Jumpy Timing

[KarlT]

Hi All

While a friend was checking emission levels the other day he put a timing light on while engine was ticking over.

The little groove in the rear pulley was jumping all over the place........4/5 degrees after dead top to 5/7/9 before dead top.

Does anyone elses do this?

Engine still sounds fairly smooth, always starts first time,

Mark seems to settle & progress as normal when given some revs.

I'm thinking worn dizzy shaft bushes. ( Are these replaceable?) What do you think? Can you buy new dizzys?

Its a DJ engine.

Thanks in advance.

[kevtherev]

at what engine speed does the engine tick over at?

[KarlT]

7/800 rpm

[Grun]

KarlT,

Did you have the two plugs disconnected from the idle stabilizing unit and connected together, and the single connector in front of the idle stabilizing unit also disconnected, (as per Haynes manual) while you were doing the timing check?

If not, I believe the system controls the idling speed by altering the timing as you have described.

Mike

[KarlT]

AAHHHHHHH!!!!

Could it be....................

Is that what happens?

Did wonder cause it still sounds ok.......(above the sound of the water pump that is)

Any other theories?

[Grun]

Any other theories?

About what fr'instance?

Mike

[HarryMann]

Any other theories?

Yes, this is quite normal at idel on almost any motor with a distributor, the idle is not stable, the timing does jump around quite a bit, just take the average position. Dizzie shaft wear will make it worse, but don't expect a good stable strobe adavnce indication till the engine is up at a slightly higher rpm.
By definition, the idle is usually the slowest you can get the engine running smoothly... but the thing isn't breathing particularly well down there either, it might also indicate poor mixture control at idle (worn carn spindle, that sort of thing) or even poor sparks, making the idle speed vary more than you think. Magic things, strobes aren't they?