Backfires when shifting

[MariaAZ]

I FINALLY got my 260Z on the road... what a feeling! I bought a rebuild kit for the round tops from ZTherapy & followed the video on installing the stuff... adjusted the carbs and ran her through emissions just for grins & chuckles. I passed 3 of the 4 tests with flying colors, and with the emissions stuff removed or disabled. The 4th test, HC at idle, is still pretty high but the guy at the testing station said to recheck timing & idle setting. I'm taking the lady to a local mechanic who is well known for his talents at getting Zs to pass emissions; I'm letting an expert take over at this point so I won't waste $$ paying for testing until I get it right.

After the emissions test, I richened up the carbs so she would run better. There's no backfire except for a noticeable pop when shifting gear, especially at higher speeds. I searched the boards but couldn't find reference to this particular issue.

Is this part of the normal backfire at decelleration, or am I running too lean?

[Bambikiller240]

Originally posted by MariaAZ

After the emissions test, I richened up the carbs so she would run better. There's no backfire except for a noticeable pop when shifting gear, especially at higher speeds. I searched the boards but couldn't find reference to this particular issue.

Is this part of the normal backfire at decelleration, or am I running too lean?

That is what the Anti-Backfire valve is meant to minimize/stop. I suspect you removed it with all of the other emissions equipment.

[kyteler]

Does the POP in any way harm or change the cars behaviour?

I have two brothers, 1 has a MkII 2.8 Supra, it pops on decell on occaision, you probably wouldn't notice it with a stock exhaust but he's running extractors then through a 2¼" pipe to a turbo flow exhaust and thus the pop is somewhat amplified.

My other brother has an R32 RB20 Skyline with stock exh. manifold running a 2-3" pipe to a larger type muffler and he can make it pop on gear changes at the right revs and also slightly on decel. I like the pop. Unless it sounds too large or just plain WRONG I wouldn't be too worried about it, see what your specialist emission man says about it.

[beandip]

This backfire is it from the exhaust or from the carbs? If form the carbs , it could vary will be a lean pop . If from the exhaust it could be too rich.:classic: Which I doubt if it was adjusted to pass emissions it wont be rich.

[240ZX]

Just a refresher.............BACKFIRE = out the carbs, AFTERFIRE = out the tailpipe.