Kickback causes

[Ohio Tom]

Are you sure it is "kick back"?

I ask because it could also be:
fuel filling a cylinder after shut down;
In correct starter/flywheel depth;

Do you physically hear it bucking back when you crank?

I had a motor like that once. It was tearing up starters fast, chipping flywheel teeth just like yours.
We found that the initial timing was too much.

However, you sound like you set it properly.

The theory that it doesn't' know where it is for a few revolutions sounds plausible.
Consider re-indexing the encoder wheel??

[Ohio Tom]

Lastly, have you tried cranking w/o ignition on?

Just to see if the starter works?

[theDrew]

and your suuuuuuuuuuuuure the starter is disengaging once its started? Depending on how you wired it, it could keep the starter on even after you let off the crank position.
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Turbo 2276 MS3X build http://www.thesamba.com/vw/forum/viewtopic.php?t=673125
1985 Vanagon Campmobile w/ 2005 EJ25

[mikedjames]

What if your starter is so super powerful cranking, the battery voltage is dropping and causing the EFI / ignition to 'brown out' and restart, and 'open' the points as it resets causing a random fire at first.
Try a larger battery, put an oscilloscope on the power rail to the EFI, check it stays good.

Or fit a smaller starter that takes a bit longer to get up to cranking speed- its going to be the current drawn as the solenoid cuts in and the starter motor is stationary is the worst case.

Some ECUs dont fire the plugs until the engine has definitely completed a rotation or two of cranking.

And are you totally sure the starter does not start spinning until the gears are properly engaged , because the sequence could be..

Starter gear moves in on solenoid.
Solenoid closes contactor to starter just before the gear is engaged.
Starter is stationary so draws maximum current.
ECU browns out, fires coil, causing a random engine movement under internal combustion power, meets starter motor pinion which continues travelling in .

If this is the case you may have to fit a diode and capacitor arrangement to the 12 volt feed to the ECU to stop it browning out.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[challomoner]

No leaky injector so that's hydro lock ruled out.

Thanks for all other suggestions.

Battery voltage stays good while cranking. I can't do any more testing until I replace the flywheel.

If I drop cranking timing down further it may help safeguard against losing another starter before it even starts?

[Ohio Tom]

Yes. Back it way down and start there..

[challomoner]

[Alstrup]

I agree. FWIW when I program ignitions on ACVW´s I always set cranking timing to no more than 8 degrees, mostly 7. (400-450 rpm) then 250ish rpm higher I set the catch line. This way there is usually no kick back unless the system gets EMI from the ignition wires or something like that. A trigger wire too close to a high voltage wire can cause noise which can cause kick back too.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[challomoner]

[mark tucker]

get one of those fancy bore scopes( cheep these days I bought one at wally world for about $20 a few years back...a lizard cam or something like that. have a look in the chambers at the pistons. be sure one isant contacting a head. and rocke the cranks some to be sure a bearing isant going south... and do what somebody else said... spin with no fire. also be sure the degrees are right..many pullys are rong.

[challomoner]

Pulled it today, damn broken teeth near ground the gearbox bellhousing in half

[challomoner]

[challomoner]

I have new flywheel fitted and back up and running. No issues so far, I dropped timing to 5 degrees and rerouted the trigger wheel sensor lead. Thanks for the suggestions.