I am working on getting my idle jets correct. My mains seem ok.

At idle (800 rpm) I am getting a reasonable air fuel ratio (14.8 using innovate a/f gauge). I'm using 50 size idles. If I slightly press and hold the peddle to a steady 1200 to 2000 rpm the a/f goes to 19. The car drives like crap until I reach 2000 rpm when the main jets kick in- at the same time the a/f ratio goes to 14 or so.

What adjustments can I make that will leave idle at the same mixture however rich up the mixture til about 2000 rpms? I thought that was mainly idle just only?

I did try to increase the idle jet size to 55. The idle mixture goes down to 11.8 at 800rpm and is perfect between 1200 to 2000 rpm. Confused- I can either get the idle correct OR the low rpms?

I have followed weber's info on best lean each time I switched jets.

Ideas? What am I missing- i'm sure its something simple.

it sounds like your close. does the car sputter and fart thru the WHOLE progressive circuit or close to the end. an easy way to tell is to pull your main stacks and drive it. not a few blocks but for a few hours. this will give you the best understanding about how the progression circuit works. your on the right track.

what distributor are you using? what size engine? big cam? accelerator pump connected?

Hi,

What size motor, What size vent are you running?

Carlos

2258
Mallory distributor
Yes- big cam- scat c45 .507 total lift (I forget the rest of the numbers)
The accelerator pumps are connected
36 vents

I don't understand how I can Make the mixture richer at 1200 rpm while keeping the mixture the same at idle (800rpm)?

you dont want the mixture to be richer at 1200 rpm you want it to be leaner. you want your idle/progressive circuit to be as lean as the engine will let you. your mains are what you want to be rich. 12.5 A/F.

a lean idle progressive circuit will run cooler and yield the best gas mileage.

your idle/progressive circuit is behaving exactly as it was designed to.

The idle jets set the mixture for progression holes and also is a rough setting for the idle mixture screws. . . Idle itself is set by the idle mixture screws. . . which controls how much of the mixture given by the idle jets goes on to the lower side of the butterfly. with the butterfly's closed. .

You want to make sure the butterflys are all the way closed in the idle position. . then balance with the air bleed screws. . if they are open, then the idle mixture screws won't have as much effect. . because you're actually running on the lowest progression hole at idle. .

So go back to the idle jets where is was running good at 1/8 throttle, and open the idle mixture screws to fatten it up at idle. If you can close the idle mixture screws all the way at idle, this generally means the idle jets are too big.

It helps if you look at a picture of the carb idle circuit and progression circuit. .

I increased my idle jet size to 55. Now the engine runs great. At 1200 rpm, I am getting an air fuel ratio of around 14.4 however at idle I am getting an air fuel ratio of 12. I have done the lean best idle procedure as directed by weber and idle is still 12. Is it ok that the idle a/f ratio is so low? When I had a smaller idle jet installed- I did the lean best idle procedure and I got the same a/f ratio- I just had to back the mixture screw out more.

Any thoughts?

How does it run when it's cold and just started? a bunch of 'sneezing' and popping? That's usually the sign of the idle mixture too lean. . If it starts and idles fine cold , I'd leave it alone, but if it's burping, see if backing the idle mixture screws all out 1/2 turn fattens your idle readings. .

Do all the mixture screws make a change? are they all approximately turned out the same amount ? 1-2 turns ? If they are 3 or so turns out, then the idle jets may still be too small. .

What do the plugs look like?

I went out tonight and started the engine cold- it started right up and ran great. No burping or sputtering. All of my mixture screws are out 1.5 turns. I haven't checked the plugs yet. I will check them soon.

Considering that the car is running very well- Is it ok that I am getting an a/f ratio of 12.? at idle. I always hear about rich conditions washing fuel off the walls. I really don't want to hurt my engine more than needed.