AFM Adjustment

Carbs & F.I.

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SlowLane
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Re: AFM Adjustment

Post by SlowLane » Mon Aug 05, 2019 5:05 pm

We're rather spinning off from the "AFM Adjustment" thread topic here.

New thread justified?
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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Amskeptic
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Re: AFM Adjustment

Post by Amskeptic » Tue Aug 06, 2019 7:10 pm

SlowLane wrote:
Mon Aug 05, 2019 5:05 pm
We're rather spinning off from the "AFM Adjustment" thread topic here.

New thread justified?
Oh yes .... people just walk all over these threads in single-minded pursuit.
Colin
BobD - 78 Bus . . . 112,660 miles
Chloe - 70 bus . . . 206,845 miles
Naranja - 77 Westy . . . 121,400 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 91 Lexus LS400 . . . 92,435 miles

Kossco
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Re: AFM Adjustment

Post by Kossco » Wed May 13, 2020 4:24 pm

Thanks for this solid write up. I have read thru all the replies and see numerous AFR readings provided and am wondering if there is a guideline that an ameuter could follow in regards to what the AFR to road speed to head temp relations should be?

Something like -
Warm idle - 13-15 AFR
Highway no grade, cruise 55mph - 12.1-12.6 AFR - no higher than 400F* CHT
etc etc

Or AFR readings through the revs on each shift point like -
1st-2nd gear, should be between 10.9-12.3 AFR
2nd-3rd, between etc etc.

Or AFR numbers and what state the engine should be in to see that number like -
AFR 8-10 - Very rich, shouldnt be seen while driving under proper conditions
AFR 11-12 - Rich, seen during heavy load acceleration and before shift points
AFR 13-15 - Nearing/past lean stage, should only see when cruising under light loads at 1/2-3/4 throttle
Etc etc.

I have been tweaking and making adjustments based off the LM-2 readouts but am not certain on what ideal AFR readings should be so I guess I am just looking for clarification/confirmation of what makes our T4 engines happiest with quantifiable numbers.

72Hardtop
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Re: AFM Adjustment

Post by 72Hardtop » Wed May 13, 2020 7:47 pm

If your 1/2 - 3/4 throttle (in a bus) you best be on the mains (if carbed) and AFR should be no richer (ROP) than 12:5 13:2 or so. Part throttle would be up to 1/3rd throttle or so.

Bus will run cooler with AFR of 16:0 at part throttle. Cooler than 13:0
1972 Westy tintop
2056cc T-4 - 7.8:1 CR
Weber 40mm Duals - 47.5idles, 125mains, F11 tubes, 190 Air corr., 28mm Vents
96mm AA Biral P/C's w/Hastings rings
42x36mm Heads (AMC- Headflow Masters) w/Porsche swivel adjusters
71mm Stroke
Web Cam 73 w/matched Web lifters
S&S 4-1 exhaust w/Walker 17862 quiet-pack
Pertronix SVDA w/Pertronix module & Flamethrower 40K coil (7* initial 28* total @3200+)
NGK BP6ET plugs
002 3 rib trans
Hankook 185R14's

Kossco
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Re: AFM Adjustment

Post by Kossco » Thu May 21, 2020 10:07 am

Thanks Hardtop. What do you mean by 13:2 AFR? Iv tried running around 16 but am hitting 430*CHT too easily when I go above 55mph. Being in the AFM topic, this is not a carbed engine, all though I imagine AFR correlations to CHT wouldnt matter if it was carbed or FI.

I have fought high head temps whenever over 50mph in the FI vanagon westfalia for years now. After melting a few valves out I opted for a CHT gauge and am now keeping my valves intact but find I am driving by CHT readings rather than speed limits now. The engine can move the van no problem, but the CHTs climb above 400* and stay there far too easy. I have played with the AFM the last few days trying to move it rich and lean etc to see how it affects CHT. Interesting how everything works together. But I have yet to find a combination that allows me to cruise without raising over 400*. So I guess I am looking for a good breakdown of what AFR # should be in relation to the driving condition that I should be in to obtain that number and what I should see my CHT do in response to that driving condition change.

72Hardtop
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Re: AFM Adjustment

Post by 72Hardtop » Thu May 21, 2020 12:06 pm

AFR.jpg
AFR.jpg (23.95 KiB) Viewed 1445 times
Kossco wrote:
Thu May 21, 2020 10:07 am
Thanks Hardtop. What do you mean by 13:2 AFR? Iv tried running around 16 but am hitting 430*CHT too easily when I go above 55mph. Being in the AFM topic, this is not a carbed engine, all though I imagine AFR correlations to CHT wouldnt matter if it was carbed or FI.

