72 Super sputters under load

[Hydro626]

1972 Super Beetle, 009 dist with H30/31PICT carb. Has run flawlessly with this combination for almost a decade. A few months ago I was on the way back from getting pizza when it started sputtering whenever I'd take off from a stop. At this point I thought maybe I was running out of gas but not only was it not empty but topping it off changed nothing. I left it alone for a bit and the next time I started it up it seemed to be running fine, but after driving it around just a bit it started sputtering again and got worse the more I drove it.

It's most prominent at the bottom of each gear and especially under load. Sometimes revving it up and letting back out on the clutch will get me through it. Sometimes just easing off the gas will keep it from stuttering depending on the sort of load its under. Hills make it worse but highway speeds are fine. Again, it'll start fine but get worse as I drive it.

In the past few months I've tried replacing various things, some of which it needed anyway:
-new Solex H30/31PICT
-new Bosch coil
-new Bosch condenser, points, rotor and cap

After installing all this and still having issues, I sent it to my local aircooled VW guy and he made several crucial adjustments including properly setting the points, adjusting the timing, fine tuning the carb and tightening the throttle cable, which he initially thought sorted it all out. However, after driving it for a few minutes it goes right back sputtering. His only suggestion at this point was to use some seafoam and see if it clears up.

I have no idea what it could be at this point. After ALL of that, it's still doing the exact same thing. I can't tell if it's a fuel or a spark issue, especially since it seems to be running fine one second and then running horribly the next. Listening to it idle you'd never know there was a problem. Even without being in gear you can still hear the beginnings of a sputtering problem when revving once it appears.

Thoughts?
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1972 Volkswagen baja Super Beetle "Elizabeth"
1989 Cadillac Brougham D'elegance

"Never name your car...too much unhealthy emotional connection coupled with your human dark/light,yin/yang energy affects the mechanical health of the vehicle and causes magnetic convergences like the one you just had.that, or some old f**k backed into your car,its hard to tell..." -johnnypan

[Joey]

Sounds like fuel starvation. Maybe crud in the tank. Disconnect the fuel line going to the pump to see how much fuel comes out. It should be a fairly steady stream. It could also be the fuel pump.
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Joey

‘60 Kombi - '74 Bus - '79 Panel - '65 Beetle

[goober]

"Hills make it worse but highway speeds are fine."

Does it have an original '72 engine?

Did you ever overheat the engine?

[Hydro626]

[Joey]

[Hydro626]

[Starbucket]

Remove and plug the hose from the tank at the fuel pump and get another piece of hose and put it on the fuel pump and run it into a gas can and take a drive.

[Hydro626]

[virusdoc]

Is it possible that your heat riser has become clogged over time, and you are no longer heating your manifold sufficiently?
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1976 Convertible Super Beetle, "June Bug".
FI-->34PICT3 carb conversion-->now dual 40 IDFs
Self-rebuilt 1904 (after totally botching a 1641 rebuild, cussing a lot, and throwing lots of cash in the fire)

[Hydro626]

[virusdoc]

[Hydro626]

[Igpoe]

Have you ever reached underneath your air compressor and opened the drain valve to get the condensation out? The air rushing out behind the water is Very cold, even icy! This is what is happening in your manifold. Without constant heat the atomised gasoline from your carb will fall out of suspension in the very cold air underneath the central carb and be intermittent in reaching the combustion chambers. Sputtering, and rough running in general is the result.

Many people have lost their lives in airplanes whose carbs and manifolds have "iced-up". This can happen any time of the year.
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'73 super.

[virusdoc]

[Starbucket]

Your accelerator pump may need adjustment. Remove air cleaner and (engine off) look down carb and slowly open the throttle, the accelerator pump should start streaming gas as soon as you move the throttle arm, if not adjust the linkage.

[Hydro626]

[Hydro626]

UPDATE

Shortly after the last post I went under the car to look around and found the fuel hose coming from the tank to be rotten and coming apart. I took that opportunity to take the tank out and check it while I was replacing that hose. The inside of the tank still looks pretty good but it turns out there's no sock in there, so that's not the issue at all.

I put it all back together and installed a filter under the tank for good measure, even though I'm not sure there was ever a sock in the tank to begin with. After that it ran better but still somewhat poorly. I noticed the oil spots under the car were bigger than normal so I pulled the dipstick and smelled gas in the oil. So I replaced the fuel pump and changed the oil and now it runs a little bit better still but still hesitates sometimes in first.

The only thing I haven't checked at this point is the hard line. I'm thinking what if there's a partial obstruction in there from where the hose in front of it came apart? The filter under the tank seems to be more full on average than the one just before the pump, which is almost always mostly empty with the engine running lately. I might try blowing the hard line out.

As for the heat exchangers, something I never mentioned before is that I have stinger headers, so the factory ones are long gone. I have lengths of copper line wrapped around the headers and shoved into the carb heater tubes instead. This setup has worked for me for over a decade, including in the dead of winter.
_________________
1972 Volkswagen baja Super Beetle "Elizabeth"
1989 Cadillac Brougham D'elegance

"Never name your car...too much unhealthy emotional connection coupled with your human dark/light,yin/yang energy affects the mechanical health of the vehicle and causes magnetic convergences like the one you just had.that, or some old f**k backed into your car,its hard to tell..." -johnnypan

[Starbucket]

Have you been putting a drop of oil every oil change on the felt pad under the rotor? Give the rotor a twist and see if it springs back, you may not be getting your mechanical advance. Remove the hose from before the fuel pump and blow in it, you will be able to tell if the hard line needs cleaning out if it's hard to blow into and you don't need the other fuel filter if you have one under the tank.

[consvws]

Which type of fuel pump are you using? Have you checked the pressure of the new pump?

Conrad

[Hydro626]