Need Some Serious Timing Help!!!

[ready2hunt]

Workin on my 86' 720 with the z24. I previously replaced the timing set, and everything went well. Recently I decided to put the heads off my parts truck on, as the are almost brand new. Well, the tensioner popped. I decided to pull the motor, to clean everything up, and fix some other stuff.

In the photo, you can see, I have the colored links aligned with the punch marks. I set TDC prior to pulling the motor, and "thought" I was cautious not to move the crank. I fired the truck up today, and I rev's to 3-4 grand, then dies. Moved the oil pump one tooth, would not run for crap. Tried a tooth the other way, no dice. When I pulled the valve cover, my colored link is no longer on the the #2 punch mark on the cam sprocket.... It's off 4 teeth.... The tensioner is still in place, and chain is tight. No clue how it moved.

Even though, when I put the crank at TDC, my dizzy is at #1, and the cam key hole is at 12 o'clock.. What gives, ONLY thing I can think of, is somehow I spun my crank 360 degrees..... Any other idea?

Again, in the photo you can see the colored links are lined up with the punch marks, now they are 4 teeth off... But everything "appears" timed, other than the truck running.

[doctor510]

From the looks of the chain tensioner, the chain looks stretched.
Which hole is used on the cam gear. If it is not #3, it should be.
Forget the colored links, paint make the link on the chain where
the numbered dot is (not the gear) and re-install the cam gear so the #3 hole is used,
be sure to block the tensioner before you remove the gear.

[ready2hunt]

Hi Doc, well the timing chain is only 6 months old, so it shouldn't be stretched...

Are you sure on the #3 position on the cam? Everything I have seen say's #2, as in the photo below. That's how I have it. And the cam lobes are at 5:30 and 6:30 as they should be.....

[ready2hunt]

Just throwing this out there not sure if it would matter. I did cut out my automatic choke harness, as I have a weber with a manual choke... Would that effect anything?

[doctor510]

Moving the cam gear to the #3 hole advances the cam to compensate for the chain stretch, if that is the case. If the motor is not revving like you said, there is a timing issue some where. A 6 month old chain shouldn't stretch, but... My diagnosis came from the picture you showed, the tensioner show too much of its "piston". Maybe the curved chain rail was not positioned at its adjustment limit.

[ready2hunt]

Well, I think we're leaning toward vacuum/air leak somewhere. Beings the engine does fire after several seconds of cranking, and the rev's it'self up to 5k, and stays there. It's run's fairly flat at 5k, with a little backfire out the exhaust... And it will only run with the choke on.

[xsdg]

5k? Is your secondary butterfly not closing or something?

The thing is: extra air won't make the engine rev unless there's fuel to match. On the stock feedback carb, it would detect a lean mixture and add fuel. With a non-feedback carb, though, it cannot add fuel on its own. So either you're leaking air _through the carb ports_, or you have a giant air leak and you cranked the idle air mixture super-rich to match.

(Note: speculation) Part of me thinks that you can rev an engine by advancing timing, but I'm not sure that's actually accurate. I think part of that part of my brain might be trying to invert the logic that you can definitely _drop_ revs on the engine by retarding timing.

Anyway, fact of the matter is that if the engine pops up to 5,000 RPM on its own, something is almost definitely up with your carburetor. Not just a vacuum leak, unless it's a vacuum leak through your carb barrels.

[ready2hunt]

Well, turns out the PVC valve elbow came disconnected from the brass hose, "behind the engine" so I didn't see it. Runs now!!! BUT, I have knock in my top end when I rev it. Will check my valve lash, but wondering if when I was d!ck with my timing, I smashed a valve....

After all this, I'm seriously considering starting from the ground up with the block sitting in my parts truck. Going to talk to an engine rebuilder today to get pricing to dunk and hone my block, and go over the new heads to make sure they are ok.

I'm tired of screwing with the old engine. Would like to start with a fresh slate.