i just recently bought a 625 road demon with electric choke vac secondaries. my problem is that it bogs after 3/4 throttle before the secondaries open(either that or the secondaries run dry for a moment), its almost devestating in first and annoying in second( 4-clyinder t-5, deep gearing) it replaced a holey 4160 600 cfm side hung floats that ran perfectly( i have another use for it, replacing an edelbroc). im pretty sure a jet increase of 2 sizes would fix the problem, but im unfamiliar with the demon. does it use the same jets as a holley because i have a holley jetting kit. i dont want to jump into something i dont have parts for. any info would be helpful.
Anyone here with road demon experience
- Thread starter ashford
- Start date
Blue Thunder
15 Year Member
The Race Demons use Holley jets, too. If the part numbers are different, it's likely due to the fact that Demon is owned by Barry Grant, not Holley, and there was/is a big lawsuit in the works concerning the similar basic designs of BG Demons and Holley carbs.
As for your issues, I would experiment with lighter secondary springs and see what affect it has on your car's performance. If performance is what you're after,(Is there anything else?) you want to go as light a spring as possible, that doesnt cause a poor vacuum signal/engine bog when the secondaries first crack open. If the motor is slightly undercarbureted, you may get away with secondaries flying open very early in the RPM range, without any bog at all. (Especially with a Demon, because their venturii/booster/throttle plate design is superior to Holleys, and allows you to run a lower vacuum signal without losing the fuel pull.)
By the way, I believe Demon still offers free tech support for their products,(the number is printed on the yellow tag that comes with the carb) and from what I've heard, they're pretty knowledgable guys.
As for your issues, I would experiment with lighter secondary springs and see what affect it has on your car's performance. If performance is what you're after,(Is there anything else?) you want to go as light a spring as possible, that doesnt cause a poor vacuum signal/engine bog when the secondaries first crack open. If the motor is slightly undercarbureted, you may get away with secondaries flying open very early in the RPM range, without any bog at all. (Especially with a Demon, because their venturii/booster/throttle plate design is superior to Holleys, and allows you to run a lower vacuum signal without losing the fuel pull.)
By the way, I believe Demon still offers free tech support for their products,(the number is printed on the yellow tag that comes with the carb) and from what I've heard, they're pretty knowledgable guys.
I would maybe try to getting them to open a little later. The bod is more likely to be because it opens a little to quick for the circuit to flow. Or you can try a slightly higher float adjusment for quicker tip in with the faster spring. You may also want to look at a different power valve size. The bigger the number the quicker it will open. Go up one size(5.5 to 6.5). This may help with secondaries that open too fast.
a little further test driving it seems like after the accelerator pump goes out ot juice it dogs till the secondaries open up. i get a short burst of power then a bog the the secondaries opren up(you can really hear it on the demon) then it goes fine. so im concluding its lean in the primaries or the power valve passage is plugged.
other question. it has a 4 corner idle but the secondaries didnt have a throttle stop screw in it so i made one eith a locking nut and opened it a little(just enough to expose the idle port in the venturi) did they forget this in the q.c. process ?
thanks for the replies on the jet interchange the was the most important info i needed, and thanks for the other tips, i think i might still have some secondary springs for holley.
other question. it has a 4 corner idle but the secondaries didnt have a throttle stop screw in it so i made one eith a locking nut and opened it a little(just enough to expose the idle port in the venturi) did they forget this in the q.c. process ?
thanks for the replies on the jet interchange the was the most important info i needed, and thanks for the other tips, i think i might still have some secondary springs for holley.
Hey, I've got a 625 demon on my 66 289. I am pretty good at tuning it but I have a question for you. The "bogging", does it occur right after you get on the gas? If it does, then its an off idle stumble. If this is the case, adjust the four screws on the base plate out at a 1/4 turn all the way around and test it. Repeat if neccesary. If it isn't that, and your float level is too low on your secondaries, then just loosen the screw, turn the nut counter clockwise to raise it and clockwise to lower it. Mine had a problem if the secondaries were too high so I set mine at about a 1/4 sight glass from the bottom. If its still there then check your accelerator pump and make sure its not too tight/loose. It should be barely touching as it sits. Hope this helps. Please let me know how it goes after you check that.
BlueMonster65
Founding Member
tuning the demon
i bought my demon when it first came out and i must say it is by far the best carb i have ever used. to determine what is causing yor bog, or hesitation, first you must determine at what rpm you are experiencing this problem. i purchsed a book titled "how to tune your demon and win" it is a very good book, but i don't know what i am going to win? the book explains that if your bog is under your cruising range say 2000 to 3000 rpm, it is most likely the acceorator pump circuit. if you experience a bog and then a surge when the secondaires open then the spring is opening the vacuum secondaries too soon. stock jets on the road demon 625 are a little big for a 302 even slightly modified. but that will only cuase you to run slightly rich and will not create a bog or surge so i woul not change the jets. the pink accelorator pump that is stock on the road demon is big, and chances are you are not running out of fuel in the transition from idle to cruise. if anything you could step down on this, i currently have the red cam installed. which is a couple steps smaller than the pink cam. the stock vacumme secondaries spring is probably opening too soon. step up to the next size. when they are opening too soon here is what happens, the spring opens allowing more fuel to enter the engine but the engine doesn't need it yet so you effectively flood it, then as rpm comes up the engine needs gas, well now the engine rpm matches the fuel delivery and bam you feel a sudden burst of power.
check these things in this order first before changing the spring in the VS.
fuel pressure
float setting
curb idle and transfer slot.
air fuel mixture.
hope this helps
Joe
i bought my demon when it first came out and i must say it is by far the best carb i have ever used. to determine what is causing yor bog, or hesitation, first you must determine at what rpm you are experiencing this problem. i purchsed a book titled "how to tune your demon and win" it is a very good book, but i don't know what i am going to win? the book explains that if your bog is under your cruising range say 2000 to 3000 rpm, it is most likely the acceorator pump circuit. if you experience a bog and then a surge when the secondaires open then the spring is opening the vacuum secondaries too soon. stock jets on the road demon 625 are a little big for a 302 even slightly modified. but that will only cuase you to run slightly rich and will not create a bog or surge so i woul not change the jets. the pink accelorator pump that is stock on the road demon is big, and chances are you are not running out of fuel in the transition from idle to cruise. if anything you could step down on this, i currently have the red cam installed. which is a couple steps smaller than the pink cam. the stock vacumme secondaries spring is probably opening too soon. step up to the next size. when they are opening too soon here is what happens, the spring opens allowing more fuel to enter the engine but the engine doesn't need it yet so you effectively flood it, then as rpm comes up the engine needs gas, well now the engine rpm matches the fuel delivery and bam you feel a sudden burst of power.
check these things in this order first before changing the spring in the VS.
fuel pressure
float setting
curb idle and transfer slot.
air fuel mixture.
hope this helps
Joe
BlueMonster65
Founding Member
correction
just wanted to correct myself.
if the VS are opeing too soon the air door will open and fuel won't come into the engine until the engine speed catches up to the available throttle area and creates a strong enough signal. direct from "how to tune your demon and win!" so you would actually be leaning it out by allowing more air in,not flooding it.
i apologize for the error
just wanted to correct myself.
if the VS are opeing too soon the air door will open and fuel won't come into the engine until the engine speed catches up to the available throttle area and creates a strong enough signal. direct from "how to tune your demon and win!" so you would actually be leaning it out by allowing more air in,not flooding it.
i apologize for the error
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