An Odd Problem

[KFH]

I have a very odd/ weird problem with my FC.  Usually it runs fine, however, on a few occasions after pulling up a hill in top gear from my place at about 20 mph and continue along a relatively flat road it starts jerking.  Jerking only occurs when I have just enough power on to maintain speed.  Apply a little more power or take the foot off the accelerator the jerking disappears.  There is no lack of performance when the problem is present.  I can cure the problem by pulling over, stopping the engine and restarting it.  Presto - problem gone and runs fine for the rest of the trip.  Going up the same hill in 2nd gear does not create the problem.  The engine is an all standard 132.

Any thoughts on this problem?  Maybe turning it off and restarting it "resets the computer"!!

Keith

[FCRB26]

mine did similar i reckon its something to do with your vaccum advance plate or a timing issue .?


Pete

[Harv]

Keith,

Why is it that early Holdens are so damn good at "playing up" under the wierdest circumstances?

Is it jerking when you are going up the hill, or on the flat section? Coming over the crest of a hill, the carb will back off the power circuit and return to the main metering circuit.

If its jerking under load, it could be the power circuit in the carb is leaning out. Unlikely though as the power circuit is normally way rich - you would see heavy pinging say pulling a trailer (or five heavy mates) up the hill.

Jerking under "cruise" conditions can be a sign of the main metering jets in the carb being too lean. Unusual that is does it only after going up a hill though - should do it any time you are under cruise, and be worse at high speed cruise.

To see if it is a carb lean-out issue, try cracking open the choke slightly when it is doing it (may need to try different amounts of choke)... if the jerking goes away under choke, it may well be too lean.

Pete may well be right though - changing throttle position and engine load changes the vacuum signal to the vac advance.

Cheers,
Harv.

[ardiesse]

Keith,

Your ignition timing is too advanced.  The best way to fix it is to run the engine off-idle, but not racing (around 1500-2000 rpm, 30-40mph top gear equivalent), and slowly retard the timing until it stops stumbling, and runs smoothly.

One other way to determine that over-advanced timing is the culprit is to disconnect the vacuum advance pipe at the carburettor.  If the engine then runs sweetly as you slowly speed it up from idle to about 2000 rpm, you need to retard the timing.

Now, having said all that, the condition of your centrifugal advance mechanism is really important.  Here's a quick check:  Take the distributor cap off, but leave the rotor on.  Turn the engine over by hand until the points are closed.  Turn the rotor conter-clockwise against the spring tension, then release it.  Then see whether there's any free travel by turning the rotor clockwise.   The distributor cam should return to the stop freely but without any looseness.  Worn centrifugal advance tends to leave the timing too advanced.

Grey motors don't ping when there's too much ignition advance, instead they behave much like you describe.

Rob

[NES304]

Nope, definatley a computer problem 

[KFH]

Thanks all for the replies in particular Rob.  I checked the timing with the timing light and found it advanced to about 6 degrees.  I dropped it back a couple of degrees and the problem has not occurred since but I guess time will tell. The centrifugal advance mechanism was fine as I had overhauled the distributor during rebuild. I hadn't heard any pinging on heavy pulls so was un aware that it was not noticeable on grey motors - interesting.

Keith

[petrolhead]

Also check your fuel pick up pipe it has a gause on the end of it that may be getting blocked