5 Star Rising

It didn't work

I been dealing with this same issue since day one and so many times I thought I had fixed the issue but some how it still remains. Early 71 240z that I bought last year from a tow yard and don't know the history of the car. What the car does: When revving engine it misses and spudders in all RMPS and backfires, seems like it runs a little better when the choke is pulled back then when opening the choke all the way it will bog down and back fire sometimes, just runs like crap and I have yet to take it out for a test drive other than a few feet down my court when I hit the gas it just bogged down like it was flooded and I had to feather the throttle to get it back up into my garage. Things I have done: Removed and rebuilt the carbs after watching the 4 hr Just Su video, set the float levels, still ran like crap. Did new tune up, plugs and wires, cap and rotor still ran like crap. Did compression test 168 psi across the board, found plug wire 3 and 4 swapped from prior owner, RAN GOOD for a while in garage HAD SMOOTH IDLE and I was able to set timing. Let car sit for a few weeks and then started it and it ran like crap again and backfired, I thought maybe a bad balast resistor,points or coil, said what the hell and bought and New Pertronix Ignitor and 3.0 Ohm coil started car up and it ran like crap still with the new set up, after pulling my hair out I took off the new distributor cap and checked the rotor, everything looked fine but I noticed wow I can move the rotor side to side about 1/8", the series 1 distributor shaft had a TON of play, I thought a 100% sure this was my problem, so I bought a new reman dizzy from Auto zone and the shaft was tight even came with a new vacuum advance in which my old unit was shot. Installed the new dizzy and swapped in the new ignitor and fired it up ,same issue still spudders and backfires!! I'm wondering a few things, the past owner was a tweaker from what the tow truck driver told me lol, I found crazy wiring behind the dash, his own homemade toggle switch to run the headlights because the factory switch broke, also he had installed a aftermarket fuse box that actually fits nice and uses the square fuses. But I'm wondering if this guy has some kill switch wired somewhere allowing the car to run but poorly, wonder if I can bypass the ignition some how. I also wonder if my carbs are screwed up some how, or if this guy put in some kind of cam in the motor, it's sounds lopey at idle but may be just due to it running like crap, I thought about adjust valves but with 168 psi in each cyl I didnt adjust them. What gets me is after I found the 3 and 4 spark plug wire swapped i truly thought I had solved the riddle cause it ran WAY better and didnt backfire anymore it had a smooth idle down to 700 rpm, but after letting it sit something happened. Could it still be electrical? like bad ignition switch or relay? It sounds electrical to me lIke the plug wires are swapped or something is not firing right in time. There are not much to these old cars what am I missing here?

I found the problem and it was a stupid one. Firing order was off. Prior owner had 3 and 4 plug wires on the cap switched. Car runs great now..

Do you 240 guys have Anti Backfire valves on your cars. My early 71 doesn't have one, it may have been removed from the previous owner. I went and reset my float levels and I'm still getting back fire issues at all rpms after I plugged a major vacuum leak.. Wondering if I need a anti back fire valve installed. I'm going to get a new PCV valve tomorrow and try that.

Sounds like the 70-71 are a little different. I might just get the late 260 seats and buy new covers for a late 260 and put them in. The car is going to be slightly modified with a front air dam, so i guess the seats are not that big of a deal to be perfectly stock.

I have a 71 series 1 240z that came with some red recaros seats, they were worn and i didnt like the red color so i sold them. Im now looking for a set of seats. I think i would like to go back to stock on this car as its a series 1. I was thinking i could find a set of 240 seats locally but no luck so far. I did find a guy with a set of late 260 seats and he wants 50 bucks for both of them. I wasnt sure if the seat foam was the same as the 240. I was thinking about buying them and then getting a new set of 240z seat covers for them but i dont know if they are the same. I do have a set of 240z seat rails. I searched the forums and couldnt find a straight answer to this, only found what other seats from other cars would fit in my 240. I want to make this particular project stock as possible. Also need a series 1 hatch but thats a different issue i will deal with later.

So Im guessing the weight of the float is not supposed to sag down and push the needle valve half closed when holding the float assembly upside down and setting float levels. Weak needle valve spring clips on new aftermarket needle valves?

