CarburetorsCarb discussion and questions. Upgrading a Third Gen carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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my demon is running really rich. i need some help leaning it out. i havent taken it apart yet, so i dont know what jets are in it. are demon jets the same as the holley jets. any suggestions would be a great help. oh yeah i forgot to mention that it is a 950cfm on top of a high 500hp 434sbc. thanks for any help
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__________________ 1984 camaro Z28 sunset orange
scott shafiroff 434sbc(576hp 582 ft-lb)
tubular front end
If you bought the carb new, you can look up on Demon's site for what jets are in it stock. Yes the jets are the same as the ones used in Holley carbs, a lot of parts interchange. Just start by stepping down the jets 2 sizes at a time and see what it likes. I'm having to go the other way since I'm running too lean. 2 steps up in the secondaries gave me 3 mph more.
should i step the primaries down 2 jets or the primaries and the secondaries at the same time. the carb is brand new but it came on the motor. i have some paperwork on it but it doest say what model it is. thanks for the reply
i took the primary fuel bowl off and it had 76 jets. doesnt that sound really small for a 950 carb. i through 74 jets in the primary. i stil have to take the secondaries off and see what they are.
i took the primary fuel bowl off and it had 76 jets. doesnt that sound really small for a 950 carb. i through 74 jets in the primary. i stil have to take the secondaries off and see what they are.
i dont know. how can i tell. i really dont know much about this carb. i dont know what was chaged on it. it was dyno tuned with the motor.
There should be a serial number stamped on the carb some where, or with your instructions. There is the page to decode the serial number at Barry Grant. Unfortunately the link will not work. But it is a page that says on the right hand column: "How to identify your Demon Carb".
Is this going to be a dedicated drag race only engine? That's a pretty potent engine combo....but a 950 Demon could be a bit much if you plan to Road Race or drive it on the street.
Demons have a larger ventiri than a same size Holley. We found this out on my buddies 462ci Poncho motor. We ordered an 850 Demon WITH Annular boosters. Now Annular boosters are important...because they provide a stronger booster signal. Booster signal is the Holy Grail of carb tuning. The stronger the signal the larger the carb you can use while still maintaining driveability.
A larger venturi kills booster signal. The only saving grace with my friends carb is that it had annular boosters.
Now he has a 462 ci Poncho motor....30 more cubes than you with an 850 Demon. We had to do a lot of tweaking to get it to run right. Even at that it's too rich on transition.
I have a bad feeling that your 950 is going to have down leg boosters. These produce a much weaker booster signal than annular boosters. Add to that you have a 950 Demon....that has even larger venturies than the 850 Demon....so booster signal goes down yet again. See where we're going with this? Weak booster signals end up running sloppy rich to get any driveablity.
Dyno figures don't equate to every day driving....or even response on the track ( Drag, Circle Track or Road Racing). What RPM are you going to run? 7,000 to 7,500 rpm? If not then, IMHO, the 950 is simply too big......and you likely won't be able to get it to run lean enough.
Post back with the carb serial number.
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Here is a reply from BG Tech regarding the difference in Annular boosters vs Down Leg boosters. ( In a rather simplistic viewpoint ).
07-08-2005, 09:38 AM
Tech @ BG
Technical Support Barry Grant Join Date: Jul 2003
Location: Dahlonega, GA
Posts: 975
When it comes to annular vs. downleg boosters, there is not a clear right or wrong. It’s a matter of what’s going to work best on the application. There are Pro’s and Con’s to both sides. An Annular booster can give you better atomization on an engine, which can result in better torque, HP, and acceleration. They can also allow you to get away with some components that may be too big for the application. Since the carburetor is generally the last thing that gets bolted onto the engine it has to make up for or compensate for a multitude of sins or mismatched components beneath it. If the cam is a little big, or cylinder heads, or not enough compression, etc. these things need to be taken into consideration. There is not a clear cut one is better than another, it would be much easier than, only having to offer one part. It’s more a matter of giving additional options to help fine tune, or tailor the application. On an engine where a 650 may be a touch small, but a 750 is going to be too large, a 750 with annular boosters may be a great option. Bottom line you need to go over your entire combination with your carburetor builder to determine which one of their carburetors is going to work best on your specific combination.
Last edited by Chickenman35; 05-15-2006 at 09:20 AM.
