nastee383

I have a Mighty Demon 750 annular w/mech secondaries. I could not find the specs anywhere including his site and their air bleeds aren't stamped. So I called tech and he gave me the following: IFR-.036 IAB-.070 HSAB-.039 main jet-67 sec jet-75. Does that jetting seem a bit small for that carb? I haven't taken it apart yet because I wanted to get the bleed info. If it indeed does have that jetting I'll be very surprised.

MotorHead

Pri 75 Sec 83

http://barrygrant.com/demon/default....e=29&specs=29d

nastee383

That's the downleg 750 jetting. I saw those specs on the site but they don't have the 750 Annular booster specs there.

lars

The jetting on the annular carbs is significantly smaller than the downleg carbs - AD carbs typically have jetting at least 5 sizes smaller than the downleg carbs.

MotorHead

I switched over to annular boosters on my 825 Race Demon. I have an LM-1 and the carb is tuned about as good as it gets for idle, cruise and WOT, the jetting is 76/82. Out of the box with downleg boosters it is 76/84, I could probably go to 84 on the secondary side and it wouldn't make much difference.

IMHO if those are the jets shipped with the carb they are overcompensating for the annular boosters.

chevymans 77

how does it run? maybe I have missed the post of the issues you are having with the carb.

Neal

nastee383

Initially, out the box there was a pronounced hesitation under very light throttle input at low speed and my narrow band a/f gauge (I know I know) showed a very lean condition during the stumble. If the motor is at say 2000rpm and I punch it there was no hesitation it just took off acceleration was brisk to say the least.

I experimented with the IAB's going progressively smaller, .069, .067,
.065. With each cahnge the low speed hesitation got better. .065 was the smallest I have and the hesitation is almost gone. I haven't opened the carb up yet because I wanted to see what changing the IAB's would do. Acceleration (2000+) with each change was still very good.

Before the IAB experimentation I put a .035 squirter and hollow screw in and it did not help the matter at all.

Sometimes I talk too much but to make a long story short other than the slow speed hesitation under light throttle it runs extremly well.

chevymans 77

I am tuning with narrow band meters, they are good enough to tell you what is going on. They are deffenantly better than nothing at all.

tip in stumble is usally a lean condition or an out of adjustment pump. Try backing out on the idle screws 1/2 turn, and take a drive see if this gets rid of the stumble. The moves on the IAB is the right move to help.

Neal

Retro78

I just bought the same carb, 750 Annular Mighty demon. I was surprised to see the jetting so low. Right out of the box it came with 70/78. I put it on my 383 with a 248 roller cam and it ran rich! I have a wide band LM1 to montor the AF.. it smelt rich and read 12 AFR at 3500 RPM. My previous 750 holley ran with 73/81 and 13.8 AFR.

Bottom line, Lars must be correct again, annular needs less jet size.

I will downsize jets tomorrow. Even with my current rich condition I can feel the increased responsiveness of the annular immediatly.

MotorHead

What is the reading at idle ? Lean it out with the idle mixture screws first to 13.5:1 and then see what it is at cruise before changing jets

Retro78

Thanks Motorhead. With the screws only 3/4 open the best I get at idle is 12.2. I cannot get it any higher. Should I try downsizing the IFR's first?

MotorHead

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