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engine is not running right after warm, movies and pictures included

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Alrighty lets get to it.

car: 10/1972 240z with an L24 and an E88. completely stock engine.

I have recently been able to get my car to move under its own power, but it seems that problems keep coming about. Yesterday while taking her out for another test drive she drove fine for about 1/8th of a mile then she started to sputter, i gunned it and once i got past 3kish rpms the car pulled like I was hoping this car would be capable of. but as i started a to do some normal driving, 2k rpm cruising and 3krpm shifting the car started to sputter, lean pop, and backfire again and again.

brought her back into the drive way and started testing there. she revved fine and it seems that whatever the problem was it was gone. and then after i let it idle for awhile it came back. so i came back here and started looking at what to do. This is what I have done in hopes to stop the problem.

cleaned both of the carbs, replaced gaskets where needed

checked float - 10.31mm

checked timing - 0deg

set valve clearance - with engine warm .012 exhaust .010 intake

checked carb air balance - unisyn at idle

checked carb fuel - tried colortune on cyl. 1 and 5, but it kept acting up and resorted to the SU carb tuning tech on classiczcar

checked timing again - 0deg, and jumps to 20+ when at high rev.

then I let the car sit for a night because it was getting cold and damp. double checked all of my info and found that: the timing should be at 7-10 deg not 0, i should balance the carbs at 3k rpm not idle, and colortune at 3k rpm on cyl 2 and 5.

started the car up this morning, in hopes that it would all be sorted out with the inproper set up, but it obviously wasn't.

here is a vid of the first start up

that pop at the end is both backfire and a lean pop. awesome.

So I started to re-tune everything.

timing now set to 8ish deg

synced the carbs with unisyn, backed down all of the screws equally and set idle to 650-700 rpm. turned off the car, and then pulled the #2 plug


looks normal, and they are less than 20 miles old. stuck the colour tune on and here is what it is at idle

and then i set the idle to 3k and tuned it.

movie doesnt show it well, but color that I achieved, bunsen blue with hints of orange.

turned off the car and pulled #5 plug


tuned the rear carb at the same rpm and finally got the same color that I got in the front.

then I checked to see if my needles and nozzles were binding.

the rear piston is a bit harder to pull up than the front, so I am planning on dunmping the ATF and using some 10w30. To see how the carbs were actually balanced I used the lifting pin to see how the engine ran on only 1 carb.

from what I have read about the pins, the carbs look to be too rich, but according to the colourtune they are at their best. So meh.

Then I checked to see how the car revved through the power band. All of the jumping around is me playing with the throttle.

It seems that all of my problems were solved! So I took a photo of my temp gauge to show you all what "normal temp" is on the car, to see if that is what everyone else sees.


and while i was doing that the car started to act up again.

so i checked to see if both carbs were actually working, twice. and showed you the difference in nozzle richness.

So yeah... I have no idea what is wrong. please someone give me some advice. The only thing that I think it could be are the needles and/or nozzles, but why would it only happen after the car was warmed up, or under load?

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fuel filter is about a week old, but i'll be replacing it today with a clear one so that i can see when it gets dirty. i'll also be pulling the pistons, and nozzles out of the carbs to get another bit of cleaning on em. pull the mech fuel pump off and see if there needs to be any cleaning done there.

going to re-set the timing to 12 deg, not 8ish.

i'll let you know how it goes after the morning's coffee

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okay so I replaced the fuel filter with a clear one, re-cleaned my needles, piston, and nozzle; set my timing to 12 not 8, the richness to 2.5 turns down; then tried to start her up again.

with the lack of every bit of emmisions it takes a bit of work to get her running, but once she does start she is quick to turn over. once i got her running she was lean poping here and there so i made adjustments to both of the carbs and within about 5 min she was running normally.

I checked to make sure that the carbs were synced, and there were a hair off so I made the adjustment. checked the richness of the carbs by the method decribed in classiczcar, and then sat in the car and this is what is going on.

this is probably one of the best examples of what happens.

