what is causing my demon to idle +200 rpm after a drive?

dawg · Jul 1, 2008

MY FIRST 69 said:
well i ended up taking the carb to a pro. i had the carb shop take it all apart and inspect it. $350 later i have a remachined and reworked demon.

my dad picked it up for me today. the tuner said the carb was packed full of metal shavings and the metering blocks were all screwed up. he ended up replacing the metering blocks, changing the jet sizes, cleaning everything, and remachining the throttle bores.

it really sucks to know that a huge company such as barry grant sells such a poor product. i guess the myth about demons poor quality was true.

the problem with your demon carb is barry grant!
I seen countless guys end up either selling them or chucking them in the trash.
BG used to make a good product but now its all about making money.
geez for the price you paid for the repair work you could have bought a new Holley.
then sold the POS demon.
BTW I was suckerd into the demon carb craze years ago and had the same problem.
turns out mexican machinist dont clean their parts after machining.
And BG quality control (there isnt any).
try and get some money back for the repairs from BG!
Sorry tech@BG but your sitting behind a desk and dont see what us comsumers are seeing about the carbs lately.
I just wish BG would go back to the way they used to make the carbs and check each and every one for proper operation.
BTW Holley isnt made in the USA either (they are made in Korea)

77wolf10.85 · Jul 2, 2008

Also as oil temp rises idle speed increases due to decreased load from the oil pump. More pronounced on an engine with a big cam cuz they got nuthin down low.

BG did me OK on my Race Demon RS. And I've talked to this BG rep on the phone...he is good people.

Eric68 · Jul 2, 2008

I can tell you that I've dealt with both Demon and Holley Tech Support and Demon was BY FAR better to deal with.

When was the last time any of you guys saw a "Tech@Holley" posting on a web site trying to help folks figure out a problem?

MY FIRST 69 · Jul 2, 2008

i didnt mess with the timing anymore i just bolted the carb on started the car and let it warm up. at operating temp the car was idling high at around 1000 rpm with no adjustments. i gave both the primary and secondary butterflys a 1/4 turn and the idle smoothed out to 850ish.

i then took it out and gave it a wide open throttle pass only in first and second gears shifting above 6000 rpm, drove it about 2 miles then parked it in the garage. the idle was then 1000rpm.

my days off have finally arrived and i will be able to play with it more wednesday or thursday. dont get me wrong, the car pulls like no other and actually scared the hell out of my dad (thank god for BFG drag radials) but i would actually like to hear my cam more. i say my carb ran better on my old engine because i didnt have eratic idle problems. then again it wasnt a carbed LS1 either. i still think my throttle springs are so tight they are causing havoc on my linkage. i need to come up with a better return spring solution.

also after the rebuild best fuel pressure i could get was 5 psi. it used to run about 6.5 psi. should i prime my fuel pump more?

when my dad builds his FE stroker for our mustang im sure he will choose a holley.

Tech @ BG · Jul 2, 2008

MY FIRST 69 said:
i didnt mess with the timing anymore i just bolted the carb on started the car and let it warm up. at operating temp the car was idling high at around 1000 rpm with no adjustments. i gave both the primary and secondary butterflys a 1/4 turn and the idle smoothed out to 850ish.

i then took it out and gave it a wide open throttle pass only in first and second gears shifting above 6000 rpm, drove it about 2 miles then parked it in the garage. the idle was then 1000rpm.

my days off have finally arrived and i will be able to play with it more wednesday or thursday. dont get me wrong, the car pulls like no other and actually scared the hell out of my dad (thank god for BFG drag radials) but i would actually like to hear my cam more. i say my carb ran better on my old engine because i didnt have eratic idle problems. then again it wasnt a carbed LS1 either. i still think my throttle springs are so tight they are causing havoc on my linkage. i need to come up with a better return spring solution.

also after the rebuild best fuel pressure i could get was 5 psi. it used to run about 6.5 psi. should i prime my fuel pump more?

when my dad builds his FE stroker for our mustang im sure he will choose a holley.

The rebuild on the carburetor should not have caused the fuel pressure to change . You may want to try doing a volume test on the fuel pump and make sure there is nothing strange going on there. The fuel presure will also need to come back up to at least the 6.5 you had before.

MY FIRST 69 · Jul 3, 2008

i got a chance to play around with the car tonight. i installed my jegs throttle return bracket and bent up some new throttle linkage from 1/4 threaded rod. here is the new setup.

i still have my idle problem. to confirm the rpm i plugged the lap top into my MSD 6LS ignition and used the digital tach to confirm rpm. my engine temps were 200-210* with my electric fan cycling on and off the entire time it idled in my drive way. with no modification i get a idle rpm of 830-880 but as soon as i give it a good rev to 3000 or so (just like shifting out of 1st) and snap the throttle shut i get an idle rpm of 1050. i can get out of the car and push on the linkage at the return spring and watch the primary butterfly move ever so slightly. idle rpm then drops back to the 800s and all is well. if i dont push down on the throttle the idle will slowly creep down in the mid 900s. also lifting up on the gas pedal yields a 50 rpm drop.

i tired taking some timing out of it setting it at 15* initial from 0-1000 rpm. it struggled and chugged at around 680 rpm. i then brought it back to 17* and all is well.

the throttle response is awesome. no stumble, no nothing! with the new return spring i can quickly change gears and loose little rpm. i don't get that clunky okay im in the next gear feel. i actually don't even feel the gear change.

am i being too picky here? guess the only other thing to do would be to try another carb right? which doesn't sound fun.

