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Sun Oct 19, 2025 8:51 pm

Went on an 80 mile cruise yesterday, to enjoy the fall colors. The fun was cut short when after driving about 30 miles I made a pit stop, after which the engine would start but cut off immediately. The more I tried to start the worse it got, and at a point wouldn't start at all. It's as if it wasn't getting fuel.

After a few minutes of letting it rest, I tried again multiple times, hitting the gas pedal as well, and nothing. When I realized it's tow time and I have nothing to lose, I tried again, this time more aggressively on the starter - meaning let it turn over longer than you would feel comfortable with... but hey, it fired up and I was able to keep the rpm high for like half a minute, before attempting to drive off. And voila, it ran perfectly! There was no sign of fuel starvation or any fuel related issue once it ran. It idled perfectly at traffic lights and behaved normally. I drove all the way home (didn't shut the engine off until in my garage lol). Trying to start again once home and got the same problem.

So my initial suspicion is the fuel pump. But wait - isn't there a bunch of fuel in the bowl of the carburetor to at least start the engine even if the fuel pump isn't working?

Today I took out the fuel pump and tore it down to inspect. It is perfect and clean with nothing to report (it's a Pierburg original rebuilt less than 1300 miles ago).

The carb is a Solex 28 PICT-1 I got a month ago from Volksbits and only put 50 flawless miles on it. If you've seen his work you'd know it's practically new.

Ideas and insight would be greatly appreciated.

Sun Oct 19, 2025 10:50 pm

Coil? Condenser? Be prepared to check for spark the next time it fails. If you have it, be prepared to give it a shot of starting fluid. If it starts on that, you may have a fuel issue.

Sun Oct 19, 2025 11:03 pm

I can rule out the condenser, because a few weeks ago I played around with some condensers and at one point put in a bad one and the engine wouldn't fire up at all. Then put in a good one and it fired up immediately. That taught me that a bad condenser will prevent the engine from starting at all.

With the problem I'm having now the engine actually starts for a second or two and then dies like it's out of fuel.

As for coil, wouldn't a bad cause the engine to also run poorly once started?

Mon Oct 20, 2025 2:21 am

Bad condenser can also start a car but fail after that. I had a new one that did that.

But check for air leaks.

Byas

Mon Oct 20, 2025 7:03 am

Coils going bad can be erratic just like condensers. Find an NOS condenser. Their quality is far superior to brand new.

Mon Oct 20, 2025 7:43 am

tasb wrote: Coils going bad can be erratic just like condensers.

Yes to this.
I had similar symptoms once with my car. I drove it 12 mile to the store on a hot day. It ran a little rough. I was in the store 15 minutes and when I came out the engine would not fire. I confirmed the accelerator pump was pumping fuel into the carb throat. It was too light out to get a good read on the color of the spark, but there was "a" spark. I called a tow truck that was going to take an hour to get there. I waited about half an hour, tried the starter, and it fired right up. When I got home, I was having the same symptom. Put a new coil on it and never had the problem again.

Mon Oct 20, 2025 1:59 pm

A bad condenser can act like a fuel issue as well.

Mon Oct 20, 2025 3:52 pm

Next time it dies or fails to start quickly, stop cranking. Walk around to the engine and remove the top of the carb. Look down into the fuel bowl. Is the fuel level at the correct height? Is the bowl mostly empty?

I wonder if you have replaced the fuel pump spacer/stand recently? A common problem is the engine case expands when heated and constricts the snout of the pump stand restricting movement of the fuel pump pushrod. The pump stops pumping fuel. With the engine cool, the pump removed and the push rod pulled out, does the stand have some wiggle room in the case opening? If it seems like a snug or restricted fit... take some sandpaper and reduce the OD of the portion that goes into the case. Make sure there is some wiggle room around the snout so when the case expands it cannot squeeze the snout, restricting the push rod.

Mon Oct 20, 2025 8:52 pm

Could be vapor lock, the symptoms are the same. Are your flexible fuel lines in the engine compartment insulated from heat? Do the gas stations in your area change from Summer to Winter blend around now? Original engine or bigger displacement replacement without deck lid louvers added? Pure gas or ethanol blend? All engine tins and seals present and in good shape? These factors can increase the likelihood of vapor lock.

Mon Oct 20, 2025 9:38 pm

Quote: A common problem is the engine case expands when heated and constricts the snout of the pump stand restricting movement of the fuel pump pushrod.

