AK260

One of the chaps in the UK dropped one into his Z - it’s an ABSOLUTE monster!!!!!! Such a sweet sweet engine!

Wise ones, I need you wisdom please! My original fan clutch was shot, so I bought another. That one doesn’t seem to ever “turn on” and I can stop the fan blades with my fingers even with the gauge 3/4 across! I can make it work if I give it a couple of very brief blasts with the blow torch so the mechanism inside clearly moves. I figured it must be just adjusted too high and ordered another. I just received an Aisin one from Rockauto, currently being tested as I type :p At 85c it still wasn’t feeling any stiffer and I can’t imagine it getting much hotter than that when in the car. So what temp is it supposed to work at? Nothing I can see in the FSM other than how it’s supposed to operate not at what temps. One last thought, does it have to be spinning at speed to work or should I be able to turn it by hand and feel it become difficult to turn?

You cracked me up! I had the exact same conversation in my head too!!! I figured “secondary” would just cause confusion ;) Maybe top dog and underdog!?

One very dumb last question, have you dropped the jets down a couple of turns since taking the photos of them? If not, that may well be the reason as to why it dies if you reduce butterfly opening further.

To add my two cents: I ABSOLUTELY LOVE my Fidanza flywheel and exedy clutch! I think they do a great package on eBay but just check you are getting the right one for your car ... https://www.ebay.co.uk/itm/EXEDY-CLUTCH-KIT-06029-w-FIDANZA-FLYWHEEL-for-70-75-DATSUN-240Z-260Z-2-4L-2-6L-/324528069103?_trksid=p2349624.m46890.l49286 And I have to echo the sentiments - replace all the bits that wear out and you’ve done it once!! Having said that, I didn’t replace my slave cylinder as I preferred the original part to the new one I had bought! Somehow it felt better built. We’re no longer allowed to say “salve” cyl are we? What is the new correct phrase?

Fantastic progress, well done. That butterfly position is FAR more like it. It’s been frustrating for you but you’ve learned a lot about your car at least, so next time you are better able to troubleshoot it. There is nothing complex or magical about any of it - remember what I said about timing, fuel and air is what makes engines rev? Apply that same principle again. The great news is that your flow meter is off the charts showing that you don’t have an air or vac leak down stream, making the rest of it easy. Unless you have a full race cam you absolutely should be able to get the idle down a bit. I can get mine to idle at 700 rpm but it would be rough and won’t be good for pulling off the line smoothly, hence it’s dialled up to 1000. I actually vary mine with timing as I’m happy with the mix. If the idle is higher than normal you typically close the idle screws, if that makes it die then you can richen the mixture a “tab” or two at a time and try again. Or alternatively dial back a degree or two of “static” timing if the mix is good. BUT .... you must bring the engine up to full operating temp before doing this. On a well adjusted carb without an over rich idle you will still need a little bit of extra fuel until at operating temp (notice how your modern car will still smell rich for the first few mins even on a warm day). Simple way to adjust carbs is: on the left front side of each carb, you will find from the underside a “lifting pin”. This allows you to lift the piston up a little. If at idle you raise the pin by say 1-2mm and the engine dies, you are too lean. If it speeds up and settles down (while you hold the pin in the same place) you’re good. If the engine speeds up and stays high then you’re too rich. Have a good read of this ... http://sucarb.co.uk/technical-h-type-carburetter-tuning-single In your case you have good flow, but the engine dies - to me that suggests too lean at idle. But of course changing the mix at idle affects the mix elsewhere so it’s a balancing act. Do you have an AFR gauge / UEGO? It makes tuning aooooo much easier! Hang in there - you’re nearly there now!! EDIT: one last thought - what idle timing do you have and is vac advance connected when you check?

Yeah, I can see visually that there is WAY WAY too much airflow for idle right there. I think we’re starting to get somewhere. You definitely need to back off those idle screws a lot and or figure out why your butterfly is being held open.

Good work there. So it’s good that we’ve eliminated the possibilities of blocked holes etc. The drop test is exactly that and it should be a relative quick drop and thunk! Your last borescope photo shows me it’s way too open for idling at sensible revs. If I put yours and mine side by side below, and we use the throttle shaft butterfly screw as our scaling datum in each photo, you will see yours is way more open than mine!!! Now it’s interesting that putting them back on is causing them to open - you’re now starting to point to a potential linkage issue. Are you able to put the carbs on and back off all the linkage screws such that both carbs are independent of each other. And to be very clear - no choke cable connected either! You then want to back off completely on the idle screws such that the butterflies are completely shut when on the car. Inspect visually. Now, feeling the butterfly with fingers on one hand, you can turn the idle screw with the other until you feel it “just” start to move. Do the same on both sides and inspect visually to ensure they are equal and not more than a hair width open. Now try to start the car and let’s see what happens!

It took a while but I got to finally say hello to the car today, so here is mine for comparison Bear in mind with my cam it has a high idle at 1k revs and 16 degrees timing.

