Why Won't My Engine Start ?

You just finished building an engine or are reviving one that has sat for a while and now it simply will not start.  This article is for you.

Why should an engine that has everything right still refuse to start.
Well, it takes 3 things for an engine to run:
Compression
Air/Fuel mixture
Spark

Here are some hints and tests to perform to find out why it won't start.
Be methodical in troubleshooting.  Don't take anything  for granted!

COMPRESSION:

   
Get out the compression gauge and have someone crank the engine for you. A new engine should read somewhere around 140 psi.  But even an old, tired engine with only 60-80 psi should run.

If you don't have a gauge or just don't think loss of compression is likely, at least do a touchie-feelie test.   Turn the engine over by hand (with the spark plugs still in).   Turn OFF the ignition!   You can turn the generator pulley rather than the crank pulley.   Watch the crank pulley.  You should feel a definite "tight" spot twice each revolution of the crank.  Do the test
a few times to get the feel of it.   You should be able to tell if one or more cylinders have low or no compression.

If you haven't already done it, this may be a good time to check the valve adjustment, just for kicks.

Fuel:  

You have been cranking and cranking away on the engine, so the carb should be full of fuel, right?  But, how do you know  that it really is?
One quickie test is to look down the carb throat with the air cleaner off.

Pull the throttle lever open and watch for fuel to squirt out of the accelerator pump discharge nozzle.   If you get a steady stream, there may at least be something in the carb.  This test isn't foolproof though.  Sometimes the carb bowl is empty but there is enough fuel left in the accelerator pump passages to give a few squirts.

I much prefer to know for sure that the bowl is full.  

Take the top of the carb off (5 screws).  Take care not to damage the gasket or lose tiny parts.   The level of the fuel should be roughly 3/4" below the rim of the bowl.

If this is an engine that has been sitting around or if there is any question about the condition of the gas in the tank, I strongly  recommend draining the fuel in the bowl and manually refilling it with gas you know to be fresh.  It's easy to drain by unscrewing the plug on the left side of the bowl.

Spark:

Spark is the hardest of the items to verify.   You really can't see it happening and it's even harder to tell if the spark is happening at the right  time!

Definitely do a test for spark at the plugs.  Remove one of the plug wires from a plug and hold it near grounded metal.  (If the plug end has a long insulated shroud, you may have to improvise to get ground close enough to the end of the wire.)  Have someone crank the engine while you watch for spark.   If you get an 1/8" or so of spark, that should be enough to fire.  

If you don't have a helper, you can do it this way:
Pull the hi-tension lead out of the distributor cap and hold near ground.
With ignition On, turn the engine pulley CW past the TDC mark.   You should get some kind of spark, although if you turn slowly the spark may be weak.

Check the distributor cap inside for signs of cracks or carbon arc tracks. Also, check to see that the little carbon contact for the center terminal is in place; without that you can have spark but it won't get to any plug wires!

If you have no spark no matter what, go here:      

Start with new, fresh plugs.   Or, at least take them out and check them.
It only takes a couple of non-firing plugs to keep the engine from starting.
Check the gaps (.025") and dry the porcelain off.  Look for signs of residue, like Never-Seez on the electrodes.  Look for oil or fuel-fouled electrodes.

Check the rotation of the plug wires.   The best of us have gotten them mixed up!    This might also be a good time to test whether the distributor drive tang is engaged.  The distributor may look like it is inserted all the way into the case, but sometimes it will fool you.   Take the cap off and try to turn the rotor.  Normally, it will turn a little bit as the mechanical advance turns.  But if you can turn it a quarter turn or fully around, the drive is not engaged and timing will be off.  

What else could possibly go wrong?  You've got the plug wires in the right holes and you know  there is spark but the damn thing still won't start. What else could be wrong?   Well, what we haven't done is determine if the spark is happening at the right time!  

Timing:    Never mind which distributor you have or what the tuning specs for your engine are.  Right now we are only interested in getting the thing to run.   I have found that the engine will start the first time much better if the timing is set to TDC or, even better, retarded just slightly.   Let's do that. Disconnect any vacuum hoses to the distributor and plug them.   If you know how to statically time, do that now and set it to TDC.

As a quick test of the timing, remove the Hi-tension lead from the distributor cap and place it near grounded metal.   With the ignition ON, rotate the pulley CW until you get a spark.  Turn the distributor slightly if needed so the spark occurs at TDC.

I did all the tests and have the spark set at  TDC  and it still  won't start!!
This happens a lot.  Suppose, for example, that the spark is indeed occurring at TDC, BUT is not  occurring when the cylinders are ready to fire!

How can that happen?   Well, we might have put the plug wires in the wrong place.
But I put #1 plug wire in the hole where the notch is in the distributor body!
Yes, and that usually  works.   But, what if...you or the previous owner installed the distributor drive gear a few teeth off where it's supposed to be.   Or...if the distributor has been rebuilt in a way that makes the notch meaningless.  Happens.

What we need is a foolproof test to find out if #1 plug wire is really  in the right hole in the cap.

The Test:

Turn the pulley so that the rotor is pointing at the #1 plug wire.
The pulley should now be at TDC.

NOW, remove the valve cover on the right side.

Check the Intake and Exhaust valves for #1 cylinder.
Both valves should be closed.   (If they are closed, their rocker arms will feel loose and the stems will be all the way out.) When both Intake and Exhaust valves are closed, that cylinder has completed the compression stroke and is in position to fire.

If Intake and Exhaust are NOT closed at this time, there is a problem with the distributor setup and the engine will not run.

If the test shows that Intake and Exhaust on #1 are not  closed, turn the pulley one more complete revolution until it is at TDC again.   Go back and re-check the #1 valves.  Now, they should be closed.

Next, see where the distributor rotor is now pointing.   Move the #1 plug wire to the hole where the rotor is pointing.   Re-arrange all the other wires so that they are in the firing order 4, 3 ,2 clockwise from #1.

I know, I know; #1 plug wire will no longer be next to the "sacred notch".
Forget the notch; it simply doesn't matter.  

Now, try to start the engine.   If nothing else has been overlooked, it should run!

But I thought the TDC mark always meant #1 cylinder firing position.
You're right.......half of the time!    Picture what happens inside a 4-stroke (4-cycle) engine like the VW.   Start at TDC.  As the crank begins to turn, #1 piston goes down, sucking fuel into the cylinder.  The crank pulley has now turned 180 degrees.  As it continues, the piston goes back up, compressing the mixture.   The pulley is now at TDC and #1 is ready to fire.
The explosion forces the piston back down and the pulley turns another 180 degrees.   Finally, the pulley continues for another 180 degrees, forcing the piston back up.  As the piston goes up, exhaust gases are forced out. We are once again at TDC but #1 is getting ready to suck fuel in, not to fire.

So......each cylinder has two times that the piston is at TDC and only one of them is the correct firing position.

Once you get the engine running, go back and set the timing to the correct spec for your distributor.  Note that the timing spec is dependent only on the distributor you have.  If it's not the stock model, the factory specs for the engine tuning do not  apply any longer.   Forget about the timing marks on the pulley too; if the distributor is not stock (or if the pulley has been replaced) the marks won't mean a thing.

One last word about the distributor notch.  If you relocate the distributor more than about a quarter turn from where it normally sits, the distributor shaft may not get oil.  Look at the side of the distributor casting (where it fits in the case); you will see an opening for oil to enter. This must roughly line up with the oiling passage in the engine case or the shaft will be starved for oil.