1976 Bus - Test for AFM? ** It's still bucking!!**
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1976 Bus - Test for AFM? ** It's still bucking!!**
Is there a test I can do to know if my AFM is working properly? I have (what appears to be) a mixture problem. I've got a high level of confidence that I've tracked down and fixed any vacuum leaks (although haven't done a leak down test on the engine yet). Going to do a fuel pressure check and compression check tonight.
1976 VW Bus aka tripod
FI ...not leaky, and not so noisy...and she runs awesome!
FI ...not leaky, and not so noisy...and she runs awesome!
hambone wrote: There are those out there with no other aim but to bunch panties. It's like arguing with a pretzel.
- Gypsie
- rusty aircooled mekanich
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Bentley gives resistance specs for the contact points on the afm connection port. I believe that should let you know if the they have porper resistance.
I think there is another process to test if the swiper is making proper contact with the 'circuit board' at the various points.
Have you tried Colin's AFM adjustment pocedure? I would start there, as it is just a process to narrow the lean/rich range done with a screwdriver and a tach if you are not comfortable guaging RPMs by ear.
make notes about your starting point and any changes for reference.
I think there is another process to test if the swiper is making proper contact with the 'circuit board' at the various points.
Have you tried Colin's AFM adjustment pocedure? I would start there, as it is just a process to narrow the lean/rich range done with a screwdriver and a tach if you are not comfortable guaging RPMs by ear.
make notes about your starting point and any changes for reference.
So it all started when I wanted to get better gas mileage....
- airkooledchris
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- chitwnvw
- Resident Troublemaker
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- Gypsie
- rusty aircooled mekanich
- Location: Treadin' Lightly under the Clear Blue!
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http://itinerant-air-cooled.com/viewtop ... hlight=afm
There are other threads that have it in them but this is one.
Search AFM in title only and there are several
There are other threads that have it in them but this is one.
Search AFM in title only and there are several
So it all started when I wanted to get better gas mileage....
- chitwnvw
- Resident Troublemaker
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I am running too lean.Your best field test for mixture, once it is running decently enough to not require babysitting at the AFM, is to simply nudge the wiper infinitesimally counterclockwise or clockwise with your chubby finger and listen to what happens:
if the idle goes UP counterclockwise, it is still too lean.
if the idle goes down counterclockwise, it is too rich.
if the idle goes UP clockwise it is too rich.
if the idle goes down clockwise it could be OK if it recovers the instant you let go.
Is CCW richer sooner?Your dynamic adjustment (B) changes the slope of the map. Imagine a nice curve up towards "richer sooner", or imagine a curve towards horizontal which is "leaner later."
It seems to be affecting my engine differently. The dynamic dial, 'seems' to be enrichening the idle/low rpm/ no load, feels leaner than before adjustment of dynamic dial at higher rpm. By that, I mean that there is a subtle feeling of loss of power at higher rpm/under load. Feels like my carbs did before they were dialed in.Your dynamic adjustment (B) changes the slope of the map. Imagine a nice curve up towards "richer sooner", or imagine a curve towards horizontal which is "leaner later." If you rotate the black plastic cog (by prying the chrome lockwire away from a tooth with your regular screwdriver tip and rotate the cog CCW (richer) or CW (leaner) you either unwind the spring coiled in inside, or wind it up still further.
This adjustment primarily affects the higher rpm/load.
Are we looking for a best compromise between adjusting at idle and at rpms? Or do we adjust for idle and then do the same at RPMs?, and that's where we leave it?So now we have to check the high speed rpm. Bring engine to 2500 to 3000 rpm and hold it there with whtever mechanical means you can. A screwdriver expertly wedged is good. Sit and watch the engine hold that speed consistently. Now gently nudge the wiper barely 1/16" of an inch (maybe 1/4" if no noticeable change) CCW. Revs go up? Or do they go down? Now nudge CW 1/16" (or 1/4" if no change was noted). Revs go up? We want to know if any of your nudges brought revs up. . .
We really could use some graphs...
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just curious ... Colin always gives the warning abt no being 'ham handed' with the wiper when adjusting the mixture. I notice when at idle, that if I am ham handed (move wiper tip more than 1/4 inch) in the CCW (richer) direction) it has a significant increase in idle speed (several hundred rpm) before bogging/decreasing.
