Asking for help Interpreting AFR readings from new Weber 32/36

[Madkaw]

I have very good vacuum readings but I also know I have a vacuum leak on the inboard side of the carb-found by spraying carb cleaner on there. I have tried no less than 3 times to keep vacuum leaks from this carb, but I think the adapter plate is prone to issues .

I am currently about 1 turn out on the mixture screw.  

[datzenmike]

A vacuum leak does not cause a normal engine to rev up. Think about it. The idle mixture is a 'perfect' mixture of fuel and air providing enough power to spin the engine at 700 RPMs, so how can adding more air make it rev up????? The only way this could happen is if the mixture is over rich to begin with then adding air would burn the extra and the idle would increase. You have ab A/F meter... what does it say for idle???

 

 

That is manifold vacuum, there could be a leak or something above the throttle plates.

 

Adapter plates tend to have their fasteners come loose so owners over tighten them... the the adapter cracks. Use some kind of thread locker.

 

If the adapter was leaking it would affect the vacuum reading.

 

 

What is the base idle at? if above say 800-900, mechanical advance creeps in. Engines at idle have a very weak cylinder filling and will want more advance then part and full throttle. Due to emissions all engines are held back from what they want, in effect too retarded at idle so they naturally will rev if advanced.rev up if you twist the distributor in the advance direction. Pull the vacuum advance hose off the distributor and see if the random revving stops.

[matrophy]

43 minutes ago, datzenmike said:

A vacuum leak does not cause a normal engine to rev up. Think about it. The idle mixture is a 'perfect' mixture of fuel and air providing enough power to spin the engine at 700 RPMs, so how can adding more air make it rev up????? The only way this could happen is if the mixture is over rich to begin with then adding air would burn the extra and the idle would increase. You have ab A/F meter... what does it say for idle???

 

 

That is manifold vacuum, there could be a leak or something above the throttle plates.

 

Adapter plates tend to have their fasteners come loose so owners over tighten them... the the adapter cracks. Use some kind of thread locker.

 

If the adapter was leaking it would affect the vacuum reading.

 

 

What is the base idle at? if above say 800-900, mechanical advance creeps in. Engines at idle have a very weak cylinder filling and will want more advance then part and full throttle. Due to emissions all engines are held back from what they want, in effect too retarded at idle so they naturally will rev if advanced.rev up if you twist the distributor in the advance direction. Pull the vacuum advance hose off the distributor and see if the random revving stops.

Lambda at idle is around 0.96. I don’t have random revving, I just have a lean AFR reading while accelerating and cruising at 60 mph. It’s not way lean but at the top of what I understand is the max for the range. Steady readings of 1.07 or so. Definitely sluggish through the gears. I want to eliminate a vacuum leak before I proceed with any other changes and spraying carb cleaner at the base of the carb in small bursts doesn’t affect the idle but if I spray a large shot, I get a small idle increase( maybe 50 rpm) so right now I am wondering if it’s overspray that gets sucked through the air horn rather than an actual leak at the adaptor. I was going to hold a piece of cardboard against the side of the carb to prevent overspray and spray a large blast again to see if there is still an RPM increase. I DID have a leak on the driver’s side of the adaptor and I replaced all of the gaskets and thread locked the studs, etc. Torquing the nut that also holds down the spring bracket is difficult because the bracket wants to move in a clockwise direction and make the spring tension higher than I would like. Do you use 2 nuts- 1 on the carb base and one holding the spring bracket? That might be the best way to get the 1st nut torqued well enough. 

[datzenmike]

A vacuum leak might affect idle but again, think about it. The leak (if there is one) is a fixed amount. The hole does not adjust larger. It might be enough to lean the small amount of idle air, but as revs go up under load, the intake vacuum drops, so even less outside air is pulled in and it's mixed with a hundred times more air and fuel mix and the leaning effect will be diluted. If the vacuum leak was sufficient to affect mid range, highway driving or WOT, the leak would be so large the engine wouldn't idle.

 

You have a 32/36? Stochiometric is ok for light throttle acceleration and good mileage. For full out high performance acceleration you want somewhere in the mid 12s, so put a larger jet in the secondary which is only engaged above 1/2 to 60% pedal. When you want richer it will be waiting there for you.

[matrophy]

5 minutes ago, datzenmike said:

A vacuum leak might affect idle but again, think about it. The leak (if there is one) is a fixed amount. The hole does not adjust larger. It might be enough to lean the small amount of idle air, but as revs go up under load, the intake vacuum drops, so even less outside air is pulled in and it's mixed with a hundred times more air and fuel mix and the leaning effect will be diluted. If the vacuum leak was sufficient to affect mid range, highway driving or WOT, the leak would be so large the engine wouldn't idle.

 

You have a 32/36? Stochiometric is ok for light throttle acceleration and good mileage. For full out high performance acceleration you want somewhere in the mid 12s, so put a larger jet in the secondary which is only engaged above 1/2 to 60% pedal. When you want richer it will be waiting there for you.

Good logic on vacuum leak. I assume you’re referring to the main jet? If so, wouldn’t a larger primary main jet also help with the acceleration through the gears? 

