Slight backfire through exhaust with throttle release at higher RPM's, Timing?

[tbeaty4]

I have a 75 280Z which supposedly had significant motor work done, the extent of which I do not know. It has custom 6-2-1 headers and what appeared to be new parts under the valve cover as there was very little to no signs of wear. I took off the valve cover and checked tappet clearance. I timed the car according to the factory spec. but it has a little backfire when the throttle is released especially at higher rpm's. I think it's out of time slightly but I can't remember which direction i should go to try n fix this. Timing? or should I look at other things as well?

[Zedyone_kenobi]

Does it backfire through the carbs or from the exhaust

[tbeaty4]

through the exhaust, its fuel injected

[LeonV]

Sounds like lean-popping on decel, which is not a big deal. You'd have to adjust the mixture in order to get rid of it, and since you said the engine supposedly has extensive work done, we can't help further without more info. Post a video, and at the very least describe your modifications and the popping that you get in more detail.

[tbeaty4]

I'll see what I can do. The guy I got the car from died like two months after I got it which was a couple years ago. I didnt start working on it till just a few weeks ago and I'm having a little trouble tracking down the mechanic who was supposed to have done the work. It also does not go into higher idle when its cold. It starts perfect but wont idle without giving it a little gas and runs rough until the engine warms up. probably has a bad water temp switch or air bypass valve. I'll read through the fuel injection manual some more and see what I can find.

[Pomorza]

tbeaty4,

For what I remember 280z's are supposed to have a fuel cut at high RPMs when the throttle is released. That is, say you're at 4500rpm and release the throttle the injections is supposed to stop injecting fuel. The general principle of this is simple, since you're decelerating your engine doesn't need fuel as there is little if any load. If you are injecting fuel some of it won't burn and thus you get said backfiring.

Hope that helps

Jan