1968 Beetle engine refuses to start

[chatdgouttiere]

1968 1500cc beetle engine.
Engine will not start.
Battery is energetic and the starter make the crankshaft turn and sounds healthy.
Solex H30/31 was taken apart, checked and cleaned up.
Coil was replaced as the primary circuit was burned out.
Spark plugs were replaced and gapped.
Fuel pressure is slighly high but steady.
Fuel filter was replaced.
Obviously, timing can't be checked, but static timing reveals a slight advance of 7 degrees.

So... I try starting the engine with different settings for the "volume control screw", and I hardly get to hear any explosions. Also, interestingly, after cleaning the spark plugs and trying to start the engine 5 to 10 times, the spark plugs are black like they've been through a coal mine, and the ones in cylinders 1 and 2 are also slightly humid. I understand this means the mix is too rich (right?) but I get the same results no matter what I set the volume control screw at, even as far as 5 full turns out.

Just as a little background history: the engine was running last summer until one day it died on me. I've been working on it on my spare time since then doing the above listed work.

Any suggestions would be greatly appreciated.

I have the Bentley shop manual, and some basic mechanic knowledge, but I'm out of ideas on what to look at next to move forward with this issue.

Thanks!
Dan

[jsturtlebuggy]

First thing I would do is a compression check to see if all cylinder are working.
The second thing I would do is if compression is low is to check valve clearance.
If you have correct valve clearance and low compression on any cylinder I would then do a Leak Down Test.
You are putting compressed air through the spark plug hole and seeing where any air would be leaking out. This could be air leaking by the valves, rings, or between cylinder head and cylinder.
Another thing I would check is the muffler to see if something may have made a home there and blocking the air flow.
And since you said engine just stopped a while ago, when it stopped running did it smell like it may have gotten overheated?

[chatdgouttiere]

I remember clearly that when it died on me there was no overheating smell.

The compression was checked by a mechanic as part of a pre-purchase check, less than 500 miles before it died, and all cylinders were fine, with one being slightly lower than the other 3. But I'll get myself a kit and will definitely look in that direction. You never know with an engine almost as old as me!

I didn't think about covering the muffler ends for the winter (which I always do for my motorbike), so yes, there could be a nest in there...

And I've never checked the valve clearance since I bought that buggy, so I'll do that, as well as a Leak Down Test (new-to-me type of test and sounds like basic troubleshooting in a situation like mine).

Thanks Joseph for those tips! Much appreciated!
Dan

[lastmanx]

valve clearance would be my first fix. next check points and condenser. I once had wrong condenser that had too short wire that rubbed dist. shaft till it broke, car died. also condenser needs to be grounded at dist. forgot to do it once car no start. points in dist. can fail anytime, I always carry spare, but if not set correct car won't start. you have now screwed up the carb. setting. set it 4 turns out and follow tune directions from there. the muir idiot manual gives many suggestions in this area. think your issue is whatever caused the initial stoppage. as a default setting 5 degrees before top dead center always works for static timing. but I have never found a buggy project that ever had its valves adjusted since the factory setting. good luck.

[jsturtlebuggy]

You have not done anything wrong with trying to adjust the carb. Don't let anyone make you feel dumb with what you have done. Trying different things is one way to learn.
I will ask if you have checked the spark plug wires and the rotor in the distributor. The stock spark plug wires use a 1K ohm resistor ends and copper wire in the actual wires. The rotor for most of the Bosch distributor is 5K ohms of resistant. They can go bad. All the other things you have checked are fine for trying to solve the problem.
What I was trying to tell you is you first have to know you have a good engine to start with. By doing a compression check, you should have about 110-125psi in each cylinder. 90psi is the lowest reading that VW recommends before you need to do work internally on the engine.
If you have low compression the leak down test will show you where it is going.

I speak from experience, I started working in VW shops when I was 13yrs old in the 1970s and helped out my Dad before that on the VWs we owned.
1970 was when we built or first fiberglass dune buggy, still have.
Have fun with you buggy and enjoy life, there nothing else like driving a buggy.

[lastmanx]

forgot to say make sure the idle cut off valve is working. they are electric, and can fail anytime. I carry spare, but has happened to me. wen bad it won't let engine run.