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Discussion Starter #1
The Speed Demon 750 mechanical secondaries, no choke is history!!!

Now, the question is what to replace it with?

I am leaning toward a Road Demon 625 vac secondaries, electric choke.

Anyone have experience with it? It vs a Holley Street Avenger or???

It's a 390 with an Edelbrock Performer RPM, RV cam, 2.5 in exhaust with Flowmasters...
 

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There is precious little difference between the original Holley 4V (C80F - D) that came on a 1968 GT390 and the Road Demon except that the OEM Holley has an outstanding calibration for your car while the Road Demon is calibrated for a Chevy 350. The originals are out there and still pretty reasonable. Several vendors sell restored ones for slightly more than the Demon. I am not talking about Pony Carbs, they do fine work but are a rip off price wise. Hank Huisman or Mike Ulrey keep them in stock, so do Mansfield Mustang (see below).

Another good option is the original equipment 428 CJ carburetor that is still available brand new. Holley still offers it P/N C9AF-9510-U. You must purchase it through a vendor. These are 735 CFM and are fantastic in terms of driveability and performance.

Either of these is available from Bill Upham at Mansfield Mustang. Bill specializes in big block parts and is great to deal with. Here's a link:
www.mansfieldmustang.com
 

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Discussion Starter #3
Thanks for the tip Royce :)

I checked the Mansfield site and there weren't any carburetors listed in the on-line catalog. I am going to give them a call.

Do you think the mods made to the engine (manifold, cam, 10:1 forged pistons) would favor one of those carbs over the other?

The main reason for replacing the Demon 750 were drivability issues...

Ken
 

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I'll second Royce's recommendation of the original Holley GT390 carbs! I had one from almost every year (66-69), but am down to just the one now. That carb is doing quite nicely on BetaCat's 351C. I haven't found a better 600cfm carb out there. BetaCat is running about 10:1 compression with a mild aftermarket cam (Crane 260 Econopower) that is close to the stock 351CJ cam specs.

The only problem with the 'original' 428CJ carbs is that everyone expects to get big bucks for those just because they're 428CJ carbs. Go figure.

Anyway kvinmn, the Road Demon 625 sounds like it will do you just fine.

Good luck and have fun!

Milo
 

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kvinmn, since your not concerned about it being original and your not building a race car have you considered the eldebrock carb?

Basically they are very good bolt them on and forget em carbs. 2 piece bodys keep the fuel level below any gaskets for no leaks and you can change jetting somewhat by just changing metering rods with out taking the carb apart.

By the way I have owned some Barry Grant (maker of the Demon)carbs before and belive me there is no service after the sale with them. I will never buy another carb from them myself.

My friend just put his fairly new Barry Grant silver claw on the shelf because in his words its a $700 piece of junk. Got a new one from Gaerte and is very happy with it.

I just put a new factory reman eldebrock 600 on my pickup and couldnt be more pleased. Best part it was like $184 from Jegs. Thats the 1406 electric choke model also. mm
 

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Discussion Starter #6
No, being original isn't important. Since it was a 2bbl originally, the 4bbl should make it perform better without reducing drivability. If the PO would have built the %&#$ motor right in the first place I wouldnt be having these issues!!! :)

I'll check out the remans...

Royce - where are those Holley carbs available from? I checked their website and none of the part numbers are even close to what they advertise there...

Ken
 

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Holley Carbs?

Royce --

The latest Holley catalog has discontinued the carb you call out. The Holley p/n for the C9AF-9510-U has always been 0-4514-1 (or non -1) but it's a 730 CFM according to Holley.

As of 2002 that carb disappeared from the listings on their website and printed material. If your supplier has stock it's probably worth snatching up. How much were they asking?

Bill
 

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Discussion Starter #8
One other engine mod to consider as well...

A mechanical advance MSD distributor with an MSD electronic ignition. Do the vacuum operated secondaries rely on vacuum advance in the distributor? Is it another tuning nightmare in the making???

Ken
 

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Re: vacuum source:

No. The vacuum operated secondaries on the carb rely on the vacuum in the carburetor, and open when there is high airflow AND high vacuum (lot's of throttle and still under load). The vacuum advance on the distributor is source off of the base of the carb, I believe it's off of the "ported vacuum" (all, please correct me, it's been a couple of years since I set this up). From what I've heard over the years, mechanical advance is the way to go for strict performance/competition, but is a nightmare on the street (either bog/no throttle response or bad gas mileage -- trade off). Vacuum distributors can provide good performance while maintaining driveability, provided it is set up and tuned properly (the Accel electronic distributor that I use had decent instructions for setup; out of the box, it was WAY advanced (something like 48 degrees total advance at 2500 rpm). For a while I ran without hooking up the vacuum advance, just relying on the basic mechanical advance. I still need to properly tune it, I think I have a few MPG to gain between that and the carb (running a Holley 600 straight out of the box).
 

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Holley 735 carbs

Holley has never offered them directly. They were a special run and distributed to specific vendors. I know that Mansfield Mustang, Tony Branda and Semo Mustang have had them recently. Price is around 500 bucks. Don't bother clicking around their websites, call and ask before it's too late.

For roughly the same price Hank Huisman, Joe Bunetic or Mike Ulrey sell restored C9AF-U carbs. These are mid to late 1970's CJ replacement carbs so they don't have that "numbers match" cache' of some other very pricey original CJ carbs. These restored carbs look better than any of the originals ever did and are guaranteed.

