So yeah...logic doesn't work here, AFR goes lean after attaching hoses and air cleaner can (1 Viewer)

[Infinity00]

Winner of a failed smog. High CO after passing the first time but gas cap failed. Replaced gas cap and retested, then high CO popped up. Well, I knew my carb was running a little rich, and I had tried the lean drop method a couple years ago but didn't understand it enough to do it right (now I know to read more carefully, and after maxing rpm, reduce it by leaning the mixture screw from 690 rpm to 650 rpm (that's clockwise about a quarter turn for future reference)). It didn't help that the mixture screw wanted to be out at 4.5 - 5 turns which just didn't seem right. But I'm at altitude and we are dealing with illogic.

Logic = higher altitude = less air available = lean mixture screw (turn cw, to lessen richness) to attain stoic
illogic = higher altitude = less air available = enrichen mixture (turn ccw, to increase richness) to attain stoic

This assumes I understand richer mixture is attained by rotating screw out, or counter clockwise and a leaner mixture is made by screwing mixture screw in, or clockwise.

Anyway, I purchased a AEM wideband AFR and was able to tune it exactly, and surprise, the lean drop method works well if you can follow the 3 step process. I apparently couldn't, and had to spend yet more money on the princess. But I like gauges. Mix screw 4.5 turns out and 14.3ish on the meter. Great.

As many of you know it's near impossible to adjust the mixture screw without taking off the top of the air cleaner. Assuming, using logic here, the mixture would get richer when I put the cap back on because less air is getting to the carb inlet, I gave the mixture screw a quarter turn clockwise to lean the mixture before putting it all back together. Start her up, expecting perfection but being jipped, now AFR is at 16-17. Way too lean! Back the screw the other way a half turn and with everything buttoned up I'm back at stoic, 14.3ish.

Please school me!!!! Something isn't adding up.

And now when I run it down the highway at a steady 55mph, it is def running lean at 16. Scary. But it couldn't have been lean before since it failed for high CO. But then again out here in Boulder County the report doesn't show you what rpm they tested it at when it failed. Could my idle mixture adjustment have caused the engine to be lean at 55mph. I was under the impression that would be a no. The mixture was producing at idle about 12.5 AFR before I performed the correct lean drop and got it closer to 14.7 (it bounces a little bit around 14.2-14.7)

 

[mwebfj60]

Using a screwdriver bit, it's possible to keep the air cleaner on to make adjustments.

When you are adjusting with air cleaner off, are you capping the line for the HIC coming from the PCV T? That might explain the difference.

For the highway cruising, you can adjust the linkage for the secondary slow cut, depending on if you have the throttle open that far, if the secondary slow isn't open when it should be, that would cause a lean condition. That and float level.

 

[NeverGiveUpYota]

Yup. I made mine just like above tho added a 1/2” stretch of silicone tubing over the end instead (it was what I had). And a glove w/ the finger tips cut off the pointer and thumb so I can get a good grip on the tubing. Add a good pen flashlight pointed from the left side and you’ll be golden to make adjustments w/ the air cleaner housing fully installed.
Works like a charm.

 

[OSS]

I have a professionally rebuilt carb (tuned by J.C for standard smog compliance) and I took my cruiser to a performance shop and they put it on a dyno with a wideband O2 sensor installed in a bung in the exhaust pipe.

They then started the engine up and took it through its paces, then let me drive it on the rollers at normal highway speeds and loads. I also ran it through all the gears.
While I was "driving it"'on the dyno, their big screen AFR display was easy to watch and never during the whole time, from idle to freeway speeds, to light throttle cruising, did the AFR get near 14.7. It was always down near the 12s. The only time it would pop up was during a shift or engine braking deceleration.

I smog tested my cruiser a while after that and ozone was almost undetectable (0.1). All other pollutants were far below the maximum as well.
So based in those findings, I'd hazard to say that a 2F shouldn't be running a stoichiometric AFR at idle. It's too lean.
Maybe try to tune the idle mixture near the high 12s or low 13s and see how that works

 

[Infinity00]

Mweb, love the tool idea, thanks for the tip. I did not take that hose off or plug it, just left it on. Would that still explain it? That one runs to the bottom piece of the air cleaner IIRC. I just take off the top piece of the air cleaner and slightly move it aside. By the time I was done, I really didn't even take the big hoses off that come from the smog stuff, but those were the ones I was referring to in my post.

That makes sense about the secondary and float. The float is set correctly to the middle of the window while idling. I didn't mention previously that it still runs lean if I hold it at 45mph. Jets are original and vehicle was originally from Oklahoma. I bought some smaller jets thinking i would need to lean it out, but again, illogic rules.

After I failed, I pulled the plugs and changed the air filter and tried advancing the timing. It really doesn't like the timing advanced. The HAC and vacuum advances are working, so I set it to the bb (7 deg btdc) and let the HAC pull it to 13-14. Plug coloration: 1 and 6 were lean, and the rest were fairly fouled, before tuning. I haven't pulled them since replacing and changing the mixture. Also, when I was fixing the linkage issue you helped me with, I pulled the carb and found standing gas sitting in the intake manifold below the carb. I guess that could have been from me repeatedly trying to rotate the throttle linkage and the fuel squirted down.