I am making a run to the parts sotre and picking up some brake cleaner to see if there are any vaccum leaks after i post this, and then check the float level (forgot to check while i was cleaning).

I am almost damn positive that it is a fuel at this point, and I am pretty sure it has to do with the rear carb. The reasons why I am moderatly sure that it is the rear is due to it needing a ton more richness. then again, it could be that vaccum leak and it needs a crazy amount of richness just to get the right mixture.

On a related note, I think, I am occationally hearing rod knock sound coming from the rear of the engine, cyl 5 & 6ish. This is my first pistoned car and am not really used to sounds like this, but from what I have gathered does this mean that the rear is running lean? it doesnt happen all the time, and I have yet to really pinpoint when it exactly does.

hopefully this will bring more light, and spark more ideas in your heads to help me figure out this issue.

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yes i have made sure the nozzles are up all the way every time i make an adjustment to the nut. they occasionally stick, but it doesnt seem like it'll be an issue since i no longer have the cables.

I am running points; 3 week old cap, plugs, wires, and points. point gap set to .020, spark plug gap set to .035.

I cleaned and made sure that both of the floats were at 24mm through the blow through method; blow through the inlet tube and once it stops the air that is where it'll sit, measured twice with calipers. the float needle, or whatever it is called, is the one from thezstore and stamped with 1.7, the older ones that i has were both 2.0; dont know if that could help.

After i did this it seems that the car is running worse... i re-synced the carbs, adjusted richness on both carbs, and the rear is still much lower (near complete bottom) than the front.

also noticed that i am spitting some white smoke out of the back of the car, so I am sure that i am running rich somewhere.

tried to find if there was a vacuum leak, but the car never raised rpm wherever i squirted carb cleaner or brake cleaner.

also noticed that the engine slows down its RPM whenever i turn on the e-fan, would this also mean that the spark plugs are getting less juice, and therefore not getting enough to explode all of the gas in the chamber? I have been planning on the GM alternator as well as the 280z HEI mod, but was kinda waiting to get this problem sorted out before i went crazy with that stuff.

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I know I am going to catch a bit of heat for this....

My 73 was having some of the same symptoms. I would have it running good for a bit then I wouldn't run worth a darn. I replaced the plugs every fuel filter, took the carbs apart and cleaned them. I could not afford a set of rebuilt SU's so I bought an Arizona z-carb manifold and a brand new edelbrock 1403 with elec. choke. problem solved. the car runs amazing.

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White smoke COULD be a sign of coolant getting into the combustion chamber(s). Also hearing a knock or ping on cylinders 5 and 6 could indicate a bad head gasket.

Also, have you done a compression check yet? Bad compression does not mean that you have a head gasket leaking water into the cylinder.

Black smoke is an indicator of a rich condition. Blue is oil.

Edited by oldhemi
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heh, if this problem keeps up for the next week I am gonna scrap these SUs and go with a tripple weber or mikuni...

White smoke, along with the other symptoms, makes me think you're getting coolant into the combustion chambers. Maybe a leak in the carb warming lines, if you use them? I had that in my '73 when I bought it.

And if you think SU's are tough to tune, good luck with the triples!:classic:

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The white smoke leads me to head gasket leak - but also think you need to test the compression of all the cylinders.

Why do you think that removal of the emissions gear would make it harder to start? Are some of the hoses/fittings not capped or plugged?

If your dizzy is more than 15 years old than the breaker plate is probably sticking and you are only getting mechanical advance. Do you have a mechanical fuel pump? Is it reading between 3-4 psi? Is the tank full of FRESH gas?

