so my buddy has spark to the distributor cap. Verified with a spark tester. No spark past that. We have replaced the cantankerous “crab” distributor cap and the rotor with new OEM Volvo penta parts. We still aren’t getting anything beyond the center point on the cap.

is it possible the crank sensor has failed and is firing “in between” points on the distributor?

this is. 5.7L gx (carbed motor).

As a side note, he replaced the speedometer about the time this issue arose, but I don’t see that having any bearing since there is spark at the distributor. I’m baffled - could the rotor not be the right “size”?

1st: Take off cap. Leave rotor on. Crank engine and see if rotor turns.

Yes - tried that yesterday. It’s spinning.

What kind spark tester are you using ?

Well, speedo’s are typically mounted next to the tachs. If he hooked speedo ground or + to S (sender) terminal of tach by mistake, that cause no run.

one of the light up kind. Where you plug in inline.

wouldn’t the Speedo/tach you mention cause no spark at all? It’s odd that I have it to the center of the distributor……

You have no spark EVER on the inline testers? My first thought was it’s out 180 on the distributor…now I’m wondering if the rotor is right size or if points are worn, corroded.

you could be grounding out somewhere as SB mentioned. Might be worth the time to eliminate that possibility no matter how unlikely. After you make sure you aren’t robbing it somewhere conventional wisdom would say replace distributor. You could also test your wires for continuity and resistance but odds of 8 wires going out at once would seem practically impossible (corrosion?).

Rereading op’s posts, What also sounds weird to me is having the hvs crab/flat cap style distributor and a crank sensor with a carburetor. I’m thinking some terms or parts are being confused about ?

Here is the pic of the hvs dist (crab cap style.)
This what you have OP ? If so, sure not tbi (throttle body injection) and not carb ?

you need to cut an old cap open to get rotor phasing correct rotating the dist does not change the timing but changes when the rotor and contacts line up

on the hvs you use tdc and a mark in distributor. No ?