 

[Infinity00]

OSS, that's where it was when I failed, so I adjusted leaner hoping to then pass, but I don't want it anywhere near the smog station running 16 lean. I get your point though, and if you passed smog 0-60 mph with it running around 12 then I should be able to. It definitely likes it better running fatter. I'm thinking of changing the mixture back to where it was and checking the behavior at 45 and 55. I know it isn't supposed to do much but it will give me a baseline of where I was before

 

[mwebfj60]

How about this logic...putting the air cleaner back on reduces the airflow a bit but that reduced airflow causes less fuel to be pulled through the primary slow circuit and leans out the mix...

 

[Infinity00]

Right! Interesting. Makes sense.

 

[Infinity00]

Changed the mixture to a richer setting. It’s back to around 5 turns out at idle and warm, the AFR is steady at 13. Running ALOT better across the board. When I earlier said it didn’t like having an advanced timing, as it turns out, that wasn’t the problem. The previous idle mix that was set to create a 14.3ish reading exacerbated the lean running at higher speeds causing a very poor running vehicle. Including detonation or precognition (or maybe just lack of gas sounding the same) when giving it gas to get up to highway speeds that I thought was timing related but wasn’t, it was running too lean. All that is gone by setting my mix to run at 13. Thanks @OSS and @FJ40Jim for providing similar assessments, and mweb for pointing out causes of lean xditions.

Jim routinely states, and I’m paraphrasing, to set these carbs starting 4-5 turns out, trim for max rpm, set base idle speed and timing, and make sure the AFR reading 13. I’m not quoting him, and the steps may be out of order, and he is much more succinct. But that’s what I got from reading lot us of carb posts by him.

I was under the impression changing the idle mix doesn’t impact the other circuits, but in my case, it did. Overall, the AFR readings have come down. There are states that occur while driving that lean or enrichen it, which is normal, but then it’ll mostly stay around mid 13s if I’m just cruising at 35, 45, or 55 mph. There seems to be something that will cause it to jump around a little bit, mostly lean, when cruising at certain speeds before it settles down. I don’t know if that is a normal oscillation of the smog stuff or not. A little concerning but I’ll continue to check my smog gear, maybe block my egr (B.B.between Q port and EGR) and see if it goes away.

A couple other things I noticed, the gas in the sight window is maybe just slightly shy of center. When the car is off, after running, the gas in the window is higher, definitely more centered. There’s a difference, but I believe the level while running is still reasonable. This led me to look at the gas flowing through the gas filter, I was disturbed when I discovered the gas is only filling the filter about a quarter of an inch. It’s only 10-20% full while running. What’s up with that? Any idea what could cause it to behave that wayt?

The other shocking thing was when I pull out the choke, the AFR goes really lean. With it in I’m at 13, pull it out and it jumps to 16. I’m thinking since the idle plate is moved when the choke is pulled, the carb is no longer on the idle circuit and there might be a small clog in my primary circuit? Does that sound like a possibility? I rebuilt the carb a few years ago but A). There’s no screen in my fuel line, and B). The HAC has put crud in those carb holes in the past. I’ve cleaned the carb and all the steel and silicon vacuum lines after that happened, but you never know if more has entered somewhere.

 

[OSS]

The fuel is -sucked- by the fuel pump from the tank. If there's the tiniest leak in the supply line to the filter, the pump will pull in some air too. Maybe sloshing fuel in the tank creates tiny bubbles too that get sucked into the filter.

If the fuel filter has a lot of air in it, it's probably clogged. A little bubble can dry out the filter element in that spot (along with the accumulated dirt) which won't allow air to pass through. Kinda like creating cement. Then more bubbles accumulate and the problem gets increasingly worse.

If you're running a stock Aisin carb, the choke opener system prevents the choke from operating when the engine is not cold. When you pull the choke knob on a warmish engine, all you're really doing is just advancing the throttle. Pressing down on the gas pedal a tad would accomplish the same thing.

My advice is: Now that you've set the AFR correctly, remove the gauge from the cab and forget about it. It'll just create unnecessary excitements.

 

[Infinity00]

The fuel is -sucked- by the fuel pump from the tank. If there's the tiniest leak in the supply line to the filter, the pump will pull in some air too. Maybe sloshing fuel in the tank creates tiny bubbles too that get sucked into the filter.

If the fuel filter has a lot of air in it, it's probably clogged. A little bubble can dry out the filter element in that spot (along with the accumulated dirt) which won't allow air to pass through. Kinda like creating cement. Then more bubbles accumulate and the problem gets increasingly worse.

If you're running a stock Aisin carb, the choke opener system prevents the choke from operating when the engine is not cold. When you pull the choke knob on a warmish engine, all you're really doing is just advancing the throttle. Pressing down on the gas pedal a tad would accomplish the same thing.