Ugh been working 11 hr days this week.. this probably why I haven't posted so much in the last 10 years lol.. time... I plan on working on the car later today or tomorrow but I like to get a good plan to jump into and start testing all the variables thanks for the info, stuff like this really helps. Also question about the floats.. When you remove the float lids and flip them over so that the float is in front of you resting upside down. When adjusting the float level. SHOULD the weight of the float be enough to push the needle valve half closed as you are adjusting your float level? Seems like the spring clip in the needle valve would be strong enough to hold the weight of the dry float up and keep the valve fully open so you can set your level. Seems like mine sags down and pushes the valve half closed in a resting position as I'm trying to adjust the float level Is this normal, or are these cheap needle valve assemblies I got making it impossible to set my proper float level? Thanks

After I set my float levels I will blow through the valves to check for leaks at first these cheap needle valves were not sealing great I had to push them up and down a few times and get them wet to where they would fully seal air. These were the only things I questioned in the rebuild the cheap after market parts. I did a gravity test on the Pistons and they both fall at the same speed and you hear the metallic sound when the hit bottom at the same time. The jet needless are set like the video states aND I am aware of howhat the fuEl operation works in these after watching the video 3 times. "The gardenext hose affect". I will check for any more vacuum leaks using carb cleaner around the intake carfully. But I doubt finding more leaks and fixing them would make the back fire go away because the whole reason the back firing started was because I plugged a HUGE vacuum leak. If anything fixing more vacuum leaks would make it worse haha. But yeah I definitely don't want any leaks.. But got to get to the bottom of the back firing. I will check float levels again and timing as well, I have yet to check timing at all since I got the car.

Right but the video doesn't specify whether you may encounter a problem with a weak spring tension on a cheap needle valve. My floats are set to specs but it's with the natural weight of the float collapsing the needle partially that I was concerned about. On my old needle valves that I removed I noticed that the needle spring tension held the needle all the way up so that the valves were fully open even with the weight of the float and tab pushing down on the valve. Again the back firing only happended after plugging the large vacuum leak. Guess I could try to install the old needle valve and set float levels again to see if that makes a difference.

These are 4 bolt SUs. Both springs are installed. I'm using a cap full of Merc/Dex Transmission fluid in each carb. I had no back fire what so ever and was able to tune and Rev the car with the vacuum leak, as soon as I plugged the vacuum port the idle went smooth but the back firing started. It's almost like the engine can't breath and it gasps for air, thus causing a small back fire at the carbs which I think slams the Pistons upward causing the "click sound". The back fire at the carbs is not a loud pop it's more of a cough in which both carbs puff out a mist of raw fuel, almost like the pop is happening in the intake and then back out both carbs simultaneously. When the car is running and you shine a light inside the face of the carbs it is not wet with fuel or does not have fuel pouring out the nozzles. When setting the float levels I do remember being unsure if the needle valve was supposed to be partially closed by the weight of the float or if the new valve was supposed to be stiff enough to hold the weight of the float with out depressing the needle. I installed a new set of valves but they seemed cheap compared to the ones that came out. As I was setting the float level I noticed that the weight of the dry float pushing down the tab was actually closing the valve. it sure if this is normal. But I set my float levels with where the float rested naturally.

Yeah I heard that in the video too. I set both carbs as rich as they would go and still got the back fire at idle and when when you hit the gas. The idle is smooth but all the sudden you heAR a "click" and the rpm drops and both carbs spray out puff or mist of fuel and then you hear the tail pipe pop continously. As soon as I plugged that major vacuum leak on the port this started happening. The clicking from the carbs almost sounds like a AC compressor kicking on and the RPMS drop and then the backfiring happens. (I don't have AC in my car, just sounds like the click of a compressor). It there another valve of some sort opening in the engine like some sort of EGR or something?

Here is a pic of the port I plugged..

