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5 Star Rising

240z misses and spudders same issue thought I fixed it..

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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?

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Posted (edited)

It didn't work

 

If you're lumping all of the individual suggestions in to one big IT then you probably didn't really use most of them.  You wasted the time of everyone who posed there.  You should try new fuel like morbias says, and also hive the engine a general tune, with new plugs, etc.  You need a good solid baseline to start from. 

 

I'd also avoid jumping to unwarranted conclusions.  Like why would the ballast or coil go bad all of a sudden?  It ran well, think about what could change over a "few weeks".  

 

"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, "

 

A "spudder" is a person who works with potatoes.

Edited by NewZed

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I did put new gas,full tune up,set timing,removed/cleaned/adjusted/rebuilt/set float levels on carbs, Checked firing order, Compression check,checked for vacuum leaks, I wanted to move to an igniter regardless if any of those components were bad for bigger spark and easier cold starts,replaced worn distributor, I found the prior owner had his way with the wiring and was questioning other possibilities in the electrical system that could affect this missing type symptom.

 

Thanks for proper definition of "spudder" I can now go about my day knowing the forum police lent a helping hand haha. smh

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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, 

 Just having some fun.

 

I'd focus on what happened in the few weeks after the above.  You had it in your hands, and it got away somehow.  It "sat" only?  You timed the engine, shut it down, went about other business for a few weeks then it ran like you never fixed anything?  Did you do any stuff that "couldn't possibly be part of the problem"?  

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I'm liking this music,car show feel with a message. Yeah the reason I let the car sit for a few weeks maybe a month is because I was working on the interior, had to locate a set of seats so I could go test drive the car, I found a set a prestine late 260z seats locally for 50 bucks and couldnt pass up the deal so slapped some 240 brackets on them and put them in, I can get some correct series 1 seats later if I go that route. Had the Vinyls and carpet out,the console removed and newer aftermarket plug n play fuse panel unbolted and pulled to the side. After putting every thing back in place and getting excited to take my car on its first test drive I fired it up to back it out of the garage and it ran like crap again and back fired, that's why I was getting ideas of electrical issues since I had my hands in the wiring under the dash.

 

The prior owner has wires twisted together with house wiring Wire Nuts I think mainly for the stereo but could be some other funky connections some where since he ran his own wires for the headlights haha.

 

Here is another odd thing I recall happening last year. One time I started the car and it would only keep running if I held the key in the on position I didn't hear the starter still engaged while holding it like that, but that was the only way it would get power and stay running, also the tach was bouncing all over the place. I remember it being late at night in the garage so I fumbled with ignition switch turning it back and fourth,sprayed some wd40 cause the key was kinda getting stuck also, and that seemed to help the key but didn't doing anything to the switch I doubt and still had the starting issue.

 

Then being late, I think went over to the Relay under the glove box (right kick panel area) and cleaned the terminals with wd40 and banged on the side of the relay a few times haha. Then I went to the Balast Resistor and cleaned the terminals and went to start the car and it started right up and stayed running like before,not sure if the relay or balast resistor was causing the issue but it has never done that again, it got me thinking if maybe there was still an issue with one of those components causing the backfiring issue, so the other day I changed out the balast resistor and added a pertronix ignitor and 3 ohm coil, and the car still runs like crap,so i know it's not the balast.

 

I was thinking maybe the ignition is getting a weak or intermittent signal some how. Maybe the 46 year old ign relay is going out or bad ignition switch. Definitely a headache. Thanks HuD I will check the choke as well. Is there a way to bypass the black/white wire going to the + coil from the tach? Was thinking about bypassing all the electrical components if possible and have the engine run by its self as if it was on a test engine stand.

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So I'm still having the backfire issues through the carbs and tail pipe upon reving the engine and there is a small miss at idle.

