SIII on ~two cyclinders/no power

[Lawrie]

Alright, assume this is what this board is for = help.
I should be able to figure, but you folks will make quick work of it:

1978 SIII petrol - electronic points, otherwise stock:
Ran fine all summer, in daily use, last week, no power, but starts and runs, evens idles seems as if it is running on two cyl. no smoke, no muttering, just no power, rev's up with lame sputter

->pulled plug wires -one at a time while idling: and engine stumbled on two of them, but did not stall. spark was arcing on all as wire went back to plug

->wires/cap/rotor/plugs look ok - (two plugs good brown tint/two plugs with some gas/oil = I have replaced all above items

->pulled rocker cover - valves clearances/pushrods/rockers/rocker lock nuts in general order (did not adjust) = no closed valves cutting off cyl power

->pulled Zenith carb half open -float alright, needle moving.

sprayed carb cleaner in, no change in running (I have meant to spray petrol in to see if engine speeds up.

this is compounded as i am a diesel guy, and so, i ran toward the igntion as the issue -but i have spark/compression and fuel but maybe not enough.

I am now thinking:
a) carb has a jet clogged (as fuel was run down low, may have introduced dirt, and engine starving, that is why no single plug wire removal stalls engine?
b) can coil give poor spark to allow such dramatic change?
c) i assume a electronic ignition would fail altogether rather than half way.
d) fuel pressure - maybe pump/line semi clogged? - I assume zenith has a required pressure delivery spec. I can check the manual here.


please other ideas?
thanks

[artpeck]

Have you checked the timing? If it somehow slipped way off you could (I think) be getting enough spark to run the engine but very badly. I have old-fashioned points so don't know the implications of electronic ones but I assume you still need to time it. If the tightening nut came loose on the distributor that could explain the sudden change. Check to see if the distributor turns by hand. Just a guess.

Art

[Lawrie]

Thanks Art, yes Dist was loose - (and yes electronic points require timing) - i did an "ear" timing, have not put light on it.

I am now thinking may have blown a head gasket between cyl. -

[artpeck]

Got it. Easy to check the compression and get a yes or no on that.

I know that there are a lot of people who swear by ear (or beer) timing. I have never had much success doing it without a light. Good luck. Curious what you find.

[Broadstone]

I would say head gasket between cylinders. I assume the two you pulled with little difference to how it runs are next to each other and can both be pulled with little change at idle.