Bug dies at altitude
 

My '69 Beetle runs great, starts hot or cold at 900 ft. When I get up towards my place (4765 ft.) it bogs down & the oil light comes on until I downshift to raise the engine rpm. If I stall the engine it will not restart. I tow it home & the next morning it starts immediately. The question is: What would be a good main jet size to put that engine at around 2500 ft.? I'm guessing that I've got to compromise on jet size to make that car work at all altitudes. I set the timing at low altitude & checked it up at altitude & I didn't see a difference.

Vic
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Is it the default engine or an over bored engine?

Setting the ignition timing makes no difference to altitude.

If it cuts out and want start does it have a good spark at the plug leads?

If its an over bored engine which carburettor is fitted?

Is it getting fuel?

2 simple things to check.

Thanks for your suggestions! I checked the timing only because the mechanic at the shop asked me to. The motor is a 1200cc with a Solex H30/31PICT carburetor on it. I don't feel I have a gas supply or spark problem because the only requirement for starting the motor at altitude is that it be cool, indicating to me that the gas/air mixture requirement (choke) is different than for a hot engine. Today I'll pull the main jet, get its number & go from there.

Vic

I replaced the main jet #120 with a #115 and the idle jet #65 with a #55. No help! I towed it home again. It wouldn't pop, even with a shot of ether. I have a really good spark coming out of the coil. Because it wouldn't fire at all with a good shot of ether, I'm thinking along the lines of something electrical getting hot, like the condenser that's mounted outside the distributor. Any thoughts?

Vic

Yesterday I ran the engine & heated the distributor with a heat gun. Nothing happened. I simulated going down the road to get the engine hot with a forced air heater. After 10-15 minutes I noticed that the fuel filter bowl was getting a few bubbles from the pump and the level went down quite a bit. At that point, the engine slowed down. A tester indicated that the spark was good at all times it was running.
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Before it stalled the bowl filled up again & the engine recovered. I blew out the line from the tank to the pump with forced air. The fuel pump is new. Is that pump bad or is an electric pump in order?

Vic

I towed the VW home for the forth time yesterday. After about 10 miles it quit, just as the other times. I immediately had my wife turn over the engine & I noticed that the filter bowl was empty & only bubbles from the pump were showing through the glass. That's after I opened the tank to release any kind of a vacuum. Today I took the line going to the carburetor off & the pump worked fine, filling up the filter glass & shooting gas out the hose. I dismantled the pump (with maybe 50 miles on it) & it looks fine. I had to plug the line coming from the tank after disconnecting it because it was running gas on the shop floor. I'm looking for the next troubleshooting step.

Vic

Was there are vacuum in the fuel tank did it hiss when you took the cap off?

Leave the cap off and drive it around to see if it cuts out.

This isn't an easy question to answer on a forum.

There was no vacuum detected when I removed the gas cap. I will try what you suggested, but it seems to me that after removing the cap & reinstalling it, the pump ought to be able to pump a bit of gas into the filter bowl before the vacuum builds up again. As I said, I immediately watched as only bubbles showed up in the glass after removing the cap and turning over the engine. Only when the engine cools down does gas show up in the filter bowl and the engine starts.

Vic

Which vacuum are you talking about vacuum in the fuel tank which there shouldn't be any or the vacuum from the fuel pump?

There shouldn't be any vacuum in the fuel pump only the intake side which sucks fuel.from the fuel tank.

If the engine cools down and it starts then it is something heat related.

I'm talking about the same vacuum you asked about previously. There is none! I know it's heat related, but what?

Vic