A correction - when metal gets hot, the hole should expand, not contract.

Wed Oct 22, 2025 2:55 am

bnam wrote: Quote: A common problem is the engine case expands when heated and constricts the snout of the pump stand restricting movement of the fuel pump pushrod.

A correction - when metal gets hot, the hole should expand, not contract.

The spacer is made of plastic or bakelite

Wed Oct 22, 2025 9:35 am

Yes. Does the Bakelite expand more than Mg-Al with temp?

Edit: I looked it up. mg Alloy coefficient of expansion is 26 (x10^-6 m/(m-degC)). Bakelite was listed as 22 but another source said it could be 80-100. So it is possible that some bakelites expand faster than the case causing them to tighten on the push rod. The range of the coefficient of expansion seems to vary a lot and it is possible that some versions we get have a higher coefficient than stock.

Wed Oct 22, 2025 10:17 am

bnam wrote: Yes. Does the Bakelite expand more than Mg-Al with temp?

Edit: I looked it up. mg Alloy coefficient of expansion is 26 (x10^-6 m/(m-degC)). Bakelite was listed as 22 but another source said it could be 80-100. So it is possible that some bakelites expand faster than the case causing them to tighten on the push rod. The range of the coefficient of expansion seems to vary a lot and it is possible that some versions we get have a higher coefficient than stock.
Quite a few folks have reported their fuel pump stand grabbed the steel pushrod when engine got hot.

Also the steel fuel pump pushrod o.d expands when hot.

Not one person here on this site will agree that all modern/aftermarket parts are 100% equal to what the original parts were.

Wed Oct 22, 2025 3:22 pm

bnam wrote: A correction - when metal gets hot, the hole should expand, not contract.
So you got me thinking... :?:

If you have a metal washer and you heat it... there is nothing constraining it so it can expand in all directions. Sure the OD of the washer will get larger, but does the ID of the washer get smaller as the metal expands in all directions? What prevents it from expanding inward making the ID smaller?

Now instead, take a large block of metal and drill a hole in the block. It is a solid block of metal except for the hole. Constrain the outer sides so it cannot expand outwards. The only direction not supported is the inside of the hole. As you heat the block would it expand inward to make the ID of the hole smaller because there is nothing contraining it from expanding in that direction? Is this similar to the fuel pump opening in the VW case? Especially if the metal around the pump opening is thinner than the thick body of the case... allowing the metal around the hole to heat faster/sooner than the overall case expansion?

Maybe I'm just overthinking it?? :?

I also agree it could be the plastic base that is expanding inside the hole in the case. A snug fit between pump base and the case, the base expands until it is contrained by the metal case which is expanding at a slower rate. The plastic cannot expand outward so it starts to expand/constrict inward.
Also, the plastic doesn't have to expand so much as warp so the opening thru the plastic is no longer a straight hole and starts to drag on the pushrod.

While you could open up the hole in the case, the easier and non-permanent fix is to reduce the OD of the pump stand to allow room for either the case or the stand to expand into the gap/space. Just don't go overboard and whittle the plastic down so it cracks and breaks off... a common problem with old stands... the snout breaks off as you pull it out from the case and you have to fish the broken piece out. :cry:

Wed Oct 22, 2025 3:38 pm

Wed Oct 22, 2025 3:46 pm

bnam wrote: Yes. Does the Bakelite expand more than Mg-Al with temp?

Edit: I looked it up. mg Alloy coefficient of expansion is 26 (x10^-6 m/(m-degC)). Bakelite was listed as 22 but another source said it could be 80-100. So it is possible that some bakelites expand faster than the case causing them to tighten on the push rod. The range of the coefficient of expansion seems to vary a lot and it is possible that some versions we get have a higher coefficient than stock.

Note the Coefficient of Linear Thermal Expansion is NOT the same as the Coefficient of Volumetric Thermal Expansion so it is careful to not mix measurements. Your 26 I believe is the Linear coefficient.

Linear expresses the change in Length whilst Volumetric expresses change in Volume. Volumetric for Mg is about 3 times more than Linear. It may be more relevant to use the Volumetric coefficient in this case, but it probably makes little difference.

And as bnam has said some newer plastics may have a far greater coefficient of expansion than the original first plastic (i.e. bakelite), so a well meaning but ignorant, part reproducer making a dimensionally identical pushrod stand to the original bakelite stand may in fact be making the problem worse if the new plastic expands more than bakelite.

