Sputtering once warmed up

[jvaleski]

An unfortunate pattern has emerged. First thing in the morning, I take my 356 out for a 30 minute spin to a cafe. After a 20 minute coffee, I get back into the car, fire it up, and drive back home. About 5 minutes into the drive the car starts to stumble a bit while at constant speed (55mph or so). After around 10 seconds, everything is back to normal. Then, after a minute or so, the stumbling/sputtering starts back up, and calms down after 10 seconds or so. This goes on until I get home (sometimes stalling completely at stop lights when I come down from speed).

It’s as though the car is fine until *after* that first drive, and then, the rest of the day (intermittent short errands) it drives w/ that stumbling/sputtering.

Obviously I’m doing a poor job describing the stumbling/sputtering; let me try harder. When it starts doing this, giving it more gas on the throttle is met with nothing, and in fact it seems to exacerbate it a bit. It’s as though it’s only running on two pistons or something... severely underpowered, and as though there are gaps in firing or something. It sounds sputtery instead of the usual purr.

When it breaks out of those sputtery spells, everything seems (power... sound) fine.

Does anyone have any thoughts on what could be wrong? Thank you in advance.

[RolandD]

Blocked vent for the gas tank?

Roland

[kpf]

Failing condenser?

Actually I had what sounds like the same symptoms. I replaced all of the ignition consumables and still had the issue. It finally went away when I replaced the whole distributor. I’m still not sure what is bad about the old distributor, but I plan to have it professionally restored.
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1971 Super Beetle

[saddlesore1]

[Danwvw]

[janerick3]

I had that exact problem.

It turned out to be rotted bits of fuel line rubber trapped behind the needle valves of both Zenith carbs. Cleaned the crud out; the sputtering went away.
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Thanks,
Jan K.

[jvaleski]

Thank you all for your insight/ideas/thoughts.

I replaced the coil and the condenser, and unfortunately the issue persists.

It’s actually gotten worse as the outside temp has increased over the past couple of days (summer’s here!). Yesterday it completely stalled out... had to let it cool overnight.

So, it definitely seems connected to outside temperature and temp in general. First thing in the morning, it runs great for awhile, and then, downhill from there.

I’m starting to wonder if there’s an issue w/ the fuel pump... if the temp increase is causing trouble there... boiling of fuel?

[Danwvw]

Perhaps check some basic's Like Fuel Pressure and Float levels. When Zeniths get heat soaked a 356 won't start very good even with everything else working but they will eventually start if you don't pump them just hold the throttle open and crank. When was the last time the fuel pump got a new diaphragm?
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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[jvaleski]

How do I check those things?

I don’t know about the diaphragm.

[kpf]

[kpf]

To test fuel pump pressure, you will need a fuel pressure gauge that can measure in the 1-5 psi range, a “T” fitting, and some extra fuel line. Presumably your fuel pressure is sufficient when the engine is cold, so you should test after it sputters out. Maybe someone here can tell us if cranking with the starter is enough to generate fuel pressure. If so, you’ll need a helper to crank while you read the gauge (or vice versa).

To measure the float level, you will need a caliper or small metal ruler. Check your shop manual for the correct procedure, but generally you run the car briefly to make sure the float bowls are full, then remove the tops of the carburetors and measure from the surface of the fuel to the top of the bowl. The manual will provide the proper range.
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1971 Super Beetle

[Starbucket]

Water in the carbs and pull the plugs and see what they look like, Black sooty = float too high, bad plug bad wire bone white = fuel starvation, and tan = everything ok fuel wise.

[Danwvw]

This is me checking it on my 36 horse engine. You will need some kind of extra fitting to maybe hook up to the fuel pump with it disconnected from the carbs. It should idle long enough before it runs out of gas. I think the 36 horse fuel pump may use the same fittings. And the Fuel Pressure gauge is just a cheap one from the auto parts store. Mine had too much fuel pressure.

Link

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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[saddlesore1]

How old is the coil? Is it positioned correctly (terminals down)

What is the running temp of the car when it dies?
Yes as outside temp goes up so does the car. However...
Do you have a fuel filter on the car? A clear one will indicate if gas is making it to the bowls. It could be a vapor lock but not likely. The lines run behing the shroud then alone the intake. Not a tremendose amount of tempurature change.

Another thing you can try is once its hot and dies pull the air cleaner off squirt some gas down the bowl and see if restarts. Squeeze small amount of gas down throttle bodies to see if it still runs. Be shure to have something to snuff out possible fire since these are natorious for that.

[ensys]

I should think a plug reading or two could be illuminating.

The business of air temps makes me think in terms of a rich condition that runs well in cool dense air, but which chokes on thinner hot air.

Just a thought.
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Keep 'em flying...

S.J.Szabo

[jvaleski]

well, this remains an issue. I appreciate everyone's suggestions and thoughts. I haven't been able to check fuel pressure. I'm starting to wonder if the 356 motor (dual zenith carbs) in my '65 beetle body is struggling with the VW fuel lines and fuel take venting/pressure, and somehow as things warm up it's drawing too much/little fuel from the tank. totally guessing here though, I have no actually clue.

things I've adjusted:
- I noticed the gas vent near the gas cap was pinched, so I opened that up; no change.
- I've had the timing tuned; no change.
- I've had the fuel pump rebuilt w/ a new diaphragm/gasket kit; no change.
- I tried a new condenser; no change.
- I've checked the distributer points/gaps (all good there); no change.
- I've tried different octane fuels; no change.
- I've tried wrapping the fuel lines with aluminum foil (I read somewhere else that shielding them from heat might help with potential vapor lock); no change.

in an attempt to trigger any ideas/solutions, and now that I've been living w/ the issue a bit longer, let me describe it again.

when the engine's cold (after a couple of hours of non-use), the car starts great and runs great for 15 minutes or so. at that point while cruising along (3rd or 4th gear) it start to sputter a bit. after a few seconds, it smooths out again. if I keep cruising, it'll happen again in a few minutes, and the cycle continues.

when I downshift on my way to a full stop, the downshifts sound great. once stopped, the engine will generally die (unless I'm able to catch the throttle in time once I can get my foot off the brake pedal) and I can usually crank it back to life with full throttle pumping. from there I can usually move through the gears while it's sputtering.

once I get it parked and switch the engine off, after about five minutes of sitting, it's just dead. it turns over, but never catches. I then have to wait a couple of hours for it to cool down.

I've added some videos of me playing with warm re-starts... you can clearly hear it NOT firing properly. these are basically the sounds it makes when it's struggle at speed too.


Link


Link


Link

[Jon Schmid]

- I've tried wrapping the fuel lines with aluminum foil (I read somewhere else that shielding them from heat might help with potential vapor lock); no change.

Aluminum is a conductor, not an insulator. Don't trust condensers if they are Turkish or Brazilian made. Check your fuel lines and make sure there is not a piece of crud in your fuel tank. Good luck!

[Starbucket]

Take a sparkplug wrench with you and when it starts to sputter pull off to a safe place and pull a plug from each side and see if they are wet I think you may have a float needle that's not shutting off the gas and the carb if overflowing flooding half the motor.

[kpf]

[RolandD]

Our beekeeping work truck is a 1977 grumann with a chevy 350. But this is a Porsche forum???? . It DOES have one Zenith 32NDIX carb on it. Last summer it sounded like your car on hot days. Turns out the fuel was boiling in the fuel pump(Poured water on it and it ran). The fix was an electric fuel pump near the tank.

Crazy Roland