Advice/thoughts on Holley jetting

MilesnMiles · Post by **MilesnMiles** » Thu Jul 09, 15 7:08 am

Having fitted my new headers I took the car for a test drive and made the following observations.

Progressive throttle opening shows 13s on the AF as I come off the cruise and about one third throttle. As I tip the throttle in further the AF leans out to mid -high 14s which is lean.
Opening throttle further and the power valve kicks in and I've got mid 13s which is good.
Into full throttle and AF at 11+ who is too rich and it feels a bit flat

Thing is I have the 670 VS carb pretty lean jetted at 66/70
Maybe the lean part throttle is down to a) power valve opening too late, b) smal primary jets?

Cannot see how 70 main jets can produce 11 AF at WOT?

Any thought?
The car runs really well, but I do have some pinking as the throttle gets pushed through that lean spot. And it feels a bit flat at WOT

Mick · Post by **Mick** » Thu Jul 09, 15 12:35 pm

Have you verified the timing ? if so jet up a couple on the back for wot. The car shouldn't detonate on those numbers, unless you've got really bad quench. JMO but i think the carb is a little small for your car.
Mick

Adrian Worman · Post by **Adrian Worman** » Thu Jul 09, 15 12:37 pm

Try not to focus too hard on getting perfect AFR readings, it only tells part of the story. It's a good tool for tuning but don't get hung up on it.
Aim for the jetting that produces the crispest throttle response & best power, just remember its a carburettor and it can't so everything right

It goes without saying but recheck timing before you try & baseline the carb.

The figured you've quoted aren't that lean, my 440 shows 15:1 at about 50 in top but is responsive as Bananarama! & tools around lovely.

Try a couple of different PV's, go higher & lower to see what it does, you may be surprised.
What does your vacuum gauge show at steady state cruise?

MilesnMiles · Post by **MilesnMiles** » Thu Jul 09, 15 1:04 pm

Thanks boys, Mick I can't put any more timing in as it will drag down the starter.
Ade, I've been doing some reading and yes, not getting hung up as you advise, but I have read that as vacuum drops the transition between the transition to the point when the PV opens can see a lean condition. As you say, I think I'll try a bigger number PV although the car didn't like it when I tried before, but that was before headers.

Mick it maybe small, but I'd like to persevere. Surprised that I'm seeing 11s AF at WOT.

I could refit the 750 Demon, but that showed a constant 11AF at cruise speeds which did get me hung up as a rich condition at cruise for hours could be a big problem down the road a bit.
shame really, cos that pulled way harder at WOT than the Holey does.

MilesnMiles · Post by **MilesnMiles** » Fri Jul 10, 15 6:23 pm

Pulled a touch of timing out and the car runs great. Shifting manually through the gears and the car really takes off now. The new headers have made the car run quitter and cleaner too. Well worth the effort.
Haven't touched the carb and will continue testing for best options. No flats spots and pulls hard now.

Adrian Worman · Post by **Adrian Worman** » Fri Jul 10, 15 7:16 pm

Nice one miles

That's how it goes tho, one major change then a weekend pi55ing about tryin to make the most of it.
That's the bit I most enjoy actually

MilesnMiles · Post by **MilesnMiles** » Fri Jul 10, 15 9:30 pm

Absolutely Ade, sums up owning these cars