AK260

Dear Z gang, We have a member here whose L28 runs-on with SU carbs. He is running a compression of 210PSI and believes this is normal behaviour for high compression combined with using SUs. Mine with 205 PSI, high quality UK RON 99 fuel and SUs does not run on anymore after being rolling road tuned. Is anyone out there on SUs getting run-on after turning off and what dynamic compression do you run? Or indeed is anyone pulling 210PSI (or more) with SUs and NOT running-on ? Would be interested to hear your experiences. Apparently it doesn't happen with DCOE carbs, is that correct in your experiences? Does anyone out there have a good explanation of why it happens on SUs rather than just that "it is common"! The DCOEs like SUs will continue to feed a pumping cylinder so is it just a case of DCOEs running richer and hence cooler?

Ps. I LOVE the home made spark plug idea.

And then there is this ... https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F201984173362 I have one and it's very useful.

I run a 10.5:1 comp L28 with a very ported head and large valves + high lift cam on twin Z therapy SUs with SM needles, mech fuel pump only. Had the same problem as you before I went for a rolling road tune where they reprofiled the needles - it most certainly is no longer running lean!!!! The mech fuel pump is plenty man enough for the job.

Wow!!!! That is a very poor show for a high end object of desire. Maybe BHJ made it that way as a "feature" for it to feel at home in a Datsun! ;) Will you be sending it back to BHJ?

That is one sexy bit of kit!!!!! Nice work. This is what I had to do - it's rather large but it will never vibrate onto the damper especially as it's 2mm thick steel ;)

Oh and I forgot to mention, if you are attached to the classic look of a mechanical fan like I am, then you have to space it forward by about 7mm to clear the stickie outie bolts on the front of the damper.

Nope Jon, he used the washer but the bolt was too short for his liking on the ATI so he had one made just like it but longer ... Kameari on right new on left with washer on. You can just about make out that the new bolt is about a bolt head longer.

Ok, I know the OP has resolved their issue but here is my 2 cents in case anyone else is asking this question / reading this thread in the future. I run an ATI super racing damper on my very modified street driven L28 because it really is one of the best non-fluid dampers out there. Yes the bolt does need to be longer than stock and my engine builder had one machined for me. The stock pulley is 150mm but the ATI is 70mm. So it is turning the alternator and water pump at less than half the stock rated speed. Cooling: Have I ever overheated idling in traffic on a 30c summer's day? No. Has the temp gauge gone higher than before - totally! The gauge has gone to just over three quarters which it never did with the stock size pulley - it rarely passed half way before. The temp gauge fluctuates more on and off the power than with the stock pulley. In reality a mechanical water pump / fan will be spinning at half the speed that the stock pulley would drive them. Charging: I had my alternator rewound / uprated to 90A constant capability and a slightly smaller pulley put on. At an idle of 900rpm the volt meter dances between 12v and 13v. At 1200rpm it's steady. The LED headlights do flicker at idle between 900-1100 rpm. Most alternators do very little below 1500 spindle rpm. Other options: Kameari do a fluid damper with two pulley sizes one closer to stock and one that iirc is about 110mm (ATI is 70mm). See RHDJapan website for the street version. Another benefit is that the fluid damper will never need to be rebuilt. BTW - on my stock damper on original stock engine I found it to be loose and moving 1cm back and forth!! Gulp! So it does happen even on bone stock engines.

Seems like a daft question, have you tried taking a fused wired directly to the coil from the battery + terminal to the coil!? If she fires up you can stop the engine by pulling the fuse! ;) But at least you know for sure the problem is car wiring. A word of warning on the 123 - don't trust the no.1 marking on the cap. Check the position of the rotor relative to the cap. I stupidly didn't and with timing 120degrees out, blew my muffler trying to start - at least I knew there was a spark :p

Shell V-power Nitro, local garage

A few of us quietly lurking ;)

Jon lives his life a quarter mile at a time! ;)

My Z is on a strict diet of pump RON 99 in the UK at $8 a gallon

I bought mine from eBay via Malaysia but be warned that the rubber in the original item is wedge shaped, the ones on these are flat. So while in other circumstances it is bad advice, in this scenario it's worth cleaning and reusing your rubbers!!! [emoji1787]

Lots of good advice here. With compression that low I'd be surprised that the car is starting and / or not smoking like a chimney. She would feel like a salted slug if true - I bet she doesn't, right? I would question the test equipment first and foremost. The operator does appear to be somewhat intelligent and competent :p This is what I use and have found owning one a very useful thing. https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F143013635153 One other thought, when doing this test I always hook up a battery charger on "start" mode to eliminate any effects of battery drain. For comparison, my L26 that was burning a litre of 20w50 every 1000 miles ran with 155psi dry, 185 wet. My freshly rebuilt L28 with static compression of 10.5:1 and the 270 cam does 205psi wet or dry across all cyls +/- a nat's sigh. I would be amazed if your car is genuinely running that low and not feeling massively sluggish. Regardless of the absolute numbers, the variation across banks is a thing to consider. Cam clearances will of course have an effect and while you have the rocker cover off check head bolt torque too. If you find after all this you still have the same readings, get a "leak down test" before tearing the motor down. https://mobiloil.com/en/article/car-maintenance/car-maintenance-archive/how-to-do-a-leakdown-test Oh the joys of owning old cars! Good luck buddy.

