All back together, but won't start

[240ZMan]

I finally got all the pieces for my new exhaust and assembled it all but can't get it to start. What I've done:

- Removed my tired L24 and replaced it with an L28 block bought on ebay with my existing E31 head on it.

- Installed a new MSA 6:1 header and 2 1/2" exhaust

- I did not remove the oil pump so I figured I could just put my old dizzy w/Pertronix back as it had been on the old motor.

- I didn't change any settings on my carbs as they ran pretty well before.

What happens is that during cranking now and then a puff of gas comes out of the carbs. I also hear something from the exhaust, like a muffled backfire? The engine never sounds like it's about to start.

I've moved the timing around within the limits of what the dizzy can move (+/- ~10 degrees) but it doesn't make any difference. I connected the timing light and it flashes when cranking. I checked and when the crank is at TDC the rotor in the dizzy is pointing to the #1 plug wire.

I'm out of ideas without starting to tear things apart. Of course, I'm tired and may be missing something obvious. Thanks in advance for any suggestions.

[LanceM]

Run a quick compression test on a cylinder, sounds like the cam timing is way off. If you have very low or no compression you can figure the valves are either never closing (bad adjustment) or open at all the wrong times.

Lance

[beandip]

You could be 180 degrees out , this may be why you hear firing out of the exhaust. Remember the engine could be at top dead center and not on a compression stroke ! And yes the cam timing could be off but check the timing first . What I do is pull the plugs and turn the engine with a socket on the crank with my finger on the plug hole . You will know when the compression stroke is and then shine a light in the hole or insert a length of copper wire so you can see the movement to TDC. Then start her up. :classic:

[240ZMan]

Thanks guys, that's probably what it is. I didn't check to see the position of the dizzy shaft when I put the head on and set the cam timing. So the ignition would be firing 180 degrees off from what it should be, right?

This is one time when it would be nice if the dizzy WASN"T keyed to go in only one way... :stupid:

[240ZMan]

Just thinking this through a bit further, since I already have the head on the engine, the only way to do this is going to be to drop the oil pump and put the shaft back in 180 degrees rotated, right?

[LanceM]

if you don't care that it matches the manual you can just switch the plug wires 180 degrees.

[240ZMan]

That was it. Rotated the oil pump shaft 180 degrees and it fired up on the first crank.

Now to deal with the exhaust leak from the header...

[zeiss150]

Hey Z man I just wanted you to know that I feel your pain. I am going through the same exact thing with my L 28 right now. but my dizzy shaft is only about 40 degrees out:stupid: that damn thing is so tricky or I'm just realy lame. Once I fixed my timing VRRRRROOOOOOOOMMMMMMM!!!!!!!!

Rock on Z brothers!

Matt-

[beandip]

Zman , A friend , that is also a member , builds Z engines for raceing and with headers he recommends the heavy duty gasket from Motorsport. He says they will last and last and they even have used the same one after removing the headers more than once and reinstalled .

[240ZMan]

Thanks Beandip, turns out I'm using the MSA header and its gasket. But when I first installed it I wishfully hoped that I could "ignore" that the header flange wasn't as thick as the intake manifold. That didn't work. So I went back and ground the washers on one side to level them out. But i think I might have bent at least one stud the first time and so I still have a leak. I'm going to tear it all apart next week and see what I see. I hope I can see some discoloration where it's leaking and make the appropriate fix. Of course, nothing like doing something 3 times. I'm getting pretty good at taking the carbs off!:stupid:

Have to say that it sure revs better and smoother. Can't wait to get rid of that nasty sound that comes from an exhaust leak. That sound just bugs me!