechanical advance a bit and add that to your initial #'s. would help w/ the idle richness a bit, and at worse also help your tip in response.

you also said you changed the PV? did you get a bad one perhaps?

 

Do you trailer your car, i remember seeing a white m*llet being trailered on highway 4 comin off of 680 and thought to myself "this place isn't big enough for the 2 of us"

 

Yeah but it hasn't been white in a year, hasn't been on a trailer for over a month and it's never been down by where you're talking about I'm about a 4 hour drive away in the Chico area.

 

alright, talked to the tuner today. He said that a 750 CFM carb is to big for a 530 HP 383 stroker. He was saying the CFM size goes by engine size, not horsepower. He said that a 650 CFM would be good. He was saying switch to edelbrock carb actally....

 

Take that with a grain of salt...

 

birds of a feather...

 

Uhhhhhh right. I'd never run an edelbrock carb on a performance engine. I guess the 850 carb on a friend's 350 is too much yet with stock jetting his car runs 11.80's and plugs look damn good. As I said before, my 750 was lean and had to up the jet sizes. Now the 850 Mighty I had was too much carb and never could get it leaned out enough and drivability was terrible.

 

yeah I kinda thought it was insane. Im thinking about just buying a double pumper (holley) and tossing it on. The shop wants 600 to dyno tune my carb, but I dont want my car on the dyno, if they blow it up, im screwed...I dont know...... I would just hate for the carb to be screwed up (which i know it is) and a 10 dollar part fix it.

 

600 seems really high, most around me have quoted in the 100 to 300 dollar range. The CFM calculator I have says anywhere from 650 for 100% VE and 850 for 120% VE. So your fine on cfm. A holley is going to be almost the same as the demon your running. That's alot to spend just to try something slightly different. I would definately stay away from the edelbrock if your just wanting to make power. It's more of a daily driver/gas mileage carb. If you can sell your demon to pay for the double pumper then maybe its worth it.

 

What shop was this? I am right down the road from you..

 

romar.....

Okay here is the update. I put a 3.5 power valve in it, and went to barry grant.com to read some of there tech articles, I lowered the float levels on the primarys to the 1/4 mark. I adjusted the butterflys to adjust the transfer slots so that they look like a square, and they say. When they are like that though, my engine doesnt want to idle, so i had to open them a little more. Im thinking about opening the secondary butterfly more then the primary so that it will run a little leaner off idle. WOT is so much better now, but still runs rich off idle. Im going to slap a vaccum gauge on it, and see were the idle mixture screws get me.


Onebad82z, I know, you live in bloomingburg, we've talked before. Are you any good at tuning carbs and stuff?

 

Got a pretty solid understanding, and have some knowledge with the Demons. I will PM my number to you, maybe we can get together and I can lend a hand...

 

Tell your tuner to put down the crack pipe before handing out retarded advice like that.

 

well, up to this date, its still running rich. At this point, I have black speckles on my bumper. Im going to try to lower the fuel pressure to 5 PSI, then I have to start swapping jets..... Any other suggestions?

 

got the same problem. i put the 750 demon on a slightly modified 350. ran very well; turned on and idled very good. a year later, put it on my 395 stroker and this thing is leaving the plugs soiled w/ carbon.....
granted i have no exhaust past the headers, but still..... definatley paying attn to this thread........

please keep me posted .....

thanks

 

pop the bowls off and check the jet sizes.. my annular 750 mighty came with downleg 850 jets.. only 15 sizes too large.. lol it ran like crap.. it will come around after a good tune..

 

Okay, heres the update. I called up BG to see whats up, they told me if nothing changed on my motor, and everything is the same, then dirt or debris got in the carb and to rebuild it. So I ordered a BG rebuild kit, ripped it apart, cleaned everything, blew each orifice out with compressed air, cleaned it again, and blew it out with compressed air again. I noticed there were 78's on the primarys and 87 on the secondarys (jets) I put 76 and 85s in, to see where that grts me. There isnt any power valve on the secondarys, is there a rule on hoe many jets up it should be?

 

I've heard 7-8 difference. But I don't know if that's the law. If it's rich I'd think your going in the right direction.