M Demon lean out of the box?? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-10-2010, 01:05 PM
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M Demon lean out of the box??

750 Mighty Demon annular, on 392 stroker - according to my Innovate wideband meter, it's lean out of the box all the way up. I've set the 4-corner idle at around 13-13.5 (very hard to get the idle below 900, with or without the idle-eze) and I'm getting a vacuum of around 16", but on the road it goes to 15-16:1 all the way up. Light load is not too bad, around 14.5-15, but hard acceleration drops to 16.
Stock jets are at 70 primaries and 77 secondaries. I've gone up a couple of sizes on both, but no noticeable change. I guess I've just got to go a LOT richer on the jets - just seems odd as most people note new carbs as being very rich. Any thoughts?

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Old 07-10-2010, 01:22 PM
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Seems too lean. If it refuses to idle down, it could have a vacuum leak, which could cause it to be lean, especially at idle and light load. The high load lean condition is from too little jet area. Add 3 numbers to each jet and retest.
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Old 07-11-2010, 09:47 AM
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Make sure your exhaust system is leak free at the head surface. Leaks here will show as too lean on the AFR. Even a loose header bolt will show up.

Been there.
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Old 07-11-2010, 09:50 AM
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I agree, check it for vacuum and exhaust leaks. It may also be a good idea to disassemble your demon and clean it. Every new demon I`ve ever delt with still has shavings in the passages from the CNC process.
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