I whole heartedly agree with Mark. Do all the tuning stuff first. BTW I had a VERY similar problem - the car would humble modern cars on the go but struggled to idle and would eventually stall at the lights. Spent HOURS AND HOURS playing with carbs. Turns out I had a vacuum leak where the carb joins the manifold on the rear carb, the nuts "looked" tight but had loosened off. When idling, the butterflies are near shut and manifold vac high, so any leak becomes material. Operating the choke lever not only drops the chokes but also opens the butterflies a little, therefore would hide a vac leak. So in short I would advise checking all your manifold nuts, carb to manifold nuts, checking for carb spindle bearing leaks, top hat to carb body sealing, manifold gasket leaks, vac pipes to brake booster etc. FWIW my 270 deg cam with .46" lift likes 1000rpm and given I use a fidanza (half stock weight) flywheel, it does have a gruff lumpy idle - kinda race car like ;) BTW, that's a stunning car!! [emoji106][emoji106][emoji106][emoji106]

Great to hear, well done. [emoji106] Imho those plugs look on the hot side, look at this ... If those colours were on the same bank of 3 cyls I would have said carbs, but since they are not, I'm tending towards valve clearances. Now, two questions: 1. Have you adjusted your valve lash clearances? They determine how much / little or consistently across the cyls your valves open and shut and their timing relative to each other. I find my engine (a highly modified L28 but with a mild cam of 270 degrees and .46" lift) reacts very strongly to well adjusted valve clearances. It's more noticeable on a modified engine but the principle is the same for yours. 2. As for your idle, are you running a working vacuum advance? Have you checked it is actually working? Your mix at idle or part throttle will be lean and will require more timing for it to burn well. Mine has a base timing of 17 degrees (higher than stock due to cam) and vacuum advance adds 12 degrees at idle. But as soon as I go on the throttle and open the carb butterflies, the manifold vac drops and timing goes back to 17 + mechanical advance as the revs rise to a total of 34 degrees (without Vac! With vac connected, add 12 degrees to that). A lean mix without sufficient timing will burn hotter. With vac advance, you will find your idle will improve and engine temp at idle or cruise will drop noticeably. Also the cruising to on-power responsiveness improves (not to mention gas mileage). Think of it this way, imagine you have two plates full of gun powder on the floor, one packed with dense gun powder (rich) and one sparsely packed (lean). On the rich one, the gun powder particles are touching, on the lean one there is air between them. Then you light both from the centre - the plate with the denser gun powder burns faster towards the edge. Now imagine you had a fixed amount of time of say 1 second for them to burn before you dump the contents into the trash can. The fully burnt / rich plate dumps hot soot. The lean plate is still combusting and finishes it's burn in the trash can, burning the edges of the bin as it goes in (and that is the edges of your exhaust valves in an engine). Next time around, you light the lean plate half a second ahead of the rich plate. This time, both finish their burn before you dump them. The principle in your engine is exactly the same and your exhaust / header temps will drop with more vac timing at idle. Hope that helps, good luck! BTW, where are you able to do 100mph without getting a blue light escort!? Are you in Germany!? (Joke!) Or a test track?

Agreed! Plug fouling at idle could be caused by other things like mix, lack of vac advance, etc. Get her firing well first and then sweat the other stuff later. ;) Is it safe to assume you've already changed your cap and rotor?

Think of your gearing as a torque amplifier - it merely amplifies your engine's characteristics. So if you are bogging down @4K you have a power flat-spot that a long diff will make more prominent. L24s were renowned for having a flat spot at or just before 4K rpm - one way to "tune"' it out is to have a 6-3-2 exhaust header with long primaries and long collectors (the 2 bit) as per the Nismo or Janspeed design. The theoretical ideal (rule of thumb) is around 90cm primaries and 50cm collectors. See this fine bit of engineering ... http://www.datsun-zstory.com/echappements/headers/headers-race-sport/ Changing your diff will surely reduce the effect but the flat spot is still there. I just realised why you guys are getting such low revs, you are using an auto 'box, right? Apologies to the OP for taking the thread off track.

I've used similar things before but the the cheapest way to see if you are getting spark is to get the engine running, set the fast idle to around 1.1krpm - take a plug lead off at a time and point it to something metal on the block - you will soon see/hear the spark. BTW did you get the new leads? Remember the old ones can have a break inside and give intermittent spark / intensity when vibrating under normal conditions. As a rule of thumb you should be sitting somewhere between 2.8-3.1k rpm at 70mph depending on which variation of diff ratios/gearbox / wheels you have. The typical range is somewhere between 21.5-22.5 mph per 1000rpm. Use a free app on your phone like track addict and you will have a better view of your speedo accuracy.

I think your speedo may be a little optimistic - the longest R180 was a 3.364 which means you should get 22 (ish) mph per 1000rpm. Unless of course your gearbox has a super long top gear. [emoji14] Mine is pessimistic around 30mph (i.e. Shows 25mph) then gets accurate at 80 and optimistic above 90! Ahem - All tested on a track of course, officer! Don't always trust your old dials. Other possibility is that your rev counter is being pessimistic and you really are doing 100 in which case your real (not indicated) revs are around 4.5K RPM! And if you think that the max speed of your car is around 120mph and max torque at c.5.5krpm, then the 22mph / 1000 rpm works. Or are you running some super tall tyres!? :p

100mph @3krpm!?!? That is a seriously long diff you have!!! So are these pics with new leads or your old ones?

Of the list on rock auto I guess you can't go wrong with NGK. Glad your car isn't backfiring - mine took out the baffles in the silencer and deformed the whole thing - you can see where it started blowing through the joints!!!! [emoji14]

Ps your number 6 looks like it's not firing at all when compared with the others - just get some new leads - they are dirt cheap! https://www.rockauto.com/en/catalog/nissan,1977,280z,2.8l+l6,1209248,ignition,spark+plug+wire+set,7224