'67 VW Bus Hesitation

For many years my venerable '67 VW Bus has run perfectly. However, after an extended period in the garage, she has developed a hesitation during acceleration, when climbing shallow hills or when hurtling down the freeway at 60Mph. We have already changed the spark plugs and the coil. The hesitation seems to disappear when the engine is still reasonably cool but as soon as she warms up things get choppy. It’s been running on 87 but I’ve been told a higher octane might help. The hesitation is somewhat intermittent though but when it does occur there’s a rapid succession of hesitations in a row. Incidentally, the little red light on the dashboard (alternator/generator light) comes on dimly periodically then fades back out. It never fully lights up, just dim. Related? What should I hit with a hammer first?

You replaced the plugs and coil, but not the points and condensor? Why?

I agree with MG. You stopped at half a tune-up. New points (properly gapped) and a condensor may help. How old are the plug wires on this thing? Bad wiring or poor connections can cause it to miss.

Was the bus stored with fuel stabilizer in the gasoline? If not you may have some varnish build-up in the carburetor. When the engine’s cool the choke is partially closed, and the mixture is enriched. Once the little beastie warms up and the choke opens (it does open, doesn’t it?) you start having problems, right? That makes me think carburetor. I don’t think higher octane gas will help anything.

I’d have the output from the generator or alternator tested, and check all the wiring connections in the charging circuit. If there’s a separate voltage regulator you may want to have that tested, too.

If you don’t already have it find a copy of 'How to keep you VW alive; A step by step manual for the complete idiot. Not only is it a great repair/maintenance manual, but it is a great read.

Great idea Joe. I got mine on ebay. There are several available right now. http://search.ebay.com/search/search.dll?from=R40&_trksid=m37&satitle=how+to+vw+alive&category0=

the generator light comes on because the engine has slowed down. what you have is cloged air passage inside the carb. your excelerator pump
in carb has gone bad from seating . it is not hard to rebuild this small carb. or take it a shop.

I still have my original copy from the early '70s. What a wonderful book! It saw me thought many years with a '71 bus (last of the upright, air-cooled engines). I still enjoy reading that book.

When I drove a bug I used to carry a “pre-tuned” distributor with me. When it acted up, I would just swap the distributors and retime it by ear. It was quicker than messing with the points.

The generator light may be incidental and not related to the hesitation. Check belt tension and battery cable ends first, followed by brush inspection of the generator.

The hesitation could be any one of several things. Check the contact points first and then the plug wire resistors. The resistors are those little plastic things on the end of the plug wires and are prone to failure over time. With a VOM they should check out at around a 1000 Ohms or so.

The problem could also be an accelerator pump problem in the carburetor.
I don’t think this is your problem you might look in the top of the carb and see if the brass discharge nozzle is still in place. They’ve been known to come out and get swallowed by the engine. Also eyeball down the carb throat and make sure the nozzle is pointing directly at the opening side of the throttle plate. Sometimes the nozzle shifts and if it’s not pointed correctly the engine can hesitate like this.
If it’s in place then work the throttle by hand several times. You should see a good steady stream of gas from that nozzle each time you open the throttle.

If not, you have either a faulty acc. pump diaphragm or a sticking check ball in the pump circuit. To access that ball and clean the circuit out you will need to remove the very tiny pin on the side of the carb and dump the ball out.
This ball is referred to as a “Jesus Ball”, because Lord help you if you lose it. It is extremely small. Hope that helps.

Taking a few points of advice I decided to rip out the confounded carburetor and give it a new vacuum diaphragm, accelerator pump, and float valve. Wasn’t quite sure which super tiny pin I was supposed to yoink to get to the jesus ball so I left it alone. Slapped it all back in and I still have a hesitation. My mechanic seemed to think the points were fine but I don’t know about the resistors yet. Gonna check those now. Still hesitating after the new accelerator pump though which I had high hopes for. So maybe the timing is simply off, though I wouldn’t think sitting would throw it off or it could be the resistors. Whack-a-mole comes to mind. Thanks for the help though guys! I’m mechanically uninclined.

Keep going greenmtn . . . you’ll hit it sooner or later. Can only be a few things, and you’re eliminating things one by one. My experience with air-cooled VWs is limited, however the ignition stuff that has been raised seems to be the way I would go. Do you have another distributor available? These guys wear out and slop in the shaft, a worm out advance mechanism, worn-down lobes for the points, etc, etc., need to be eliminated. As always, OK hit on a real possibility with the carb. Here too, I’d have an extra carb laying about to address the problem. One possibility might be fuel filters . . . which can clog and un-clog, causing the problem of hesitation as you describe it. Keep trying . . and be careful in that Bus, not the most safe vehicle on the road. Rocketman

Have you tried operating the throttle by hand while looking down the carb throat as I mentioned? You should see gas squirt instantly each time you move the throttle. If not, you have a problem in the acc. pump circuit.
Here’s the pin I was referring to. Note the third pic down. See the choke housing with the orange tag? Below that is a brass plug. Below that is a rib in the body that runs vertically and that tiny little speck at the bottom is the pin in question.