Reason: Automerged Doublepost
thank you Chickenman35. im glad you responded. you were a HUGE help when i was trying to dial in my holley that one time.
well you were right. it does have down leg boosters. i use the car more as a street car than i drag car. i do plan on taking to the track when i get a better trans and rear. but it is by no means a drag car. so it looks like im going to have to get a new carb. i could not find a serial nummber on the carb(i didnt take it off the motor), but i didnt see anything on the main body or the fuel bowls. if i have to get a new carb, what would you suggest. do you think i should stick with a demon or go with a holley or other brand. also what size should i be looking at(im thinking somewhere along the lines if 800-850 depending on what company). this kinda sucks because i payed extra for the carb and the tuning. oh well another lesson learned the hard way
thank you Chickenman35. im glad you responded. you were a HUGE help when i was trying to dial in my holley that one time.
well you were right. it does have down leg boosters. i use the car more as a street car than i drag car. i do plan on taking to the track when i get a better trans and rear. but it is by no means a drag car. so it looks like im going to have to get a new carb. i could not find a serial nummber on the carb(i didnt take it off the motor), but i didnt see anything on the main body or the fuel bowls. if i have to get a new carb, what would you suggest. do you think i should stick with a demon or go with a holley or other brand. also what size should i be looking at(im thinking somewhere along the lines if 800-850 depending on what company). this kinda sucks because i payed extra for the carb and the tuning. oh well another lesson learned the hard way
Unfortunately that is what I feared. Downleg boosters on a 950CFM carb. Simply too much for a street driven car. Makes great numbers on the dyno...but unfortunately that does not equate to steetabilty.
You want a really hot tip. By an HO or Super Mod series from AED. They will custom tailor the fuel curve to your combination. And their custom tailored carbs are actually cheaper than some brand new Holley HP series. I would recommend their Super Mod 750 series Part number 750M2. Note that all of these carbs are modified to flow more that the stock rating. So you're probably seeing more than 800cfm...but you have a smaller venturi size and that gives good throttle response. Cost is $639.95...which is a deal. This carb comes with downleg boosters, but AED will build the carb however you want. So specify that you want Annular boosters...and they will custom tailor the fuel curve.
Edit: Just found AED's special on their new 750 HP-HO series ( $559.95 Introductry price thru July ). Basically a Holley 750HP series....but $70 cheaper:
Personally I would go for the AED 750 in either the HO series or the Super Mod series....but specify that you want Annular boosters. Don't forget...you get your fuel curve custom tailored for your car from AED. Not something you get from Holley.
Last edited by Chickenman35; 05-13-2006 at 11:28 PM.
You know....before you go ANY farther, lets properly identify just what Demon carb you really have. Reason being....I cannot find a 950 Demon listed anywhere on Barry Grant's site. You might actually have a smaller carb than you think. That would actually be good in this case.
Phone Barry Grant and find out just where exactly the identification number is. Then post back and we'll go from there. I wouldn't want you taking off a perfectly good Demon carb, because you think it is a 950.....then actually finding out that it is an 825 Mighty Demon.
Edit: Here is an identification chart to help you out. Looks like you'll have to pull the carb to see the markings:
i pulled the carb of the motor today. i looked all over it and found no numbers. so i pulled the fuel bowls and metering blocks off and still no numbers. so looks like im going to have to make a call to barry grant tech line tomorrow. to me the jetting seems small. it has 76 in the primaries and 84 in the back. also i was reading my carb tuning book and they said the Annular boosters are for high performce race applications were the engines make lower vaccum at lower rpm. would i still be alright with annular boosters on a street car.
i believe my 850 double pumper holley came with 76/84 from the factory as well, there should be numbers on the rear metering block on the right side of the carb.
__________________ my car thats never done
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......also i was reading my carb tuning book and they said the Annular boosters are for high performce race applications were the engines make lower vaccum at lower rpm. would i still be alright with annular boosters on a street car.
Annular Boosters are just fine on a street car. They are NOT just for Race applications. In fact in Strret use, Autocross and Road Racing.....basically anything where you want good throttle response, Annular Boosters are far superior to anything else....possible exception being The Carb Shop's "Super Boosters" which are a type of modified Annular Booster.