MY FIRST 69 · Jul 3, 2008

also, here is a pic of the old gasket.

Tech @ BG · Jul 3, 2008

Are you trying to idle the carburetor primarily off the front butterfly or do you have the rear ones open as well? How much of the transfer slot is showing on the front vs the rear? How far open is the idle-eze?

camaroman7d · Jul 3, 2008

Just looking at the picture of your Jegs return spring set up, it looks to me like you don't have enough tension to close your throttle. The other thing I read is if you manually close the throttle the idle will drop, that tells me your linkage is binding or you don't have enough tension on the return spring to close yout throttle. I am not sure engine temps have anything to do with it. Most of us don't go out for a blast with the engine cold (for good reason).

Just a couple things I picked up reading your post. Try a stronger return spring and see if that doesn't cure it.

Chuck · Jul 3, 2008

I have been fighting the same issue with my Mighty 650 Demon ever since I got it. I can set it nuts on, take it around the block and the idle changes. Usually, 150-200 rpm higher than I had it set. Nothing binding, throttle plates set correctly. I've finally got it close enough so that it stays around 1000 rpm. I'd rather have it a little too high than too low. That results in better splash oiling for the cam and higher idle oil pressure. 900 rpm is as low as I'd want to go. Got an LM1 A/F meter on the way to try help dial it in at idle and above. Car screams otherwise. No stumbles, hesitations ,or any of that. Throttle response is awesome. Nail it in 2nd on the on ramp and it'll be at 6 grand real fast. Maybe a wandering idle is a small price to pay.

MY FIRST 69 · Jul 3, 2008

chuck, your setup sounds exactly like mine. i had a huge solid roller in my old small block on a 106* LSA that absolutely had to idle at 1000 rpm. most of my engines have idled at a higher rpm so maybe i had this problem all along.

Are you trying to idle the carburetor primarily off the front butterfly or do you have the rear ones open as well? How much of the transfer slot is showing on the front vs the rear? How far open is the idle-eze?

i never inspected the transfer slots after i got the carb back. my dad bolted it on the car and had it running while i was at work. how it sits is how the guy at the carb shop tuned it. the idle eze has never worked. i could screw it in and out as much as i wanted and it never changed a thing. i dont even understand its function.

Most of us don't go out for a blast with the engine cold (for good reason).

210* with the fan cycling is cold?

Tech @ BG · Jul 3, 2008

MY FIRST 69 said:
chuck, your setup sounds exactly like mine. i had a huge solid roller in my old small block on a 106* LSA that absolutely had to idle at 1000 rpm. most of my engines have idled at a higher rpm so maybe i had this problem all along.

i never inspected the transfer slots after i got the carb back. my dad bolted it on the car and had it running while i was at work. how it sits is how the guy at the carb shop tuned it. the idle eze has never worked. i could screw it in and out as much as i wanted and it never changed a thing. i dont even understand its function.

210* with the fan cycling is cold?

The idle-eze is there to duplicate the same results from drilling holes in the butterfly that we used to do. Now with the idle-eze if you are finding that you cannot get the carburetor to idle with the transfer slots under .020 instead of drilling holes in the butterflies you will open the idle eze up to take the pressure off of them and then close them back down. You may find depending upon the cam duration and engine combination this adjustment may be anywhere from a turn and a half open to 3 or even 5 or 6. If you have the secondaries closed all the way and idling primarily off the front ones then you would want to open the secondaries up a little and close the primary side back down. Based on the engine combination listed we would probably start both at the .020 and the idle-eze at a turn and a half . If the idle is too high at this point then close both butterflys down a little evenly. If the idle is low then you would want to open the idle-eze up .

Tech @ BG · Jul 3, 2008

MY FIRST 69 said:
i never inspected the transfer slots after i got the carb back. my dad bolted it on the car and had it running while i was at work. how it sits is how the guy at the carb shop tuned it. ?

Once it was bolted back on were the mixture screws adjusted out on it for best idle?

MY FIRST 69 · Jul 4, 2008

i checked the carb. the 4 corner idle screws are out 1.5 turns and the center idle eze is closed tight. at the moment if you stand behind the car the exhaust smells a tad rich but the garage doesnt stink and my eyes dont water.

well im loosing fuel pressure now. i noticed it went as low as 3 psi at the gauge. i unscrewed the gauge and filter before the carb. no leaks, the filter was new since the swap so maybe 6 hours run time on the pump and fuel lines. i gave my edelbrock fuel pump one complete screw outward and upped the fuel pressure back to 5 psi. i drove the car around the block going easy on it, rowed 1-5th with no issues. parked it and noticed fuel psi was down to 3 psi again. its not starving, no chugging in very light throttle situations like monkeying it back into the garage.

i unscrewed the fuel line at the filter and placed it in a bucket. it flat out shoots fuel out! instant flood. so im thinking my gauge took a dump because the needle bobs around quite a bit. the car pulls 14amps no problem. the only other time i had a pressure drop was when my alternator wasnt charging.

back to the idle...

i gave my return springs more tension and it did seem to help some. i also gave the idle eze screw 1.5 turns out with no noticeable change. with the car warm it idles at around 900 and then floats to 1000 after a quick rev. it then slowly returns to around 900-950. not really a huge change.

