Tuning my new engine

[Tuner]

^^^ this is why the jets are threaded ^^^

[PRH]

Oh, I totally understand.

I just wonder what the combo has to look like for the as delivered calibration to be at least somewhat “close”........ when a 300hp motor peaking at well under 5000rpm is 3 points lean on the a/f ratio.

[MadBill]

Probably one with a really restrictive air filter...

[travis]

Where would be a good place to start on this 670 Holley? I’m thinking maybe 68 primary/74 or 76 secondary jets, and maybe an 8.5 power valve?

A 31 squirter should be plenty, right?

Does the primary jetting have anything to do with the transition from the idle circuit into the mains? Is there any other place I need to be looking to get more fuel into the idle to primary transition?

I have a rudimentary understanding of Holley carbs, but I’ve never had to work this hard to get one to work well even on engines with considerably more power than this thing.

[af2]

Ok my thought.......
Lets start from scratch.

The pump arm should be on the cam at idle not away by .015
The power valve if blown will make it rich at idle also.

If you can set everything back to the original it came with you have a good starting point.

[travis]

I ended up going through the 670 Holley much more thoroughly last night, running a piece of wire through every passage thinking maybe a piece of trash or something was causing the super lean part throttle condition, but found nothing. Factory jetting was 65/68 (seems like a strange setup to me), with a standard 6.5” PV. Changed to 68/74 and an 8.5” PV...it drives drastically better, cruise is a touch lean (15.3-15.6), WOT is super fat now (like mid-high 11’s afr), but that damn light throttle roll in mega lean spot, while better, is still there. I still have the 31 squirter in there, but I have a 35 to try as well now. But I’m tired of messing with it for now, and put the 650 Edelbrock back on with a leaner secondary jets. It’s about perfect now.

A coworker of mine recently inherited a very low mileage ‘74 chevelle 2 door, with the bottom of the barrel 2bbl 350. Here a while back I built him a low buck engine for it after the stock cam went flat. About 8.8 compression, some low mileage newer 76cc crate motor heads lightly ported, a generic 204/214 hft “performer” type cam, stock exhaust manifolds and dual 2” exhaust. He ran it for a while with the 2bbl intake and carb, then yesterday I installed a new performer EPS intake and a 1850 Holley. It ran great out of the box after some minor IMS and idle speed adjustments. Before I sent him home with it today, I put the 670 back to baseline and installed it on the chevelle...and it runs great

[Geoff2]

That's a Holley for yer....runs great one day, but the next day...