I did change it, from the one that came with the Demon to one that I had on the Holley and had worked fine. Both are 6.5.

Joey, could not tell if you also changed the power valve.  If so 6.5 or 5.5?

You gotta have the right tools and know how to use 'em.

TC - Austin, Texas

Wasn't able to get to it right away, but everything is back together now. Hooked up the analyzer yesterday and at idle she was purring away at 600 rpm. Runs strong. I really believe it was a combination of better adjustment of throttle blades, getting a slightly smaller idle feed, and also ensuring bowls were set right and everything was clean. I didn't have to touch the air bleeds. The only issue I have now is with the manual choke. The choke rod keeps slipping off this little plastic cam. There's too much resistance from the throttle spring.

Anyhow, thanks much to everyone for all the great advice.

I like the Blue Thunder alot,I have it on my mild 292 in my truck.I had it on my gasser since 03 or 02 when Mummert came out with em.Im looking forward to trying the new Mummert intake on my new race motor when I can afford one.Sometimes those demon carbs like a lower float setting than normal.Maybe your power valve just has a hole in it?Ive had mixed results with the overratted demons.Im going to try one of those Summit Racing carbs next.My son has one on one of his cars and likes it,(mustang), He also has a Holley street avenger 570 on his 292 in his 60 f100 and it runs real good after a few jet changes.It has real strong throttle response off the bottom and screams on top,(hes running an ISKY rpm300 cam).

55 fairlane gasser 312 /c4, 57 f100 292/c4, 52 mainline gasser 302/t10 4speed

Thanks. I'm going to put in another 6.5 from my Holley that I know works. I've finished putting the Demon back together. Did the wire thing on the idle feed restrictors, and went down on the primary jets from 62 to 60. Also blew everything with the compressor, cleaned out the bowls, and added a manual choke setup while I was at it. Later today I hope to hook everything up and see how it goes. Will let you all know.

Thanks Nathan. I know when you close up the mix screws it shuts right down. I really think it's just a combination of little tweaks that need doing.

How do you like your Blue thunder intake?

Thats funny my sheevie didnt last long enough to wear out,it was new when it blew!

55 fairlane gasser 312 /c4, 57 f100 292/c4, 52 mainline gasser 302/t10 4speed

The "analog" gauge we look at to measure vacuum - is damped more than we know. Some pulses are low enough to jar the valve on its seat......and we don't see them at all. 

The reason I say this.....I had a chebbie 402 motor with an "RV" cam that wouldn't idle right to save my soul - I fixed everything twice and was about to toss the carb (a Holley1850 x 600cfm) "over Fibber's Roof" (tavern next to the shop). A guy I worked with, looked over my shoulder and said - "change the power valve so the idle screws will answer". I couldn't see any reason to do this off the handheld gauge - but changing to a 5.5 made it work. might have made it work to change to another 6.5 but II didn't have one that day.

 
 Steve Metzger       Tucson, Arizona

As long as the vacuum is above the rating of the power valve and the valve is functioning properly, it shouldn't affect idle. It's just something that needs to be ruled out.


Lawrenceville, GA

I have the exact same cam in my truck and have had a couple of BG carbs on it.I never had to change power valves or air bleeds?My engine idles 600 rpm all day long,runs smooth and powerfull.

55 fairlane gasser 312 /c4, 57 f100 292/c4, 52 mainline gasser 302/t10 4speed

I always thought the power valve only was used when you put your foot on the gas hard?So how does that affect the idle?

55 fairlane gasser 312 /c4, 57 f100 292/c4, 52 mainline gasser 302/t10 4speed