now my carb is running horrible!
09-07-2008, 02:35 PM
#1
now my carb is running horrible! i have been battling my demon for ages now. the damn thing just wont return to idle, it will just float 500 rpm after the throttle is opened. the only way to get it down is to get out of the car and press down on the linkage.
i converted my car to a cable throttle yesterday and noticed that the new return spring location was causing the idle to go crazy. so i stretched the hell out of the springs and it still didnt help. i dont think its wise that the carb has 10,000 lbs of spring pressure to hold the butterflys shut.
turns out the "carb shop" adjusted my carb to idle off of the rear butterflys. they were almost 4 turns out. adjusting the primaries did nothing to change the idle. so with the carb installed we closed off the primaries and slightly adjusted each side. we achieved an idle of 850 rpm and seemed to solve the floating idle confirming rpm with the msd software. the idle does rage 50 rpm or so.
here is the new kicker. the same timing and ignition curve is causing my car to stumble off idle and any rpm below 2000. also upon shut down she runs backwards and shoots gas out of the top of the carb like its retarded.
so whats causing this? i did accidentally run the bowls dry when i forgot to turn on the fuel pump, think i passed something? im going to pull my plugs and see if i fouled them.
im so fed up with this demon im considering either buying a holley or parting out my LS1 and switching to a reliable gen 1 small or big block.
i converted my car to a cable throttle yesterday and noticed that the new return spring location was causing the idle to go crazy. so i stretched the hell out of the springs and it still didnt help. i dont think its wise that the carb has 10,000 lbs of spring pressure to hold the butterflys shut.
turns out the "carb shop" adjusted my carb to idle off of the rear butterflys. they were almost 4 turns out. adjusting the primaries did nothing to change the idle. so with the carb installed we closed off the primaries and slightly adjusted each side. we achieved an idle of 850 rpm and seemed to solve the floating idle confirming rpm with the msd software. the idle does rage 50 rpm or so.
here is the new kicker. the same timing and ignition curve is causing my car to stumble off idle and any rpm below 2000. also upon shut down she runs backwards and shoots gas out of the top of the carb like its retarded.
so whats causing this? i did accidentally run the bowls dry when i forgot to turn on the fuel pump, think i passed something? im going to pull my plugs and see if i fouled them.
im so fed up with this demon im considering either buying a holley or parting out my LS1 and switching to a reliable gen 1 small or big block.
09-07-2008, 03:19 PM
#3
i feel ya. i recently spent $350 to have the demon looked at. i had the metering blocks changed, new jets, and all sorts of crap done to it. still nothin.
i dont know anyone that has a holley i can borrow. i even thought about throwing a q jet on top just to see if it idles better. never in my life have i seen so many problems with a carb. my dad is an old school mechanic and is stumped by these fuel problems.
i pulled the #1 spark plug. its dry and a burn orange color. would a lean condition cause my stumble?
i dont know anyone that has a holley i can borrow. i even thought about throwing a q jet on top just to see if it idles better. never in my life have i seen so many problems with a carb. my dad is an old school mechanic and is stumped by these fuel problems.
i pulled the #1 spark plug. its dry and a burn orange color. would a lean condition cause my stumble?
09-07-2008, 05:00 PM
#4
Your first problem is the demon carb. They might be good for a street rod but if you want performance you need a holley. We have dyno'ed engines with demon carb. on and lost 30hp. more than one time!( I like real #'s) Holley makes alot of carbs., If you don't want problems(rich conditions) get a 750 hp ... I am looking for a carb. intake what is the make of yours? I have a wiring harness,computer,intake,tb and related parts. If you wand to trade.Hope things get better for your project. thanks JC
09-07-2008, 10:32 PM
#5
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There a couple of a guys over on camaros.net in the Engines forum that know the Demon pretty well. And if you bash Demon enough over there, someone from Barry Grant will show up and reply 
09-07-2008, 10:43 PM
#6
You're saying the engine diesels? Mine started that when i added a few gallons of 87 last week. I have been tuning and tuning my holley 750 and i must say its definately just about on par with an EFI setup. No stumbles, misses, cruises at about 14:1 afr (for now) and WOT is about 13.2. Its a very very smooth running setup.
09-08-2008, 07:00 AM
#7
lets face it, the demons are not the best prepped carb form their factory, but will work-i have had pretty good luck with them, once i got them dialed in
i am running a procharger on my lq4, so i had to do some serious calibration to the carb, lol
one thing i have found, to high timing at an idle will make the engine idle high, and turning in the butterfly stops wont reduce the idle enough, you may have to lower the timing, if a 6010 by way of a laptop
also the carbs seem to like the green pump cam, a little more agressive shot, at least if a vic jr intake
if the butterflys are to far open, when you shut it down, it still dumps raw fuel in the engine, causing run on
another thing you have to watch, sometimes the butterflys are not seated properly on the shaft, and wont return w/o some tweaking (i even found some screws loose on new ones)
i would start with resetting the butterflys with the correct transfer slot amount showing, reset the floats, make sure the n/s's are clean, ilde adj. screws about 1 1/2 out, and go from there
i am running a procharger on my lq4, so i had to do some serious calibration to the carb, lol
one thing i have found, to high timing at an idle will make the engine idle high, and turning in the butterfly stops wont reduce the idle enough, you may have to lower the timing, if a 6010 by way of a laptop
also the carbs seem to like the green pump cam, a little more agressive shot, at least if a vic jr intake
if the butterflys are to far open, when you shut it down, it still dumps raw fuel in the engine, causing run on
another thing you have to watch, sometimes the butterflys are not seated properly on the shaft, and wont return w/o some tweaking (i even found some screws loose on new ones)
i would start with resetting the butterflys with the correct transfer slot amount showing, reset the floats, make sure the n/s's are clean, ilde adj. screws about 1 1/2 out, and go from there
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09-08-2008, 08:37 AM
#8
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Demons are wonderful carbs but are VERY picky when it comes to tuning. The same methods that apply to most all Holley based carbs are achieved differently when tuning a Demon. I have had two and while they worked very well I realized that having to go through an entirely new learning curve just wasn't worth the headache. I ended up going back to a trusty A.E.D. and was done. I realize that this doesn't solve your problem perhaps going to another carb might.
Jim C.
Jim C.