Dougs72Nova · Jul 4, 2008

MY FIRST 69 said:
i checked the carb. the 4 corner idle screws are out 1.5 turns and the center idle eze is closed tight. at the moment if you stand behind the car the exhaust smells a tad rich but the garage doesnt stink and my eyes dont water.

well im loosing fuel pressure now. i noticed it went as low as 3 psi at the gauge. i unscrewed the gauge and filter before the carb. no leaks, the filter was new since the swap so maybe 6 hours run time on the pump and fuel lines. i gave my edelbrock fuel pump one complete screw outward and upped the fuel pressure back to 5 psi. i drove the car around the block going easy on it, rowed 1-5th with no issues. parked it and noticed fuel psi was down to 3 psi again. its not starving, no chugging in very light throttle situations like monkeying it back into the garage.

i unscrewed the fuel line at the filter and placed it in a bucket. it flat out shoots fuel out! instant flood. so im thinking my gauge took a dump because the needle bobs around quite a bit. the car pulls 14amps no problem. the only other time i had a pressure drop was when my alternator wasnt charging.

back to the idle...

i gave my return springs more tension and it did seem to help some. i also gave the idle eze screw 1.5 turns out with no noticeable change. with the car warm it idles at around 900 and then floats to 1000 after a quick rev. it then slowly returns to around 900-950. not really a huge change.

Just a thought. I had a few liquid filled gauges that were showing a drop in pressure once the car warmed up, but it was the gauge that was the problem. I drained the liquid out of it and the gauge read correct there on in. Is your gauge liquid filled? Not saying this is your problem, but i have have seen this happen.

MY FIRST 69 · Jul 4, 2008

yes it is liquid filled, im going to buy a replacement and give it a try.

Dougs72Nova · Jul 5, 2008

MY FIRST 69 said:
yes it is liquid filled, im going to buy a replacement and give it a try.

I should have elaborated. My gauge was mounted on the carb line. There was something about the liquid in the gauge and the underhood temperature that was throwing off the gauge. Not sure what, but when i drained the fluid the gauge worked great. I thought i was having a fuel pressure problem and was not. I had this happen with more than one of the liquid filled underhood gauges.

67SS&99SS · Jul 6, 2008

Any closer on your idle issues? I just read the entire thread, and am wondering why you chose to do the carb route on the LS1? Easier tunability? Did the engine come out of a salvaged vehicle? If so, do you still have the LS1 intake/fuel injectors/pcm/wiring harness? I have a 4th gen SS with an LS1 and am familiar with various cam/fuel upgrades to the engines. Texas Speed, the maker of the magic stick cam does offer mail order (fuel injection) tunes for your application and the car should maintain idle consistancy and probably pick up a good deal of power. I know this is probably the last option you want to pursue, but it is an options. Upgrading the stock LS1 intake and TB with a ported fast 90 mm intake, nick williams 90 mm tb and a full dyno tune would probably net an increase of 40-50 hp and 25-35 ft lbs at the rear wheels. How high are you spinning your motor? A friend of mine had that cam in his 2000 Z28 and run 11.90s with a 4.10 gear, and the stock ls1 intake and tb. He was shifting at 6800-7000 rpm Many of my friends have had large cams in their LS1 cars similar in size to your cam, some slightly larger and they all seemed to idle best around 1000-1100 rpm.

RickD · Jul 6, 2008

As a side note, the engine compartment heat will perculate the fuel and show as a drop in pressure. You can insulate the lines but the fuel pump is a huge heat sink (if you have a mechanical pump).

MY FIRST 69 · Jul 6, 2008

67SS&99SS

i chose to go the carb route because it was cheaper at the time. i actually bought a really nice long block and sold all the efi stuff off of it. i was still missing the pcm and wiring so i made my money for other swap parts from the sale.

i would have went efi if swap parts such as headers, t56 parts, clutch, fuel upgrades, and so on werent so expensive.

the only way i would go efi is if i started over on a new car. my 69 has been through too much. i would have to blow the entire thing apart and re wire it for efi.

what is causing my demon to idle +200 rpm after a drive?

dawg

77wolf10.85

Eric68

MY FIRST 69

Tech @ BG

MY FIRST 69

MY FIRST 69

Tech @ BG

camaroman7d

Chuck

MY FIRST 69

Tech @ BG

Tech @ BG

MY FIRST 69

Dougs72Nova

MY FIRST 69

Dougs72Nova

67SS&99SS

RickD

MY FIRST 69

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