ol doc gully Posted September 18, 2014 Share Posted September 18, 2014 I've been chasing this for a while but i think its time i get some input. the setup: I have a 72 240Z with a L28 (N42/N47) set up with round top SUs. compression was not great (bumped when tested wet so likely rings), have not retested since i got it running. I bought the car not running, among other things found the dizzy wasnt advancing so replaced it with a remanufactured '1979' 280ZX electronic dizzy - Cardone part number 31-619, just like this one. it was enough to get things going and drivable. carbs were recently rebuilt and came right off a buddy's race car, although one piston is leaking a bit more fluid than it probably should. the basic problem: i originally had the advance set to ~12 BTDC static but it wouldnt rev past 32-3300 rpms, higher gears would barely get to 3000. when it maxes out it has a very raucous sound, but is consistent, it will slowly increase speed until it maxes out. it wasnt pinging at all so i kept bumping advance, seemed to keep helping marginally. Now ive got the plate maxed out and, according to the 3 row crank pulley, static timing is at about 35 degrees - which seems high to me. still not pinging, even on throttle at low rpm. but it still wont rev past around 3500 rpms. potentially related issues: - spark is pretty inconsistent when i put a timing light on it. sometimes it is solid, but often after revving the engine when back at idle the light will indicate plug 1 firing but timing mark is nowhere to be seen, id say this can happen 1 out of every 3 shots. the advance is fairly consistent but once it adds around 10 degrees it seems to scatter and lose consistency completely. - i was having traffic overheating issues for a bit (fan, clutch replaced and shroud added so not as much of an issue now) and when it gets too hot i get definite hesitation on acceleration. i presume to be from vacuum advance which is kind of what i feel like is my problem here. - vacuum advance is connected to the port on the SU carb just outside the throttle plate. solutions: 1. did i buy the wrong distributor? maybe the cap is bunk (new at NAPA)? it is very consistent about when it loses power and something seems to be awry with the ignition system in general so i feel like its a distributor issue. how can or should i troubleshoot it? was goinig to try to get my hands on a vacuum gauge next. 3. the only thing i havent done is check valve lash, which i need to do. is this something that could be causing these type of issues? valve noise is minimal so i feel like its set well (probably never been touched) and id rather try to isolate one variable at a time 4. i currently have the gas tank evap and vacuum (the T fitting by the coil) just open, i dont see why this might be affecting anything but i thought it was worth mention sorry that is long but i figured it was better (less annoying) than not giving enough info. im at a loss and being able to rev to redline is the only thing keeping me from some track/autox before the seasons over - any advice or insight is greatly appreciated Quote Link to comment Share on other sites More sharing options...
zguitar71 Posted September 18, 2014 Share Posted September 18, 2014 You could have the cam sprocket off by one tooth. That will cause the rpm issue you are having. I do not use the vuccum advance on mine I have it pugged off. The static timming is at 15 degrees and all in is 34. Quote Link to comment Share on other sites More sharing options...
ol doc gully Posted September 18, 2014 Author Share Posted September 18, 2014 ahh good call, i have not taken off the timing chain as yet. i had checked the alignment according to the service manual, and it looked spot on, but in all honesty it was hard to make sure i was looking at the right marks relative to whats printed in the manual. i will definitely double check that as well (and/or take a picture and put it here) - thanks! Quote Link to comment Share on other sites More sharing options...
Leon Posted September 18, 2014 Share Posted September 18, 2014 Do a valve adjustment. Quote Link to comment Share on other sites More sharing options...
BlueStag Posted September 20, 2014 Share Posted September 20, 2014 I can only say my very tame 260z with a pair of SUs spins up to 5k but is a bit hectic there. Real power only comes above 3k. Good luck. Quote Link to comment Share on other sites More sharing options...
madkaw Posted September 20, 2014 Share Posted September 20, 2014 Until you narrow down the timing issue, you will chasing your tail. Those numbers aren't even close-why? Does #1 wire line up with the rotor at TDC Compression-should be close. Keep vacuum advance disconnected until you get your number closer-it just confuses the issue. As mentioned-a tooth off? Does the tang line up on the dizzy drive at 11.25 oclock at TDC? Quote Link to comment Share on other sites More sharing options...
ol doc gully Posted September 22, 2014 Author Share Posted September 22, 2014 Until you narrow down the timing issue, you will chasing your tail. Those numbers aren't even close-why? Does #1 wire line up with the rotor at TDC Compression-should be close. Keep vacuum advance disconnected until you get your number closer-it just confuses the issue. As mentioned-a tooth off? Does the tang line up on the dizzy drive at 11.25 oclock at TDC? thats the only thing really keeping me from diving in on the valves is that i feel like the 3500 cutoff (as well as all the other inconsistencies) is indicative of a timing issue and id rather not introduce another variable by doing a valve job, unless of course it could be a reasonable cause. ALSO i meant to mention that with no load (ie just revving while sitting still) the engine revs much higher (5k+), another facet that seems to be point in the direction of a timing problem good call, im just going to disconnect vacuum for the next bit of troubleshooting. sounds like i definitely need to check in on cam timing, i will get on that, i should get a whole evening to work in the garage in the next couple days and actually the tang drive is 180deg off so my cyl 1 is at ~5:35. i only recently came to find this isnt how its supposed to be but i havent had an issue with running out of room for timing adjustment so havent felt the need to restab dizzy. it is definitely on the to do list Quote Link to comment Share on other sites More sharing options...