Also make sure the vacuum advance in the distributor is operative. Remove the dist. cap and suck on the vacuum hose that is attached to it. Hold your tongue on the end of the hose much like you would a soda straw. If the advance does not move it could be frozen up. If vacuum does not hold then the diaphragm in the advance is ruptured.

I checked the accelerator pump squirt and it seems fine. A fair bit of gas shoots out and into the right part of the carb. I also checked the idle jet and that was so clean it looked new. I might pull it apart again tomorrow and check things like the jet in the fuel reservoir.

Do you mean the vacuum hose that goes between the distributor and the carb? The metal one with some funny kinks in it?
When I remove the small pin, I assume the jesus ball will just roll out. Is there anything I need to check inside the carb or am I just checking the condition of the ball?

Yes, the hose between the carb and dist. is the one I’m referring to.
As to the Jesus ball, this may not be a problem. It depends on the definition of fair amount of gas and how quickly it squirts out of the nozzle. It should be instantly and each time the throttle is operated with no delay. If the squirt of gas is instant then the pump circuit should be fine.

The ball will not roll out of the hole that the pin is in. The top of the carburetor must be off, the pin removed, and the ball will then roll out when the carb body is inverted.
The ball will seldom go bad; the problem is that deposits may accumulate in that small port and cause the ball to stick or the passageway will become partially clogged.

As mentioned, check those plug wire resistors also. They should be at about a 1000 Ohms each but when hot the resistance could spike upwards and cause this problem.
Other possibilities could be an ignition switch failing due to heat.

Another possibility, and one that should really be checked in the interest of engine preservation, is valve lash adjustment. If you have valve lash that is a little snug it’s possible that expansion of the metal could be tightening the lash to zero or less when the engine warms up. This is not good since it could cause cylinder head/valve/valve seat damage.
If the valve lash is inspected you should pay VERY careful attention to the exhaust valve clearance. The reason for this is that the exhaust valves can have a real tendency to suffer “valve stem stretch”. When the stem stretches the clearance lessens and if you find exhaust valves are abnormally tight you should be very worried about this.

The reason why is because a stem will only stretch so far and is usually the precursor to the valve head popping off the stem. Needless to say, when this happens the results are going to be catastrophic, especially at highway speeds. This is not unusual for the air-cools and is why valves are always replaced rather than reground during an overhaul.
Lash checks are recommended at every 6k miles and if tight exhaust valves are found then it’s time for cylinder head work, engine overhaul or not.

I just checked the vacuum system and that seems to be fine. I might replace the hoses on each end of the vacuum line just because they’re old and brittle but the diaphragm and distributor do what they’re supposed to. I’m going to fish around for a voltmeter tomorrow and see if I can measure the resistors. I’m supposed to yank them off the spark plug, attach the positive of the voltmeter to the inside and ground the negative right? I assume I have to have the engine running to register anything.

Everything I know about this engine I’ve learned from you guys and various google searches in the last few days. Hell of a learning curve.

No. It would be best to remove the resistors from the plug wires and test them. This is done with a non-running engine.
The resistor threads onto the plug wire so simply unscrew it, set the VOM on the 0-10k scale or whatever, and probe each end of resistor. Simply screw them back on when you’re done.

Replacing the all of those braided fuel lines around the engine is a good idea also since many a VW has burnt to the ground because of those hoses.

If these test fine you might give some consideration to checking the valve lash. I don’t know if you’ve ever performed this procedure or not. It’s not difficult to do but does require some care along with a pair of new valve cover gaskets.

Small victory! I grabbed a dwell/tach and a strobe today and had a go at the timing. Plugged the vacuum hole in the carb then found the TDC notch and made a mark 11.5mm and 45mm to the right of it. Got it to idle around 900 and adjusted the distributor such that the 11.5mm mark was at the engine seam. Then ramped it up to ~3400rpm and rotated the distributor to bring the 45mm mark onto the seam. Clamped the distributor down, reconnected the hoses and took her for a spin. GOBS of power!! (I know, it’s relative but it was heaps more than I had). Ran great so I took it down to my local super friendly mechanic who has had busses forever and works on lots of them around here. I wanted to make sure I hadn’t done anything that would result in my bus becoming a fireball while hurtling down the freeway. Looked ok to him except he thought my advance was WAY too early. He did a static test, without the strobe, but it makes me wonder. Did I misread something in the directions when I set the advance marks??

New problem has arisen after adjusting the timing. I set the maximum advance to 45mm BTDC at 3400 RPM. That meant that the idle advance dropped to about 1/2" ATDC!