Well, I’m forever stunned at how little air / fuel a healthy engine needs to rev up without load. So not too sure chap. I will get you a photo of mine shortly. The good news is, you can see one piston shooting up more than the other, so now you have something to work from. Forgive me if I’m going over things already discussed / suggested, I’m just trying to go back to basics and eliminate possibilities in my head. The simple fact is, at the most basic level an engine only needs timing, fuel and air to rev up. So, we’ve determined your timing is OK, let’s park that. As for fuel, I know you’ve checked fuel bowl levels and I’m assuming your jets aren’t set overly rich and are equal. So for now let’s also ignore them. I am also assuming you don’t have a sticking piston and have done the “drop test”, so I’m making an assumption that your pistons move freely. The only reason a piston rises is, sufficient airflow across the bridge that with a pressure differential overcomes the effects of gravity and the carb spring. So either you have one carb with little vacuum on the inlet side compared the other or not enough resistance against the piston. You have a balance tube - so at idle, theoretically, you have equal vacuum across the manifold side of both carbs which should raise both pistons equally. An inlet manifold vac leak would be shared across the carbs - do we agree so far? Would you please do me 2 favours: 1. Test your spring rates - I did mine very simply using books and kitchen scales to prove they were pushing equally at the same height (67mm). Let’s prove you have equal resistance between your carbs so as to eliminate that. 2. While you have the domes off, check that the hole(s) in one of the pistons isn’t blocked (red markup). The one that “communicates” manifold vac to the piston. Also check the small carb inlet holes that “communicate” atmospheric pressure (yellow markup). These are the only mechanisms by which the piston is lifted. If blocked, or restricted, the rise will be affected. Give them a good squirt of carb / throttle body cleaner and a small brush / wire through the holes. Also ensure that the washer at the bottom of the spring isn’t blocking the piston holes when reassembled. Once we prove the above: Let’s try something a little different to prove you have or haven’t an air leak. I want to separate your carbs from each other. I want you to block the balance tube with a home made rubber gasket at both ends such that we eliminate any possibility of any leaks through it and prevent the equalisation of any manifold side vac leaks between the carbs. After that, you can disconnect the balance “bar” such that both carbs work independently of each other. Now you can measure air flow with an airflow meter through each carb and adjust idle screws until the airflow is equal. This will very quickly show you a difference between the two. The one with a vac leak would have the larger opening. Then we can start to work on that side of the manifold and investigate any false air sources.

OK, MEGA dumb question - are you certain both carbs have the depression springs installed on top of their pistons? Also that gap looks a little wide to me - could be just a trick of the camera. I will take a photo of mine later today for comparison. If memory serves, mine look almost completely shut. A vac leak between carb and intake does not make the piston rise - in fact quite the opposite. Air flow THROUGH the carb does. [mention=23570]siteunseen[/mention] - no tricks just the iPhone camera. The CCD being infrared sensitive picks up the hot manifold and makes it look way hotter. To the naked eye it was just a very slight dark red glow / barely visible but enough to make me want to take a photo!

A little late to the party, but here is my 2 pennies worth: It can’t be your cam as it’s only affecting 3 cyls not all six. So IMHO it’s definitely fuelling / carb / intake related. The only time my headers have been visibly glowing is when I’ve been heating the car up at night on choke at around 2-2.5k rpm with an AFR of around 12 (so read very rich). The camera does make it look 10x hotter than it was to the naked eye!!! 4k is high indeed for a leak but also do we know how advanced your idle timing is? Just advancing the distributor I’ve had the engine at 2k rpm, let alone adding in a leak. Either way, I would focus on the carb serving the bank of 3 not glowing. Good luck, I’m confident you will find something simple soon as the culprit!

Utterly brilliant chap - massively applauded!! Yes it is but don’t forget the white washer that goes at the bottom to stop air locking if bottomed out.

I have to agree, I was surprised. To their credit they did send me a new set but in all honesty only the rear ones went on (last year) as I really couldn’t be bothered to remove the bumpers / had more pressing work on the car. I believe they offer an option of having the bumpers without the rubber holes drilled but includes the rubbers in the package. That way you can have the option to install yourself or keep the corners shiny! And I have to agree the S/S does pick up scratches more easily. However my father in-law’s experience convinced me I wanted S/S. You see, in the UK the weather is constantly humid even if you don’t drive in the wet. He had his Volvo 123 Amazon bumpers re-chromed and in under 10 years they started to go again. So when I met him (about 12 years ago), I helped him fit the Harrington bumpers and to this day they look stunning!

OK, let me answer my own question! A kind Uk member who bought them but not installed, dropped them off the other day. They are radiused to just over 180 degrees so I’m not sure if you can say fully radiused as I have seen some made from a single billet and fully radiused. They fit is 99% perfect to under 0.5mm difference between them and the carb mouths. They do look good quality. I have yet to do a back to back performance test, so more to come!

