914 2.0 T-IV Weber Set-up, Chokes & Jets Options

[Keith914]

Thanks for the generous advice. I am waiting for the 220 air correction jets as my next step.
What air/fuel ratio at cruising speeds (say above 3000 rpm) is a good target?

[jmill]

Thanks for the generous advice. I am waiting for the 220 air correction jets as my next step.
What air/fuel ratio at cruising speeds (say above 3000 rpm) is a good target?

Jake Raby posted his recommendation a while back. I can't remember what he said. I do know he pays more attention to EGT than AFR.

IMHO @ 13.5ish. I'd be happy if it stayed under 14 and above 13. I have an ancient Heathkit AFR so accuracy is a factor.

[Keith914]

Thanks Jim, that is what I am shooting for, high 13's/low 14's at cruising above 3000rpm.

[Boomingbeetle]

Keith, I'm jumping into this thread kinda late, but I have a 2430 built by a pretty reliable source *cough cough*.... it obviously has had a MASSIVE amount of head work done, but it was delivered with 44s, 160main, 190air, and 55 idle. Zoom in to see in the pic

[iankarr]

Sweet! What size vents?

[jmill]

Sweet! What size vents?

With jetting like that I would guess 36mm. You'd drown an engine with 160's and 32mm vents. 34's would be overly rich. My question is what ET and pump jets? If it's the F7, you have the same jetting as my old bug.

[jmill]

This is where I start for engines in 2.0 - 2.5 liters with a 2.00 AC jet. Yes, they can fall out of the range below but chances are good that it'll be close to it. There are a ton of variables. ET also plays a big factor.

32mm vent = 115 to 130
34mm vent = 125 to 140
36mm vent = 135 to 165

You may find that the 145 mains are too large for 32mm vents. The smaller the vent, the higher the air velocity passing through it. The higher the velocity the lower the pressure. The lower the pressure the more fuel that will be drawn from the mains.

From a different thread but relevant.

[brant]

very late to this thread
the 36mm vents are great for high rpm and racing
but on a street car
one that is fighting a transition

that is a clear sign that you need more air velocity to pull fuel through the mains..

the smaller vents (venture effect) will pull fuel during that transition problem where you are not seeing enough air speed currently

it will run better
it will have more mid throttle response
it will be faster....

unless your racing and can use your gearing to keep it always above that rpm

[Jake Raby]

In the last couple of years ethanol enriched fuels, and varying oxygen levels in fuel blends have changed all the rules with jetting. Engines I used to optimize with a 140 main will want a 155 today, with no other changes... Thats just one example.

[72hardtop]

In terms of EGT and AFR....

The deathzone is 14:1 - 15:1 range to stay out of at WOT.

Once you go lean of 15:1 the EGT will drop quickly. But you need added advance. Will not work with centrifugal only advance distributor. (light load cracked throttle cond.)

When I tuned my bus (72 Westy) I ended up with...

28mm vents
47.5 idles
125 mains
180 air corrector
F11 tubes
Float height 10.5mm (ball not pressed gasket in place)
Float drop 32mm


At cruise on the highway (flats) with cracked throttle the AFR will hover 16-18.

Slight incline/hill with steady peddle the AFR will go mid-high 12-13.2 or so.

WOT and the AFR goes low-mid 12's - 13

Around town cracked throttle (light load cond.) 16-17 generally with slight bumps to 18.