Just installed a innovate air fuel gauge. I have always suspected that my mixture was lean. The gauge now confirms it. At idle my readings are about 10.5-11.5. At 4k rpm the readings are about 12. Of coarse, when I let of the throttle, the numbers go up to around 13. I have played around with the setting quite a bit- the changes do make changes however still not getting me close. Here is what I have-

dual weber 44 idf's
60 idles (lean even with three full turns of the idle mixture screw)
150 mains
190 air
f11 tubes
(I don't remember what I set the float height to- 11mm? however I don't think that would mess up my idle mixture?)

2258 engine
scat 45 cam (.507 lift, dur 262 at .050")
9.5:1 CR
2.0l heads 44intakes 38 exhaust

my three theories-
-just need to keep going up on jet size (just seemed like mine were getting a bit big)
-float issue may actually effect idle mixture? (doubt)
-possible that my gauge is wrong. I see no reason to believe that. I had just calibrated it and it is installed correctly according to the instructions.

isnt it the higher the number the leaner, the lower the richer?
i suspect you are very rich at idle.

That was my understanding- that high is lean and low is rich. I also thought that 7.4 was perfect, higher is leaner and lower is richer. Not sure but thats what I thought.

gasoline

14/1 is ideal = idle and cruise

12/1 is under full load.


e85 is down to around 10/1 ideal

and 7/1 full load

read here
http://www.carcraft.com/techarticles/116_0...eter/index.html

Not sure how I screwed that one up. Damn. Thank you for pointing that out for me. I've posted here 565 times, only about 3 posts were half way intelligent. I think I need to go on a posting hiatus.

post more learn more then teach more

actually you want to lean out your idle and cruise as lean as your engine will let you. 15:1, 16:1, 17:1. thats how you get your mpg up.

WOT you want in the 12:7 - 13:5

stoich (14:7) is the death zone. that is where cylinder pressure and egt is at its highest.

please explain and support.

He's claimed this before... But I dont agree. Theres a damn good reason why new car manufacturers tune to stoich...

Yes - they have water-cooled engines and EPA mandated mpg requirements...

But seriously, there are at least three driving regime numbers you need, not just two, and that makes tuning carburetors a challenge. Lean at idle is good, since there is no load. Keeps plugs clean and mpg good, since if you're sitting still, miles is 0 and fuel flow is something.

WOT - every engine will be a little different (there's that tuning thing again) but something in the 12-13 range is typical. Unless you are driving at Daytona or Talledega, you don't spend much time there.

The other number, the one you feel every day, is cruise. Some steady load part-throttle value probably between 3000 and 4000 rpm. Here is where you really have to pay attention. You get best efficiency at or lean of stoich - but heat is a factor.

This is really a factor on Webers, and -really- on something as big as a 44, because at part-throttle cruise, you're probably not on the main jets yet. So you need idle jets that can keep the engine happy at cruise and not bo so stinky-rich at idle your eyes burn from the fumes...

Go too lean at idle and it'll be hard to get off the line without bogging, especially with 44's. Accel pumps will be your big friends here.

14.7 is stoichiometric for 100% gasoline.

14.13 is stoichiometric for 90% gasoline 10% ethanol that is prevalent everywhere in the US now.

John

I think that the problem with the 44 mm size carbs is that they don't really provide enough of a draw through the venturis with a stock engine, especially at idle, so they never really run correctly. The Weber book seems to indicate that a 40mm carb throat is a more appropriate size for a street engine.

The effect of the ethanol in gas and the change in the correct air:fuel ratio is something I hadn't really considered, but it certainly would make sense. And I only thought that ethanol destroyed old cars by dissolving o rings, gaskets, and plugging up fuel filters!

Definitely 12.3 - 13.1 at WOT, especially at redline
watch what the last 1500rpm do as you approach redline
usually a motor is leaning out more and more
don't let it hit lean at redline as that is where most of the damage is going to happen...


better to run a little rick in the 4k range if it means avoiding lean at the redline

As i understand 14.7 is full burn of all entering fuel.
No point in adding more fuel than is needed for cruise and idle which is why it was recomended for lean.
Richer than stoich will give more power just leaves some fuel unburned which helps cool everything while working hard. Allows more choice of timing.
How many cars now tune for stoich? sure some of the time but not for all running conditions.
Cheers
Edwin

whether they are 40s or 44s the venturi or choke size is important depending on the application. the size is usually on the top of the venturi and can be seen with a flashlight without breaking down the carbs. 34, 32, 28 etc and can be changed out to suit your needs. for a stockish 2.0 engine the 28s give good throttle response and little to no bogging.

k