I have fought high head temps whenever over 50mph in the FI vanagon westfalia for years now. After melting a few valves out I opted for a CHT gauge and am now keeping my valves intact but find I am driving by CHT readings rather than speed limits now. The engine can move the van no problem, but the CHTs climb above 400* and stay there far too easy. I have played with the AFM the last few days trying to move it rich and lean etc to see how it affects CHT. Interesting how everything works together. But I have yet to find a combination that allows me to cruise without raising over 400*. So I guess I am looking for a good breakdown of what AFR # should be in relation to the driving condition that I should be in to obtain that number and what I should see my CHT do in response to that driving condition change.
Being stock configured you'll be pushing the bus (working hard). Get the AFR (Air fuel ratio) down to 13 - 13:5 range when working hard. 12:5 or so WOT (Wide open throttle).

Cruise would be on the flat scenario. No hill, grade/s. The hottest AFR range is 14 - 15 AFR. Get above it...16 and it will run cooler (on the flats). You using a VDO gauge or a digital gauge? Where do you have the sender placed? How well is it placed (installed).

Tells us more of the engine specs, distributor etc...
1972 Westy tintop
2056cc T-4 - 7.8:1 CR
Weber 40mm Duals - 47.5idles, 125mains, F11 tubes, 190 Air corr., 28mm Vents
96mm AA Biral P/C's w/Hastings rings
42x36mm Heads (AMC- Headflow Masters) w/Porsche swivel adjusters
71mm Stroke
Web Cam 73 w/matched Web lifters
S&S 4-1 exhaust w/Walker 17862 quiet-pack
Pertronix SVDA w/Pertronix module & Flamethrower 40K coil (7* initial 28* total @3200+)
NGK BP6ET plugs
002 3 rib trans
Hankook 185R14's

1jmpshot
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Re: AFM Adjustment

Post by 1jmpshot » Sat Aug 08, 2020 12:03 pm

Following the original directions for the AFM Adjustment, I attempted to "bottom out" the mixture screw C. This is on a 1981 Vanagon, Federal model. I have rotated the mixture screw CW, in my case a 5mm hex, until it just rotates, never stopping. Now I'm attempting to rotate the mixture screw CCW, and it does not return to the original position. I can see the threads on the side of the chamber but the screw does not engage them. I have tried putting pressure on the hex wrench trying to force the screw to engage the threads. I have removed the AFM and held it upside down while rotating the mixture screw with no movement in the screw up the chamber. I have removed the air cleaner housing from the AFM and removed the two screws on the bottom of the AFM. I was unable to pry the bottom plate off the AFM in order to see inside the chamber. Previous to this issue, I had managed to adjust the AFM so I had steady idle and good power up through 3rd gear, before power fell off in 4th. Now, the engine starts but runs rough to the point I'm not comfortable in trying to make adjustments. Any suggestions on how I can adjust the mixture screw C?

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SlowLane
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Re: AFM Adjustment

Post by SlowLane » Sun Aug 09, 2020 8:36 am

1jmpshot wrote:
Sat Aug 08, 2020 12:03 pm
I have rotated the mixture screw CW, in my case a 5mm hex, until it just rotates, never stopping. Now I'm attempting to rotate the mixture screw CCW, and it does not return to the original position. I can see the threads on the side of the chamber but the screw does not engage them. I have tried putting pressure on the hex wrench trying to force the screw to engage the threads.
Oh, dear, that's a tough one.
Maybe a narrow-nosed pair of snap ring pliers could be inserted into the hex socket and used to pull upwards while rotating CCW to catch the threads. You would need to be very careful to not let the jaws slip out lest they damage the threads in the bore.
Good luck.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

1jmpshot
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Re: AFM Adjustment

Post by 1jmpshot » Sun Aug 09, 2020 2:27 pm

Hey, thanks for the quick reply SlowLane. I decided to try a fix last night and just tested it. I cut off a hex key, that fit the mixture screw, so that it would clear the engine lid when closed. I super glued the hex key to the mixture screw opening and let it cure. I have successfully turned the hex key while lifting it so that the mixture screw has moved part way back up the chamber and seems to have engaged the threads. The hex key did separate, but a regular hex key seems to be moving the screw CCW. I will spend more time, at a later date, in adjusting the AFM, but for now I'm a happy camper that the fix worked. If I need to make the hex key more permanent, in order to lift and turn, I'll try JB Weld the next time.

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SlowLane
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Re: AFM Adjustment

Post by SlowLane » Mon Aug 10, 2020 9:37 am

1jmpshot wrote:
Sun Aug 09, 2020 2:27 pm
I cut off a hex key that fit the mixture screw, so that it would clear the engine lid when closed. I super glued the hex key to the mixture screw opening and let it cure. I have successfully turned the hex key while lifting it so that the mixture screw has moved part way back up the chamber and seems to have engaged the threads.
Very creative. Glad you got it sorted.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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