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Demon Carb

4507 Views 18 Replies 10 Participants Last post by  Wag
I have an oppertunity to pick up a 650CFM Demon with mechanical secondaries. My Boss is a 97 ZZ4 Clutch. Is this a wise choice? Too small, too hard to dial in? Or better to stick with the Edelbrock with vacuum secondaries.

Jack Phillips
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If you want performance it is a no brainer--go with the Demon. Mileage will most likely take a hit but if you like to twist the throttle Demon or Holly. My 950 did not take really any adjustment except for the float levels but it was made for the motor. I am sure there is someone here who can help you with the details as you are not the 1st to make this switch. When you get finished please post and let us know how much better the response is? Mine was night and day to put it mildly!
Edelbrock Carburetor

Just to set the record straight, both the Edelbrock #1901, 750 cfm and the #1910, 850 cfm used on the Boss Hoss have mechanical secondaries.
My # 1901 has vaccum controlled secondaries. Unless you go WOT and the vaccum drops the pod will not allow the secondaries to open.

a nice quad article ;

Quadra-junk, Quadra-bog—you’ve heard them all before. Why do so many gearheads love to hate the Rochester Quadrajet? Because it’s arguably the most intricate, precise carburetor design ever produced? Because its small primary bores allow stingier fuel economy than most two-barrel carbs? Because its vacuum-operated secondary circuit ensures your engine is never over-carbureted? Because even the smallest Q-jets flow a respectable 750 cfm?
Edelbrock secondaries


I feel bad as it seems you and I always get hung up in semantics.

There are two sets of butterfilies on the Edelbrock carburetor secondary. The lower set is directly connected to the throttle via an eccentric cam lingage. When the primaries are about 60% open, this linkage begins to open the lower secondary butterflies. At 100% throttle, WOT, both the primary and secondary butterflies are 100% open. The opening of the secondary butterflies with direct mechanical linkage, by definition, is called "Mechanical Secondaries".

Vacuum operated secondaries do not have mechanical linkage directly connected to the throttle. They have a vacuum diaphram that opens the secondary butterflies based on ported vacuum. There is no mechanical linkage connected to the throttle whatsoever.

In addition to the secondary butterflies just described, (the ones mechanically controlled by the movement of the throttle), there is another set of butterflies at the top of the secondaries. Edelbrock calls this the "Air Valve". Its purpose in life is to enrich the secondary mixture as we transition from the primaries to the secondaries (60% through WOT). This valve has a spring to control the tension on the air valve, i.e. the richness of the secondary mixture during this transition period. This set of butterflies is "pulled open" by air moving through the secondaries.

Finally, the part you are referring to is the "de-choke" or "wide open unloader". This is a small vacuum diaphram that is operated by manifold vacuum. Its purpose in life is to prevent the Air Valve and lower secondary butterflies from opening fully if there is no engine vacuum (engine not running). This vacuum diaphram was added to the carb to aid cold weather starting and, as is revealed by its name "de-choke", it is used in conjunction with the choke (which is removed in the Boss Hoss application) to prevent the secondaries from opening if you open the throttle wide open and then try to start the engine. This is a "Cold start" procedure.

Since we do not run a choke, this diaphram and its linkage is pretty much worthless. It is in its fully operated position (has no effect on the carburetor) whenever the engine is running. You could take this vacuum diaphram and its associated linkage off and throw it away and it would have no effect on the performance of the Boss Hoss.

If you would like to read more about the function of the de-choke / unloader diaphram, it is described on page 23 of the Edelbrock Owner's Manual. Or, a full description of the de-choke / unloader and the mechanical secondary linkage is available in Doug Roe's Carburetor book on pages 17-21. It is one of the best written descriptions I have seen.
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fasteddie said:
My # 1901 has vaccum controlled secondaries. Unless you go WOT and the vaccum drops the pod will not allow the secondaries to open.
I'd like to see the only one made with vaccum secoundarys. Hang onto it Fast, because you have the only one around.

Unless you have a lot of time and talent the Demon is not the Carb to own. I have 3 friends that are above average and all have tried to make the Demon work but never could and went back to Holley's.
Demon now makes one just for the ZZ 4 motor and told my friend that most Demons will not work on that Motor with out major work.

1901 vs: Demon

Thanks all!
Again very educational. Looks like for me, I should stick with the 1901. My overall goal is for a reliable prime mover, that's also a HOOT when spanked. I don't have the money, skill, or patience to "experiment" with a different technology that might make my Boss less ridable. If I want sustained triple digets, I still have a ZZR1200 and a Blackbird. Put stabil in both tho, because the Boss is so much fun.
I'll let that Demon oppertunity slide past, and look (at a casual pace) for another Edey 1901 to send to Mike.
Thanks again, didn't intend to stir up any controversey.
Jack Phillips

I am confused. I thought that I had a choke. When I have a cold start up, my engine runs at a very high idle. I normally let it run this way for 20 - 30 seconds. Then I give it a twist and it settles down to normal idle.

Is this not a choke???
:?: :?:



To the best of my knowledge all Hoss's come from the factory with the choke mechanism (heat sensing bithermal spring) removed and the choke butterflies either disabled or removed.

I, of course, don't know the history of your bike. Is it possible someone added a choke?
A friend bought a trike from Stamford and the choke on it works. I know if you twist the throttle after it is warm it will reset the choke and then you have trouble getting it started. When we talked to Debbie she said that they makethe chocks on all the small blocks active.
Hawk..I too have considered the Demon but the Edelbrock is running so well and have seen so many posts here about dialing in the Demon that I've decided to stay with the stocker. I run an electric choke. I also do most of my riding on highways and seldom use the secondaries but when I do I love the ass kick I get. I also like the gas mileage on long trips and get 22 mpg at high speeds on long trips even with my stroker. Sometimes, as we say in the operating room, "better is the enemy of good."
Neil - you're correct but semantics sure do make things interesting..

Hawk - check out e-bay item 7915194962 it's a #1901
1901 vs demon

Thanks again all! Including the e-bay link. I'll sit on this for a couple days hoping for 2 sepeate answers on feelers I have out. 1 here in Fl, and 1 in Okla. These sites have been the best "Educators" since the last Army Maintenance Test Pilot course I attended in Va. You all have advanced my learning curve tremendously in a very short period of time; kept me and the Boss running (Boss better than me), and saved me spending money needlessly (that I don't really have)!
Thanks again.

Jack Phillips

I bought a Holley sreadbore to try out.
I figure it's a holley, already know about them,
It's a spreadbore so hopefully I will retain the gas mileage.
It has mech secondarys, and the only thing I don't care for is it has side hung floats but they have that so the original fuel line will work.
I haven't put it on yet, too busy.
Holley Spreadbore

Keep us posted plese, when you install it, how hard is it to set up, etc. Which model and size is it?

By the way, thanks for maintaining the "help site" and links. The site is worth lots of time just appreciating the site itself! Very well done.

Jack Phillips

Thanks for the kind comments about the help site! My ISP is doing a major server change and it has made it difficult to update lately.

Here is the link to the Holley I bought:
http://store.summitracing.com/partdetai ... 19D9D9C%7D
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