Is this normal, or is this indictive of a bigger problem that I need to address?
Is this normal, or is this indictive of a bigger problem that I need to address?
1976 VW Bus aka tripod
FI ...not leaky, and not so noisy...and she runs awesome!
FI ...not leaky, and not so noisy...and she runs awesome!
hambone wrote: There are those out there with no other aim but to bunch panties. It's like arguing with a pretzel.
- chitwnvw
- Resident Troublemaker
- Location: Chicago.
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Pretty sure that is normal. He stated in the quote of Gypsie that what you want it 1/4" of movement w/o affecting rpms.TrollFromDownBelow wrote:just curious ... Colin always gives the warning abt no being 'ham handed' with the wiper when adjusting the mixture. I notice when at idle, that if I am ham handed (move wiper tip more than 1/4 inch) in the CCW (richer) direction) it has a significant increase in idle speed (several hundred rpm) before bogging/decreasing.
Is this normal, or is this indictive of a bigger problem that I need to address?
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OK - trying to eliminate all potential issues:
Compression test
# 1 115
# 2 ?? Has an timecert so can't check (plug is married to it)
#3 110
#4 110
That's with all plugs in and cold ..
manifold vacuum @ idle aprox 15
Fuel pressure is a steady 33-34 psi at idle 35 at high rpms.
Based on the operational symptoms, and low vacuum with decent compression, I swear it has vac leak...but I'm having difficulty finding it. Maybe the AFM, haven't checked per Bentley .. yet
Compression test
# 1 115
# 2 ?? Has an timecert so can't check (plug is married to it)
#3 110
#4 110
That's with all plugs in and cold ..
manifold vacuum @ idle aprox 15
Fuel pressure is a steady 33-34 psi at idle 35 at high rpms.
Based on the operational symptoms, and low vacuum with decent compression, I swear it has vac leak...but I'm having difficulty finding it. Maybe the AFM, haven't checked per Bentley .. yet
1976 VW Bus aka tripod
FI ...not leaky, and not so noisy...and she runs awesome!
FI ...not leaky, and not so noisy...and she runs awesome!
hambone wrote: There are those out there with no other aim but to bunch panties. It's like arguing with a pretzel.
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Did you look for the sneaky vacuum leak through the valve cover gaskets. Does your idle change noticeably if you remove the oil fill cap while running? Does one or both of your valve covers drip oil only when the engine is not running? do your valve cover gaskets look like they've been sucked inward?
1/20/2013 end of an error
never owned a gun. have fired a few.
never owned a gun. have fired a few.
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- IAC Addict!
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Sure did check the valve covers ... based on posts I found here =). Driver's side did appear to be sucked in at the top, so replaced it.
Idle does change if I remove oil filler cap ... what does this indicate?
Idle does change if I remove oil filler cap ... what does this indicate?
1976 VW Bus aka tripod
FI ...not leaky, and not so noisy...and she runs awesome!
FI ...not leaky, and not so noisy...and she runs awesome!
hambone wrote: There are those out there with no other aim but to bunch panties. It's like arguing with a pretzel.
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- IAC Addict!
- Status: Offline
Indicates strong vacuum in the crank case through the crankcase ventilation hose. Disconnect the hose and plug it, see if that changes anything. If vacuum in case is strong enough and the valve covers are warped or the bails are old and tired, replacing the gasket may not be enough.TrollFromDownBelow wrote:Sure did check the valve covers ... based on posts I found here =). Driver's side did appear to be sucked in at the top, so replaced it.
Idle does change if I remove oil filler cap ... what does this indicate?
1/20/2013 end of an error
never owned a gun. have fired a few.
never owned a gun. have fired a few.
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- IAC Addict!
- Location: Metro Detroit
- Status: Offline
Which hose is considered the crankcase ventilation hose? I don't recall seeing a pcv valve ... if it's got one, where would it be located?
1976 VW Bus aka tripod
FI ...not leaky, and not so noisy...and she runs awesome!
FI ...not leaky, and not so noisy...and she runs awesome!
hambone wrote: There are those out there with no other aim but to bunch panties. It's like arguing with a pretzel.