I have these on my car and pretty happy with them! BUT ... if I did it again, I would buy them without the rubbers. The rubber corners perished within 4 years, and my car is garaged for 98% of its life! https://groupharrington.com/product/datsun-240z-and-260z-bumpers/

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Ps. Googling the part numbers in my photos for you throws this up ... http://shop.exedyusa.com/exedy-oem/exedy-oem-clutch-cover/nsc534/i-393841.aspx http://shop.exedyusa.com/exedy-oem/exedy-oem-clutch-disc/isd104us/i-394116.aspx A bit more google action or a call to Exedy should help you decide if these match your other numbers.

Sadly not dude, but looking back through my build thread I came across some photos that may help! I measured the clutch plate height to ensure I didn’t need a new collar The photos below show the numbers stamped on the pressure plate and the clutch disc ...

I haven’t fully read all the comments above, so this may be a dumb suggestion/ repetition. The only time I’ve had back-firing when on the power was when my Magnecore 8.5mm plug leads failed and there was unburnt fuel in the exhaust, popping as it hit the silencer / fresh air. A cheap set of Accuspark 8mm leads at a fraction of the price of the Magnecores fixed the issue and there was no performance drop over the more expensive leads. So check your leads / plugs or swap them out for new given how little they can cost to fully eliminate them. Also the vac leak hypothesis works here too, especially if you are setting up over-rich for idle and with a weak spark. Also check your break booster hoses / connections and any other vacuum take off from your balance bar. Again, brake booster hoses can get brittle and leak + I’ve found loose connections on mine too. Check any blanking bolts and the gaskets on the balance bar too. On my 123 ignition dizzy, I can see coil voltage/current. When I connected the ballast resistor to my 1.5ohm flamethrower as an experiment, the voltage didn’t even register on the gauge and the current was minuscule compared with where it should to be. So just bypass the ballast resistor for a while to eliminate it (if you haven’t already) while trouble shooting. I’m sure someone has said this already, check all your manifold nuts are torqued up properly - I’ve found that even a 1/6 or 1/12 of a turn tighter made my life so much better - also all the carb to insulator nuts. Again, my carbs had rattled themselves loose in 300 miles of being put back on. Using the spray something around potential leak points, I found even on my ZTherapy carbs (after 7 years of hard use) the throttle shaft cap on the rear carb needed re-sealing (probably due to a HUGE carb pop and exhaust backfire I had when I once got the leads 1 position wrong and tried to start the car on WOT)!!!! Do you have a vacuum gauge to connect to the balance bar on the manifold (or vac advance nipple if not ported vac) to see what is happening at idle? It’s one of the essential trouble shooting tools for these situations IMHO! Something like this .... https://www.ebay.co.uk/itm/Gunson-Vacuum-Pressure-Tester-Engine-Fault-Petrol-Pump-Lo-Gauge-LSR5-/123731949087?_trksid=p2349624.m46890.l49292 The only time I’ve had intake popping was when the timing was way out. But I see you’re on that now. Good luck - these are simple engines and with a systematic approach you WILL find the gremlin(s).

Brother, I LOVE your creativity!! [emoji106]

So here’s a question - what think ye wise ones about the 50mm fully radiused MSA trumpets? They look very good quality and I like the radius / small taper but do they perform well on the L6? Has anyone used them and noticed any differences in engine behaviour or performance?

That’s really interesting! Something I have to prove to myself ;) In all seriousness, my under bonnet temperatures get horrendously elevated standing still. Since I made my own heat shield, the carbs not longer get hot. In fact, they are fridge cold to the touch after a good blast! Also with the biggest hole at the front of the car being the radiator and a fan constantly sucking air through it, I have always imagined hot air being pushed into the engine bay more than fresh cool air. Having said all that, if someone has measured it then there is fact there. I’m still keen to try it out and prove it to myself. I want to put the factory air box back on and have a sensor inside it, got for a drive, then repeat with the CAI and compare and contrast!

Ps. Beyond the issues people have quoted with them deforming and collecting / dripping the fuel from the standoff mist, the thing I really don’t like about the Ram Air filters (or any trumpet filter) is the sucking of hot air!! I am planning on getting a couple of temperature sensors under the bonnet to measure what temps I’m getting. While doing my search, I came across this VERY good thread / experiment. https://www.jaguarforums.com/forum/xjs-x27-32/under-bonnet-hood-temperatures-166641/ Mr. Vizzard has a chart showing that for every 11c drop in intake charge temp, he gained 2.2% HP. Now imagine ambient 25c and under bonnet temps of 68c as an example. That’s 6.6%!! On a 200bhp engine that is worth 13 ponies. 13 very easy and cheap to have ponies. I know all of this is old hat but I’m always intrigued at how few people care. I guess not everyone is chasing ponies and prefer the sound. And oh what a lovely tune it is too!! [/Rant off]

Ooooh! That’s really nice work there! What did you use to get such a good finish / result? I’m not sure what you gents have discussed in the past but this airbox, while it looks carbon is all fibreglass. I have to say, I would prefer it if it was just smooth. I REALLY love the one @HS30-H has on one of his cars and wish it was more readily available. I’d gladly pay top dollar for that item!