Running lean on light throttle

[Ricko1966]

You should have more like 20 in the dizzy 16 initial and another 12 pulled in by vacuum advance at idle. Now your timing at idle would be 28 now you can back out of the transitions and set your mixture.

 

[Steven Munoz]

The 14 degrees I mentioned is centriqual not initial. If you are running 34 total and 21 initial now things just got even worse because it's only got 13 in the dizzy.

I didn’t test total right now cause it’s too late in the day. But I don’t think it’s a timing issue. I just drove it home and it was running lean everywhere all of the sudden. So tomorrow or the next day I’m going to rejet and just see what happens

 

[Ricko1966]

Somethings not right here.If you were running 13/1 afr earlier today and didn't change jets. And now all the sudden you are lean something else is going on.What do you consider lean? I consider your cruise numbers you put up earlier rich. Stoich is 14.7. 12/1 AFR numbers and no vacuum advance that's WOT drag car stuff not daily driver stuff.

 

[Steven Munoz]

Somethings not right here.If you were running 13/1 afr earlier today and didn't change jets. And now all the sudden you are lean something else is going on.What do you consider lean? I consider your cruise numbers you put up earlier rich. Stoich is 14.7. 12/1 far numbers and no vacuum advance that's WOT drag car stuff not daily driver stuff.

it runs 13:1 when I say go a certain throttle then let off a little it stays in acceptable range. But when I hit the gas farther even super slow it goes lean it’s hard to explain

 

[Frankenchevy]

Floats adjusted properly? Fuel pump providing adequate volume/pressure?

 

[Steven Munoz]

Floats adjusted properly? Fuel pump providing adequate volume/pressure?

Yes I was unsure at first, I have a holley mighty mite putting out a nice 6psi and floats in the middle of the sight glass

 

[Ricko1966]

In your first post you said you had 12.5 to 13.1 AFR. On the highway and around town. That didn't seem to alarm you. What do you consider acceptable AFR numbers?.And once more no vacuum advance and only 14 degrees centrifugal is drag car stuff not a distributor setup correctly for a street car.

 

[Steven Munoz]

In your first post you said you had 12.5 to 13.1 AFR. On the highway and around town. That didn't seem to alarm you. What do you consider acceptable AFR numbers?.And once more no vacuum advance and only 14 degrees
centrifugal is drag car stuff not a distributor setup correctly for a street car.

I’d rather rich then lean,I want it to sit around 13.5-14 which it does just not as often as I’d like. The ifr’s are much bigger than stock at 43 and it’s curbed a lot of the right off idle issues. And I’ve looked up the issue before and came up with ifr again. I just got the truck back on the road after a few months so my memory of all the exact details are foggy but I’ll be going over it all again anyhow. The distributor, it’s a street fire hei right out of the box, it had been sitting for some time but nothing crazy. I originally was going to put heavier springs in it so I could utilize the vacuum advance but never got around to it

 

[Ricko1966]

Well the numbers you are putting up here are not right or your distributor is messed up. A street fire should have 20 or 21 degrees of centrifugal. So if your idle is set right and you've got 21 initial the total is 41 or 42 degrees ,which is definitely too much.Vacuum advance is not a factor on your total which should be 36. So to get 36 you need 15 btdc at idle, and 21 in the distributor.Now hook up the vacuum advance which will pull in more advance at idle. Check how much it brought in at idle it needs to bring in around 12. So now you have 36 total. 27 at idle and 48 at cruise. You also need to know what vacuum your engine makes at idle and what vacuum your vacuum advance is designed to work at. They are not even close to all the same. Your carbureator will never be right if your distributors not right. As for your new lean condition.What do you consider lean. Read this, all of it,

https://www.v8buick.com/index.php?threads/vac-advance.126150/
I ran across it a few minutes ago, while I was gathering up some info to show you.What I was going to show you was that some of the baddest factory engines out there had vacuum advance. I typed in 1970 Olds w30 and found a distributor to show you with vacuum advance on it. Next I typed 1970 buick gsx distributor specs and this is what I found. This where I stopped. I didn't see the need to go further.

https://www.v8buick.com/index.php?threads/vac-advance.126150/

 

[hirschdalechevy]

Something to add,

I just put a gm sp 350/357 crate motor in my k5 blazer and I have been working with two carbs, (quick fuel off road 600) and a, (holley street warrior 600) trying to dial them in and learning a lot as I go along.

