manifold vacuum help's in off idle and transition on a demon better then ported/timed. his complaint is a over rich off idle performance problem not a WOT problem. thye are 2 diferant thing's. i am not gona hash over what is better because it depend's on too many thing's. just what demon recomend's and i have found out with my own demon carb. i had the same problem he has...and after understanding why i got the problem i fixed it. i am just sharing that info with a fellow that has the same problem.
now the secondary air door adjustment stuff and other stuff...........
on a holley it would work fine, but a demon is more picky about the transfer port. you have a 4 coner idle on a demon, this make's it very important about the tranfer port setting. on a standard holey you do not have a 4 coner idle, so you can open the secondary butterfly's more then a demon and not get the off idle stumble or over rich idle.
the demon is a more presise carb and respond's to air flow faster then a holley, this is how bary grant made it. i noticed that i had to adjust my idle very carefully over a holley. a 1/4 turn of the idle adjustemnt screw gave more of a responce than on a holley and the idle mix screws are the same way.
therorecticaly you should get better performance with a demon over a holley, this is because of how fast it react's to the flow of air. this is also why it flow's less fuel then a holley but get's the same or better performance out of the motor.
people like to say a demon is a holley clone, well in a way it is but it is an advacnement over a holley in the way it react's to air flow and meeter's the fuel.
i tried the old holley trick's on my demon and they did not work. demon's like the motor to have a idle timing of about 15*BTDC or better because of the air flow it creat's. the carb was not desiened as a emision's carb in any way, it is a performance carb. if you call demon and get a good tech on the line he will recomend manifold vacuum for the vacuum advance. this is because of the signal it will give the carb, and barry grant made the carb to use it more so then ported/timed vacuum.
it has a ported/timed port on it but i feel that was to make the fed's happy. even tho it is sold as a race/off road carb not a direct replacement carb it still has to have the ability to use ported/timed vacuum. if it dosen't the fed's and the CARB board get grumpy with you.
this is polatic's plain and simple, not performance. the EPA and CARB board dose not care about performance, only emisions and to de-tune what we have. thay have all but said performance kill's so we want to be big brother and protect you from yourself.
if you get over .030" of transfer port showing on a demon(primary or secondary) it will not "dial" in at all! i tried, every thing i mean that. the closer you are to the .020" the better. demon is very adimit about this, because it is what the carb was desined to use, too much and it get's too fat(rich A/F) in the idle/offidle circit's. holley is not as picky. i have seem holley's work fine with up too .050" of transfer port showing. this is because they do not react as fast to the signal from the motor as a demon dose.
between demon tech suport and my own resurch i figuared out the it was ment to use manifold vacuum. demon tech suport told me the carb was ment to have atleast 17" to 20"+ of vacuum at idle, more is better they prefer 20" but 17" is fine on a dyno. this is for the road demon and street demon, the race demon and king demon will work with less but still like's high vacuum at idle. but a dyno is not a rolling cahasie with all the varriable's. it is a tuning tool. what work's best on the dyno 99% of the time need's to still be tweaked in the car.
the race and king demon are sold as race only carb's. they have no vacuum port's on them. this is because a race car normaly has a very radical cam and has timing of around 17*BTDC or bettter to run and idle. also they idle in the 900 to 1500 RPM range. they do not use vacuum advacne. only mechanical, and are not set up for idle/off idle performance. they are ment to run at 3000RPM or higher. a race car is not set up for easy starting or hot starting just WOT runing.
i though the demon carb's where a holley clone with a few improvement's. after i got one i found out it is a diferant carb all to gether that just share's the same princiapl's as a holley. that is why holley sued barry geant over the "claw" carb's. he cloned a holley to well. he re-desined the "calw" carb's to make then diferant and better so that holley has no right's to sue him again.
oh just for a little trivia, the vast majority of patent's in the U.S. are for auto part's/improvement's. the is how barry grant got burned on the "claw" carb's. he now has pantent's pending for what he changed on the "claw" desine to make the demon carb's so that he can not get sued by holley again.
this is also why alot of people have not been happy with there demon's. they have not tried or taken the time to learn a few new trick's and to relize that a demon is not a holley.
they also get the wrong demon, like a race demon when a street/road demon is what they need , and do not listen to what demon say's about picking the right carb. thye also get a 750CFM carb when a 650CFM is all that they need. larger is not always better for idle/off idle performance, at WOT it is a help tho some time's. did you know that on a ZZ4 GMPP crate motor GMPP recomend's a 750CFM holley carb, well a 650CFM street demon out performe's a 750CFM holley on a dyno and in a chasie on this motor, properly tuned ofcourse. demon say's a road demon is good for up to 350HP well that has been proven wrong i have seen motor's make over 400HP and be drivable and very nicley tempored with road demon and kick A$$ on the strip. they sell the raod demon as a entery leval carb, but the only diferance between a road and street demon is the street demon has a quick change vacuum secondary pod on it, the road demon is not avalable in a double pumper, and the booster's on the larger street demon's are diferant. that is why i got a road demon over a street demon the price. at about $300.00 or $450.00, what would you do???? if you want to buy a demon carb with vacuum secondary's?
i do like my demon carb, and i am not a holley fan. i tolerate them as they do make good performance carb's. i feel after more people learn how to tune a demon you will see more of them in the race car's and street car's. they have better throtel responce then a holley and give the same or better performacne with better MPG. this is because they mix the fuel and air more efeciantly and react to the air flow changes faster then a holley.IMHO
oh well i did it again i posted a long winded one..
..just trying to give you guy's all the stuff i have learned....
[This message has been edited by ilbl8 (edited 04-18-2001).]