240z Backfiring at idle and any rpm HELP

[Chickenman]

Can't see where the other end of your PCV hose connects to, but it should be connected to the Block breather tube as in the following picture. Is it?

[5 Star Rising]

24 minutes ago, Chickenman said:

Can't see where the other end of your PCV hose connects to, but it should be connected to the Block breather tube as in the following picture. Is it?

Come to think of it I had a few vacuum leaks with the small hoses detached on the top picture. I forgot that I took a picture of this a while ago. I had unplugged the pcv valve hose on purpose on the top pic but the other hoses were just chilling.

 

The bottom pics shows everything plugged and that's when the backfiring started. Well the car still ran like crap with those leaks but didn't back fire haha

[5 Star Rising]

Yes it does..

[5 Star Rising]

On Tuesday, January 17, 2017 at 6:33 AM, siteunseen said:

What do the new plugs look like now, first three compared to the last three?    A new rotor button and cap are cheap and will get that out of the way.

The only large hose I can think of on the balance tube is the brake booster hose towards the rear and then the PCV fitting and hose in the middle.

Good luck, hopefully it's something small. 

 

#1 was white almost, 2 black soot, 3 a little oily, 4 soot, 5 soot, 6 soot

[gundee]

On 1/17/2017 at 1:21 AM, 5 Star Rising said:

I have a timing light, actually 3 ..I can't set the timing properly cause I can't get the car to run stable, the rpms drop due to the back fire constantly. Jumped into a car that I don't know the history of. 

 

 

 

There is the main fast idel screw on top. Use that to crank up the RPMs to check timing.

This timing check is a nothing deal. 

Does sound like an ignition issue. Not sure what though right now.

[gundee]

Running points. If so replace and set gap correctly.

I fixed onejust  like yours and that is all it was.

[siteunseen]

Looking at your picture I think the timing is off, retarded.

The vacuum advance dashpot should be close to 8 o'clock.  If you set the high idle screw like Lumens suggest, turn the distributor clockwise to advance it.

[JSM]

^^^^ siteunseen, I don't think that is actually his car, but a sample photo chickenman posted to show the block breather location for reference.  Good point though and a good check.

I agree you need to check valve lash, but usually backfiring in the exhaust is un-burnt gas indicating a rich condition.  Did you adjust both carbs 1/2 turn in to lean the car out at all?  Continue at 1/2 turn until it stops?  Also does it smell rich? Do you see a black smoke when you try and open it up at all?  Do you have a standalone wideband AFR Gauge to check? I have an older Innovate LM1. 

Edited January 19, 2017 by JSM

[siteunseen]

24 minutes ago, JSM said:

^^^^ siteunseen, I don't think that is actually his car, but a sample photo chickenman posted to show the block breather location for reference. 

Ooops!  Sorry about that, thanks for correcting my mistake. 

[5 Star Rising]

I will need help setting the points and backlash of the valves. Is there a link to this info? Haven't done it before.

 

(I had points in my Chevelle but ripped out that dizzy and put in a HEI.)

[Chickenman]

I kinda ruled out valve lash because his compression figure were all good.

How sharp is the spark? You should get a sharp blue SNAP with a good points ignition and HT lead from coil held about 1/8" to 1/4" from a ground. Weak spark or yellowish spark indicates a problem. One thing that is often over looked is the condenser. A weak condenser can cause sooting of plugs. Ignition will also break down at load and can cause backfiring through carbs.

Since you recently changed plug leads, triple check that you got the firing order right. It's really easy to swap a couple of plug leads. Engine will run, but will be rough and you often get backfiring through carbs. In original post, owner mentioned back firing through carbs. That is unusual and normally points to Valve issue or ignition problem. Since his compression readings are very good and consistent, that rules out a valve lash problem IMHO. Still, it wouldn't hurt to check. But I think this is more of a fine tuning issue.

 

[Zed Head]

I like the points suggestion.  Sounds like the OP really just needs to give it a good tune-up.  That would cover points, condenser, valve lash, timing, etc.