Itinerant Air-Cooled

So I'm getting a little what-I'd-call bucking when I either get into, or get out of the pedal, especially in 1st and 2nd. Not bucking like an out-of-control seizure or anything, just a decent chug-chug-chug.
What could it mean? Vehicle is a 1971 Squareback with intact fuel injection. It runs pretty well otherwise.

Slightly lean.
Excessive engine/transaxle compliance
Excessive slop in driveline

My Squareback does it too. The whole rear engine/transaxle/suspension is mounted on a subframe. If the rubber "bounce" (compression/rebound) is the same as your foot on the accelerator, you get a self-amplifying moment of sheer spasticity.
Colin

Amskeptic wrote:Slightly lean.

Interesting.
The gassy smell and soot above the tailpipe had me thinking it was running rich. (Of course that the exhaust is routed directly into the bumper overrider (to be remedied post haste) may have something to do with the soot.)

How do I adjust the fuel/air mix on this thing? It's been a long time since I had a fuelie Type 3. Is it that screw on the driver's side of the intake air distributor?

Amskeptic wrote:Slightly lean.

whc03grady wrote:How do I adjust the fuel/air mix on this thing? It's been a long time since I had a fuelie Type 3. Is it that screw on the driver's side of the intake air distributor?

Yoo hoo! Before you adjust stuff, may I throw this out for discussion.

I had this same exact phenomenon on my bus earlier this winter. At first I thought it was bad gas, which might be technically true. I don't know if they do it in Montana, but we have 10% ethanol added to our fuel here. Apparently (according to the TV news ) the ethanol in the fuel absorbs water when it's in the storage tanks at the gas station. Then you pump it into your vehicle and now you've got watered down gas.

Would water (albeit small amounts) in the fuel alter it's ability to burn to the point it would create a slightly lean condition? Here's what I mean. Say your injector squirts an ounce of fuel in the combustion chamber and when the fuel is "good" you actually get an ounce of fuel and the air/fuel mixture is correct. When the fuel is watered down, the injector squirts an ounce of the new "blend" which may only be 3/4's of an ounce of gas and a 1/4 ounce of water. Less fuel versus the same amount of air equals a lean condition. Obviously the numbers I used aren't real, but you get what I'm talking about.

Now that the weather has warmed up, my problem has gone away and my bus runs like a dream. To support my theory, when I was experiencing the phenomenon, my BA6 gas heater would backfire and otherwise not run well (perhaps lean?). Now it too runs perfectly and warms me to my soul. Apparently the water-absorption-by-the-ethanol may be temperature dependent.

Does any of this theory hold water? That's a joke, son, holds water, water in the gas, ah kids these days.

With D-Jetronic, little things like valve adjustment, ignition timing and charging system voltage are ABSOLUTELY CRITICAL to proper functioning.

Make sure the valves are set at 0.006 all the way around, check the ignition timing. With the engine running, check voltage at the battery. Anything less than 13.5-14V Es No Bueno, if you get 11.5-12.9 check the brushes and replace the voltage regulator. Low voltage makes the system run rich.

Mixture is adjusted with a screw on the MPS, that "ray gun" looking thingy to the left side of the engine compartment .. but it was factory-sealed with epoxy and shouldn't be messed with. See if the epoxy is still there, make sure the diaphragm holds vacuum -- but don't try adjusting it. Even people who really, REALLY know D-Jetronic don't mess with that screw unless they have to, and then only with a crapload of equipment. If the epoxy is gone, try and find one that hasn't been monkeyed with...

This got me to thinking...

whc03grady wrote:(Of course that the exhaust is routed directly into the bumper overrider

.. whatchoo got on there right now? Stock with "issues", or something aftermarket? An all-pieces-present stock system wouldn't dump exhaust into the overrider. If aftermarket, please tell me it's not one of those godawful 4-tip "Monza" deals, those things flow like a stock muffler with a potato shoved in the tailpipe...

I've got an OE '73 muffler sitting in the driveway if you need one, complete with the upper preheat exchangers. This is the "big tailpipe" unit, best exhaust flow characteristics of the stock TIII mufflers .. which are all tuned, equal-length systems, contrary to what the aftermarket vendors claim to try and get people to Buy Their Chinese Crap.

I didn't want to imply that I was going to go poking and "adjusting" where I shouldn't poke or adjust. It was more me thinking out loud, "Now, where was it that the mix is adjusted?" It's been a long time since I had a fuelie Type 3--the last one I had departed This Mortal Coil sometime in 1996.

The overriders are too far outboard is (part of) the problem. The exhaust isn't a four-tip (while I like their look, I understand from painful personal experience that they're garbage).

Thanks for the tips. A full tune-up will be performed soon, followed by repositioning the overriders, installing a new hatch seal, and dumping in some gas drier, unless such is contraindicated.

whc03grady wrote:It's been a long time since I had a fuelie Type 3--the last one I had departed This Mortal Coil sometime in 1996.

Heh .. that's about when we got our first one (and our first aircooled VW, too) -- it's still in the driveway.

Nothing wrong with using gas drier, but it's just alcohol .. usually methanol, sometimes ethanol. If you've got gasahol (10% ethanol) or E85 at the pumps in Missoula you might as well use that instead of buying something in a bottle. Fill it up with gasahol, or maybe 1/2 gallon of E85 along with "pure" gasoline.

I did jack up the fuel pressure a tad to get rid of my LEAN condition. I was in an experimental mood and had my pressure gauge. My plugs were whitish too. You may have a different circumstance, of course. A blackened bumper and tailpipe is not a sufficient indication unto itself of engine mixture. Plugs can be helpful indicators . . . after a highway run.
Colin

Fixed! The bucking anyway. I replaced the MPS and am now running smoooooth. Richness to be determined later; let me enjoy this for a while. Here's a link, be sure to call me out on anything I say that's false:
http://www.ludwigandgertie.com/2010/02/ ... to-my.html

In my experience with Djet what you are describing is from partload being lean. I would check/change all the vacuum hoses too as the MPS can't really read a vacuum leak. Any extra air leans out the AFR so thats why folks over the years have adjusted the MPS to try to cure symtoms that can be caused by unseen vacuum leaks. You should run a vacuum test on all the areas where the manifolds mount to the heads, into the plenum etc too. I use a propane torch not ignited but turned on with the engine running and point it at the suspect spot. If the rpms go up (with the extra fuel) thats a vacuum leak.
Make sure you are using German high pressure fuel hose and the proper clamps, not screw type gas line clamps. Cracked fuel lines are a real problem with 30lbs of fuel pressure, fire often is the result.

whc03grady wrote:Fixed! The bucking anyway. I replaced the MPS and am now running smoooooth.

That was the solution for mine too. I spent weeks chasing the bucking, and finally found that someone had replaced the MPS with one from a 1971...

I'd like to think I'm running lean but this...



...leads me to believe otherwise. Plus the bucking is gone now with the correct MPS. (That is, the incorrect MPS, as Gertie is a '71 with '72 California fuel injection.)

Please tell me you got that "new" muffler installed since that picture was taken.

tristessa wrote:Please tell me you got that "new" muffler installed since that picture was taken.

No, but I've taken the overriders off and cleaned it off some. It's getting there....