I'm running a 350 4 bolt main, bored .030 about 10.5:1 compresion ratio or maby a little more with 461 heads, cam has a .500/510 lift 256/270 duration 112 deg lobe separation, solid lifters. I have a torker II intake now but am planning an air gap later and an MSD system; car is a 4 speed wide ratio M21 I'm also running headers and glasspacks. I'm thinking about a 700 or 725 speed demon. What I'm looking for is a quick responce carb that not to much hassel to setup.
Thanks for the help.

750 holley

750 double pumper. With that cam you will want to get one with four corner idle adjustments to help get a decent idle. If you do go with a speed demon just be warned BG has had some guality control problems, buy at your own risk.

psalms, I have a simliar engine and had problems for the last 5 years. The problem is the cam you have will not develop a lot of vacuum. Vaccum is what helps the carb have the correct amount of fuel at idle. Without enough vacuum you will dump too much gas at idle and have a lean problem at the higher rpms. Carbs you buy off the self are set for either race or mild street. Your engine is fairly serious. I would spend the little extra and buy one from Patrick at http://www.pro-system.com/ More than likely it will be the one for $599 that is tax and ship***g included. It will be built just for your application. I got mine and bolted it in and had to tweak the idle and that was it. 5 years of frustration gone with 1 call. A new (750) holley or Demon will cost about $450, plus jet extensions and finding the right jets for your buggy, not to mention several sets of plugs until you have it set right. Due to their poor customer service, and my frustration with my demon, I would never recommend a demon, and holley was not a lot better. Just my $.02

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Bob

<font face="Arial,Verdana" size="2">Originally posted by z28smokin:
psalms, I have a simliar engine and had problems for the last 5 years. The problem is the cam you have will not develop a lot of vacuum. Vaccum is what helps the carb have the correct amount of fuel at idle. Without enough vacuum you will dump too much gas at idle and have a lean problem at the higher rpms....

</font>

How does low vacuum cause a carb to 'dump' gas at idle? I was operating under the assumption that vacuum is what attracts the fuel out of the carb, and less vacuum results in less fuel. How is the low idle vacuum related to the operation at higher rpm's?

[This message has been edited by onovakind67 (edited April 28, 2005).]

I agree with the 750DP with the 4 corner idle as well.

demons are junk get a HOLLEY,had a demon and gave it away.

I have had the opposite experience. I have a 383 running a solid lifter cam with long duration. I could not get a Holley 750 to idle properly. I worked with Holley and made all the suggested modifications. I contacted a tech at Barray Grant, and he speced a 650 Mighty Demon. I was skeptical at first, but I got the carb and it has been fantastic. The only modification I had to make was to upsize the squirters.

www.barrygrant.com (http://www.barrygrant.com) has a Demon selection guide which is based on displcement, cam duration and converter stall speeds.

Jon

onovakind67, a carb can dump gas with low vacuum because you will have to open the throttle plates to get more air into the motor. This uncovers the transfer slots and thereby lets excess gas into the motor at idle.

At least thats the explanation Holley gave me. They suggested drilling holes in the primary throttle plates to let in more air without uncovering the transfer slots. This di not work for my application.

Jon

What keeps the gas from running out the slots when you shut the engine off? If it dumps gas while it's running, what makes it stop dumping when you shut the engine off? Could it be that the manifold vacuum is what actually attracts the gas out of the slots?

I recently installed a 750DP carb on our little 490 hp 331" road racing motor. I had trouble with the idle being too high, I had to close the throttle plates way down to get the idle down to 1000 rpm. The secondary plates are closed all the way.

[This message has been edited by onovakind67 (edited April 28, 2005).]

<font face="Arial,Verdana" size="2">Originally posted by stratman315:
I have had the opposite experience. I have a 383 running a solid lifter cam with long duration. I could not get a Holley 750 to idle properly. I worked with Holley and made all the suggested modifications. I contacted a tech at Barray Grant, and he speced a 650 Mighty Demon. I was skeptical at first, but I got the carb and it has been fantastic. The only modification I had to make was to upsize the squirters.

www.barrygrant.com (http://www.barrygrant.com) has a Demon selection guide which is based on displcement, cam duration and converter stall speeds.

Jon</font>

I too have had great performance with my 825 Race Demon on a little 355.I gained over a tenth from my 850AED.

Well now I'm relly confused....

<font face="Arial,Verdana" size="2">Originally posted by psalms19:7-11:
Well now I'm relly confused....</font>

LOL, I didn't mean to confuse you by adding the bit about the Demon. I did agree with the majority because of your combo.My combo is a fair bit more radical and is strictly a track toy so I have no idea at all how the carb works at part throttle,just that at idle and full throttle it's flawless.
You could possibly gain a few hp with the perfect carb but at the same time it's pretty hard to go wrong with a 750dp espicially if its new.