[RocktimusPryme]

Im working on tuning a Holley. Im currently using a nice 850 double pumper that I inherited with the engine. Its not an off the shelf unit, has billet metering blocks.

Runs and idles fine. But holy hell is it pig rich at part throttle cruise. Once it warms up light throttle cruise is like 10.8-11.9 on the wide band. Idle I have tuned the mix screws to where it idles at like mid 13s, but the idle screws are only like 3/4 of a turn out. Any more and idle gets rich as well.

It had 78s in the primaries and a 6.5 power valve. I put in 76s, and a 4.5 (just to see on the PV) The 76s helped some, but it only got me into the solid 11s, AFR which is still rich.

This is a big engine, so Im skeptical of continuing to drop down in jet size, because I think its just going to lean out WOT. Would a 500 ci 700 HP engine really only want a primary jet size in the low 70s? Im thinking its maybe time to consider drilling the idle air bleeds to a larger size to try and lean out light throttle?

What say the group? In reality, rather than drilling on this 850 I think Im going to throw on a 930 annular booster HP body I have because it has screw in air bleeds I can play with. But I still think the answer is going to be air bleed related rather than jets.


As far as WOT, I cant fully test that, because Im fairly certain I would vaporize the bone stock unknown miles t56. But I can say that if you have your foot in it accelerating, the AFR is in a more accetable range than sustained cruise.