High RPM Miss

79SuperVert · Posted: Sun Jan 01, 2012 9:00 pm Post subject: High RPM Miss

1200 stock 6 volt stale air engine. Tuned, and timed statically. Spark plugs gapped, valves adjusted. Professionally rebuilt original carb and fuel pump, new fuel sock in tank, clean fuel screen. Starts instantly and runs very well at all but high RPM's.

Symptoms at high RPM (above 30 mph in second and 45 in third) are a miss, with accompanying "tweet" at the exhaust pipes. Sometimes it is worse, sometimes it is better. When I turn on both the wipers and the headlights, the miss becomes more pronounced. Since my fuel system and timing appear to be functioning correctly, is this an electrical problem?
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Central Jersey VW Society

Wanted: Art Collins VW (Savannah, Georgia) items - license plate surrounds and other items. Also ivory "AM", "FM" and "SW" buttons for a US Blaupunkt Frankfurt.

KTPhil · Posted: Sun Jan 01, 2012 9:16 pm Post subject:

Check the resistance of your spark plug wires, connectors, cap, and rotor. The connectors get baked over time and sometimes have an open that fails at high rpm.

DWitcher · Posted: Sun Jan 01, 2012 10:18 pm Post subject:

Check your ground wires. Coil might be going bad too.

61SNRF · Posted: Mon Jan 02, 2012 8:31 am Post subject:

This type of miss can be fuel or spark.
But since you describe the fuel system as being sound, the ignition more likely. X2 on the coil or the power supply to it.
A simple swap is the easiest way to rule one out unless you can find an old timer with a coil tester.
_________________
-Bruce

An ounce of prevention is worth a pound of cure.

79SuperVert · Posted: Mon Jan 02, 2012 8:39 am Post subject:

Thanks for the thoughts. I'll look at those things.
_________________
Central Jersey VW Society

Wanted: Art Collins VW (Savannah, Georgia) items - license plate surrounds and other items. Also ivory "AM", "FM" and "SW" buttons for a US Blaupunkt Frankfurt.

66 Bugman · Posted: Mon Jan 02, 2012 5:31 pm Post subject:

What about your choke setting? This happened to me, because my automatic choke was set too rich and wasn't giving the carb enough air... which caused it to stumble at high RPMS.

Just a thought.

-colin
_________________
"All around you people will be tiptoeing through life, just to arrive at death safely. But dear children, do not tiptoe. Run, hop, skip or dance, just don't tiptoe."

79SuperVert · Posted: Mon Jan 02, 2012 8:45 pm Post subject:

I remember reading in the Bentley and on TheSamba about how to set that. So you're saying the choke might not be fully open once it's "warmed up"? Could I confirm that by looking down the carb throat?
_________________
Central Jersey VW Society

Wanted: Art Collins VW (Savannah, Georgia) items - license plate surrounds and other items. Also ivory "AM", "FM" and "SW" buttons for a US Blaupunkt Frankfurt.

66brm · Posted: Mon Jan 02, 2012 9:02 pm Post subject:

66 Bugman · Posted: Tue Jan 03, 2012 6:12 am Post subject:

Yes.

Take off your air cleaner, and you'll see the butterfly valve. With the engine cold, look at the valve and it should be fully closed (engine cold). With the engine fully warmed up, it should be completely vertical, not at all horizontal, as that would restrict airflow into the carburetor.

Here's a good link on how to adjust the automatic choke-- very easy.

http://www.vw-resource.com/choke2.html

-colin
_________________
"All around you people will be tiptoeing through life, just to arrive at death safely. But dear children, do not tiptoe. Run, hop, skip or dance, just don't tiptoe."

79SuperVert · Posted: Sat Jan 07, 2012 12:26 pm Post subject:

Today I checked and cleaned each of the connections on the coil and spark plug wires and made sure they were tight. I found one spark plug wire that wasn't inserted all the way onto the distributor terminal: the rubber shield was too far down on the wire, preventing the connector from being fully pushed onto the terminal.

I took it for a drive and found the hesitation was significantly diminished, although not altogether gone. I checked the choke and it was fully opened. So next week I will swap out the coil for another one I have and see if that alleviates the remaining hesitation.

I also realize I didn't check the spark plug ends of the ignition wires to make sure those connectors are snug. Another thing for next weekend.

Thanks for all the suggestions.
_________________
Central Jersey VW Society

Wanted: Art Collins VW (Savannah, Georgia) items - license plate surrounds and other items. Also ivory "AM", "FM" and "SW" buttons for a US Blaupunkt Frankfurt.

79SuperVert · Posted: Sun Jan 15, 2012 10:29 am Post subject:

I cleaned the insides of the spark plug connectors and now there is virtually no miss. Nice.
_________________
Central Jersey VW Society

Wanted: Art Collins VW (Savannah, Georgia) items - license plate surrounds and other items. Also ivory "AM", "FM" and "SW" buttons for a US Blaupunkt Frankfurt.

79SuperVert · Posted: Sun Feb 05, 2012 4:41 pm Post subject:

And finally, the rest of the miss went away when I replaced my tired battery with a freshly charged one. 6 volt batteries give you plenty of advance warning when they are losing their charge. Failing to start the car is only the last warning. Before that comes steadily slower blinkers, slower starting, and the high rpm miss. From now on I will charge my spare battery once a year so it is ready to take over when the service battery starts giving me these warnings again.
_________________
Central Jersey VW Society

Wanted: Art Collins VW (Savannah, Georgia) items - license plate surrounds and other items. Also ivory "AM", "FM" and "SW" buttons for a US Blaupunkt Frankfurt.


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