AFM ADJUSTMENT w/o gas analyzer

[Gypsie]

Don't you go throwin' more variables in the mix, dang ya!

Sheesh!

May be a contributer but I don't thinnk so.

[IFBwax]

You know I did a cursory check on the net and I don't know that we're going back to a pure gas blend ever again. I sure can't find anything that says we return to the fall blend on so and so.

Too bad you're not going to be at the Lab tonight. I know two people who own one of those exhaust gas analyzers who might be there tonight.

[markd89]

My CHT goes to 450 (!) going up a steep hill on the freeway. I've checked timing, etc. and know that is OK. Cooling system OK, so I know it's mixture. Probably too rich as my MPG is poor.

My question is -- do I risk anything by leaning up a little bit as long as I watch my CHT. i.e. If my CHT does 430 on that hill after I adjust, then I'd know I'm going the right way?

Mark

[Ritter]

My CHT goes to 450 (!) going up a steep hill on the freeway. I've checked timing, etc. and know that is OK. Cooling system OK, so I know it's mixture. Probably too rich as my MPG is poor.

My question is -- do I risk anything by leaning up a little bit as long as I watch my CHT. i.e. If my CHT does 430 on that hill after I adjust, then I'd know I'm going the right way?

Mark

Leaning will make you run hotter.

[Westy78]

My CHT goes to 450 (!) going up a steep hill on the freeway. I've checked timing, etc. and know that is OK. Cooling system OK, so I know it's mixture. Probably too rich as my MPG is poor.

My question is -- do I risk anything by leaning up a little bit as long as I watch my CHT. i.e. If my CHT does 430 on that hill after I adjust, then I'd know I'm going the right way?

Mark

Leaning will make you run hotter.

Not necessarily. A rich mixture makes for an inefficient burn which equals less power which equals more effort for the engine to keep at a given speed which of course leads to more heat in the heads because the engine is working harder. It's a fine line between running to rich and to lean.

[Gypsie]

AHA! I think I was on the Rich side of this pendulum. I am now swinging back toward lean/just right according to temp readings.

[Amskeptic]

Settle down people. Y'all thinkin too much.

A lean mixture is the deadly heat generator. A rich mixture that is so rich that the engine chokes to death, is a cool death. A lean mixture is the guy on the chain gang who is busily busting rocks with the best of them when he keels over with a . . . valve sticking out his head. Um, let me go work on my metaphors, I think I lost this one. But lean is deadly. Rich is not.
Colin

[Bleyseng]

unless its so rich that the mix is washing the oil off the cylinders so that you are running metal to metal. yep, that happens pretty quick if its too rich!

[Gypsie]

A lean mixture is the deadly heat generator. A rich mixture that is so rich that the engine chokes to death, is a cool death... ...lean is deadly. Rich is not.

Just for clarity a few points worth noting

On the trip to montana, fully loaded (bus, not driver) I had pedal to the metal to maintain freeway speeds, and then just barely. full throttle adds the enrichment circuit (ie more fuel). Not overly hot but quite a few 400-475 stretches (inclines and such).

Upon return the tail pipe has had that charcoal black sooty appearance.

Leaning out (at this point 8 clicks to the lean from starting point pre Maupin and post new rings) temps have not increased and I do not need to floor it for freeway speed since leaning out.

I am monitoring the CHT and plan on continuing the lean out until I see temps increase.

Oil change this eve. (not changed since Montana before Maupin)

I have increased mileage from 12 to 15 and am hoping for a few more.

Let me hear if there are concerns with this plan.

Would the CHT miss something that will harm the engine during this experimentation process?

[bretski]

Have you done a valve adjustment before or since you started clicking to the lean?

Also, have you done the IAC "Wiper-bump" since then? Don't trust the CHT gauge as an absolute measure of temps...click your AFM with caution, my friend.

[hambone]

Why not borrow that analyizer from Jasan? No more guesswork.
(things are so much simpler with a single barrel Solex. With a cost of course)

[Gypsie]

Have you done a valve adjustment before or since you started clicking to the lean?

Also, have you done the IAC "Wiper-bump" since then? Don't trust the CHT gauge as an absolute measure of temps...click your AFM with caution, my friend.

Agreed on the AFM adj.

The issue here is that the wiper bump was giving a "too lean indication" and the other indicators (tailpipe emissions, carbon, mileage and temps were indicationg 'too rich'

I will check valve lash tonight when I do the oil, though I would guess that the hydrolic lifters will be fine.

My bump here was to inquire about what conditions might be giving the 'bump test' false readings.

There was discussion recently about the operating conditions being under load and the test not. Ideas???

I also had a flash about head torque as I did not do the 35fp overnight and then back down to 22fp the next day. I will check the nuts I can reach (unless I should leave them alone???). Oh, the variables!

What is the concern about the CHT? I will double check the temps with my IR sensor though I 'feel' things are fine with the cht readings.

[Amskeptic]

Under full throttle, the AFM is completely out of the equation. The wiper gets floored in the WOT position and that's that, you're then relying on the full throttle enrichment circuit in the ECU. Then, all the other variables of your engine's operation come into play on the confounding continuum. Again, don't get too thinky.
ColinOnARock

[vwlover77]

Seeing this thread bumped back to life reminded me that I had not checked the AFM at-speed since the camshaft in my engine was changed back to stock from the "Torque Special" and the compression ratio raised from 6.6-1 to around 7.1-1.

When Colin visited last year, prior to the engine work, he moved the wiper 1/2 tooth to the rich, and went seven clicks rich with the big clockspring wheel as well. This was done to a factory-set AFM (since we had to break open the factory glue seal to get the plastic lid off). Now, call me a fool, but after the engine work, I set the cog wheel back to the lean 3 teeth from Colin's setting, figuring since I would be running a stock setup, the AFM could be moved back toward the original factory setting.
The Bus ran well, spark plugs looked good, and mileage was consistently 18-18.5 mpg for a mix of "around town" and short highway drives. Head temps? Unknown.

But, I decided to check it anyway....

With a 4x4 block on the accelerator holding 2600 rpm, I slowly pushed and held the wiper slightly to the lean and heard the engine rpm dropping off. Pushing it slowly to the rich, the engine gained rpm rapidly. I adjusted the cog wheel back to Colin's setting of 7 teeth to the rich. I got pretty much the same result and went another 4 teeth to the rich. Pushing the wiper toward lean did not cause as rapid a drop in rpm, and pushing it toward the rich still increases rpm, but not as rapidly. The "flick" test in either direction did not give a noticeable speed change.

I stopped at that point. Do I really want to continue indexing the cog wheel until the wiper is in the "sweet spot" where the engine loses rpm if pushed in either direction? I'm now 11 teeth to the rich from the original factory setting!

I was able to re-adjust at idle using the bypass screw with no problem.

The Bus seems to have a little smoother power delivery, but just in the 40 miles I've driven since I made the adjustments, it seems like the fuel gauge is dropping more rapidly than previously.

Thoughts?

[Westy78]

With all due respect to Colin I am finding that that method of adjusting the mixture on the AFM will put you into very rich running and higher than normal temps. You don't want your cylinders being washed down with unburned fuel. After adjusting my engine with Colin's method I lost power and mileage not to mention other minor issues that mimic ignition problems. I'm back dialed in with the LM1 and seeing much better high RPM power and the same temps. Idle is also much more stable. I know Colin may dispute this but I've seen it in real time over the last 1000 miles, and of course, YMMV.