240260280z

Is the bolt stripped in the hole? Please provide more details of the failure and we can provide better advice.

I also noted that on these carbs, 23mm of fuel to fuel bowl top lip height is ~13 turns (1.3cm) down (max) of the jet.

I'll concur...~14 a/f at zero turns of jet depth. I think it may be due to the shorter needle.

Found the problem. Turned out that the new short N54 and M49 needles were the culprits. Grrrrrr. It was supposed to be a 240z kit they came from.

Thanks again John. You are spot-on. I figured it out (silly me)... the main trick is that the meter is best viewed when rotated sideways 90 degrees . I was first trying it in vertical and 180 degree rotation but the parallax was preventing a useful measurement . I also figured out (now that I could see the scale in more detail side on) that around ~2,000rpm I could set fast idle screw so that the front carb measures exactly 25kg/hr I could then measure the rear carb and adjust the balance screw so that it matched exactly at 25kg/hr. It was very easy to balance at off-idle and at idle and more importantly, absolute and repeatable measurements. I would recommend the BK version to others to tune in the higher rpm range.

I always used a friend's Unisyn flowgauge when balancing carbs. It worked fine at low RPMS and at high RPMS. IT DID THE JOB. I am now using an STE Synchometer with absolute measurement dial but it pegs at higher RPM's. I tried the two different rubber fitting that came with the STE tool and also tried to use the holes in these fittings as bleeders but no luck. How can this tool be used at 3000rpm?

Yeah, everything check OK. I'll have another look at the fuel rail for an obstruction on the return. I'll also change the fuel pump today.

I read about using a propane torch...use Google to find out if it works. edit: http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1612066 "Hillbilly reasoning"

De rien

No holes, and I tried 3 different floats/tops.

that is nearly the same... maybe we should take parts from each others carbs and the levels will be in the right spot. How I managed to run rich with no turns on the jet knobs still confuses me. I think my carbs are haunted. I have a second set of new needle valves and a used fuel pump that I disassembled today to ensure no surprises. I'll try theses and see if I can find the elusive parameter that is causing the problem.

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Arne.... a lone z is out there somewhere looking for you calling "Arne Arne where art thou Arneeeeeeeeeeeeeeeeeeeeeeeeeeeee!"

An old thread but it just happened to our club racer so I figured I would try to simplify the great info above. From what I understand: Basically in right high G corners, the fuel sloshes to the left side of the car. Inside the carb, the sloshed fuel works itself up through the fuel bowl vents and gets sucked into the top of the air jets (which are supposed to suck air, not fuel). The problem is that Mikuni has only one fresh air inlet into the carb to feed both the jets and to vent the fuel bowl. The mod basically makes the stock fresh air inlet only for the jets and a new system is used to vent the fuel.

It is nice to be in good company. Actually it is the first time I actually measured the fuel height as the 90° technique has worked fine. This time I used my calipers and scribed two accurate marks on the outside of the bowl at 23mm down from the lip and at 25mm down from the lip. I used a brass "T" and three sections of clear hose to connect the bowl outlet to the jet inlet and to run vertical for measuring. I'll swap fuel pumps today and see if that helps.

Thanks! That is appreciated and all on the net who search will find your data too!

I normally set the needle valve closure point on carbs by blowing in the inlet and adjusting the tab so that the valve is shut at 90 degree point of swing (top of float is parallel to top of fuel bowl). The carbs I have set like this have always worked fine. However, I ran into some problems today with a set I did this fuel level technique too so I decided to check in more detail as I could not get the A/F ratio to work no matter what I did with the jet height. I decided it was best to back track and recheck every thing. I first tried adjusting the fuel level at 23mm in the bowl and also the other technique of meniscus 10 turns of the jet down the well. The carbs initially were ~ 25mm and 23mm for the front/back bowls respectively (distance from bottom of gasket to top of fuel) with the same needle valves and tab bridge heights (not the 72 carbs). I readjusted the tabs and got the offending one to ~ 24mm and left it. After this I put new M49 needles in the pistons and set the correct needle depth using the "jet-push-piston-home" technique. I ran the motor and it was super rich. I tried bringing the jets up but it was still 12:1 with zero turns on the jets! I then tried new N54 needles and it was only mildly leaner (14:1) at 0 turns of jet depth. I then re-checked the fuel height and it was still 24mm. I then re-bent the tab many times (drain, bend, run starter for 15sec, wait for fuel to finish rising and I always got 24mm...I repeated ~ 5 times until the tab was nearly pushing the needle valve closed with only a few degrees of freedom. It was as if the new needle valve was not working. I then tried an older fuel bowl top with old float and old needle valve but the same problem...24mm of fuel level. I then thought that the fuel pump or return lines may be the problem. I was able to confirm the fuel rail return flow a few days ago, and today I blew on the return line to the tank and could pass air and hear it bubble so no problem there. I am thinking the lines are fine but the fuel pressure is too high. I do not have a fuel pressure gauge nor an adjustable FPR for carbs so I am thinking of rigging a hose to check the column of fuel height the pump can head and then converting to PSI.... any input? I am also lost as to why I still get 24mm of fuel height and not over flowing? It is like the needle valves are working independently of the tabs. I had a quick inspection of the jet holes and they look fine. I put a 2.40mm brass rod in each and visually confirmed similar side clearance to the wall and round shape. Also the floats are not cracked or sinking. ?????

Sorry all,CO is spot on. My middle-aged eyes misread N49 for the correct M49.

Can't find detailed data on the net. (Comes up as "Repair Kit (B)" with "improved needles"). They came in an eBay "NOS 240z carb kit for 70-72 240z" They are ~5mm shorter than stock 240z needles Kit Supplier NJC Autoparts Labels on box: "Datsun x6010-E4926" "39-5063"

I love the precision! Excellent skills!

I am wondering if an extra wrap of a coil or two at the inductive tap on the back of a 240z tach will make it work with the ZX distributor?

Has anyone tried these on a track car? Are the spring rates and damping suitable for the track?

It won't hurt to try. Install the transplanted towers in order with the bolts only snug. Install the cam and rotate it while you tighten the cam bolts. It should turn freely. Oil the cam or use rebuild grease on its bearings when inserting.

Our club is planning NH next year!