aircobra Posted October 15, 2017 Share Posted October 15, 2017 have been trying to improve the idle on the car, so have tried everything on this forum ( and beyond) checked sparks checked points gap fiddled with the mixture knobs to about 2.5 turns checked for vacuum leaks checked float levels then, went and got one of those fancy all in one timing lights ( my tacho is in repair at howard's instruments) ,,, and then was surprised that the dwell is sittng at 30 degrees at 750 RPM. FSM says 17 deg ,as far as I can tell i actually found 3 settings 7 ( in FSM), 17 ( supplement) and 5 i(n owners manual below) http://xenonzcar.com/s30/files/Owners%20Manuals/1970%20240z%20ownersmanual.pdf so I rotated the distributor counter clockwise ( vac off) till its about 17, went for a drive and it's lost at least 30% off the top end power, accompanied by a bit of backfire idle is not great either what haven't i checked ? Quote Link to comment Share on other sites More sharing options...
Cozza Posted October 15, 2017 Share Posted October 15, 2017 have been trying to improve the idle on the car, so have tried everything on this forum ( and beyond) checked sparks checked points gap fiddled with the mixture knobs to about 2.5 turns checked for vacuum leaks checked float levels then, went and got one of those fancy all in one timing lights ( my tacho is in repair at howard's instruments),,, and then was surprised that the dwell is sittng at 30 degrees at 750 RPM. FSM says 17 deg ,as far as I can tell i actually found 3 settings 7 ( in FSM), 17 ( supplement) and 5 i(n owners manual below) http://xenonzcar.com/s30/files/Owners%20Manuals/1970%20240z%20ownersmanual.pdf so I rotated the distributor counter clockwise ( vac off) till its about 17, went for a drive and it's lost at least 30% off the top end power, accompanied by a bit of backfire idle is not great either what haven't i checked ? Sounds a bit strange. Dwell shouldnt change by adjusting your dizzy. Dwell is relative to opening time of the points. Do you mean timing? Quote Link to comment Share on other sites More sharing options...
aircobra Posted October 15, 2017 Author Share Posted October 15, 2017 yes, sorry timing Quote Link to comment Share on other sites More sharing options...
aircobra Posted October 15, 2017 Author Share Posted October 15, 2017 forgot to mention that the mech. advance works ok, as i can see the timing move as the revs go up couple of US forums mention 10 (idel) 35 @3500 rpm as the perfect mix Quote Link to comment Share on other sites More sharing options...
Linton Posted October 15, 2017 Share Posted October 15, 2017 have you done a compression test, is it good, have you rechecked the valve clearances. Quote Link to comment Share on other sites More sharing options...
Roady Posted October 15, 2017 Share Posted October 15, 2017 (edited) Can you give a bit more info about the engine? Ie do you know compression ratio, cam (is it standard), type of carbies? Some of these things can affect your idle forcing you to adjust timing. As an example the engine I am currently using has a 72 degree cam, which was ok with an initial timing of around 12 degree with SU's (with max mechanical advance of 28 degrees. But when I changed to the triple Weber set up I had to advance the initial timing up to around 17 degrees (I haven't recurved the dizzy as yet), giving a total advance of 33 degrees. More info if possible.. Edited October 15, 2017 by Roady Quote Link to comment Share on other sites More sharing options...
aircobra Posted October 15, 2017 Author Share Posted October 15, 2017 stock standard L24 with twin SUs. Fully rebuilt ground up about 200ks ago have not checked clearances or head bolt torques since then Quote Link to comment Share on other sites More sharing options...
zeds4ever Posted October 15, 2017 Share Posted October 15, 2017 That 10* is advanced I think you will find or did you set it at 10* retarded .Jason or Lurch should be able to put you on the right track with this . Mine is set at 10* advanced on a 280ZX Ef with a mild cam , starts / idles / runs fine . Head should be re tensioned after 1000klms . Regards : Alan . Quote Link to comment Share on other sites More sharing options...
1600dave Posted October 15, 2017 Share Posted October 15, 2017 (edited) Are you checking the right thing with your "fancy all-in-one timing light" ? ie you're not checking dwell, but you're messing with timing ? ? ? I don't have the exact figures for a zed, but 17 degrees sounds reasonable to me, 5 or 7 sounds way too low. Reason I ask is that 30 degrees is probably in the ballpark range for dwell, but way high for ignition timing......... Edited October 17, 2017 by 1600dave Quote Link to comment Share on other sites More sharing options...
aircobra Posted October 17, 2017 Author Share Posted October 17, 2017 ok, here's some photos 1.pulley and marks https://www.flickr.com/photos/62957688@N08/37059725043/in/dateposted-public/ 2. distributor rotated all the way counter clockwise https://www.flickr.com/photos/62957688@N08/37698088992/in/dateposted-public/ 3. inside the distributor TDC on #1 https://www.flickr.com/photos/62957688@N08/37059684813/in/dateposted-public/ i believe the distributor and the pedestal is from a 280 ( based on the , although I'm not sure. Can someone confirm? Also, should there be a spring somewhere on the vaccum gadget or is it internal in this model. Seems very, very stiff Quote Link to comment Share on other sites More sharing options...
aircobra Posted October 17, 2017 Author Share Posted October 17, 2017 http://www.supercheapauto.com.au/Product/ToolPro-Professional-Angled-Timing-Light/385507 Quote Link to comment Share on other sites More sharing options...
