Engine Cranks but won't start when hot ?

[dootch]

Recently my Bug has been a pain to start when at operating temps. Like if I stop to fuel up or something the car just cranks and cranks but doesn't catch or takes along time then starts. So far I rebuilt the carbs,set the timing did plug wire points and cap change aswell as coil and set the reset the valve gap. I was told that the coil might not be getting enough amps as the starter may be robbing it? Any Help would be great!

[dragvw2180]

Or you may be getting vapor locked , fuel turning from liquid to vapor when hot. It will be hard to diagnose until you are able to duplicate it with someone checking for spark while you crank it. If it is a low voltage concern at the coil you can test it by using a jumper wire from the positive at the alternator or generator and jump it to the 1.5 terminal ( positive) on the coil . If it was low amps or low voltage it should start immediately. Mike McCarthy

[FJCamper]

Hi Dootch,

When you've been running your engine long enough for it to get hot, and randomly park somewhere, turn off the engine, and it just cranks and cranks, heat has affected something.

The most obvious (but actually not really common) cause is vapor lock. That means the fuel line has gotten hot enough to form a bubble in it, and prevent fuel from flowing. And, if this were the case, there would be some fuel in the carb float bowl -- enough to start the engine for a few seconds.

But, if you have a dying ignition coil, and it gets hot, it won't work again until it cools off. And of course, one day, it won't work at all.

You're not saying the starter has any trouble turning over, which is a heat-related problem.

An outside rarity is carb icing, which can happen on stock single-carb systems. It can happen summer or winter, but you'd feel other symptoms as the carb throat filled with ice.

FJC

[dragvw2180]

Hi Dootch,

When you've been running your engine long enough for it to get hot, and randomly park somewhere, turn off the engine, and it just cranks and cranks, heat has affected something.

The most obvious (but actually not really common) cause is vapor lock. That means the fuel line has gotten hot enough to form a bubble in it, and prevent fuel from flowing. And, if this were the case, there would be some fuel in the carb float bowl -- enough to start the engine for a few seconds.

But, if you have a dying ignition coil, and it gets hot, it won't work again until it cools off. And of course, one day, it won't work at all.

You're not saying the starter has any trouble turning over, which is a heat-related problem



An outside rarity is carb icing, which can happen on stock single-carb systems. It can happen summer or winter, but you'd feel other symptoms as the carb throat filled with ice.

FJC

He already has replaced the coil, cap , wires and rebuilt the carbs per his post . Mike McCarthy

[Jim Ed]

If he increased the fuel pump output would that help?

[dragvw2180]

I think we need to know if its electrical or fuel problem after he duplicates it . Mike

[FJCamper]

Hi Dootch, DragVW,

Yes, I saw that Dootch had swapped out his coil, and of course what we at a distance can't see is was the replacement coil new, and was the replacement coil in good shape, never run hooked up backwards, etc.

And how hot is the engine when it refuses to restart? Too hot to hold the dipstick?

Is the ignition switch hot?

And, the big possibility is a clogging fuel tank pickup, maybe something floating around in there. A clear fuel filter spliced into the line between the fuel pump and carb would show this quickly. On a no-start, the filter would be empty.

FJC

[Piledriver]

....A clear fuel filter TEMPORARILY spliced into the line between the fuel pump and carb would show this quickly. On a no-start, the filter would be empty.

FJC

Fixed that for you. A clear fuel filter in that location (esp. on a stock carb) is a fire hazard for multiple reasons, but OK for short-term diagnostics.

I run my coil off the battery (or starter power cable, or alternator B+ depending on what's handy) via a relay and fuse. Ignitions really, really like >=12V.

On a lot of cars you will be very lucky to see 8V down the ignition power wire when running.
That is not by design.
(That wire is easy to find, it's the krispy black one, but works fine just turning on a relay)

That setup sidesteps a lot of accumulated age-related braindamage, but it probably is not your immediate issue.
Or perhaps it is...

[landrocket]

Sounds like a vapor lock. Take the deck lid off and drive it around to simulate the problem. It fits perfect, up front in the "trunk". I had to do this until I installed the deck lid standoffs.

[madmike]

To test if its fuel related just pour a little gas down the carbs next time

[aussiebug]

If he increased the fuel pump output would that help?

Jim,

The stock VW fuel pumpscan supply (automatically) about twice the fuel flow neededto keep a 1600 running at full noise. And fuel pressure is controlled by the return spring inside the pump, so it's fixed. It's most unlikely that his problem is caused by the fuel pump.

I don't have any suggestions myself though.

[Jim Ed]

If he increased the fuel pump output would that help?

Jim,

The stock VW fuel pumpscan supply (automatically) about twice the fuel flow neededto keep a 1600 running at full noise. And fuel pressure is controlled by the return spring inside the pump, so it's fixed. It's most unlikely that his problem is caused by the fuel pump.

I don't have any suggestions myself though.

Hi Rob! I am looking for an alternator style fuel pump for my 1600ccc Beetle.. What do you recommend and where can I get one?

[aussiebug]

Hi Rob! I am looking for an alternator style fuel pump for my 1600ccc Beetle.. What do you recommend and where can I get one?

Jim,

You need the squat canted style of pump, so it clears the fatter alternator. It requires a shorter pushrod so don't forget to get one of those as well (about 100mm instead of 108mm long). And these are plumbed the other way around - the inlet from the tank is at the top and the outlet to the carb is at the bottom. These pumps will also work just fine as a replacement on a generator equipped car too.

http://vwparts.aircooled.net/Mechanical ... 7-025g.htm
http://www2.cip1.com/ProductDetails.asp ... -127-025-G
http://www.mamotorworkstv.com/vw/produc ... mp-354507/
http://www.jbugs.com/product/113127025G ... hoses-1971

There are plenty of other suppliers, but that will give you a start.

[volksbugly]

been there done this. It happend to be my fuel pump rod. pull it out and run some emery cloth over it. when the engine get hots the rod expands it holds the fuel pump rod. Another way to test if its fuel, carry a can of starting fluid with you. if it wont start give it a shot of starting fluid, if it starts the you know for sure its a fuel issue.

also I carried 2 1 gallon jugs of water with me, when it got where I couldn't start it I would just poor them over the engine.

What year is your bug? Do you have vents in your decklid? if your car doesn't have decklid vents and your running a 1600cc engine its gonna be vaporlock

[madmike]

Is It me ?? Don't you just luv it when we answer these onetime Noobie posters/Dipsticks and they don't reply