[datzenmike]

14 minutes ago, datzenmike said:

 

 

You have a 32/36? Stochiometric is ok for light throttle acceleration and good mileage. For full out high performance acceleration you want somewhere in the mid 12s, so put a larger jet in the secondary which is only engaged above 1/2 to 60% pedal. When you want richer it will be waiting there for you.

 

On a 32/36 I think the primary has something to do with the idle mix adjustment. It seems good where it is. Try a larger secondary jet. This will only ever be used when the throttle is mostly floored. The rest of the time it won't matter.

 

 

 

You say acceleration is poor???

 

 When the gas pedal is fully depressed to the floor, look at the primary and secondary throttle plates. Are they fully open and vertical???

[matrophy]

1 hour ago, datzenmike said:

 

On a 32/36 I think the primary has something to do with the idle mix adjustment. It seems good where it is. Try a larger secondary jet. This will only ever be used when the throttle is mostly floored. The rest of the time it won't matter.

 

 

 

You say acceleration is poor???

 

 When the gas pedal is fully depressed to the floor, look at the primary and secondary throttle plates. Are they fully open and vertical???

Throttle plates open all the way with throttle floored, yes.

[datzenmike]

I probably already asked this 3 times. It's the little things.

[matrophy]

What AFR do you run at idle? It dawned on me that maybe I should let the idle run a little richer and see if that changes the AFR for acceleration and cruise. When setting lean best idle, the absolute best idle has a Lambda of about 0.86 (12.6 AFR). I have been slightly tweaking to get the idle closer to 0.95 (14.1) which affects the running slightly but I maybe mistakenly thought that I should shoot for close to stoich at idle. 

[Madkaw]

I was trying to catch the 14.7 I had going at idle . 
Take a look at the kit . I believe I put in the larger double pump jet and the largest main jets and did NOT change the primary idle jet . The pump jet is just a bigger accelerator pump . Around town I can meet power needs without putting in a huge idle jet - and I’m just 1 turn out . When I mash it I have the bigger main jets -150,155.

If anything that could be tweaked is maybe a larger air corrector . Highway cruise would lean out a bit . I’d like to see about 15 on cruise in final gear , but it pulls it that big main jet to early , so it’s more like 13.2

[matrophy]

14 minutes ago, Madkaw said:

I was trying to catch the 14.7 I had going at idle . 
Take a look at the kit . I believe I put in the larger double pump jet and the largest main jets and did NOT change the primary idle jet . The pump jet is just a bigger accelerator pump . Around town I can meet power needs without putting in a huge idle jet - and I’m just 1 turn out . When I mash it I have the bigger main jets -150,155.

If anything that could be tweaked is maybe a larger air corrector . Highway cruise would lean out a bit . I’d like to see about 15 on cruise in final gear , but it pulls it that big main jet to early , so it’s more like 13.2

I don't have the jet kit. When i said 'kit' I meant that I have the carb kit with adaptor. I have been holding off on buying jets until I get everything else squared away. Does the kit have good instructions for the average shade-tree guy?

[Madkaw]

There’s enough information on line . Basically you are just replacing jets . You only adjust the primary circuit with the mixture screw . 
So replace jet , go drive it and watch AFR’s . 
I could probably get things a bit better with air corrector changes and maybe  a primary idle jet change . 

[matrophy]

17 minutes ago, Madkaw said:

There’s enough information on line . Basically you are just replacing jets . You only adjust the primary circuit with the mixture screw . 
So replace jet , go drive it and watch AFR’s . 
I could probably get things a bit better with air corrector changes and maybe  a primary idle jet change . 

Do you change both main jets at the same time and the same amount? 

[Madkaw]

10 minutes ago, matrophy said:

Do you change both main jets at the same time and the same amount? 

I believe the carbs come with the primary jet one step bigger from the secondary . I kept increasing until I had used the biggest jets in the kit . I would make one change at a time . You have to take the top of the carb off to do the main jets , but it’s made to do that easy . Try not to damage the gasket . 

[datzenmike]

 

 

[Madkaw]

Perfect Pic Mike ! 
maybe I was wrong and the primary jet comes smaller then the secondary . 
 

Edited June 28, 2021 by Madkaw

[matrophy]

42 minutes ago, Madkaw said:

I believe the carbs come with the primary jet one step bigger from the secondary . I kept increasing until I had used the biggest jets in the kit . I would make one change at a time . You have to take the top of the carb off to do the main jets , but it’s made to do that easy . Try not to damage the gasket . 

Mine are both 140.  Did you increase both as you went along?

 

[Charlie69]

Here is the Baseline jetting chart.  Remember the carb started life as a DGAV.

 

 

[datzenmike]

29 minutes ago, Madkaw said:

Perfect Pic Mike ! 
maybe I was wrong and the primary jet comes smaller then the secondary . 
 

 

I would think the secondary being larger will need more fuel.

[matrophy]

8 minutes ago, Charlie69 said:

Here is the Baseline jetting chart.  Remember the carb started life as a DGAV.

