72 VW with problems starting hot

sparkplugs

#1

My 72 super beetle will not start when she’s hot. When the weather is mild, she runs like a champion, but I live in CA in the central valley, so 6 plus months of the year, I can’t drive anywhere during the day. If I do, out of necessity, she runs great, but once I shut her off, she will not start again for several hours, until she has cooled back down. The engine turns over fine, fuel delivery seems fine, but it won’t catch. Push start also doesn’t work. What’s the deal? Anyone know what might be wrong? I want to fix her, but I don’t know what is wrong!


#2

Likely it is vapor lock. The fuel is getting too hot. Follow the fuel line in the from the carb towards the fuel pump and then towards the tank. You might try pouring a little water on the fuel pump.

I can’t remember when they switched to fuel injection (my 1970 still had a carb. Yours may have a FI and a different pump arrangement. If you can find one, the best investment you ever made would be a copy of “How To Keep You Volkswagen Alive” sub titled “A Step By Step Manual For The Complete Idiot.” by John M. Get one of the later editions that will cover your 72.


#3

You need to probe the positive side of the ignition coil with a test light or VOM while cranking the engine. This era of VW Beetles were prone at times to the electrical part of the ignition switch failing with age.
If power is provided to the coil and you have no spark then you should consider a bad ignition coil or condenser since these were also not exactly a rare problem.


#4

She has a carb, not fuel injection. I have no idea when they switched either. I have the book you mention, but the issue is diagnostic, so far the book hasn’t helped in terms of what may be wrong, just a laundry list of possibilities… Anyways, it pumps fuel fine when this is happening. Dumping a splash of fuel into the carb directly doesn’t help her start either, so this is why I think fuel delivery is not a problem. Does it make sense that she runs well when hot, no hesitation or stuttering etc, right before I shut her off, but then she won’t start? I’m no expert, obviously, but seems vapor lock or like fuel too hot should affect both running and starting, am I thinking about this the wrong way?

I did replace the coil, which reduced the frequency of the problem, but didn’t make it go away. What other components of ignition might respond badly to being hot, but function well when cold? This seems like a promising avenue, because when I did that replacement it did seem to help… What other places should I check?


#5

One culprit might be the high voltage wire between the coil and the distributor. I had this same problem on a 1965 Rambler. When I figured it out, it was a fast, cheap repair. You might just try a new coil wire. One hint was that you said that replacing the coil helped a little. Perhaps this increased the intensity of the spark to jump through a bad coil wire. For me, it has always been the simple things that are hard to figure out.


#6

I will mention the ignition switch again. These fail due to age and heat and are a common problem. Simply probe the positive side of the coil with a test light when the car will not start hot.

Now that we know you replaced the coil, did you replace it with a VW Beetle specific coil? The VW Beetle coils have an internal resistor whereas an ordinary round coil off a whatever does not. This means that the contact points and the previously mentioned condenser won’t last long if you did not use a VW coil.


#7

Take a bottle of icewater with you on your next drive. Get it up to temp, park it and go for a walk or whatever you do in central California to pass a little time (sorry, an easterner here :0). When you get back to the VW, try to start it. If she starts, great. If not . . . squirt icewater on previously selected engine parts. Don’t do this to a really hot motor . . . let it cool a bit, don’t want to crack anything. The base of the carb . . . the fuel line and fuel filter, fuel pump. Now try it. Start? Hope so. My Brother and I used to do blacktop work when we were kids and had an old Ford Dump truck that had hard start problems, and we were too broke to take it to a mechanic, we just improvised. This worked almost every time. It will help you to isolate and or eliminate things in your quest for a good running bug. Good luck! Rocketman)


#8

I have the same problem. I don’t think it’s ignition, it would occur when cold. Maybe flooding? After stopping the engine, somehow fuel gets into the intake manifold, and vaporises, no spark. My ideas: needle valve problem, cut-off solenoid doesnt’t like heat (sticks on or off?), vapor lock (stopped engine gets hotter than when running), deinstalling fuel filter in the engine compartment would help. sorry for my english, i write from Budapest


#9

First thing to do with the air cooled VW is pull the plugs (inspect the plugs) and then do a compression test. All should be over 90psi prefer 110. If all is good with a cold engine do a valve adjustment .006 both intake and exaust. Check the oil level as the fuel pumps like to leak into the crankcase. Remove the aircleaner and make sure the accelerator pump discharge nozzel is present and aimed correctly. It is easy enough to remove the top of the carb to do this then you can check the needle and seat main jet tightness and how much debris is in the carb. Install a new set of points and condensor set the dwell at 50 (.016) and timing (static 4btdc this will have to be set running if you have the dual diaphram distributor. i would just replace the distributor with a Bosch 009 model (no vacuum advance). Make sure the coil is not hooked up backwards(I think it is 1 to dist 15 to hot) car will still run with this backwards but plugs fire backwards. Make sure choke pin has not fallen out oif carb housing and that choke is properly adjusted. Check function and tightness of electromechanical idle jet (as previously mentioned). With engine running check condition of intake boots (with carb spray) in 72 these engines were dual port and these boots could leak. Does the engine pop like the heads are comming loose? I think this would have the updated case but who knows. Cant think of any thig else but make sure that valve adjustment is correct and no missing carb pieces


#10

Ignition wires are a good start- My Beetles all have a battery switch and starter button directly wired in the engine compartment for all those times that things like that go wrong.

