2.7 Weber jetting baseline

[trekkor]

'74 2.7 with Weber's that came off my 2.0 S.

I need to re-jet. Snorts and pops on decel. Feels pretty good on the mains but it needs some help.

What size chokes and jets?


Thanks,


KT

[2.7RACER]

Trekkor,
I'm running a 2.7L with Solex cams and Webers at 5,000 ft elevation.
So what I run doesn't work well in a stock 2.7L at sea level.
At 5,000 ft. my engine is happy with 34mm venturi's, 145 mains, 50 idles, 200 air correction, and F3 emulsions.

This for a car used primarily for racing.
At sea level, street use I'd start with 32mm venturi's, 140/145 mains, 50 idles, 180 air correction, F3 emulsions.
I ran 32mm venturi's for a short time. The car ran well but it quit making power above 5500.
I run 10 degree's initial advance. Less at lower altitudes.
You may end up with slightly larger mains and idles if you are running cams and pistons.
The idle jet sizes control A/F mixture from idle to 3000rpm. The mains take over from 3000rpm up.

[trekkor]

Thanks for the post. Great information.

I need to find my notes and see what I have in my carbs.


KT

[jluetjen]

Here's what I've got in my database.



PS: What are your settings now?

[trekkor]

I'm still trying to figure that out ( without leaving my desk )

I guess I'll end up outside poking around.


KT

[RoninLB]

figure out how to run somewhat lean and have a decent transition.

Heat is power and it seems the best EGTs create comprises elsewhere as unintended consequences.


my #'s necessated NGK BPR7ES when BPR5ES became hot. It still lean pops on occasion. With thee BPR5ES it happened all the time.

I have 2 sets of BPR8ES and 2 sets of BPR9ES to continue this.






ps: I ran around the country for 20k and around home for 8k miles at "good enough" settings.


The point being is do you want it good enough or.. more ?


E-cams, 8.5:1, 34 vents, 55 idles, 135 mains, F-11 et's, 190 ac.


start rich and tune leaner and leaner.

[trekkor]

I run NGK 6's.



KT

[trekkor]

The point being is do you want it good enough or.. more ?

I want the same great performance I had with the last motor without damaging anything.

This car is used 98% of the time on the track or at a/x's.
So, it's mainly full throttle!


KT

[RoninLB]

I'm no track expert.. and Webers have their own nuances. So only for discussion.




F3 e-tubes seem to be common usage. On p163 of the HP Weber book it says F3's are for a leaner lower end and on p58 of the Tomlinson Weber book it says F3 are to prevent excessive richness at high rpm, which make me guess richer idle jets are needed for something.. like transition. And as long as you're stuck with F3's you have to run bigger mains than necessary.

my F11's are said to be "common usage" in text. My 5k+ rpm EGT's are cooler than my low end. I'll keep it that way.

I have PMO's, that to me, are a dream come true.

You have Webers.. party hearty.

it's a carb vs MFI world

[trekkor]

OK...

Here's what in my carbs now:

30 vents
125 mains
180 airs
55 idles
F 26 emulsions

From my short little drive today and good high rpm 1/4 mile 'plug cut':

It's rich down low and lean up top.


KT

[trekkor]

Anyone?


KT

[911pcars]

Get closer to the setups described above.

125 mains is related to your lean high speed mixture.

Careful adjustment of idle mixture screws will help at low speed, partial throttle.

Racing isn't all 100% WOT. Throttle response is quite important.

Sherwood

[trekkor]

Anybody got any parts you'd like to send me?


KT

[jluetjen]

I'd start out by getting some 32 mm venturis -- 30's are most likely too small for your usage, especially since you do a lot of WOT on the track. They most likely give a good strong signal at low rev's (possibly contributing to your richness at lower revs). At the other end of the rev range, 30 mm venturi are most likely fine for an engine that peaks at 5000 RPM, but with your E cams your engine is most likely capable of generating peak HP up to around 5700 RPM. 32 mm Venturi should be about perfect. If it were me, I'd replace the venturis and the mains first, and then see how you're doing.

[trekkor]

I've found a very reasonable shop that will dyno tune the motor for me.

I'll report back what jetting was used to make max power and torque.


KT