78 Fuel Injection Bug Timing

[jnespor57]

Trying to tune up my'78 fuel injected super beetle. Will adjust valves and set dwell to 44-50. I will be sure RPM ~ 800. Then I will do timing with strobe light at 5 ATDC.

I have never done the advance thing. How does one do that, or is it necessary if I am right on at 5 ATDC? Thanks!

[busdaddy]

Best to do the advance thing, that -5* really only works on brand new cars, after 44 years springs and diaphragms don't work exactly like new.

Find the TDC dimple on your pulley, then mark 32* BTDC (to the right of the dimple) using a degree wheel (printable versions in the gallery). Or set the knob on your light to 32 if it has one.
Disconnect all the hoses from the distributor (plug the green one if it has one) and watch the timing mark as you rev the engine, it'll keep moving to the left as the revs increase, but sooner or later when things are getting really loud it'll stop moving even though the RPM is still climbing, at that point it should stop on the mark you made (or at the dimple if the light has a dial). If it comes up short or over loosen the distributor and move it a little and repeat, if it's worse move it the other way, when it always stops on the mark tighten the clamp and reconnect the hoses.
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[jnespor57]

Thanks Busdaddy!

Unhook the vac hoses, even though my reference books say to leave them on when timing??

Thanks again

[busdaddy]

For the max advance method you take them off, you are setting the mechanical advance as a fixed baseline, the vacuum advance can add many more degrees to the top number, but only under load conditions you can't simulate in the driveway. The factory method of -5* is with the hose on at idle, once you've done the hose off revved up procedure and tightened everything back up shoot the light at the pulley (knob set to 0) just for kicks, it may be really close, or way off.
But since you don't drive around at idle all day the safest method is to set it at speed where the damage can happen if it's got something wrong with it. Like I said, 44 year old stuff.......
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[ashman40]

I will add to the above...

The 5ATDC idle timing which is the stock distributor spec is dependent on two things:

1) The static or initial ignition timing at idle is around 3-7BTDC
2) Your distributor's vacuum retard is removing 8-12deg of ignition timing at idle.

7BTDC - 12deg = 5ATDC

If you assume your vacuum retard is working but it is actually failed, you will end up adjusting the initial timing from 7BTDC back to 5ATDC as an initial timing. That will mean vacuum advance and mechanical advance will start from 5ATDC instead of the 7BTDC it should. Your engine will run like "crap".

So you want to test your vacuum retard. After 30+ years many have failed.
Set your idle ignition timing like the spec says to 5ATDC at idle with all the vacuum hoses connected normally. While you watch the timing marks under the strobe... disconnect the vacuum retard hose from the distributor vacuum canister. This will disable the vacuum retard and you should see the ignition timing jump from 5ATDC to around 3-7BTDC. This confirms your distributor vacuum retard is working and removing 8-12deg of timing at idle.
If there is no change or the change is much smaller than 8-12deg, your vacuum retard is bad or leaking. At which point you are probably better off disconnecting the vacuum retard system (plug the vacuum port) and run your distributor as an SVDA (mechanical + vacuum advance) with your idle timing set around 7BTDC.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}