New engine won't run!

[72240Z]

My 72 has an all stock rebuild on the L24. I got it back from the machine shop about 6 months ago, and have been slowly working on getting everything put back together.

At this time it should run, but it keeps spitting and popping back through the carbs. It will crank, fire while doing so and catch for a few seconds, until the rpms start to come up a little bit and then it pops hard enough to blow all the air and fuel out of the carbs and dies.

I have verified the firing order many times over, replaced the plug wires with a new set I had on the shelf, checked and reset the valve clearance. All to no avail. I was thinking I must have a mechanical problem, an intake valve not sealing, so I did a compression test this afternoon and found an even 100 psi across the board. I'm now thinking that the cam timing is retarded, closing the intakes too late, allowing the spark/ignited mixture to come out the intake (caught my fender cover on fire.) Also figure that would allow for the low cranking compression. It was 120 psi before I took it apart. Carbs are the same, untouched since I took it apart.

I've been looking all over the net and I can't find installation instructions for a Cloyes timing chain. I have a Haynes manual published 1974 and a Chilton manual from 1980 I've been using to verify cam timing, but they're clear as mud expecting factory chain and marks.

I'm going to borrow a piston stop and verify the true 0 on the balancer as soon as I can, then degree the cam.

Anybody have more things I may have missed?

Thanks,

Devin

[Zed Head]

Firing order correct but wrong rotation direction? I did it once, the engine ran. Not well though. Correct is set from #1, counterclockwise.

Just a possibility.

[buysell]

Just a SWAG. Where is the static ignition timing at? If it's too much either way it could cause the carb. flame.

-Justin

Edited January 23, 2012 by buysell

[SteveJ]

Have you downloaded a copy of the FSM and looked at it? How about a copy of How to Rebuild Your Nissan & Datsun OHC Engine?

[72240Z]

Firing order is anti-clockwise as per my manual. Static timed at 10 degrees. I don't have the factory engine manual, only the body manual from Nissan. Do not have the other book.

Just spoke to machinist, he reused the stock cam (everything was in really good shape, this engine didn't need to be rebuilt but that's another story) so that eliminates the cam. Anybody have stock cam info to degree it?

Thanks,

devin

[SteveJ]

You can download the FSM. You may also want to get How to Rebuild Your Nissan & Datsun OHC Engine. It never hurts to have the proper references.

[72240Z]

Ok, I'll bite. Where do I go to download the FSM?

Thanks,

Devin

[Zed Head]

Just remembered that engines will do that when a cam's exhaust lobe is destroyed. I've seen it on a couple of small block chevy engines and a Mopar engine. That may not be your problem but maybe you have an exhaust valve not opening completely. Have you checked valve lash?

[Mike]

One time I had an engine rebuilt but the guy put the distributor gear in 180 degrees off. I had the same problem trying to start it. Have you tried swapping the firing order?

[madkaw]

How do you know you have the engine at 10 BTC static if you haven't got it running yet? Have you verified that the rotor is sitting on the #1 plug wire with engine at TDC? Did the machine shop do the final assembly or you?

Is it possible that the valve timing is wrong, have you verified that?

[Diseazd]

Your problem is in the ignition. Like Steve said.........get a copy of How to Rebuild your Datsun/Nissan OHC Engine. When you install the distributor drive/oil pump shaft, pay special attention to the tang position (half moon tang) that hooks up with your distributor. When your engine is on TDC (compression stroke), if installed correctly, the distributor rotor should be pointing to the number 1 wire in the distributor. Then, remember that the rotor turns counter clockwise.......verify firing order. Sounds like one of these items has been overlooked. If you have a new chain and a stock cam, degreeing your cam is not your problem. All of this assuming that you installed the timing chain correctly (of course).

Edited January 23, 2012 by Diseazd

[SteveJ]

Ok, I'll bite. Where do I go to download the FSM?

Thanks,

Devin

The link is in my signature.