Mighty Demon 750 Carburetor Street Tuning - Mighty Max

Achieving The Most From A Demon 750 For The Street

Sean Haggai Jul 1, 2009 0 Comment(s)

Air Bleeds And Idle Mixtures
Air bleeds work just like fuel jets, but instead of controlling fuel flow they allow more air in. Air bleeds can be adjusted three ways. The low-speed bleed is for idle; the mid bleed is for partial throttle; the high-speed bleed is for WOT. Mostly though, the mid can be adjusted for driveablitly since it pertains to partial throttle situations. Air bleeds change or reform the fuel curve. A large air bleed jet leans out the mixture. Example: If a good fuel curve is present but leans out slightly in the higher rpm, you can change the high-speed air bleed to clean up the fuel curve.Idle mixture adjustments change the air/fuel mixture. Turning them "out" or "in" will either fatten or lean out the fuel mixture.

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40 Timing & 78/85 Jets
After reviewing the results, McKindley suggested we add a couple degrees of timing while using the larger 78/85 primary/secondary fuel jets. The added timing would burn the additional fuel being dumped into the engine., and since Goff's 383 only had 8.1:1 compression, there was little fear of detonation with the 91-octane we were feeding it. We added 4 degrees of timing to the engine, giving us 40 total, and made back-to-back pulls on the dyno. The results showed added power and used, on average, less fuel. When it came to torque, the 383 produced more at 300 rpms sooner and even carried it higher throughout the power curve.

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40 Timing & 78/85 Jets & 8.5 Valve
For the final pull, we kept both the jetting and timing the same, but swapped out the stock 6.5 power valve for a larger 8.5 valve on the primary side of the Demon. The results didn't show any gains in the peak or average numbers, which made us revert back to the previous tune.

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Mighty Demon 750
1. Annular boosters allow the fuel to be atomized more efficiently through the use of many small holes.

2. Billet aluminum base plates for strength.

3. Air bleeds located on the outside along the air cleaner ring.

4. Primary throttle linkage for adjustment.

5. Secondary throttle linkage for adjustment.

6. Curb idle mixture screws are located on each side of the metering block and control the amount of fuel mixture to be discharge at idle.


Vaca Performance And Dyno




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