Itinerant Air-Cooled

1967 Beetle

OK, first the scenario:
I start up the beetle and drive to a friends house about 15 minutes away. Runs fine. Cruise at 60 the whole way. Takes the one hill fine. Get to friends. Chat for 5 minutes. Get back in beetle and fire it up. Hit the road, friend wants to drive for a few, the bug is clearly getting unhappy. Slight loss of power. Slight stutter/buck. This gets worse over the course of the 5 minute test drive. Drop friend off and start for home. The bug is running like crap. Hard to get it up to speed to shift. If I push it there is a slight backfire. I can cruise in third as long as I do not give it too much gas or hit a hill. Hit a hill, barely make it up. Have to downshift to 2nd. Stuttering and slightly bucking. Barely make it home.

Back story: I have had this car since last year and have not really driven it. Prior to the summer the bug was running fine. I took the engine out to fix an oil cooler gasket leak. Cleaned everything up, reassembled, tuned on an engine stand, all good. Put it back in and the above issue manifests.

This weekend: Check fuel filter, it's clean. Pull carb. Shoot it with air, squirt it with carb cleaner, inspect the choke, shoot with more compressed air, put on new gasket, reassemble, start car, drive, same damn problem.

Have checked: cut-off solenoid, choke element, fuel filter.

Any assistance would be appreciated.

I like troubleshooting in the fuel/spark/compression breakdown. And if the car runs fine sometimes, we can eliminate compression FOR NOW...

Of course, these tests only work assuming you have a basic tune-up done on the engine- valves, dwell, timing, and idle mixture.

Fuel:
-in the filter doesn't tell you much, other than rust/crap in the gas showing.
-Disconnect the choke wire and run it for a day. That will run the mixture filthy rich once the engine is warm, but it will eliminate the issue if you have a lean (lack of fuel) stumbling.
-When it gets in the stumbling groove, pull the vacuum caps off the carb(s) and see if the problems go away. This will run the engine blast-furnace lean, but it it drives better, it tells you that too much fuel is getting into the engine. Don't drive hard or for very long like this! Lean conditions exacerbate heat and melting valves. Just test and recap.

Neither of those work? Try checking spark!

Spark:
-Run a strobe timing light on the engine when it's running well. Check each cylinder for firing, then memorize what your strobe looks like when clamped on the center distributor/coil wire. Get the engine into stumble-mode, and check each wire again, and then check the center wire. If the strobe is flashing less, you definitely have a spark issue. NOW: your car may pass this test, but you still might have other issues, like a fuel-fouled spark plug or a cracked wire shorting your spark to ground. They make inline spark plug testers if you really like to test things. You can also carefully remove one plug wire at a time at idle to see if any cylinders aren't participating.
-Have you read your plugs recently? I thought I had a spark issue last week when cyl. 3 on a friend's car wasn't firing, but it turned out to be a leaking needle valve soaking the spark plug in gasoline.

I doubt your engine has good-enough compression cold and then a tremendous leak as it warms up, but I won't blame anything until proven innocent. Just like some current justice systems...

Robbie

Robbie gave some good suggestions-

I'd also investigate your coil, condenser and fuel pump. Your symptoms could be more than just one issue. If it was running fine for a while and then started falling on itself when it got hot, it sounds like fuel starvation or an electrical issue (coil/condenser).

Drop a spare distributor in there if you have one, easy to swap out. One variable to rule out, only so many left.

hambone wrote:Drop a spare distributor in there if you have one, easy to swap out. One variable to rule out, only so many left.

Stop people. We are Samba-izing. Don't do any parts replacing/swapping until you have reported back the results of the thoroughly street-but-pretty-good Robbie tests . . .
Check that the choke element is warm to the touch and actually open once warm. Check with a warm idling engine.
Colin

It takes less than 5 minutes to replace the distributor. Sounds to me like that could be the problem. Science VS getting the damn car to run.

I just like the art of diagnosis- learning it, performing it, teaching it, sucking at it, prevailing at it, you name it.

Robbie

Solved, I think. I started with the coil--after the carb. The test:
I started it last night and let it run for 15 minutes. Then I drove it for about 15 minutes to a local strip mall, mostly in 4th. Then I drove around the parking lot to emulate city driving. Then I shut the car off for 5 minutes. Then I started it up and drove it home. The issue seems to have cleared. Now I can tune it proper. Thanks guys! Definitely valuable info to be remembered for future diagnosis purposes.

jimbear wrote:Solved, I think. I started with the coil--after the carb. The test:
I started it last night and let it run for 15 minutes. Then I drove it for about 15 minutes to a local strip mall, mostly in 4th. Then I drove around the parking lot to emulate city driving. Then I shut the car off for 5 minutes. Then I started it up and drove it home. The issue seems to have cleared. Now I can tune it proper. Thanks guys! Definitely valuable info to be remembered for future diagnosis purposes.

Good news. I had a bug that had similar symptoms when the coil got hot which is why I suggested that. Glad it was an easy fix for ya.