TECH: “Got me one of those double pumpers” Carburetor Installation


Tech: Street Demon Carburetor Installation and Test

Isn’t that what you always hear at the car show “got me a double pumper” as you peek under the hood of what appears to be a stock engine with maybe a set of headers or less…but its always been about selecting the right components to make that giant air pump under your hood run, not only correctly but efficiently.

Enter what was the 12.99 Camaro – now the $1,299 ship sailed long ago, but what did not was the hodge-podge collection of parts and pieces that was planed for the build up including that Holley 750 Double pumper with mechanical secondaries that had no place on a 355 with only a somewhat aggressive cam, headers and a few other go fast goodies making it run down the 1320. Sure it was great to get it running and tuned, but the whole time I was watching this thing choke on the enormous amount of fuel the DP was trying to shove down its throat – no matter how much I tried to back it off.


And that brings us to this tech article – that, and the Holley was a loaner and the owner asked to have it back for his project.

A while back I reached out to Holley and wanted to see if they had a good street carburetor to test on a few different cars to see both mileage and performance gains and before I knew it there was a box on the front steps marked Street Demon. So the timing was right and the car needed a carburetor so here we go.

Now I’ve got experience with the basic tuning of a Holley and the steps to get one to perform correctly on a basic engine so I was looking forward to seeing where this would take me. Once out of the box and spread out on the shop table, I knew that I would spend more time typing this article than installing the carburetor itself. That is one of the huge advantages of the Street Demon, its simplicity paired with advanced technology.

It’s a given that the run of the mill Holley is a great carburetor and something that is synonymis with performance since the birth of the carb, but in the areas of materials and production techniques used to produce the Demon this carb is ahead of its time. This new composite bodied Street Demon uses technology that wasn’t even thought of in the hey-day of carburated performance.

State of the art composite materials, better flow characteristics on top of years of experience within the halls of Holley and Demon have taken what was a sort of lost art of tuning your own carburetor and made it into something that’s easy for anyone to take on – even the CI janitor.

It’s also something to advertise that anyone can bolt on a carb and get a car running in less than 30- minutes….challenge accepted., so here we go.

First was the task of removing the 750 Holley DP and getting the space clear for the new carb….that took about 5 minutes.


After making sure I placed the appropriate gaskets recommended by Demon on the manifold – it does have a dedicated hard-gasket to match the carb to just about any possible manifold, flange or bolt pattern you could come up with to use the Street Demon.


Next up was bolting it down, connecting the throttle cable and return spring and matching the fuel line to the carb – note: the Street Demon carb has a available hardware kit that made it take less than another 5-minutes to select, match and install the feed line to the now unused Holley duel-feed line. Its a small extra cost, but well worth the trouble of going to the local line-fitting supplier or rummaging around your garage or shop looking for something to make it fit.

…and that’s about it.

Yeah there should be a long drawn out explanation about the…enter cool tech stuff on the Holley Website

  • Ball burnished shiny aluminum with black composite fuel bowl
  • Designed for use on most stock to mildly modified V8s
  • Developed from the ground up with smooth styling – patented timeless design fits modern as well as traditional themed vehicles (Patent No.: US D648,746 S)
  • One piece airhorn is easy to clean and maintain
  • Aerospace Composite fuel bowl offers significant heat insulating benefits over aluminum fuel bowl – keeps fuel up to 20º cooler for optimum performance with modern fuels
  • Aerospace Composite fuel bowl offers significant heat insulating benefits over aluminum fuel bowl – keeps fuel up to 20º cooler for optimum performance with modern fuels
  • Electric Choke Management means easy cold starts
  • Electric Choke Management means easy cold starts
  • Dual mounting bolt pattern – fits most aftermarket spread/square bore intake manifolds without adapter
  • Integrated fuel bowl/main body design with gasket above fuel level and no plugged passages to eliminate all potential leak paths
  • Small 1-3/8” primary throttle bores combined with proven Triple-Stack™ boosters deliver amazingly crisp throttle response and drivability, superior fuel atomization and improved fuel economy
  • Goggle Valve Secondary (GVS™) throttle plate (Patent # D677755) delivers over twice the air flow of the primary bores for power you can hear and feel
  • GVS™ makes total air flow 625 CFM while maintaining the crisp throttle response delivered by small primary bores
  • Secondary air valve control – torsion spring valve control/adjustment permits seamless primary to secondary throttle response regardless of the throttle opening rate (unique contoured profile developed for better cylinder to cylinder fuel distribution)
  • 2 Stage metering rods control easily accessible without carburetor disassembly or removal
  • Single fuel inlet for simple installation
  • Integrated 700R4/200R4 transmission kickdown cable mounting location as well as Ford A/T kickdown for proper shifts
  • Patent pending mechanical design
  • 625 CFM specific calibration kit available for tuning and altitude adjustments
  • Available TPS kit allows use with 4L60 and 4L80 transmissions

..but I’d rather just tell you it was bolted in, checked for fuel leaks prior with the electric pump running, set the electric choke by their instructions, pumped the throttle twice and hit the ignition button and without hesitation…it fired up on the first crank – in under 20 minutes.

Now sorry I held my cell phone the wrong way, but I was expecting to have to grab a screwdriver to adjust idle or the fuel/air mixtures screws…but all I did was let the car sit down on the choke and then smooth out at 875/900 rpm out of gear making this about the easiest way to replace that worn out q-jet or bolt on a performance street carb I’ve ever encountered.

Next is a trip to the exhaust shop and the final performance tuning on the the Street Demon for the track and I’m betting I’ll be as impressed as I am with the basic install…more to come soon.

– the janitor







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