non starting 350C

[sawyer]

my 350 started misfiring (sounded like only two cylinders working) and blowing a lot of dark smoke before I managed to park it last fall, where it has sat until early summer.
With the help of a local mechanic, we changed the fuel, checked the tank strainer, bled the system to the IJ pump intake, and then bled the injectors, whilst cranking. Machine tries to fire, but won't pick up. Over the next few weeks, we have changed the fuel filter, replaced the lift pump with a spare, had the IJ pump rebuilt (professionally), had the injectors out and shop tested at the same shop, and checked the air intake system. We have repeatedly checked for air leaks in the lines and fittings. So far, #3cylinder will constantly fire, (warm exhaust port, engine loads down when that IJ line is cracked), and on one memorable day, the engine ran up for 20 secs and then quit. I have had this m/c for 20yrs, and whilst not a mechanic, have always managed to keep it running; so here comes the questions;
How much fuel should I expect at the IJ tops?
Should there be return fuel at the IJ tops boot? (we have lots from the IJ pump, but non from the IJ's, and yes I have blown through the return line to tank)
Locking pin, for timing, didn't seat on it's shoulder when reversed and inserted into flywheel, it did go further than when in a non timing position, but didn't feel positive,(we removed valve cover for TDC and watched pump timing marks), could I have missed something here?
If lift pump #2 has a torn diaphram, would you see air in the glass block filter? I would have thought so, and there is none.
From the great unwashed, I had a suggestion of a blown head gasket; not such a bad idea, but surely the m/c wouldn't have fired in that case?
Sorry for such a long post, but we're running out of ideas, love your site.

[Willyr]

just curious, what happened with a compression test? My thought is maybe (not likely) bad / broken valve cam shaft? A compression check would show this.

The 20 second run clould be explained by the above.

Otherwise has it got a primary fuel lift pump?

Black smoke says too much fuel. yet it sounds as if you have resolved that with all the injector work.

Mind you I am only speculating

[sawyer]

Yes, m/c does have primary lift pump, with priming lever. Your comment about possible comp. loss is very valid; this, I assume, could be 1) broken rings, 2) broken camshaft, although all valves seem to operate, 3)blown head gasket. I don't currently own a diesel comp. gauge, but am heading in that direction. Thanks for your thoughts.

[sawyer]

Chapter 2. after letting the m/c sit for a couple of days, primed, bled, but still not catching, I walked around it one evening, and casually pumped the priming lever on the lift pump, and was astonished to obtain 2-3 pumps, before the lever went "floppy", (neutral), so I am now assuming that there is a air bleed in the pump, or possibly the fuel line from the tank. A new pump is on it's way, so that should definitely solve this.
Many thanks to those who took the time to offer advice, or just perused the post; this is how we all learn. Fingers crossed!