My advice is: Now that you've set the AFR correctly, remove the gauge from the cab and forget about it. It'll just create unnecessary excitements.

Okay, that last sentence made me laugh!

Pulling the choke cold or hot, give some the same result.

 

[FJ40Jim]

If it passes testing & runs OK, then good for you.

But... idle mix should not be 5+ turns out. There is either dirt in the carb, or a mani vacuum leak.

 

[Infinity00]

Thanks for the response Jim. Def wants to be 5 turns out but not a twist more than that. It’s been like that before the engine and carb rebuild and after. The manifolds were planed down together by mountain high performance who seemed very experienced with the 2F engine but when I got the manifolds back I wasn’t sure they were done that well, or together. I think it’s really hard for the machinists to fixture them and to machine steel and aluminum together, at least that’s the story I heard. I tried to make it better but in the end I had to put it on and hope for the best.

So far, I have almost 17 in of mercury before everything gets warm and just above 16, 16.5 after warm. Very steady since the rebuild. I’m at 5900’ so it seemed a reasonable number. All the other gaskets were replaced then as well.and the common intake leak welded - it still looks great.

I wouldn’t be surprised if there’s still a leak, and now that you point it out, it seems obvious given, by covering the air horn (by adding choke) a leak would be showing up as air gets sucked in from somewhere else. It’s the chicken way of performing Pin_heads test, where you put a hand over the air horn and watch to see if the rpms increase just before it dies. I’m hoping it’s just a dirty car or blocked fuel filter. Slowly I’ll start blocking other sources of potential leaks in the smog system to rule that out after doing the easiest thing, replacing the fuel filter and cleaning the carb again.

 

[OSS]

On my 2F at least, the vacuum has always been lower at first start of a cold engine, then rises up a bit after the engine has warmed up for several (8) minutes. I definitely don't have any extramarital vacuum leaks (rebuilt & machined head & manifold).

Cold start (sea level)


After several minutes warming up (fast 1300 rpm warm up idle)

 

[NeverGiveUpYota]

The fuel is -sucked- by the fuel pump from the tank. If there's the tiniest leak in the supply line to the filter, the pump will pull in some air too. Maybe sloshing fuel in the tank creates tiny bubbles too that get sucked into the filter.

If the fuel filter has a lot of air in it, it's probably clogged. A little bubble can dry out the filter element in that spot (along with the accumulated dirt) which won't allow air to pass through. Kinda like creating cement. Then more bubbles accumulate and the problem gets increasingly worse.

If you're running a stock Aisin carb, the choke opener system prevents the choke from operating when the engine is not cold. When you pull the choke knob on a warmish engine, all you're really doing is just advancing the throttle. Pressing down on the gas pedal a tad would accomplish the same thing.

My advice is: Now that you've set the AFR correctly, remove the gauge from the cab and forget about it. It'll just create unnecessary excitements.

Then send it to me to try! Ha! I’d never heard of one till you. It’s really an interesting way to get a good ratio. I’m desmoged and at sea level. I gather all that would affect it greatly.
@mwebfj60 is typically the next guru on carbs. He’s pulled them apart and dissected all the systems on them. You’ll find his threads most recent in the last year or so. I’ve leaned on him tons in regards to carb fiddling.

 

[NeverGiveUpYota]

And now on the fuel filter question... should it fill more than he mentioned? Mine does the same as his.

 

[FJ40Jim]

OP, what is the altitude of the test station?
Altitude where you are adjusting carb?

 

[Infinity00]

I think I have the main carb and vacuum gurus responding to this thread! Only missing pin head at this point. Anyway I hope I can pass. The test station is around 5500’, and I’m tuning the cruiser a mile away. Same altitude.

For fun I’m posting the results. I can’t tell what order they are uploading in but the graph goes along with the failing CO test.

The original test passed CO but failed on gas cap. I drove the mile to Toyota and got a cap and drove straight back and retested. Then it failed on CO. Some background, the cat had been smelling like sulfur most of the summer so I thought it was running rich which was why I bought the wide band meter. After failing, I looked at the air cleaner and plugs. The inner 4 plugs were fouled. The air cleaner was pretty bad, and a bunch of gray or silver fine particals of what I think is from the smog pump was in the bottom of the air cleaner housing. I replaced the filter, and plugs. Oh, and I’ve never had this heat over 210 but after the smog station ran it for what seemed like forever, the engine was 220 deg. Ive never seen it that high and it concerned me. It’s always maintained between 190-210 max.

 

[Infinity00]

@OSS your vacuum readings are something I wish I had! Will never happen here in Colorado. I’ve read a lot of your posts on vacuum - I’m sure I’m missing something somewhere. It’s a slow process and to tell you the truth after rebuilding and replacing everything I could, I had to leave it alone for awhile. Especially since I passed 2 years ago with the new build and new cat. It can be a brain drain!

 

[Infinity00]

@NeverGiveUpYota your fuel filter only fills a quarter inch also?