January 19, 20178 yr comment_510595 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? Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510595 Share on other sites More sharing options...
January 19, 20178 yr Author comment_510597 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 Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510597 Share on other sites More sharing options...
January 19, 20178 yr Author comment_510598 Yes it does.. Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510598 Share on other sites More sharing options...
January 19, 20178 yr Author comment_510601 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 Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510601 Share on other sites More sharing options...
January 19, 20178 yr comment_510605 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. Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510605 Share on other sites More sharing options...
January 19, 20178 yr comment_510606 Running points. If so replace and set gap correctly. I fixed onejust like yours and that is all it was. Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510606 Share on other sites More sharing options...
January 19, 20178 yr comment_510610 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. Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510610 Share on other sites More sharing options...
January 19, 20178 yr comment_510623 ^^^^ 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, 20178 yr by JSM Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510623 Share on other sites More sharing options...
January 19, 20178 yr comment_510626 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. Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510626 Share on other sites More sharing options...
January 19, 20178 yr Author comment_510651 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.) Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510651 Share on other sites More sharing options...
January 19, 20178 yr comment_510663 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. Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510663 Share on other sites More sharing options...
January 19, 20178 yr comment_510665 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. Link to comment https://www.classiczcars.com/forums/topic/56886-240z-backfiring-at-idle-and-any-rpm-help/?&page=2#findComment-510665 Share on other sites More sharing options...
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