VW bus owner: 1974 bus with fresh 2.0. Started fine, heading to fill with gas and it sputters a bit and dies. When I turn the key at ignition, slow crank “wah, wah, wah.” and nothing.
Headlight go off when I turn the key. Battery checks out good.
New ground straps.
New positive lead battery to starter. Starter spins on bench. Will not turn over engine.
Engine not locked up. Getting 12v at starter from ignition switch.
Thoughts?
Intelligent Tinkering: 12V is low for a cold day. You need 12.5V for a fully charged battery. Some of these engines also settle into a place where they are harder to start after they have been started once on a cold day, stall out and need to be restarted. Mine is like this if I try to move off before it's warmed up. It was actually a lot worse until I switched from a single progressive to twin carbs. It seems to get a little hydraulic locking on the second start. Charge the battery up good and try again, or clip a 200 amp shop starter/charger on it and amp it up good. It might start.
VW bus owner: tried that. Same
Intelligent Tinkering: OK. Did you just charge the battery or did you also try the 200 amp? Or try a known good battery borrowed from some other vehicle or a jump start from another vehicle? Because a battery can be charged, read 12.5 V, spin a starter on the bench, and still not turn an engine. One or more compromised 2V cells would do it. Battery cell chemistry means it's possible for a cell to short out (apparently) overnight if precipitation between the cathode and anode occurs and finally connects or if that cell boils dry. And it never hurts to repeat a test, just to make sure you are not fooling yourself. It's far more likely to be the battery than anything else. But assuming that you have done a good test: use a process of elimination: If the battery is for sure good, and charged, and you can prove this to yourself positively, I'd start by taking all the battery and starter connections apart and cleaning them with sandpaper and a wire brush, then putting them back together. If that doesn't help, suspect the solenoid. The solenoid connector is the LH 13 mm nut when looking at the starter (in place) from the front. Test by shorting between the solenoid and the starter hot (positive) with a screwdriver you don't care about much. Sparks will fly and parts and the nut and tool will weld themselves together momentarily, but if the solenoid is the (only) problem, the motor will turn. If the key is on it may even start. Make sure the vehicle is chocked and in neutral before you do this, unless on a lift with all four wheels in the air, then just in neutral. If it turns over better, you will need to change the starter. You can buy just a solenoid, or at least this used to be the case, but the coils in the solenoid will most likely be just as old as the ones in the starter motor proper, so the motor is going to go soon anyway. If shorting the solenoid makes no difference, call it good for now, and test the battery to starter cable. Jump the battery positive to the solenoid and starter at the same time with a single jumper cable. It's easy enough to touch it to both nuts at the same time. If it turns better, refresh the starter hot cable, which comes directly from the battery to the RH 13 mm nut. The internal copper strands of any wire can deteriorate over time. It's about four or five feet long and you can use a good quality generic one from the parts store. If jumping makes no difference, or switching out the cable doesn't help, suspect similar deterioration in the starter coils. Either bite the bullet and buy a new one right away or find a known good one from a temporary loaner and try that. If you do the tests well and repeat them, you will be able to identify which of the three possible components it is: battery, cable, or starter/solenoid assembly. It could be two or even three, so it doesn't hurt (that much) to switch them all out. To be honest, unless I was feeling particularly Zen and had lots of time and coffee and it was nice and warm out under my lift, I would just go from switching out the battery to switching out the starter and cables at once, two steps. If I needed to conserve money I'd borrow and sub parts first before buying them. The battery is particularly easy to sub, with the 200 amp, or with a known good loaner. My time doing time-consuming tests that can be shortcut by parts-switching or subbing is worth something, and on an old bus nearly every part that hasn't been could use to be switched. There are guys that go on about the better quality of OEM German parts versus aftermarket new, and there is some truth to this, but you can take it too far and my bus works for a living.
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