71 Super Beetle running poorly after 20-30 minutes

Asked by Jul 19, 2015 at 08:01 AM about the 1971 Volkswagen Super Beetle

Question type: Maintenance & Repair

I have viewed all the videos and even researched a few more.  I feel like I have gotten pretty well educated on the carb, however my results continue to be poor.  The car does pretty well on a cold start.  It runs a little rough but warms up quickly and the choke seems to be functioning correctly and gradually opens as the car warms.  From most things I have read, it is recommended to set the warm engine idle speed to 800-900RPM.  For some reason, it does not matter how much I open the bypass valve, I can not get the engine to run any faster than 800-820 RPM.  The lower volume screw is set at 2 1/2 turns open and when adjusted does seem to act as I have been told to expect.  After making these adjustments the car will idle very well at about 800 RPM  and performs like a dream for the first 15-20 minutes of driving.  After that when you stop at a light it will idle fine, however the instant that you press the accelerator the engine will shut off.  It is extremely difficult to get it to restart and usually requires holding the accelerator to the floor until it starts and revving the engine several times to get it to idle.  Sometimes that clears it up for a few minutes and sometimes it will idle but then immediately die when you press the accelerator again.  I have not been able to understand why it is working so well one minute and so poorly minutes later.  It is constantly difficult to start the engine anytime the motor is hot and has sat for more than 15 minutes.  If you shut it off hot and restart it immediately it starts fine.  If it sits long enough to walk in the store and back out, it is difficult to get started.  I have rechecked the point gap and it is correct.  I still do not know why regardless of the adjustments it will not idle over 850 RPM.  I followed a procedure I found to check for air leaks in the intake, but I have not been able to detect any leaks. After reading many of the forums I am beginning to wonder if I am having a vapor lock issue in conjunction with something else.  Any help would be greatly appreciated.

3 Answers

19,970

Check air filter and clean carb with a can of spray carb cleaner the whole can replace fuel filter if have not done so in a while. Add a can of carb cleaner to gas tank.

Thanks for advice. One thing I forgot to mention is that carb is brand new as well as filter and fresh oil in oil bath air filter.

19,970

Carb maybe new but carb cleaner just does not clean the carb it also cleans the cylinders and valves of gum and carbon build up that may have been present before installing new carb.

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