The guys before me gave alot of ideas- but let me pick just one- those intake manifold boots. Start with that because that one fits the crime the best (even better than ignition wires.) It sounds like a classic vacuum leak- enginge cold everything shrinks down and there is no leak. Once hot, things expand and start leaking in air. It is not a problem while still running because the engine has plenty of excess vacumm to keep the gas sucking through the intake manifolds. Once turned off, the leak stays until cooled but then starter can not generate enough RPM to suck the gas in.
Whenever Vacuum leak seems likely check those rubber boots (can of starter fluid works great.) However, also check the manifold gaskets on the heads if you can, they can also leak if a bolt is loose, or the head is warped.

As far as vapor lock- funny story I took a Chilton’s book outside with my first car when I was 16 and came back in the house and proudly told my father I had diagnosed the problem with my car- I said it must be “vapor lock.” He said “you must be stupid” and slapped me in the back of the head and told me to go back outside and really find out the problem. After a new fuel pump that day and almost thirty years later, I have yet to see an actual case of vapor lock on any car ever!


#11

I don’t believe vapor lock is the problem at all on this particular car but vapor lock was, and still is depending on the age of the car, a common problem.

Back in the 70s/80s I wrestled with this problem all of the time, and especially with the early/mid 80s Subarus. Vapor lock was such a problem on these cars that a new factory modification kit was issued about every 3 months with the end result being that it often did no good.
Some Subaru owners even dumped their near new Subarus and took a financial hit because of this problem.

With the carbureted Subarus, the carbs have a sight glass on the float bowl and if one looked through that glass about 5 minutes after shutting the car off on a summer day one could see the gasoline boiling in the float bowl.

Vapor lock is also why many vehicles used fiber blocks between the carb and manifold and in some of the older Toyotas they even had a tiny fan (about 3" in diameter) mounted on the intake and which would blow air on the float bowl after the vehicle was shut off.


#12

The 1970’s were fine. The 1971 had increased power but not cooling, so that was a problem. In 1972 they increased the cooling, but they still had some problems. By the time they got that and the EPA requirements sorted out, they had switched to water cooled only in the US.

The point is 1972’s had problems with fuel and cooling. While it may well be vapor lock and that should be checked, there are ignition issues as well.


#13

VW continued with the aircooled engine up untill 1974 then it was fuelinjected. VW did relocate the engine oil cooler some years earlier and this did help with the burning of #3 exaust valve. I think the earliest water cooler (besides the rabbit) was 1977 in the bus.My 1974 comment related to the bugs (they were super bettles by then) Some 1975 super bettles are possible, still aircooled.


#14

I have to respectfully disagree with a few points. All of the old VW Beetles were air cooled through 1979, 1975 was the first year of FI, and the 1977 and later bus was also air cooled (exc. the later Vanagon).

While working for VW back in the 70s/80s I never saw nor heard of a vapor lock problem with the air cools due to the intake and carb riser design which pretty much insulated the carb from the engine heat.
Most overheating problems were usually caused by a worn and/or out of adjustment fan belt. Ignoring the fan belt was just as prevalent as ignoring the recommended 6k mile valve lash inspection.


#15

I stand corrected about what was happening and when it was happening. I do agree the vapor lock line is slim. Do the basics and re-evaluate


#16

I did not mean to hi-jack the thread with my vaporlock story. Anyway -oldschool, gets my vote- back to basics. My spider sense is just screaming out “vacuum leak.” And for VW, “Vacuum Leak” means replace those stupid manifold boots before you do anything else, and then reevaluate your situation.

Timing / Dwell, Valve Gaps, Carb Jets etc… are important for tweaking performance, but to go from start to drive and everything is alright to no start at all , then it fixes itself when you are not looking- check for vacuum problem first, maybe an electrical problem second.


#17

The problem with leaking intake boots is that a problem will exist all of the time. The OP says the car runs great and only has a problem when it’s hot outside. When the weather is mild, no problem.


#18

My experience:

the basics are set. intake boots are changed. i still think it’s flooding problem. someone wrote here about thy boiling fuel in the float bawl: this way can fuel drop into the intake manifold, causing hard-start? i noticed also: when it cathes at starting hot, the engine speeds up slowly at full throttle, but after that everything is ok. I think it means rather too rich than too lean.

I will try opening the engine lid after stopping on hot days, and i deinstalled the fuel filter in the engine case, will check if it helps.


#19

Just a thought is the engine cranking speed slower when the engine is hot. Saw a VW engine sieze on the thrust bearing and it started cranking slow before seizure. Did you verify that the accelerator dump tube is present and functioning? Did you take the top of the carb off and inspect the needle and seat this is not hard to do at all. I have seen the rod that drives the fuel pump wear short but I realise your concern is when hot.Check the routing of the fuel line after it leaves the chassis on the left side of the car,maybe someone used to much fuel line and you have a loop in it,also is the flexible part of the fuel line laying on the heater box? if it is shorten hose and route correctly. An engine that is slow to pick up speed sounds like one that has retarted timing what initial static timing position is being used?


#20

After cranking with a no start, have you smelled the exhaust pipe(s)? Do you smell gas fumes? If so you are probably flooded. Check the operation of the choke. Is it fully open on ‘hot’ restarts? Can you do an ‘unload’ on the choke using the accelerator pedal? Check to see when cold. Try to ‘unload’ the choke when it will not start hot. Also check the float level and the condition of the inlet needle valve.

Also look at the ignition coil. I have seen a bad coil produce low high voltage when warm as well as burn up the points.

Usually if the carburator is set correctly; the fuel pump is producing the correct pressure and volume; and the ignition system has been well tuned, the VW engine will always start.

Just some ideas.