Need help with an intermittent stalling problem

[Don66bus]

I can't trust my bus this spring. Sometime during a run, it will cough and fart and not hold an idle. I pull it over to the side of the road. It will respond to the accelerator pump so I can usually nurse it with higher revs. Eventually it clears itself, then it runs well and idles normally.

It was in a paint shop for the winter and suffered a brief engine fire (put out quickly). As a result, anything wired in the back has been replaced: plug wires, coil, distributor cap, condenser, etc. The carb was pulled and inspected; the idle jet checked. In an effort to resolve the stalling, I have since put in a new fuel pump, fuel filter, and electromagnetic cut-off switch to the carb. It has been fully tuned recently. When I go to the back and look, the clear fuel filter is at least half full (yes, I know the preferred position is under the bus).

So - starts great, idles well, runs fine, cuts out at least once a run. It did not do this in any previous times of the 17 years that I have been driving it.

Where should I go next?

[FarmerBill]

Any parts that were exposed to fire/excessive heat are suspect. If you’re sure about your carb and fuel system being fully functional and you’re getting spark, that leaves your timing. I would swap in a distributor that is known to work and see if that clears it up. What kind of distributor are you running? Heat from a fire could have weakened the springs, fouled up a vacuum can, warped other parts, or turned the grease into tar. Sounds like your advance might be jamming up on you.

[Culito]

I'm wondering if it's flooding / loading up with carbon from running too rich?
Check fuel pump pressure?
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Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug

[Don66bus]

I'm running an SVDA distributor. I had a 009 before. The SVDA improved mileage by about 10% after installation. The SVDA distributor has been taken out twice since the fire; it looks good on the surface. If the vacuum part was damaged and interrupted high RPM running, I would have thought it would at least permit an idle. This doesn't happen. It doesn't seem likely that a lack of consistent vacuum would affect both the high and low ends of the RPM range.

The fuel pump has been replaced and the condition persists. Flooding due to high pressure could cause the engine to choke and sputter but I would expect the transparent fuel filter to be full if flooding was happening. It is usually only partially full.

I can look again at these possibilities. I will have to keep trying until I find the fix. The bus is pretty enough now to be lawn art but I want it to be useful too.

[FarmerBill]

When does the power start to start to cut out on you? Acceleration, deceleration, cruising speed? Intermittent problems are always the toughest to diagnose. I would guess the fire did something to your distributor inside. There are all sorts of somewhat delicate parts in there. Even if your vacuum can is working, the springs and weights inside the distributor body could still be jamming up on you. The distributor body itself could be warped out of round, who knows? Gasoline fires can burn at over 3800F. I would swap in your 009 and see if that makes the issue go away. If it does you can rebuild/replace your SVDA, if not, time to give the carb a closer look.

[Don66bus]

It does not cut out with any particular condition. Yesterday it was acting up on startup. Other times it is in the middle of run. I replaced the coil and will drive it this afternoon to see if that makes a difference.

If not, I will delve into the distributor next, maybe try the 009 replacement.

[kpf]

The new condenser could be flaky. Maybe try another condenser?

Could the wire that powers the coil be shorting or breaking inside the harness from the fire?
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1971 Super Beetle

[Don66bus]

kpf asked "Could the wire that powers the coil be shorting or breaking inside the harness from the fire?"

All the wiring to the back of the bus was replaced from the frame wiring harness access point. The wires in the engine compartment were all too crispy to trust.

[ToolBox]

[Don66bus]

Wouldn't a short cause a fuse to blow before the wire melted?

I took a short run with the new coil and it was purring (but it has fooled me before). When it is not stalling, it is running perfectly with a recent tune-up and all new ignition parts.

I will take it on a longer run tomorrow. If the stalling re-occurs, I have another SVDA distributor ordered and will put it in with a new condenser. If that fails to resolve the stalling, I will try replacing the carb with my spare to see if the trouble lies there.

Thanks for all your suggestions.

[FarmerBill]

Another thought just occurred to me, you mentioned you replaced your electro-magnetic fuel cutoff. Do you have a solid connection between the wire and the connector? A crimp style connector can be less than reliable, could be the wire is a bit loose. I always solder the joint and slip a piece of heat shrink tubing over the connection.

[Don66bus]

Farmer Bill,

Good call but the connections check out OK. When the mechanic rewired, he brought a lead to the + side of the coil onto a three-prong terminus. He then did a jumper from that to the cut-off jet (and another one to the choke heater). It is not stock but it should work as well. I checked with an ohmmeter both ends of the jumper and they were solid.

[Old Paint]

I had a frustrating similar issue. Turns out my cheap new spark plug wires, (Bosch no longer makes silicone wires) were arcing from the top of the distributor to the fuel line. Wouldn't believe it if I didn't see it.
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Greg

1961 Ragtop
1961 Single Cab (Old Paint)

[ToolBox]

[Don66bus]

Well, I didn't take it out this morning as it is pissing rain and cold, which are not great conditions if you have to do analysis on a sick engine by the side of the road.

I appreciated Greg's comment about arcing of cheap plug wires. We had just installed the new, cheap plug wires and the installation was not as sanitary as it could be as far as making sure they were not touching any other wires or the gas line. So I was out at 10:00 last night with a flashlight, twisting and relocating plug wires and the hot leads. If it stops raining, I will give it a try.

Several decades ago, while on a trip across Canada, I had sporadic missing but only while night driving. It turned out to be the plastic/ceramic plug wire ends which needed replacement. They worked sufficiently well during the day but had insufficient juice when the headlights were on. We put new ones in and the bus ran fine. That was on a 6V 1962 bus.

[EverettB]

[Don66bus]

Update: after the coil replacement and re-arrangement of the wiring, the stalling has not occurred again in 40 miles of short trips. I will take it on a longer run soon to prove it one way or another. I'm guessing wire interaction with the new plug cables might have been the culprit, as the stalling had that randomness which is probably not characteristic of a bad coil.

Thanks for all your help.

[Don66bus]

Wrong again.

It had run fine for 100 miles, including some highway driving, so I figured the problem was fixed. Then, today, coming back from a kayak trip, it started stalling all over again. I changed the carb by the side of the road to my back-up carb and it fired up fine ... and then stalled three minutes later on a busy road. After pulling off the road five times in a couple of miles, I called a wrecker for the rest of the ride home. It was too risky in traffic and there were no back roads to use.

So I will probably have to pull the engine, again, and check the gas tank. It seemed like a gas problem today.

[westfaliaftw]

Does the stalling relate to engine temperature at all? A customers beetle was doing something very similar once. It would start to stall and chug and could sometimes be nursed back or sometimes it would just stall, then restart totally fine 10 minutes later. After many tried parts, adjustments and fuel flow checks it was discovered that someone had replaced the original metal fuel line with a copper like and had run it within 3” of the #3 exhaust port. The issue had started after the customer had installed an aftermarket exhaust system and it radiated heat enough to vapour lock that single section of fuel line and stop flow. Only after being driven under moderator load at full operating temp, condition could never be reproduce at idle or after a short drive under light load.
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1974 standard beetle - Africa red
1959 deluxe beetle - l41 black/brick red interior
1956 single cab - dove blue
1961 standard micro bus - mango green/dove grey
1971 campmobile - pastel white

[Don66bus]

No, there is no temperature dependence. I have had it stall in the driveway backing out, in the middle of a short run, at the end of a longer run. Today it was fine on the highway. After being parked for an hour, it started fine and then went into its reluctant routine a block away. It is more or less random.