May car puts out 350 RWHP and has a dead flat torque curve....with 370 ft lbs Tq...at the rear wheels . This is with a 355 ci motor. The car also flies through our emissions testing ( when I bolt on the cat ) with figures cleaner than my buddies 1990 Fuel Injected, bone stock 305.
I have a very trick 780VS Holley that uses Annular boosters. I can run the car well below 16:1 A\F ratio ( all the lights go OFF on my K&N A\F meter ) at cruise with absolutely no lean surge. Throttle response is absolutely amazing.
I just built a 750 CFM Holley DP using a ProForm mainbody to compare with the VS.
Swapped the complete setup over from my VS carb ( Primary side only ) as I also use a Weber Power Plate on the Primary side. The Proform main body has downleg boosters....and no way can I run this carb as lean as the 780VS with Annular boosters. Throttle response is not nearly as crisp either.
If I keep the 750 DP...the Proform body is going to get Annular boosters installed on all four corners. Yes.... they are that much better.
Last edited by Chickenman35; 05-14-2006 at 11:53 PM.
i pulled the carb of the motor today. i looked all over it and found no numbers. so i pulled the fuel bowls and metering blocks off and still no numbers. so looks like im going to have to make a call to barry grant tech line tomorrow. to me the jetting seems small. it has 76 in the primaries and 84 in the back. also i was reading my carb tuning book and they said the Annular boosters are for high performce race applications were the engines make lower vaccum at lower rpm. would i still be alright with annular boosters on a street car.
This IS the car with the Scott Shafiroff 434sbc (576hp 582 ft-lb) engine....right? How would this not be a High Performance RACE Engine???
yeah this is the one with the shaifoff 434sb. they advertise this motor as their ultrastreet 434. its a street/strip motor. when i was first looking into this motor the guy said that it is fine for the street but he wouldnt reccommend it for a daily driver. but its not a balls out race motor. there are numbers on the sides of the metering blocks but they are not long enough to decode(they are only 5 numbers) on the barry grand website. im going to give them a call today after work and see what they say.
Only carb I saw so far with the 76 84 jets is the 825 cfm Race Demon Drag Race carb. Some of the 950 carbs came with 84 92 jets.
Yeah...I tend to agree with you. If the jetting is stock then it likely is an 825 Mighty Demon. That should help out a lot. Venturi Diameter ( Both Primary and Secondary ) of 825 Mighty Demon is is 1.425" vs 1.562" on the 850 Mighty Demons. A 1.562 venturi is just HUGE...and definately would affect driveabilty.
Interesting to note the differences in Venturi sizes for Holley and Demon. 850's are the same at 1.562" on all four corners. Holley 800 DP is 1.375" on Primary and 1.437 on Secondaries. Demon 825 is 1.425" all around.
Holley 750DP is 1.375" Primary and Secondary Venturi Diameter and Mighty Demon 750DP is 1.400" Primary and Secondary.
Hopefully this does turn out to be an 825 Mighty Demon. Then the rich driveabilty problem should be relatively easy to cure.
BTW...Demon's are well known to have issues with a rich off idle transition.
Here's an interesting comparison between the 850 Mighty Demon with downleg boosters and Annular boosters. The two carbs are identical dimension wise, in regards to venturi size and butterfly size:
That is a clear indication of which is the more efficient booster. There are other subtle differences as well. The Annular booster model uses a slightly smaller idle feed restriction. Boosters come in quicker so less transition fuel is required. High speed Air Bleeds are also larger as Annular boosters pull fuel harder from the main well. All good stuff!!
Edit: Sorry for the long recital folks. Suffering from insomnia and tended to babble on a bit.
Lets hope that Dan's carb is actually an 825 Mighty Demon. That should make things a LOT easier.
Last edited by Chickenman35; 05-15-2006 at 02:07 PM.
Dan: Did you check out the page at BG that shows how to identify your carb. It's under " Demon Dimensions". The one with the schematic pictures. You should be able to nail down whether you have a Mighty Demon, Speed Demon or other. IE: Mighty Demons do not have Choke towers. Speed Demons do. Race Demons have removable venturi's that are color coded.
Then measure the venturi size. Easy way is to make up a couple of "Go\No Go " guages out of welding rod. Say you think you have an 825 Mighty Demon. Cut and file a welding rod to 1.424" ( Venturi size is 1.425" ). Measure it with some Vernier calipers. ( They're cheap these days. A $29.95 set of Digital Verniers is all you need ). If it just fits in at the narrowset section of the Venturi....then you have an 825 Mighty Demon. Of course you'll have to remove the throttle base and go in from the bottom.