 

I have been running in circles on this one and I know it's probably me leaving something out or not going in order to troubleshoot this correctly. There has been multiple time where I "thought" I fixed the problem but it seems it's always there. Tonight I used the advice of checking the choke system. I found that the front carb jet nozzle was stuck it did not want to spring back up into the carb, I thought for sure this must be the problem, I adjusted and bent the metal arm slightly and now it springs back up into place. But i still have the backfiring issue.

 

I set the timing again,adjusted the idle on the carbs, and balanced them using the air flow meter, runs somewhat smooth at idle but when reving i get the backfire. Is there another way the choke operation can be sticking or out of adjustment?

 

I'm starting to second guess all the work I did prior, like did I build the carbs right? I remember adjusting the floats a little more on one carb so that I could see a pool of fuel sitting slightly below the top of the jet nozzzle to match the other carb, I hope that was ok to do. I remember checking the compression in the car and it looked good but 1 of the cylinders spark plug was white when the others were a little oily. Even if the compression is good, could I have some kind of valve issue?

 

I still did not bypass the ignition system and see if the car ran better without the signal going through all that old wiring.

 

Could there be a defective new distributor cap?,could there still be a vacuum leak? Could there be a valve issue, could I have a faulty set of SUs that I didnt build right? Could the prior owner have added some after market mechanical parts like a cam? All these questions have been going through my mind. Sucky, just want to drive this thing for the first time.. blah

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The classic way of adjusting them requires the use of a screw driver into the carb to lift the pistons so air cleaner doesn't have to be installed. I think if I'm not mistake the filters richen up the mixture (not as free flowing air) so the trick was to leave them just a tiny bit lean.

 

Stop. 

 

Take a breath.

 

What we like to deal with here are facts and data.

 

Right now you have contradictory statements, which makes it hard to process. If it is firing out the carb then that suggests an ignition event is occurring while the intake valves are open. That means it is a timing problem. You said you checked timing, but if it is firing out the carbs that is an ignition problem. Contradictory statements, so what is it? Have you done the 3 checks for the timing? Check on the crank, check the oil gear drive shaft position and check the cam lobes? Then did you plumb the wires in the right firing order 1-5-3-6-2-4? At this point we need pictures to prove the statement. Put the crank to 0 take a picture, take the cap and rotor off and take a picture, and take the oil fill cap off and take a picture. Then replace the cap and number each plug at the cap and on the engine and take a picture. Without that pictoral proof I am not sure we can truly eliminate these possibilities.

 

Backfiring out the exhaust can also be an ignition related problem which once again contradicts the ignition being fine aspect. Granted backfire out the exhaust also requires some unique requirements. One is unburned fuel needs to make it into the exhaust, this unburnt fuel also needs a spark. Given the flames from the exhaust would most likely light the fuel off in the collector, it would require a cylinder to misfire basically to push that unburnt fuel mixture down into the exhaust to be lit off by the mistimed spark or an adjacent cylinder. That would indicate a plug not firing. If we assume the above is good and that the motor is correctly timed, then now we need to look at actual spark delivery. The ignition signal from the key is sent to the coil telling it to be active, the coil builds up charge then when the distributor rotor contacts a cap terminal it sends the spark to through the plug wire to the distributor through the rotor to the cap to the pug wire to the plug. Check spark at all these points, a spark plug measuring tool/light will be the easiest as you can just put it inline, about 4$ from harbor freight or an autoparts store.

 

Once the above two paragraphs are dealt with we can be pretty sure at that point ignition is fine then will come time to see if we can catch a failure in the system as you rev the engine. An inline spark plug tester along with a wideband would probably narrow down the culprit immensely, but as stated we have to first establish the base line we are working with is acceptable. Pictures please!

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Is it backfiring through both carbs or just one? Backfiring through the carbs can be caused by a lean running condition, if you have a white plug then it would suggest you are running lean on that particular cylinder for some reason. Perhaps the manifold gasket isn't sealing properly and is letting excess air in to that cylinder?

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I finally had some spare time today. I started from the beginning tuning the carbs, I found that I had them set very lean, one of them I had turned all the way in. I started with 2 1/2 turns down and went from the there, balanced them with a air flow meter,set the high rpm adjustment.

