1973.5 CIS Starting Problem Mystery
 

Typically, I start the car by pulling hand throttle to max, turning key to engage fuel pump, when pump whirrs for 2-3 sec, I then turn the key to the start position. It turns over twice and then roars to life.

Lately, and only after doing short trips in town, from time to time it will not start with the usual procedure. Instead, if it does not start on the first try, it will not start at all unless I let it sit overnight. When it will not start, I smell fuel when I stand outside behind the car. In those instances when I am on a downhill or have a friend nearby, I can push start it quite easily - and once it starts running, it runs fine.

Any ideas?

Brad,
Do you have an old burglar alarm installed in the car?

Not that I know of. The PO did not mention one and I see nothing that would indicate one.

Do you still have points? Have you checked them?

Have you gone through the usual tuneup items/procedures?

Points, plugs, cap and rotor all replaced about 6K miles ago and adjusted about 3K miles ago. If nothing else, it won't hurt to check them again.

Have you checked for spark intensity? How old is the battery?

Batteries are old - yet, hold a good charge.

How does one check for spark intensity?

Are you following the below proper starting procedure?

The owners manual for a 1973.5 CIS states that the hand lever should be pulled fully up (so the micro-switch on the throttle body closes and sends power to the cold start valve) for all starts when the engine temperature is less than "very high". Very high is defined as an engine temperature of 212 to 250 F. Unless the engine is running hot and the stop is very brief (so the engine doesn't cool off) this in a practical sense means the lever is pulled up for every start. The manual further states that when the ambient air temperature is below -5F the lever should be fully pulled up and the gas pedal partially depressed; then when the engine starts, the lever is positioned for a 1200 RPM warm up speed. For "nominal cold starts" (air temp above -5F and engine oil temperature below 155F) the lever should be pulled fully up without gas pedal application and then once the engine starts the lever is lowered to set the engine RPM at 1200 for warm up. When the engine is warmed up (~155-160F oil temp) the lever is fully lowered. When starting a warm (as opposed to a "very high" temperature) engine the lever is pulled up for starting and immediately pushed back down after the engine starts. For the very high temperature case (212 to 250 F oil temperature) the hand lever is left down and the gas pedal is fully depressed during starting. It is important to note that the '73.5 and (also the 1974?) CIS cold start valve (CSV) circuits do not incorporate a thermal time switch so the driver has to control this function. Note though that as usual the CSV only operates while the starter is turning, it does nothing for cold running after that time.

If you are using the correct starting procedure and given you smell gas when it doesn't start I would begin to suspect the accumulator may have failed (by leaking). Is there evidence of a gasoline leak in its vicinity? The accumulator is located just upstream of the fuel filter on the shelf on the driver's side of the engine compartment. There is also a possibility the check valve in the fuel pump may have failed. Losing either the accumulator or fuel pump check valve can make hot starts difficult.

Turn off the ignition. Remove a plug wire connector from a plug. Put a good plug into the connector. Get a wire w/ 2 alligator clip ends and attach to the plug threads and a ground in the engine compartment. Set the assembly down and DON"T TOUCH OR HOLD IT EVEN WITH INSULATED PLIERS. Have someone crank the car and see if you get a nice fat, blueish spark. If it is yellow or orangish then it is weak. Could be the coil or the battery.

Thanks for the additional suggestions and pointers. However, I may have solved the mystery. I could not start again, so I removed the air filter. It started right up. This has worked twice. I live on a dusty road and the filter is dirty (although only 6K miles on the filter). Could it be that the engine was just not getting enough oxygen?

I was searching for starting problems and came across your oldish post.

My guess is that your popoff valve was stuck open upon backfire on your airfilter. When you took the cover off, I'll bet you heard a little snap of it popping back. Has happened to me a couple of times. So if this is what happened, it was getting too much air and not starting. Not sure about it starting with a rolling start, though. That doesn't make sense.

I'm assuming, of course, you have a popoff valve in the airbox....Jack

Thanks Jack. This is worth exploring. I have assumed so far I have a vacuum leak and have not had time to dig into that can of worms.

Brad