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Discussion Starter #1
Is there any website (or book to buy) explaining the tuning of Demon carburetors on turbo applications ?
Base jettings, accel pumps CCing, secondary cam shafts settings, power valve sizing, etc . . ?

Thanks .
 

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:laugh:.... On my vacuum Demon 750...What helped a ton was a 50cc pump and the largest damn accelerator pump cam.. Also the heavest spring in the vacuum pod for the secondaries. I have also removed and plugged the power valve and have jetted way up from stock jetting....I may still be too lean too...

I am 85 primary and 95 secondary with a plugged off power valve.

Ann may be able to tell you if there is some sort of guide.
 

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There's some information on the Barry Grant website that may or may not help you. http://www.barrygrant.com/demon/default.aspx and they do have technical support that you can contact personally.

All of the carburetors come with what BG feels is a good baseline straight out of the box & it works if you have the correct carburetor for your engine IF that engine is a common / widely used application. The majority of these carburetors are used on 6 & 8 cylinder engines so they are the tuning target audience. The information & tuning tips they provide is good, but you will most likely need to tweak & filter the advice to your specific needs for your engine. With that in mind, your best guidance & reference points will most likely be from people who have experience with using the Demon in the air-cooled turbo sector. Believe it or not, there's not a lot of us out there. :no:

That said, which Demon do you have & what are your specific questions?
 

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Discussion Starter #4
In fact, i put my EFI in the trash box :nerdystraight: and swapped to a Demon setup .
750 speed demon, mechanical secondaries, i've just machined the base plate to make the power vale boost sensitive . Jetting seems good, i'm at 11.6 AFR @ 20psi of boost (i log both AFR&Boost with my small innovate LM1) , jetting is 79 prim / 86 sec . accel pump cam is the pink one . The power valve & accel pumps are those "out the box" ( carb # is 1402010) . I found this setup not very smooth, always have to rev the engine to feel "power" under the foot . What i'd like is a fine tune to have something smoother . engine is a 2387cc, T0x ? (T04 i think) Comp Turbo From marty with 40x50 910 heads , drag use only .
Carbs are new to me so a tuning guide will be very helpful . :grinwink:
 

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I like how it looks to have air bleed info.. Mine are not changeable but I know I can drill mine out, tap the holes and make them changeable if needed.
 

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Discussion Starter #8
Brian , i see you've plugged the power valve and jetted bigger . What are differences between plugged & boost referenced power valves ? Why plugging it ? In my mind, referencing the power valve affects only boost "range" Vs plugging it , you're always "richer" ? I know RLR do it on some holley setups but it's difficult to understand in my small head :nerdystraight:
 

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I cannot explain this....For the reason I don't know!! I do not have a handle on my tune.

When I boost referenced the power valve the engine responded much better. I had an issue when I rolled the throttle on too fast it would bog. Boost referencing the valve helped eliminate that. I was jetting with an LM-1 and my numbers looked good 12.5 cruising and 11.5 under boost. But I still had a hesitation if I rolled the throttle on too fast.

I removed the valve one day to try it out..Also because I was affraid if I went to start the car and if it had a small back fire it would damage the valve.

So with the valve removed and with the jetting close..It is very drivable. No hesitation when I roll the throttle on fast, it will cruise in traffic or on the freeway.

But I have made a few other changes too.. remember I have a vacuum secondary carb.. What helped the most was going to a larger accelerator pump and using a heavy spring the keep the secondaries from opening too soon. Also going up on the jetting....I am unsure what my A/F is right now but I keep going up in jet sizes and it still seems to runs well...It keeps taking the fuel and loving it.
I now have some soot in the exhaust pipe but the waste gate dump tube is very light gray (race fuel) and no soot can be found. I am going to go up two sizes on the secondary side today and see what the car does as far as MPH in the 1/4.

I don't think this will help you at all but Its all I could come up with for a response...
 

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Discussion Starter #10
I also have hesitation on fast throttle action . I'm gonna try a smaller value of vacuum on the PV (6.5 now) , if it changes nothing i'm gonna plug it like you .
Is this setup on your 20v water cooled ? Did you machine the choke tower ?
 

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52Turbo said:
I also have hesitation on fast throttle action . I'm gonna try a smaller value of vacuum on the PV (6.5 now) , if it changes nothing i'm gonna plug it like you .
Is this setup on your 20v water cooled ? Did you machine the choke tower ?
The pink accelerator pump cam you are running is the smallest one....I am running the yellow with a 50 cc pump... You have 2 accelerator pumps so things will be different, But for me more accel pump and the large pump cam took care of the hesitaion on fast action throttle.

And no I have not removed the choke tower yet....It going to take some hours to lopp it off then hand grind it all nice and smooth to match. I want to make my air bleads changable too.
 

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Discussion Starter #13
Thank you both of you . I'm gonna buy a pump cam kit and larger accel pump diaphragms . When i will receive the book, i will also make the air bleeds modification i think .
Thanks .
 
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