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

[DCx]

im running a 750 mechanical secondary mighty demon on my carbed ls1. when i first start the car it idles at around 900-950 but after a quick drive around the block it will idle at 1100 rpm. what is the major cause for this?

the carb is out of the box stock. i literally took the carb off my old 355 and threw it atop my ls1 and ran it as is. i checked the gap between my accelerator pump linkage with a .0012 feeler gauge, that checked out. i have two large springs pulling the linkage shut (sometimes wonder if the springs have too much tension) and im running a home made heim joint throttle linkage with aluminum holley bushings like these at the carb linkage and at the throttle pedal arm.

https://static1.pt-content.com/images/pt/2008/06/6a2c_1_bJPG-1.jpg

i noticed my flots are a tad low, about 1/4 of the way in both the front and back. i didnt recheck the transfer slots before installing the carb, but it ran great on my old small block. the idle screws are about 1/2 turn out if my memory serves me. the idle is a tad rich but the car has no stumble. i have the idle ease screw but it never changes anything when i mess with it.

my cam is rather large and only pulls 10" of vacuum when the gauge is hooked up to the carb.

Texas Speed Magic Stick 3 cam - 237/242 .603/.609 113LSA

i programmed my ignition to run 17* timing from 0-1000 rpm and slowly ramp it up to 29* total at 3000 rpm.

also my fuel pressure is at 6-6.5 psi constantly.

i can press on the linkage with my hand and the idle will lower as long as i put some force on it.

and lastly. here is a pic of my home made linkage. the throttle arm sits way low compared to the height of the ls1 intake. so i bent up some threaded rod. the Z shape needs to be revised. its actually too long and i cant achieve full throttle at the moment. i was thinking of making my new linkage a lazy L shape.

https://static1.pt-content.com/images/pt/2008/06/throttlelinkage1-1.jpg

https://static1.pt-content.com/images/pt/2008/06/throttlelinkage2-1.jpg

should i run this return spring bracket instead? (my old linkage is pictured. too bad it was way too short to make it to the throttle arm).


https://static1.pt-content.com/images/pt/2008/01/throttlespringbracket-1.jpg

[David Pozzi]

It may be just that the intake takes time to heat up. After heating up more fuel vaporizes and the engine runs smoother/faster.
I've found that starting up a cold engine, waiting until the gage shows warm then tuning the carb will prove to be too rich once I drive the car 10 miles and the intake has more time to heat soak.
David

[Shaker455]

Sometimes in hot weather they do pick up a little after a drive but my Mighty 825 had a throttleblade issue and it was doing the same.

I had to break the base down due to piss poor assembly and align it properly.

Reset your floats, make sure the bowl screws are tight, dial all your mix screw in with a vacuum gage, and check all your intake and carb bolts as they do loosen after a few heat cyclings.

[DCx]

will do. everyone talks about demons quality control issues. maybe ill have the carb take apart and looked at. i didnt do much tuning i just threw it atop the engine and started it up.

im going to get a FAST dual o2 air/fuel meter for it shortly.

[DCx]

found out what the problem was today, but im yet to fix it.

i drove the car and got it hot before i took some idle out if it. drove it around the block again and still had the 1100rpm idle. i then removed the carb from the engine and flipped it over to take a look at the transfer slots. i noticed the secondaries were showing a lot more than the primaries. i slowly opened the throttle all the way and closed it slowly. thats when i noticed that the secondary butterflys were sticking open. im not sure if they are binding on the bores of the carb or if the linkage is bent.

im thinking about sending it off to a carb tuner and having it taken apart and inspected.

[Shaker455]

Good idea,
I just took apart my Mighty 825 and the front blade was hanging up.

Demons piss poor quality strikes again!

While I had it apart I slabbed the shafts and teflon bushed like I do for my customers.

[DCx]

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.

[Shaker455]

Not a myth sorry.

I posted a thread on the PY forum titled "Demon Demise" ...check it out...

[RUSSSMITH3]

Were did you get the threaded rod ends?

[justanova]

http://www.speedwaymotors.com/p/3944,108_Swedged-Aluminum-Throttle-Linkage-3and16andquot;-10-32-Thread.html?itemNo=throttle%20linkage

not sure if he got them here but they have them, and most local "dirt track" parts suppliers will have them. note: the heims are at the bottom of the page. or if you want to use 1/4 threaded rod you can just get female heim's just search on speedways website.