John mentioned in a old post that the Viton tipped needle and seats were being "attacked" and apparently softened by the new generation of alcohol and additive laced fuels. A sticky situation - and mine were sticking. His solution was to use stainless steel needle and seat assemblies.

I don't have it under my nose - but there is a Holley part number for a pair of .130 orfice needle and seat assemblies (for an alcohol carb) that is reasonably priced and easily solves the problem. They screw right into the Demon carb - just try to match the installed height you found on the assembly you are replacing, to avoid a flooding situation when you start it up to set the float level. I did mine one at a time to avoid a double trouble overflow situation. Both could be installed dry by removing the bowls and setting them in the inverted position - I was just lazy....

One thing about the Demon that has caused me a bit of trouble - it has a fairly stiff integral throttle return spring. This has raised some difficulties with the stocker Ford-o-Matic kickdown system - but a stick shift car would never notice.

Don't settle on a spacer until you have the carb and get a look at the throttle bores - they are significantly larger than the bores in the late four barrel manifold (9425-B). It will require modifications to the manifold - or some massaging of a phenolic spacer to create an adapter capable of "funneling" the larger carb bore down to the manifold size. 

 
 Steve Metzger       Tucson, Arizona

Hello Steve,The response is exactly what I was hoping for from everyone who has answered.(thanks for your input)I think I am going to seriously look at the 525 road demon.Theres one on Ebay now as a factory reman at $249.00 plus mailing to Canada.What was the "fix" that John gave you regarding sticky I assume inlet needle and seat?I am a rookie at setting up these  replacement 4bbls.As someone of average(or less)intelligence are they hard to setup?I have a manifold on the way.What else do I need to this swap properly such as a spacer plate?I see some phenolic ones on Ebay for Holley application.Should I be getting one of those? What is the best one to use?Any other suggestions?Thanks, Mark

  

I have been thinking about getting a smaller carburetor. From what I've learned in the time since I bought the carburetor I think the 600 is more than I need. I've noticed that the Demon 525's are mostly for engines with cams that have less than 200 @ .050. I've found one that is less than 220 @ .050. Will it be easy to tune it to work with a bigger cam - 226 @ .050? Or may there be more complicated issues? I've also considered the Thunder AVS - with the adjustable vacuum secondaries.


Lawrenceville, GA

Not a lot of miles on it - but my 312 seems to really like the Road Demon Jr. 525 (thanx for the earlier tip Ted). The only difficulty so far has been a sticky needle - fixed with larger stainless needles and seats (thanx for the tip Hoosier).

It seems to behave as a large two barrel - primary id is pretty big - with a generous secondary to back it up - but the secondary boosters are pretty restrictive and keep up the flow velocity. The bowls are bigger than they look too, which allows for pretty heavy fuel flow. Gets my vote......got mine as a factory "rebuilt" (warranty return) for $269 with shipping from an ebay store.

 
 Steve Metzger       Tucson, Arizona

I've had a similar problem with my Edelbrock 600. I have a flat spot just as the mechanical butterflies of the secondaries open. I can feel the tension of the secondary spring in the pedal. My A/F gauge goes to lean at that moment. If I let off the throttle slightly and get back in it it does fine. Unfortunately I haven't had time to try to tune it out. The Edelbrock manual says to try stiffer step up springs so that the power mode activates earlier.


Lawrenceville, GA

Back before the dawn of time, I had two 500 Carters on a 421 Pontiac in a GTO. Had the same problem Ted mentioned. I do not remember how, but I added weight to the secondary weights and slowed, or delayed the opening. This helped. Actually the Rochester QuadraJet, with it's adjustable spring on the air valve was a lot better. He's correct though with any carb that uses airflow controlled flaps, if they don't seal when the butterflies open you get instant lean. Holley and Demon's method of controlling the actual butterflies, which do seal, Does work better. I have an 850 (Speed Demon) on a Windsor motored Ranger that is WAY too big, yet is very streetable. The quality levels of their carbs are very, very good. What Holley should have been, and wasn't.

. 

Frank/Rebop

Bristol, In ( by Elkhart) 

Seems to be a misconception out there that large carburetors make an engine run richer.  In reality, the engines actually run leaner if the carb is oversized.  But I’ve had good luck with carbs up to 780 cfm driving around just fine with the Y engines.  It’s just when the secondaries are opened that may force the issue on carb sizing but with an oversized vacuum secondary carb, air flow is diminished enough that the secondaries are either late in opening or will not open at all.  It goes without saying that almost any double pumper carb will give the engine too much air when opened at too low an rpm but a vacuum secondary carb is self-compensating in this regard.  With smaller primaries, air flow or velocity through the venturies is higher which in turn gives a better throttle response at low rpms at the expense of high rpm air flow.  Atomization is also obviously better with the smaller venturies which in turn helps with fuel efficiency.

 

I’ve had most of the popular carbs on my 272 and the 525 cfm Road Demon Jr. is the clear winner.  I’ve run several of the ’57 ECZ carbs (390-410 cfm) and these do not have the benefit seen from the advances that have occurred in metering and circuitry that’s employed in the newer carbs and although these older carbs could be tuned to satisfy either the economy or performance characteristics desired, would not do both simultaneously in a satisfactory manner.  I did run a 500 cfm Carter for a fair amount of time and although it got good fuel economy, it was always touchy when the secondaries were first opened at the lower rpms.  Part of this is due to air leakage around the weighted secondary blades and the lack of intial fuel to compensate for this.  But beyond this, still a good all around carb.

 

As usual, just my two cents worth.

Lorena, Texas (South of Waco)

Just a question.There is a 450 cfm rebuilt Holley on Ebay for a good price.This was used on the 67-69 Mustang with 289 and 302 motor.Is this too big for my application?thanks Mark

  

[quote]rgrove (7/17/2008)

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I have a 292 with a little bigger cam, blue thunder intake and ford-o in a 56 sunliner.  I had an edelbrock 500 cfm carb for a while, and found it was too big for regular around town driving.  I tried messing with jets, etc. and it was just too much carb - always very soft/lack of throttle response in the mid range no matter what I did.  Plus, my used oil analysis showed a LOT of unburnt fuel/oil dilution and accelerated ring/bearing wear, etc.

Much as I like the 390, and I do, You are the first person I ever heard with a problem that Edelbrock couldn't or wouldn't solve. Most folks like the way they work. Not sure what your problem was, but something was wrong. Not Jets either unless they were not matched to the needles.

Frank/Rebop

Bristol, In ( by Elkhart) 

I'm running a 500 CFM Edelbrock on my '62 292.  I'm very happy with the performance and ease of tuning.  Price was right too...$259 at Jegs.  It may be a bit more carb than that engine really needs but the vehicle is not a daily driver so economy is not a big issue. 

Best,  

A.J.

South Jersey

SMSgt USAF Retired 
1955 Ford Ranch Wagon & a couple of old guitars...Life's Good!