I recently finished the engine overhaul on my 56 which included the following work.

New Road Demon Jr 525 carb

new MSD ignition

engine bored .030 over

G heads

Blue Thunder intake

Reds headers

dual exhaust with Hushpower glasspacks

Mummert 265 cam (224 deg @ .050, 110 degree separation)

After completion engine would pull strongly at higher throttle settings but had the following running issues.

Idle was rich(would make your eyes water reguardless of mixture adjustment), idle mix out 1/4 to 1/2 turn. Could turn them all the way in and engine would still run.

Idle was inconsistant

Engine had a surge at all speeds when throttle was just off idle

Engine had a stumble just off idle

I tried numerous adjustments and even a call to tech support without any luck improving the running.

Finnally came up wit the following which has cured 99 percent of the issues ( still have a barely perceptable hesitation that I think furthe idle mix will cure).

I drilled the center of the base plate and installed a .050 jet to allow additional air into the engine at idle. This cleaned up the rich idle and allowed the mix to be set 1 1/2 turns out.

Reset the float levels to 2/3 of the way up the window.

Reset the timing from 12 to 15 degrees initial.

Re-jetted from .58 to .62 (this at 4000' elevation). I have to thank Tim for his suggestions on the board for this.

Secondary plate set full closed the 1/4 turn open with the secondary adjusting screw.

Idle speed set to 800 RPM out of gear, about 1/2 turn open from full closed.

Engine now pulls strongly at all throttle settings, idle is consistant hot and cold and no more watering eyes!! Mike

1956 Fairlane Victoria (ORREO)

 

Overlooking Beautiful Rimrock AZ

Is this a 525 Demon Jr or the original Road Demon with the four corner idle? This one I have now is a Jr - I tried the center hung bowl version on another vehicle (289 motor) and it fought me a lot.

Did the Demon tech guy tell you right away about the secondary throttle screw on the passenger side of the carb? Takes a long skinny allen wrench to reach through the choke mechanism. Works like a charm to fix the idle while keeping the primary at the right spot on the transfer slot.

Inconsistant idle was instantly fixed when I went to a steel needle and seat - I used the Holley.130's for an alcohol system. I think this trouble was due to the mixture of old and new unleaded gas in my tank - laced with alcohol.

I kept getting a vacuum leak from the PCV tube in the carb (?)- it was a weird size and the hose didn't fit it right. Now has a hose clamp for security.

Using #56 main jets (stocker cam). Reduced the size of the squirter to.....forget now, but it was way too big like a #35(?) Off idle driveability improved 100% when I got my bowl level up to where you are reporting yours. The last 1/32 raise was like magic - must have hit the mixture sweetspot.

The boosters in the rear bores are so restrictive - it looks like they just made their 625 into a 525 by stopping up the air flow in the secondary. leaves it operating pretty much like a big two barrel. Which spring are you using in the vacuum secondary?

Incidentally - congrats on what sounds like a really nice outfit........

 
 Steve Metzger       Tucson, Arizona

It is a Demon Jr. No Tech support was not very helpful,made me feel like I was interrupting his day. His comment was I ordered the wrong carb, should have ordered the Speed Demon 575. I did not want a carb that large both physically and bore size. I already knew about and had adjusted the secondaries a half dozen times. You're right about that last little bit of float height, that and the timing made big differences. Mike

1956 Fairlane Victoria (ORREO)

 

Overlooking Beautiful Rimrock AZ