The Mighty 258 > The Engine

Cannot tune for anything BUT curb idle

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MIPS:
This weekend was the big event where the Carter 2BBD was stripped down and rebuilt, followed by the timing and all adjustments being reset to spec.
The carb ran perfectly after and drove home last night with minimal adjustment. Today after verifying that the three ignition advance systems were working properly we reset the timing to 15 degrees as per the shop book, then reset the idle. Right now the curb idle is a solid 500rpm and sounds excellent.
The problem comes up when you try to step on the gas at ALL. The engine bogs down, stalls or backfires badly. Vacuum advance reads great at idle, until you step on the gas, then it falls off and then, same as above. No oscillating though, so it's not a really really bad blow-by issue.
Ultimately right now the distributor had to be bumped to 20 degrees before it would both idle and still be driveable but it misses and sounds like crap.

Best I can think of is the CTO is stuck. Basically everything else I can think of testing has been done and either been replaced or tested.

DAVE:
maybe the harmonic balancer has shifted or slipped causing timing to be different than what the timing light reads
I have heard that this is common

MIPS:
That would be miserable. How do you even do it remotely accurately when your reference point is off an unknown amount? Replace the entire pulley?

This morning I checked the CTO and found it configured as seen below but can someone explain what the delay does in the cold position?



The theory of operation is that the EGR remains off when the engine is cold and the distributor runs from manifold vacuum, once the engine warms up however the EGR gets vacuum and the distributor advance switches to ported vacuum. The functional testing in the manual uses port lettering and numbering but depicts switches different from the installed one above, so I don't know how to reliably test it and do not have a replacement immediately available.

Edited: Verifying if the balancer has slipped should be easy though. The manual says that once the engine is warm the CTO switches from manifold to ported vacuum for distributor advance, so get 'er warm, bypass the CTO and go straight to ported and if it still misbehaves then the balancer is bad, right?

MIPS:
Unless someone says otherwise, it might not be a plugged CTO so much as a leaking CTO.
As a test I plugged all but the manifold vacuum port and with a hand pump could not hold it for any reasonable amount of time above 5"hg. Plugging that and testing from the ported connection was no better. It got worse if I tried a stronger vacuum. I ended up driving home with the distributor hooked into the manifold directly and while I lacked power it seemed like it would behave well enough to hold me over until a new CTO arrives.

derf:
I'd just run the vacuum straight to the manifold and skip the CTO altogether.

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