 

 

This matches mine except for idle jets which were 60/55. I changed main idle jet to 55

[Jitenshakun]

On 5/26/2021 at 8:39 PM, matrophy said:

I was struggling to dial in my new Weber on my stock Z24 with all Cal smog stuff removed but the carbon canister.

Partly to help solve this and partly because it's a cool gadget, I bought an AEM AFR gauge and I am using it on the Lambda setting

because we run E10 here. I got the Weber to idle real nice after increasing the idle jet size from 60 to 70.

 

Some of the Lambda readings are a little wacky and I could use some help interpreting them.

The acceleration from a stop is real sluggish and as the AFR readings below suggest probably because it's running lean

 

Lambda converted to AFR in parentheses

 

Idle - 0.960- 0.98 (14.4) - Not sure if I am supposed to tweak the idle mixture to get a 1.0 reading but where it idled best ended up being 0.96-0.98

 

Cruise = 1.0 - 1.02 (14.7 - 15.0) 55 mph on level highway

 

Acceleration 1.07 (15.7)- lshifting through the gears from a stop and the response is real sluggish - not dropping off like what happens when you stomp on it with this carb - just weak acceleration. My understanding is that should be a rich reading - like 0.80 - 0.90

 

Under load - 0.98 - 1.01 (14.4 - 14.8) 20 mph uphill in 2nd gear. I believe this should also be richer - like 0.80 or so

 

WOT - 1.05 - 1.07 (15.4 - 15.7) I believe this probably OK and the truck accelerates decently here

 

 

No vacuum leaks

Timing is at 3BTC

New plugs

175 Compression in all 4 cylinders

68000 miles on original engine

 

I think the idle, cruise and WOT are OK it's just the acceleration reading that I'd like to somehow fix to get a little more pep.

Umm, no. 

 

Lambda is a theoretically ideal pointb. Unles you can keep your afrs at lambda - in each cylinder across the rpm range - you'll need a beefed up engine if you want any longevity. You could run higher octane (94) or E85, but that will only give you a small margin. 

 

An AFR of 13.5 is about as high as you want to go under all driving conditions. An AFR of 12.5 is as rich as you want to go. 

 

Remeber, this is the average of all pistons so whatever you see, you can bet some pistons are higher and some pistons are lower. 

 

Try to tune each jet change one at a time and be ready to go back on jetting sometimes as you adjust how the carb transitions between idle and main circuits. 

[Madkaw]

36 minutes ago, Jitenshakun said:

Umm, no. 

 

Lambda is a theoretically ideal pointb. Unles you can keep your afrs at lambda - in each cylinder across the rpm range - you'll need a beefed up engine if you want any longevity. You could run higher octane (94) or E85, but that will only give you a small margin. 

 

An AFR of 13.5 is about as high as you want to go under all driving conditions. An AFR of 12.5 is as rich as you want to go. 

 

Remeber, this is the average of all pistons so whatever you see, you can bet some pistons are higher and some pistons are lower. 

 

Try to tune each jet change one at a time and be ready to go back on jetting sometimes as you adjust how the carb transitions between idle and main circuits. 

13.5 is as lean as you want go - really . Is that just based on this motor ? 
what do you base that on? Wasn’t this motor made to run lean ? I’d cruise at 15 -16 afr . 

Edited June 29, 2021 by Madkaw

[Jitenshakun]

34 minutes ago, Madkaw said:

13.5 is as lean as you want go - really . Is that just based on this motor ? 
what do you base that on? Wasn’t this motor made to run lean ? I’d cruise at 15 -16 afr . 

 

Flipping through the FSM at idle CO% should be less than 5% CO. This equates to 12.64AFR.  

 

The FSM also says at idle "CO 1.5 +/- 1.0%", so a range of 13.56 to 14.28 AFR. 

 

This is more in the 12.5-13.5 where out gas doesn't detonate (worse on CA). I'd go 14.5 AFR with good gas, but no way will I tune for 15-16 AFR. 

[Madkaw]

19 hours ago, Jitenshakun said:

 

Flipping through the FSM at idle CO% should be less than 5% CO. This equates to 12.64AFR.  

 

The FSM also says at idle "CO 1.5 +/- 1.0%", so a range of 13.56 to 14.28 AFR. 

 

This is more in the 12.5-13.5 where out gas doesn't detonate (worse on CA). I'd go 14.5 AFR with good gas, but no way will I tune for 15-16 AFR. 

You do know I'm referring to low load kpa when I'm running 15-16? If you have good enough control of spark in relation to load you can run pretty lean . Would I recommend that everyone do this-no. Do I run my 3.2 L6 stroker that lean at lower KPA? All day. I do have fully programmable EFI also .     

[Jitenshakun]

17 minutes ago, Madkaw said:

You do know I'm referring to low load kpa when I'm running 15-16? If you have good enough control of spark in relation to load you can run pretty lean . Would I recommend that everyone do this-no. Do I run my 3.2 L6 stroker that lean at lower KPA? All day. I do have fully programmable EFI also .     

Ah ok, then you have it all in hand. Very cool.