The phenomenon of the pushrod being "clamped"by heat is indeed real.

However when someone says "A common problem is the engine case expands when heated and constricts the snout of the pump stand restricting movement of the fuel pump pushrod." is not strictly true. I've probably said this too somewhere on the SAMBA as an easy way to explain what happens.

What many people do not understand is that when you heat a "hole" the hole actually increases in size not reduces. That is, when you heat the fuel pump hole in the case it does NOT get smaller and clamp the pushrod bakelite stand, it actually increases in size. That is, you'd expect it to be looser.

The problem is that the diameter of the heated bakelite stand expands much more than the "hole" in the engine case does. This means that the bakelite stand gets much tighter in the "hole".

Now the complication is that "hole" in the bakelite stand (i.e. the internal hole in the stand in which the pushrod slides)also gets larger with heat (or tries to) but the bakelite stand is constrained in its expansion because its outside diameter has jammed against the case, so the expansion has to go somewhere. It results in deformation of the bakelite stand, upwards, downwards, anywhere. This is where the jamming takes place. A reasonable removal of the OUTSIDE of the bakelite stand allows the bakelite to reach its maximum expanded size without jamming against the case. This then allows the internal "hole" in the bakelite stand to expand unrestrained and allows the pushrod to operate freely.

As the temperature reaches the "critical" point, the pushrod jams. The engine stops. Just as quickly as the temperature of the components reach the critical temperature so too when the engine stops and the temperature cools just below the critical temperature, the pushrod is released. This can happen in seconds to a few minutes. The frustrated driver then restarts the engine as if nothing has happened and the car runs fine until again the critical temperature is reached and the process repeats itself ad infinitum. Unless you know of this issue it can be frustrating and difficult to diagnose. Oftentimes people start replacing coils, condensers, pull carbs apart with no relief.

So it is worth making the modification of grinding off the outside diameter of the bakelite stand a little to reduce the possibility of the jamming.

Sorry for the diatribe.

Wed Oct 22, 2025 3:51 pm

My diatribe was being written at the same time as ashman40 was writing.

My arthritic fingers just took a lot more time to write my thesis.

Wed Oct 22, 2025 4:41 pm

Ashman40, here’s a simplified explanation that answers your question: as metal gets heated, the atoms want to move apart more. To expand inwards into the hole they would need to be pushed closer together. So, in an unconstrained state they expand outwards. We heat up the cam drive gear to get it onto the crank because the ID also expands. In a constrained state, as Viiking explains, since all atoms want to spread apart from each other, but because there is not enough space for the outer atoms to expand into, the inner ones are forced inwards.

Wed Oct 22, 2025 8:08 pm

While all this talk about atoms and mathematics is fun, that wouldn't help much when I'm stranded on the side of the road. Actually, maybe I can go over those equations while waiting for the tow truck.

The parts are all original, have been working perfectly for over 2k miles on longer rides in much hotter weather, so the problem is elsewhere. No one has answered my question whether the fuel in the carb bowl is enough to start the engine and keep it running for more than 2 seconds, even is the fuel pump is not pumping.

While my main suspicion was fuel starvation, I tested the pump as soon as I got home by connecting a clear hose to its outlet and cranking the engine - it worked strong. Nevertheless I replaced it with another restored Pierburg and tested - this one pumps strong as well. So then is it the carb? Hard to believe because like I said it's a newly rebuilt unit by a professional. So now I'm changing direction towards the coil as advised by the experienced folks here.

Thu Oct 23, 2025 7:21 am

beetleman217 wrote: I replaced it with another restored Pierburg and tested - this one pumps strong as well. So then is it the carb? Hard to believe because like I said it's a newly rebuilt unit by a professional. So now I'm changing direction towards the coil as advised by the experienced folks here.
Hold on there !!!!

It's EITHER fuel or spark issue, not both. A carb issue (like a stuck float valve) is fuel, a coil issue is spark. Don't just blindly throw parts at this !

Spray some aerosol starting fluid into the air cleaner or carb, try to start, do this a few times. If it runs for a few seconds then quits out, you have a fuel delivery issue, start there. If it won't run at all when you do this, then it's a spark issue, work on that. This is a common first test to help isolate the problem. This is practically an ALWAYS: isolate whether spark or fuel. And remember: just because the engine can crank/spin engine fine, doesn't mean that the electrical part of the ignition switch (the "run" circuit) is OK.