On Ebay in the last week at least two have sold in the $150 - $200 range. These can be restored by any of the above gentlemen for around $200. Pony carbs charges about $400 for the same service.

Hank Huisman: 813-920-7544
Mike Ulrey: 727-772-5834
Mansfield Mustang:508-339-5409
 

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Demon

Kevin,
I have had a demon 625 on my mildly tweaked 351 windsor for just over a year. The tech service people were very helpful in setting it up and adjusting the 4 corner idle and electric choke. It works fantastic, great throttle response, the driveability is unmatched by any carb I've had on the motor and it screams at WOT. Also it does not leak, like the holley I replaced it with.
Although I would also give some thought to Royce's suggestion as I get the feeling that the Demon 625 is best suited for a small block application, and I have heard very good things about the original Holley 735.
Paul G.
69 XR7 Convertible
 

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Discussion Starter #12
I got an email back from Holley:


The C9AK9510 U is the Ford number which is the Holley number 0-4609. This
carb was brought back for a couple of years but has been obsoleted again.
There is no current stock at the plant or warehouse of this carb. Make a
note of the 0-4609 number if you run across any units at a swap meet or
something like that. Thanks and hope this information is of assistance.

Since I don't HAVE to get it running just yet (sold the Demon 750 yesterday) I will keep looking for one...

Ken
 

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It looks like Im going to get the Holley 670 cfm, vacuum secondary, dual feed, electric choke, square bore, Street Avenger carburetor. Main reason is that its on the shelf 5 min. from home and the same price as Summit.
A 66 GT 390 Holley is on the car now, but its needing a rebuild, Id rather just put it in my garage.
The engine is a 1970 351c with 1971 4v heads and headers. 670 cfm should be okay
 

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Discussion Starter #14
I picked up the Demon (625, vac secondaries) from a local speed shop on Thursday. I spent 4 hours on Saturday trying to get their fuel line to bolt on without leaking. No such luck.

I spent another 2 hours today trying to get the leaks to stop and to adjust the floats lower. No such luck.

I called the Demon tech support number on Saturday. It said to call back during their normal business hours. Who works on their (*^&$**(&*$* project car between 8 and 4:30 Monday through friggin Friday???

I'll try the help line again from my office tomorrow while the carb is sitting on my car. That should be really helpful.

Ken (why are most of my decisions the WRONG ones?)
 

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Discussion Starter #16
Ah....not to worry mate...

I'll be better tomorrow...unless of course she goes up in flames due to the fuel leak...:)

Ken (you always have to look on the bright side)
 

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Ken,

Forgot to mention, many Demon owners have found their carbs to be unusable as delivered. A friend of mine got a 750 Speed Demon and when he opened the box it was obvious the carb had been installed and run on another engine. He called Jeg's (where he bought it) and they said to work with Demon directly for warranty claims. He ended up trying to run it when Demon denied they would ship a used carb packaged as a new one.

Long story short, the carb had metal shavings between the metering block gasket and the carb body which caused internal leaks. After replacing the gaskets and cleaning out the shavings it works fine.

Jeg's no longer lists Demon products in its catalogs.

My recommendation is to have your original 600 CFM Holley rebuilt by either Mike Ulrey or Joe Bunetic. I gave you the numbers in an above post. There will be no problems and performance will be superior in every way to anything from Demon or Holley as far as off the shelf. It will bolt on, not leak and look better than new because both these guys are perfectionists. Every part is polished, replated and redyed to look better than new. The main body, bowls and metering blocks are milled to achieve perfect sealing, better than any new carburetor.
 

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Discussion Starter #18
Royce,

Thanks again for the reply. I do not have an original 600 cfm carb because my cat is an original X code car. The PO discarded the factory 2bbl but I still have the manifold.

I spoke with Demon tech support today and they suggested that I do the following:

1) Use teflon tape to seal the fuel line fitting that shipped with the carb. In the install instructions it said NOT to use teflon tape with AN fittings. That was my mistake...I should have assumed that I should have used the tape.

2) Remove the needle and seat and clean it with WD-40. Re insert and see if that helps. If not, box it up and send it back to BG.

We'll see what happens this afternoon...

Ken
 

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Discussion Starter #19
Well, there are technicians at BG after all :)

I worked on 68 KAT for another 3 hours yesterday and was able to stop the fuel leaks (for the most part) and get the needle and seat/float adjustment resolved.

The leak was caused by a bad fuel inlet kit. Seems as if BG has replaced many of these items due to a manufacturing problem from one of their suppliers. I tried the teflon tape wrap on the threads and it still leaked like crazy. I ended up using the fuel inlet from my old 750. They said to contact them today to get a replacement (made by a different supplier). The only leak I have left is on the secondary bowl float adjuster. Perhaps removing it scarred the o-ring seal.

The adjusters stopped working because they were screwed all the way down into the fuel bowls. The tech suggested that I remove the bowls and baseline the floats once again. After that process the fuel level did come down a bit - but it still seems to be a bit high.

Tune in tomorrow...same Kat time...same Kat channel...:D

Ken
 

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One thing to remember about Barry Grant / Demon carbs is that the fuel level in the clear window should be in the middle of the viewable area. This differs from a normal Holley where the float level is considered to be ideal if the fuel level is even with the bottom of the window.
 
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