Backfire from intake on startup

[Lani Kai]

I have a 1978 280Z in which I have just completed installing a rebuilt L28 engine. I had the hardest time getting it to start after the swap (it would turn over but wouldn't fire) but today, I finally got it to fire. Well, sort of. before it reached idle RPM, it backfired badly out of the intake.

I checked that my firing order is correct, and that the rotor is pointing towards the #1 plug tower at TDC. I tried adjusting timing by rotating the distributor within the movable range, but it backfired at both ends. Suggestions?

EDIT: I just realized I got the "Help me" and "Getting help" sections mixed up. Could an admin kindly move the thread over?

Edited May 18, 2010 by Lani Kai

[Gary in NJ]

You're in the right ballpark by looking at the ignition timing, but I would look at the entire timing chain-of-events; from the cam back to the distributor. If you have a non-starter, you need to confirm that the engine is timed correctly and that the distributor is installed correctly.

[ChrisZ]

Do you run EFI ? does the engine alsoback fire when warmed up ?

[Lani Kai]

Do you run EFI ? does the engine alsoback fire when warmed up ?

Yes, it's EFI. I haven't been able to get it to the point where it warms up yet. Basically, it backfires before I let go of the key to stop cranking.

[ChrisZ]

Sorry, i know absolutly nothing about EFI on these cars.

Chris

[yetterben]

Echo timing events and check plug wires for proper firing order. Timing light is your friend.

15-36-24

[Lani Kai]

Firing order is correct. I was hoping it would be something as simple as that, but it wasn't...

I'm pretty sure the distributor is installed properly. If it were 180 degrees out it wouldn't start or backfire at all, would it?

Is it safe to assume the timing is too advanced? I can't think of how retarded timing could cause intake backfire.

[yetterben]

yeah it would wizz and moan 180 off

[Lani Kai]

Well, I dropped the oil pump and re-aligned the drive spindle. I think it was off by a tooth or two. It doesn't backfire now but it still won't start.

[tlorber]

I recently put a "new" electronic dizzy from a ZX into my 240. I got some backfiring through the carbs and the car was nowhere close to running. There is only one way the dizzy shaft can fit in. However, when a mechanic friend that happened to be passing by saw the dizzy and compared it to the original, he noticed that somehow the internals of the new one were 180* off. Rather than pull the dizzy apart I just rewired the cap so that #6 became #1 and then went 1-5-3-6-2-4. Fired right up. Make sure that what you are assuming is "TDC" is truly that-with valves closed-and not a 1/2 cycle off.

One thing to look for though-after backfiring, some of the rubber caps on the carb intake ports were blown off, which then caused excess air to be sucked into the manifold. I know you have EFI, but just check to make sure that if there are/were any such plugs, that they are still in place.

Edited June 7, 2010 by tlorber