1915 engine stoppage issue

[casadelray]

Hey VW family. I’m about out of Schlitz trying to diagnose our beetle. It’s long, but I think I’ve covered it all. If you have time, I appreciate input.

We have a 1915cc, the engine starts up fine, and runs great..... then after a period of miles, it begins losing power and ultimately dying. By losing power, then engine doesn’t stall out, just not producing power. For example, I’ll be driving 50 MPH, and the speed begins to decay. I can clutch in, and rev the motor and the RPMs respond as expected, but re-engage the clutch and the motor acts like it’s starved for fuel.

First experienced this three days ago, was driving for about 20 miles and the engine did it momentarily, I disengaged the clutch, rev’d through a few times and it didn’t repeat.

Yesterday I was about 30 miles from home, driving at 55 MPH when it started acting up. Again, clutch disengaged and engine RPMs responded as expected when reving the engine, but engaged the clutch and the speed decayed. It got worse and worse until the engine just quit and wouldn’t restart. So I’m thinking something with heat, something got hot....but what?

I’m no VW guru, but what I’ve noticed is that if an air cooled engine gets hot, an audible pre-det pinging can be heard....but that wasn’t happening. Engine seemed to be running just fine, except no power. And of course after sitting off for approximately 45 minutes, the engine fired right up.

Engine has a brand new Petronix ignition system, Flame Thrower Coil and wires. Otherwise nothing unusual.

Thanks for taking the time to read, hope you all have inputs

[Dougy Dee]

Have you recently changed anything like fuel pump or pump isolator?

Can you swap your points set up back in?

[Rome]

Is your 1915 in a '61 thru '67 Beetle? Another possibility is that the fuel tank is not venting. As fuel is consumed by the engine and the fuel level goes down, the air in the tank from its last fill is sealed inside the tank. The air can create enough vacuum in the tank that it prevents fuel from leaving the tank and going back to the engine. Simple test is, that next time this happens, pull safely over to the shoulder or first parking lot. Keep the engine running. Open the tank filler and listen if you hear a "shwoop" of air rushing in. That would indicate the vacuum is being equalized by ambient air pressure.

Your tank should have a breather hose configuration like this (sputnick60 gallery), with the small hose coming off the factory nipple under the filler cap. Pull the hose either off the nipple or up from the body hole, and blow into the hose. If it's blocked, there's your problem.

I had the same symptoms on my '77 soon after I bought it nearly 30 yrs ago. The PO had plugged the vent line even though that vent was integrated in the side-panel filler pipe.