Anyway back to timing.
My cam is a hyd. roller,

215* at .050 int.
223* at .050 exh.
.473 / .473 lift
108* lsa
Vortec heads

I like to give the motor what it wants for timing and I am at 5,500 foot elevation, so this is what I am set up at.

I have my initial at 22*
A b28 vacuum can on full manifold vacuum that adds only 6*, (checked)
Put a stop for the weights in the h.e.i. to limit the total advance to 33* (vortec heads need less advance)
Springs set up to start curve at 1,000 rpm and all in at 2,800 rpm

That's what my motor like's and you can play around with different vacuum cans to get what you need or make a limiter for one you have and you may have to limit your total advance.

Ricko is spot on , you have to get your timing right before you mess with the carb. to much.

Back to your carb. I am using an afr gauge as well and they are a good tool but they can fool you here and there, like at idle. They are better for reading at cruise speed and wide open throttle and a rich miss fire can show as lean.

Anyway, I am assuming you have quick fuel slayer 600, vacuum secondary ?

Need cam and head info.

My t-slots are not square but close to it. You should be able to kill the motor with the idle mixture screws, if not you have to much t-slot opened up. Also do you have a pcv valve ? Lets more air in so you can turn the curb idle screw down and get your t-slots closer to square.

Its all a combination of IFR'S and mixture screw's, pump shot nozzle's and cams, then power valve opening by vacuum, then main jets. I have not messed with air flow restrictor's as of this point.

Anyway I had a lean tip in spot on my quick fuel carb. and I was messing with pump cams, pump nozzle's etc. and could not get it right. I had my secondary blade's open a bit more than factory to let more air in at idle with the quick fuel vacuum pod screw out 1 1/2 turns. I was revving it up in neutral while looking down the carb. and saw the secondary blade's starting to crack open a bit. So I turned the vacuum screw in all the way to shut off the secondary's and went for a drive and the tip in lean spot was gone. Went to a heavier spring and turned the secondary blade's back down to where they were ,(just cracked) and its all good now, but my t-slots are maxed out for idle. That was my whole problem, but I am still tuning on it as we speak. Dam afr gauge make you go crazy trying to get thing perfect.

So I would double check your timing and curves , get a vacuum can and close of your secondary's and go for a spin to see if that could be your problem.

On a side note the 1850 street warrior runs better on my motor than the quick fuel and I converted both of them to metering blocks instead of plates , both are side hung floats for off road use. The quick fuel has three emulsion hole metering blocks and the ifr's are high up in the block. The holley has two emulsion hole blocks and the ifr's are down low in the block. Also the t-slots are wider on the quick fuel base plate than the holley. Maybe thats why my motor like's the 1850 better, still playing with both.

I am no carb. expert but I like playing with them over the year's, hope this is some help.

 

[Bextreme04]

Another thing to think about is that O2 sensors are extremely sensitive. Where you have the wideband O2 placed will have an effect. If you have even a small exhaust leak anywhere near the O2 sensor it will throw off the reading.

 

[Ricko1966]

@hirschdalechevy I'm glad you brought up misfire showing as a lean condition.Most people don't understand this and I've never brought it up. But a misfire any misfire like a bad plug wire will show as a lean condition on an O2 sensor. Because you now have 1 part too much unburnt fuel but you have 14 parts too much unburnt air. On a factory setup this can drive the mixture rich VIA the ECM and have you chasing all kinds of ghost problems that aren't there. Just putting this out there for all that didn't know this, hoping it saves someone a it of aggravation in the future.

 

[Steven Munoz]

The 14 degrees I mentioned is centriqual not initial. If you are running 34 total and 21 initial now things just got even worse because it's only got 13 in the dizzy.

So I messed with the transition slot it was quite large actually so I lowered my idle a little making it smaller and it cleared up a lot of my problem. The squirter I think is still too large cause it I hit it hard it goes stupid rich. And her down a little. But over all much better already

 

[Steven Munoz]

@hirschdalechevy I'm glad you brought up misfire showing as a lean condition.Most people don't understand this and I've never brought it up. But a misfire any misfire like a bad plug wire will show as a lean condition on an O2 sensor. Because you now have 1 part too much unburnt fuel but you have 14 parts too much unburnt air. On a factory setup this can drive the mixture rich VIA the ECM and have you chasing all kinds of ghost problems that aren't there. Just putting this out there for all that didn't know this, hoping it saves someone a it of aggravation in the future.

I appreciate all the help you and everyone else had given ,still learning