If it's loose then you may have an 850 Demon. Make up another guage 1.561" long ( 850 Demon venturi = 1.562" ). If it won't go in at all... make a 1.399" guage to check for a 750 Demon Venturi ( 750 Demon venturi = 1.400" ).
Simple,cheap and effective. This is assuming of course that you don't already own a set of Internal Micrometer Snap guages.
i talked to the guys at barry grant. for once in my life i have some good news. the guy said that it is a 825 mighty demon. i changed the jetting from 76 to 74 in the primary and 84 to 82 in the secondary. ill have to run to the local speed shop tommorrow and get gaskets so i can reassemble it.
i talked to the guys at barry grant. for once in my life i have some good news. the guy said that it is a 825 mighty demon. i changed the jetting from 76 to 74 in the primary and 84 to 82 in the secondary. ill have to run to the local speed shop tommorrow and get gaskets so i can reassemble it.
Ahh.....that's good news. An 825 Mighty Demon should be just fine for your engine. Glad you got that sorted out.
I can't find a 950 CFM Demon listed at Barry Grant. Do they actually make one?
I saw them listed in the spec area when checking for jet sizes. Just checked on Jegs.com and they have them listed there too. Here's a part number for one of them, Race Demon 3593020DR.
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Quote:
Originally Posted by Chickenman35
Edit: Sorry for the long recital folks. Suffering from insomnia and tended to babble on a bit.
Don't mind one bit if you're babbling on, always find something useful in your posts
Last edited by EvilCartman; 05-16-2006 at 10:15 PM.
Reason: Automerged Doublepost
i took the car out for a ride yesterday. when i first started it up it was fine. there was alittle rich smoke in my garage but it was deffinately alot better. i stopped of at my friends house to show him the car. it was dark when i left but i could tell that when i started it up it blew out rich smoke. what else can i do. should i bump the jetting down in the primaries to 72s.
i took the car out for a ride yesterday. when i first started it up it was fine. there was alittle rich smoke in my garage but it was deffinately alot better. i stopped of at my friends house to show him the car. it was dark when i left but i could tell that when i started it up it blew out rich smoke. what else can i do. should i bump the jetting down in the primaries to 72s.
Couldn't hurt. You do have the idle mixture set properly? Demon instructions are for a baseline only.
1: Warm up car completely. Turn mixture screws (on all for corners) in 1\4 turn at a time till engine speed ( or vacuum reading ) just starts to drop. Then stop. If you have a vacuum guage, hook that up to manifold vaccuum and watch it closely.
2:For the secondary idle mixture ( four corner ) turn Idle screws in ( Leaner) another 1\8th to 1\4 turn. Idle should now be a bit choppy as the car should be running a bit lean. Now adjust the Primary side out ( Richer ) 1\8th to 1\4 turn till you get a good idle with MINIMUM enrichment.
Running the Secondaries a bit on the lean side allows you to richen the Primary side a tad, which helps with " Tip in" throttle response and transition. Especialy with big cam motors.
Note: Don'te forget to check how much of the Transition slot is uncovered....particularily on the Primaries. Maximum of .040' uncovered. If Primary side butterflies are open to far this will make the idle pig rich and transition will be boggy. Symptom of this is poor response to idle mixture screws. You should be able to kill the engine by turning the Primary mix screws in all the way.
If Primary butterflies are open too far, you can open up the secondary butterflie opening a tad to compensate and then reduce the Primary side opening. Carb usually has to be removed to get at Secondary idle speed screw. Small screw underneath baseplate ( At least on Holly's ).
ok . this weekend ill try stepping the jetting down to 72s. then ill set the mixture screws the way you told me to. the way i was adjusting them was, i leaned out each screw until the motor started to stumble, then i turned it back until the motor would get a good idle.
i put the jetting down to 72 in the front. the primary Transition slot has about .025 exposed. i forgot to check the secondaries but they look about the same. should i open the seconady butterflies alittle bit more.
i stepped the jetting down to 72 in the front and put the carb back on the car. started it up today, spent some time tuning it and it looks like the problem is solved(knock on wood). it starts up much better with no rich smoke. i may still have to step the secondaries down alittle more.
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