Howdy Posted October 17, 2017 Share Posted October 17, 2017 G'Day Aircobra, It's probably the carbies causing the bad idle. With the timing - set your points gap (assuming here that they are not burnt - if so replace them and the condenser). Then work backwards - disconnect the vacuum advance then set your maximum timing which means revving it to about 4000 RPM to ensure all advance is in. I'd try about 32 to 36 deg total if you are using (98 octane with 9.5:1 comp). Once that is done, connect the vacuum advance and check the idle. Should be about 10 to 15 deg. The vacuum advance can seize up with crap so you can check it is working by giving it a good suck. and see the points plate turn then bounce back. With the carbies, I always checked the jet heights first by removing the tops and pistons then use the back end of a vernier to check the depth of the jet, set both exactly the same then you can use No turns to adjust from there onwards to adjust the mixtures. While you have the tops off make sure both needles are identical part Nos, not worn on one side and set to exactly the same height. Check the springs are identical. Also give the inside of the tops (suction chambers) a good clean and make sure the piston slides in and out smoothly with no rubbing. Empty the dampener oil out of the top of the pistons. Then adjust each carb's idle screw back until the throttle plate is just closed completely then turn them in the exactly same amount (around what they were before so your idle will be in the ball park). Then adjust the balance screw between the carbies so that when you open the throttle, they both start moving at exactly the same time. Just one thing left now - Check the dampener pistons are clean and look the same then wack in some oil. The weight of oil will determine your acceleration enrichment so light oil will lean it out and heavy oil will richen it up. I nearly always used engine oil 20w50. Light oil tends to leak out faster. See how you go with that. You really should check your tappets. One other thing not normally checked which will cause rough idle is the front pulley - make sure the bolt is tight and screwed all the way in. They can unwind then seize in the crank thread. Quote Link to comment Share on other sites More sharing options...
aircobra Posted October 28, 2017 Author Share Posted October 28, 2017 i see blu260z is having very similar problems to me!!!! checked the carbs very thoroughly as per howdy advice ( grateful for that). and now for the voodo moment first point - as per blu260z thread, the timing does not move smoothly thru the rev range. i attribute that to badly worn distributor bushes, so i'm getting a replacement from stewart wilkins second point - as the engine speed increase, the timing mark moves BACKWARDS from approx 20 deg and moves past 0 Quote Link to comment Share on other sites More sharing options...
nat0_240_chevZ Posted November 2, 2017 Share Posted November 2, 2017 (edited) Sounds like vacuum supply to dizzy on on the wing side of your throttle blades, ie between throttle & head, not pre throttle.... Check this! Otherwise something more sinister.. Only as speed increases? Ie mech advance (vac disc) or throttle posn. I thought you said mech advance appeared to be working? Nat0 Edited November 2, 2017 by nat0_240_chevZ Quote Link to comment Share on other sites More sharing options...
nat0_240_chevZ Posted November 2, 2017 Share Posted November 2, 2017 (edited) Try this. Forget the degree marker for a bit. Car runs, right? Rotate dizzy till revs pick right up, then drop back a bit till revs drop down to say a high idle, 1000rpm. Then check with light, no vac adv... What does it read on your degree scale? If a weird number, check scale plate and pulley havent been changed. And ensure dizzy is suited, yes later dizzy have the differently orientation bodys, which could also be cause for your confusion. Eliminate the whoopsy factor first. Has the dizzy been apart? If so who? When etc. Need to eliminate the possibility of a bumsteer first.... Edited November 2, 2017 by nat0_240_chevZ Quote Link to comment Share on other sites More sharing options...
aircobra Posted November 6, 2017 Author Share Posted November 6, 2017 ok, big news - cleaned up the dizzy, greased it up and reassembled couple of interesting points for the pros the later 240 dizzy only have the one "fat" spring on the weights dizzy internals are very similar to the 280 with exception of the plastic ball cage and different vacuum unit new points, rotor , cap just for good measure anyway, to cut to the chase, the bushes were as tight as a fish's a..e. motor started right up, the timing mark's perfectly still and it moves from 0 to 30+ with no prob. I set the 17degress at 750 no vaccum and it runs better blu260z 1 Quote Link to comment Share on other sites More sharing options...
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