 

The backfiring went away and I got the car running good in the driveway like I had did before when I had found 2 spark plug wires swapped. So for the first time I took the car out for a test drive. I noticed the car will stumble pretty bad around 3k and it will backfire out the tail pipe. It's like I can't get the rpm range to Rev up smooth under a load, it stumbles, misses, and backfires. I was able to pull over a few times and richen and lean the carbs to try to find a sweetspot. I could notice a difference each time I messed with the carbs, sometimes the backfire would be gone but the stumble would be worse, sometimes it would be more snappy and smooth but would backfire a ton. I'm wondering if these carbs are causing the issues. Maybe I need to really go through them again and buy a good rebuild kit. I'm using the same parts that came with my carbs because the crap that came in the rebuild kit didn't fit my 4 bolt SUs, so I just ended up basically cleaning the carbs inside and setting the float levels.

 

Also for piece of mind I tried a new Ignition switch, Cap and rotor, and it didn't make a difference. Really wish i had a spare set of good SUs to slap on and see if the car ran good, then I would know if there was something screwed up with these 4 bolt carbs.

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That bar and the overlap makes the routing of the wires a bit hard to follow. Just to confirm the wires are going in 1-5-3-6-2-4 counter clock wise starting from one?

 

The cam lobe up and the rotor pointed at cylinder one are good signs, I don't recall the timing marks looking like that on the L28 on the damper so I'll leave that for someone else to determine. I would assume yellow to yellow would be TDC. 

 

You have to get a hitachi SU rebuild kit, preferably for the 240z if you want the parts to be correct.

 

With your confirmation and physical tracing of the spark plug order we can move onto fuel.

 

With it idling we can do a lot more as well. Can you get a fuel pressure gauge on the feed side? Should be able to pick one up with the appropriate fittings and clamps for very cheap. If fuel is inconsistent you might be tuning the carbs for a certain fuel condition.

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Yes 1,5,3,6,2,4.. I checked the firing order a few times. Yeah series 1 pointer is different than other Zs I have had in the past. I have a full on fuel pressure kit. I would have to mention when I got the car it had an electric FP and I had the same issues, I switched over to a manual pump and have the same issues as well. If you take one of the fuel lines off the carb and put it in a bucket and turn the motor it gets a solid stream of fuel coming out.

 

I had purchased a 240z Su rebuild kit off the Internet that said 70-73. But when I opened it up it had smaller jet needles and needle valves than what was on my series 1. I ended up returning the kit and the guy said maybe it was for late 71 to 73. He did not have another kit to fit my 4 bolts. Not to mention the parts in that kit were super cheap and I felt like they would fail anyway even if he had the correct kit so I stuck with what I had.

 

I remember having a problem setting my float levels though. In the video it shows turning the float assemblies upside down and setting the float levels that way, but I noticed when doing that the weight of the dry float would depress the needle valve slightly thus causing a inaccurate setting.

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Checking back in. For the last few months I have been building a engine on my 71 Chevelle, It is finally done and runs amazing..

 I am ready to start trying to figure out this issue with the 240z again running like crap and sometimes backfiring. Technically I never rebuilt the Su's because the kit they sent me was wrong and it was of cheap quality. I cleaned the carbs, put back all the same parts and set the float levels. I'm wondering if the guy before me put race needles in these carbs or something to make them not tune correctly. Been wanting to slap another set of Su's on the car and see if the carb's are my main issue but cant seem to find a good set local and they are a grip $$$ online just for testing purposes. I will see about getting a video up.

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My car would do the same when cold and trying to rev.  Aka Lean condition.

 

With proper float levels, and a good idle mixture it is possible racier needles have been installed in the past (Do you have a wideband o2?).  SM needles or the like, like to idle very very rich to get a proper mixture in the power band.   If your setting your mixtures at idle for stoich, then they will be running lean everywhere else.

Richen up the mixture, and maybe order some new factory needles from Z therapy.

Edited by HuD 91gt

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