OK I lied car doesn't run that great. I now have a back firing issue after plugging a major vacuum leak. I was able to tune the carbs with this major vacuum leak before. The large port on the air rail that I believe had a large hose connected to it gong to the air cleaner box was wide open. When I bought this car they had put a hose on large air rail nipple and it hung down under the carbs .it had a rubber plug on the end that had cracked open. I kept hearing a hissing sound from vacuum but thought it was the carbs pulling air. I plugged this port on the air rail and now the car idles super smooth, but after about 60 seconds both carbs give a small backfire followed by a small backfire out of the tail pipe. I tried to tune the carbs to get rid of the back fire but so far unsuccessful. It all happened as soon as I plugged the port. Do any of these ports need to be open to suck air? I have seen pics on the net of other L24s with these ports plugged. Thanks

First I was a little iffy about being told to buy a 16 year vhs/DVD about SUs. But I ended buying it from Z Therapy. Gotta say it was indeed worth it, Wish the video had chapters to jump to but I watched it a few times,rebuilt my SU's and tuned them correctly. Car runs great now. Thank you. Think I have been a member here for like 10 years or so. Should probably come to the forum more often.. Cheers

Before I pulled the carbs I noticed that the choke levers (where the cable attaches on the carbs) were bent and binding. Good to know that the video covers rebuilding. Thanks Hud

So does the video show you how to rebuild the carbs? This is my 9th 240z in 10 years.. most all of them had not run in years, installed and tuned many Su's, BUT have never rebuilt the internals of the carbs, this is the info I'm looking for.. I didn't mean that the info in the video was not important as far as tuning and explaining what they are and how they work but my question was, does this video provide step by step of the rebuilding process of the Su's? Gaskets,seals,specs? Or is a Chilton my best bet?

To be honest I'm not interested in how the SU'S work or to become and expert of knowledge about them. I would like a video or book on how to rebuild them step by step and set them to factory specs. Do they cover this info in the "Just Su's" video?

I think I'm just going to remove it. It already has a few oil leaks in different places. I got side tracked and currently are getting ready to rebuild the SU carbs. Probably yank that oil cooler off later.

No thermostat but, she comes complete with a Aircraft EGT sender drilled into the header, with no gauge of course lol..

Ok that's what I was assuming. Far from a race car here. I believe the prior owners used meth according to the Tow yard where I found this car. I am finding alot of tweaker wiring and this oil cooler was installed half ass. I thought about cleaning up the install and keeping the oil cooler but I got to thinking if it is really necessary to keep on this stock car. I will be removing it.

I have a 12/70 71 240z that i bought recently that runs like crap. I do not know the past history of the car or the past owners so I'm starting with a running car that runs, but not great. I have been replacing old parts these last few weeks and in the middle of a tune up. Removed funky electric fuel pump and switched back to a mechanical pump, new fuel filters,new spark plugs and wires, ign cap and rotor, I have not yet done a compression test on the motor. I have fuel going to the carbs and can start the car by pulling the manual choke when cold like normal, but after the car warms up and I open the choke fully the car starts to idle rough and dies out almost like it's getting too much fuel. When I have the car running best is when the choke is slightly pulled back about a quarter of the way. When you Rev up the motor there is a slight spudder or miss through out the rpm ban. Just feels like the carbs are out of tune or not adjusted right. The car lacks that snappy throttle response, and still has a slight miss. I was getting ready to pull the carbs and get a rebuild kit for them but thought I would post this first, I have not rebuild SU's before and may be over looking a few things, like a proper adjustment while on the car. I found a few rebuild threads on here that I will follow, but I'm wondering why the fully open choke kills the motor and what may cause that.

I'm going through a series 1 240z that i bought not to long ago and it came with a aftermarket oil cooler that some one had installed in the past. The installation is not that pretty but I'm wondering if I should keep the oil cooler on the car or put it back to stock. Not running a Turbo or mods. Is this cooler worth having and that benifical? I already have leaks in the oil hoses that I have to repair and I thought about just removing the whole set up. Thoughts?

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Very good info. I just got in touch with a Z collector buddy that I haven't spoke with in 5 years, he has a series 1 hatch for me and just about any 240z part I need. Great news! He suggested rebuilding those SU carbs and also mentioned the heavier beams in the doors. It may be that the hinges are different or not aligned if that is possible. When the door is closed you see a pretty good sized gap under the mirror. It's almost like the door needs to go up and in a bit.