Tony D Posted September 23, 2014 Share Posted September 23, 2014 (edited) " i meant to mention that with no load (ie just revving while sitting still) the engine revs much higher (5k+), another facet that seems to be point in the direction of a timing problem" Why is that? Why do you think timing is a problem under load when it needs more fuel than when you free rev it and need less fuel. Why wouldn't this indicate a plugged fuel filter, plugged fuel pickup sock, or my personal favorite the 'one starter jet down the other up' sucking fuel dry issue, etc? Edited September 23, 2014 by Tony D Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 23, 2014 Share Posted September 23, 2014 2 things to add: 1. Arne over at classiczcars.com tried to do this upgrade and had similar issues and after a ton of trouble, figured his out: http://www.classiczcars.com/forums/electrical-s30/37900-electronic-ignition-revisited-after-i-gave-up.html 2. The vacuum advance on the ZX distributor comes apart, and when it does the stator can hit the reluctor which I imagine gives you some scatter on the spark. I would at least pull it apart enough to check the advance mechanism. Although there are benefits to vacuum advance, I'd rather lock it down and prevent it from screwing up and just run more static advance. I was able to get 30+ mpg on SUs and mid 20s with 44 Mikunis running no vacuum advance. This page might help with the distributor inspection: http://www.jrdemers.com/280ZX/distributor/distributor.html Quote Link to comment Share on other sites More sharing options...
ol doc gully Posted September 24, 2014 Author Share Posted September 24, 2014 (edited) " i meant to mention that with no load (ie just revving while sitting still) the engine revs much higher (5k+), another facet that seems to be point in the direction of a timing problem" Why is that? Why do you think timing is a problem under load when it needs more fuel than when you free rev it and need less fuel. Why wouldn't this indicate a plugged fuel filter, plugged fuel pickup sock, or my personal favorite the 'one starter jet down the other up' sucking fuel dry issue, etc? fuel was one of my first thoughts. however there is no pinging sound when it maxes out and from what i understand most problems that are load dependent typically tend to correlate with timing issue. i have replaced the filter, but im not entirely ruling out a fuel issue yet. floats were set correctly but im thinking i may want to re-check them. also, on that note, i have the knurled jet adjusters on both carbs all the way out. i wouldnt have guessed they would need to be there but idle speed drops if they are screwed in any more. im attributing this to using original 2.4 needles on a 2.8 but figured i would mention it in case it seemed relevant. 2 things to add: 1. Arne over at classiczcars.com tried to do this upgrade and had similar issues and after a ton of trouble, figured his out: http://www.classiczcars.com/forums/electrical-s30/37900-electronic-ignition-revisited-after-i-gave-up.html 2. The vacuum advance on the ZX distributor comes apart, and when it does the stator can hit the reluctor which I imagine gives you some scatter on the spark. I would at least pull it apart enough to check the advance mechanism. Although there are benefits to vacuum advance, I'd rather lock it down and prevent it from screwing up and just run more static advance. I was able to get 30+ mpg on SUs and mid 20s with 44 Mikunis running no vacuum advance. This page might help with the distributor inspection: http://www.jrdemers.com/280ZX/distributor/distributor.html Jon, thank you, this should give me something to start troubleshooting, which is just what i was hoping for. did you notice any worse engine response on throttle tip-in without the vacuum? Arne's issues are definitely very similar to mine. i believe i have the condensor disconnected but i'll need to look back into that some more. one thing is I am using the BPR6ES-11 plugs (gapped to 0.04") and he said he had some success came from a fresh set of BP6ES. shouldnt be much difference but i might try a set of those just to see. ive already wired out the ballast resistor and have a 3ohm ignitor coil but i may just replace it too... also all in all sounds like its generally a symptom of not enough power getting to the distributor (?) thanks for the input guys, any ideas or suggestions are still welcome, i'll keep you posted Edited September 24, 2014 by ol doc gully Quote Link to comment Share on other sites More sharing options...
Tony D Posted September 24, 2014 Share Posted September 24, 2014 " i have the knurled jet adjusters on both carbs all the way out." So you have in essence stuck your jets all the way down by doing that. Check your float levels and fuel delivery. I bet money you are sucking the fuel out of the bowls and hitting the 'built in rev limiter' that occurs when that happens. I fought it for years trying to figure it out, and to my chagrin one jet was stuck down. Put it back up where it belonged and back to 7K like before I changed my head gasket! I bet you are running the float bowls dry. Put a supplementary Facet Pump inline and turn it on and see if it does the same thing under load. I bet it gets measurably better. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 24, 2014 Share Posted September 24, 2014 Jon, thank you, this should give me something to start troubleshooting, which is just what i was hoping for. did you notice any worse engine response on throttle tip-in without the vacuum? No seat of the pants difference going from wasted vac adv to no vac adv. I can't quantify how well calibrated my butt is though... Quote Link to comment Share on other sites More sharing options...
ol doc gully Posted September 24, 2014 Author Share Posted September 24, 2014 No seat of the pants difference going from wasted vac adv to no vac adv. I can't quantify how well calibrated my butt is though... I'd certainly wager its better calibrated than mine when seated in a 240Z, ha Check your float levels and fuel delivery. I bet money you are sucking the fuel out of the bowls and hitting the 'built in rev limiter' that occurs when that happens. Yeah tony i think youre right. at least that its something that makes enough sense that i need to double check. thanks again guys Quote Link to comment Share on other sites More sharing options...
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