CaptainMajestic

Looks like that's the issue. Finally got around to taking another look and the rear carb has blue throughout the range, but the front runs rich at idle and blue on throttle. Not really sure why the two are behaving differently, but at least now it's drivable. Thanks!

I've got these kind of Air filters on, so no vent lines.

Should the vent lines on the floats be capped off or left open?

Update, I quintuple checked the float tab level is about 14+ mm from the lid. I also checked the fuel levels and they seem about the same. I also took off the suction chamber again thinking the jet needle might have been shifted back some, and it did a little so I went ahead and fixed it. Still having the same issue, the colortune mixture shows rich with the mixture screw all the way up, but I lose power under load. Thanks!

I've got two washers between 28 and 29 in that diagram.

I did some exhaust work a few months ago, and when I went to put the carbs back on I accidentally attached the fuel lines to the vent on the float bowls. My dumbassery compounded when I thought it was a good idea to blow compressed air in there and clear out the extra fuel. Definitely blew the float valve. as it was basically stuck closed and would occasionally rattle open. I could start the car, but it took a while to crank over, the front bank ran lean, and I would lose power on accelerating. Fast forward to the post rebuild, engine starts great again and the rear carb is still running bunsen blue on the colortune. I'm using this carb as the reference, and balancing the front one to match. I'm pretty new to the carb world, so I'm not sure what variables can contribute to lots of fuel at the jet. May be I assembled the mixture screw wrong? Are the two washers supposed to be closer to the bottom of the carb, or closer to the knob?

Thanks for the quick replies: I've been following the FSM and https://zcarguide.com/tuning-adjusting-datsun-240z-su-carburetors/ for tuning. At the moment, the float moves freely and the needle valve seems to be working correctly. I have the float set to ~10mm from the cover, and I double checked that the float actually floats in water. The carbs have been balanced with the engine running at about 750 RPM.

Hi everyone, I recently rebuilt my front round top carb because the float valve started acting funny. I double checked my float level and it does seem to be set correctly, but when I went to tune the carbs I could not get the AF mixture correct. I'm using a color tune, and even with the mixture screw all the way up the colortune shows flame orange. Any ideas why the carb is always running rich? Thanks!

Sorry for the late update, I let the whole thing sit for a day, mostly because I was busy with the holidays, and everything ran smooth and peachy! Thanks everyone for the quick replies

Aweswome, thanks! Just pulled the air filter assemblies and tried starting the car. It was hesitant to start, but got there with what seems like a weak idle with a light whistle coming from the carb air inlet that sounds a lot like a vacuum leak. Going to check tomorrow to see if this goes away with some extra air out. Another thing, after a bit of running I saw some wispy white smoke coming from the manifold gasket area for cylinder 1, and I'm guessing it's just some residue burning off, but again I'll check tomorrow and update you guys.

Hey everyone, I want to preface this with I am a total dumbass: Basically, I was in a hurry to reinstall my round top carbs on my L28 and accidentally connected the fuel lines to the upper vent instead of the fuel inlet and ran the fuel pump until fuel came out of the front air filters. I'm guessing all I need to do is let the thing air out for a day or so before running, but any advice/concerns are much appreciated. Thanks! -Michael

Yeah, sorry I meant the sediment filter that plugs into the electric fuel pump. Tank was cleaned and sealed.

Thanks everyone, turns out it was in fact a clogged fuel pump filter. I swapped it out with a new one and the problem disappeared. I need to figure out where the sediment is coming from as the fuel tank was recently restored and cleaned. Thanks! -Michael

Cool, does the wiring line up to the connectors on these? Or do I have to roll my own?

Side question, has anyone here run aftermarket transistor ignition units? I hear they are finicky at temp

Hi @Zed Head I've put about 500 miles on the car before I started seeing this issue in the first place. The runtime before seems pretty random, I've had as little as 5 min and as high as 30 min while debugging. What's a good way to place a fuel gauge that I can see while running? Guessing electronic?

Hi guys, A bit of background. I am running a brand new electric fuel pump, cleaned out tank with the vapor chamber and no carbon canister, custom made 5/16" copper nickle fuel and return lines, and a 3/16" breather (if i remember correctly). I was using the inline fuel filter with a hacky fuel canister back when i was testing the system and had installed it in the final layout temporarily. I had the system dead ended for a while, then put on the factory fuel rail and routed a line to the return because I ran into a lot of vaporlock issues in Austins' demonic temps. Do you guys know if there is a way to test the ignition module for correct operation? I have access to a signal generator at work, or i could fashion something up with a MCU.

How did you solve it? Right now I am using the stock fuel rail as the fuel regulator. Am going to check the breather line when I get home.

Hi everyone, thanks for the quick responses! @Zed Head The car drives normally for a few minutes then suddenly the engine sounds like it's filled with cotton balls. Like @Mark Maras asked, I can rev with the clutch in, but it's still muffled. As soon as I let off the gas, the engine quiets down and dies. I have been pretty lucky to get it started again after 5-10 seconds of turning over, but the issue persists.

Hi everyone, I've got a 74 260z with an L28 and round top carbs that I've recently restored and rebuilt. The engine is timed and I color tuned the carbs recently,and up until a few days ago everything was running brilliantly. However, on my latest drive the engine started sounding muffled and I suddenly lost power. I figured it was a fuel issue, so I went head and swapped out the fuel filter and checked for fuel pressure and everything was spot on and the engine started nicely. Then on the next drive, same issue. Could it be the valve lashing? Will try to get a video of it later today. Thanks!

Update: By using the power of deduction I have determined that the bearing was probably pressed on backwards and therefore, once again, I am a total dumbass. The basic reasoning being around the throwout bearing is designed to press against the clutch spring and the shape of each side of the throwout bearing have different behaviors. If the side where the center is more pronounced faces the clutch, then the clutch springs can dig in and cause the entire thing to evaporate. If the side where the outer edge is more pronounced faces the clutch then the previous case cannot occur.

Hi guys, I finally got around to pulling the transmission and it is for sure the throwout bearing. https://photos.app.goo.gl/A2JWfv9DEgBtSZQa7 For evidence of catastrophic failure. Anyone know which direction the bearing is supposed to be pressed in? I have a feeling it put in backwards. Thanks! -Michael

Hi everyone, been scratching my head over this one. I recently rebuilt my engine (+ all new seals), and while I was at it I went ahead and replaced my pilot bushing, throwout bearing, clutch, etc. and everything ran fine for several weeks. Suddenly, now the clutch squeaks any time I press it in when the engine running, but not when the engine is off. I've read online this sound is common with a bad pilot bushing, but this one is brand new? Video: https://photos.app.goo.gl/r7FSh6LizfamRN5D9 74 260z with L28 + Round Tops and 4 speed tranny. Thanks!

@Captain Obvious Can confirm I did not let the magic out. Sorry for the late reply, got tied up at work. Turns out @Zed Head was right on the money, I drained the tank + carbs and flushed the lines then added new gas. Started right up! Carb rebuild definitely helped make it start quick! Have you guys ever had issues where when the car is choked it behaves exactly as expected, but when the choke is released the car drops well below it's expected idle? It should be timed, and I thought I did the tuning procedure correctly. Thanks again!

Going to try this tomorrow. Also, at this point anything you guys say to help I take as gospel. Thank you so much!