Timing mark wandering - 2.25p

[ashhhhh]

Hey all,

Ive been giving my engine a tune and have noticed that the timing mark flicks back and forth with regularity.
It advances a few degrees every few revolutions then settles back to the set position.

I'm pretty sure the idle speed is low enough to be avoiding vac/centrifugal advance.
There is no chain noise or issues that I know of.

What are other possible causes?
Is it a problem?

Thanks,
Ash

[d@rk51d3]

I think it's pretty normal. Check for a sloppy dizzy shaft too.

[Timj]

You should really be setting the timing with the vacuum line disconnected anyway so that should definitely not be an issue. Worn dizzy is quite likely but also check basic things like the contacts on the dizzy cap and the rotor button.

Timj.

[ezyrama]

I think it's pretty normal. Check for a sloppy dizzy shaft too.

Dead right, sounds like a worn dizzy. My moke was terrible for it.

[ashhhhh]

Thanks for that.
Its probably the original dissy so im not surprised it has some wear.

I generally do disconnect the vac line but the tuning placard says to leave it connected on this car?

[Blknight.aus]

you leave it connected and recheck the timing after youve gotten it running smoothly without it... ITs still fair game to pull it of to get the base set and for fault finding.

At dead idle with a closed throttle it should maintain the same advance with or without the vac line connected (dont forget to blank it).

[chazza]

Also caused by the distributor clamp bolt not being tight enough,

Cheers Charlie

[ashhhhh]

What I cant understand is that it is VERY consistent and rhythmic in the way it moves.

It is stable at a point for maybe 4 revolutions (dont know exactly how many). then it flicks to the more advanced point for one or two revs, then flicks back....and so on.

If it were something loose or worn wouldnt it just be wavering all over the place around the set timing point?

[JDNSW]

What I cant understand is that it is VERY consistent and rhythmic in the way it moves.

It is stable at a point for maybe 4 revolutions (dont know exactly how many). then it flicks to the more advanced point for one or two revs, then flicks back....and so on.

If it were something loose or worn wouldnt it just be wavering all over the place around the set timing point?

Not necessarily - these things tend to be rhythmic, for example, the shaft runns leaning against the downhill side until it rubs all the oil off, then the friction moves it, changing the points gap and hence the timing, oil runs in and it moves back to the same spot. Could also be the result of a small amount of hunting due to slightly wrong mixture, and the change in speed changes the position of the shaft - and the change in timing may actually cause the hunting, but the engine speed change takes a few revs due to the flywheel effect.

John