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I'll head to the autoparts store and pick up a compression tester, meaning to get one anyway, and see how the cylinders are running.

as far as the removed emission stuff, the EGR valve, the coolant lines, anything that isnt needed to run the car is gone. all of the lines were blocked off well, but with hopefully with today's test i'll find out exactly where the leak is coming from and move on from there.

yes i have a mech fuel pump, dont have a pressure gauge, i'll see if they have one and pick that up as well, and the tank is 6 gallons full of 1 day old 91 gas.

should have something to show within the next few hours from all of the testing.

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compression test

#1 - 125

#2 - 120

#3 - 120

#4 - 125

#5 - 115

#6 - 120

avg - 120.8

all seems to be fine on that account.

Fuel pressure is a solid 4psi.

the spark plugs when i took them out looked pretty much the same in the first couple of pictures. i'gave them a quick clean and put them back in.

I did however notice something exasperatingly stupid on my behalf, but then again I never thought to look for it until last night. Xnke on hybrdiz mentioned that i should check the brake booster, as it might be leaking internally. So before I started the car I did a visual check on the line to see how hard it was, and if there were any gaping cracks. I found this...



it was easily missed due to it looking like it was connected, but without that bolt in there it wasn't really doing anything at all. This somewhat explains why the car would do it sporadically, and even more so when it was hot. I am going to the parts store, yet again, to see if i can pick up some new lines to replace these with just in case and i'll keep you all informed.

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that did not fix the issue.

and a new sight, i ran the carbs a bit lean to get some lean pops and see if there was any bits smoke come out of anywhere and saw that one spray came out of the rear throttle bushing. it is the first time i have seen it, but then again this was the first time that i was looking for it as well

Edited by crazyoctopus
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Others can chime in here on the numbers - but the compression seem to be pretty low, which would impact combustion - I would think you should be looking for something in the 150-170 psi range. I assume these were obtained using a "dry test" - you could follow-up with a "wet" test by squirting a few shots of engine oil into each cylinder and re-testing. If the compression goes up more than a couple PSI then your rings/pistons/cylinder walls are worn. If it does not, then you have a head gasket or valve train issue. If your static timing is off, then the valves could be opening at the wrong time and compression may be reduced.

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My opinion - after you get the car warmed up, rev it to 2-3K for 30 seconds or better and shut it off. Take your plugs out and take a look for one that looks way different than the others. If so, that cylinder could be getting some H2O in it! Then take your compression check and see if that cylinder is lower than the others.

The reason that you want to get the revs up, is that you dont want a rich idle condition affecting your "plug chop" - reading the plugs condition. We do this on Honda 4 cyl SOHC/750's etc for main jet reading/changing when changing to different air filters, exhaust etc. I think that this technique would be applicable in this case.

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So the engine started, but it took a bit of time for it to actually run normally. When it did run properly it only lasted for about 45 seconds, and then the car died suddenly. It didn't sputter or choke out, it just died as if i turned it off with the key.

pictures of the plugs right after I took them out this morning, before putting them back in I cleaned them yet again with carb cleaner and a golf club brush.

plug 1


plug 2


plug 3


plug 4


plug 5


plug 6


I am going to pull the plugs shortly and see if there is any change in condition.

Here are the results of the comp test this morning.

1 - 150

2 - 149

3 - 150

4 - 150

5 - 146

6 - 150

avg - 149.2

Maybe I made a mistake when I did it yesterday, by dropping the timing to 12 deg, or because this time i removed all of the plugs before i did it; regardless, the comp on each cyl is still just about on avg.

Before I started the car I added a dollop of bearing grease, rags on hybridz's idea, around the throttle bearings hoping to stop the possible vacuum leak, but it really didn't seem to do anything at all.

while the car was actually running as it should I sprayed the crap out of everything front to back, and top and bottom listening for a change in rpm. Once I heard it in a particular spot I put on the straw and tried to localize the drop. Even with bearing grease on the throttle bushings (on both ends, and on both carbs) I was hearing a drop in RPM whenever I sprayed the side where the linkage comes into the carb body, not on the outboard side.

So does this mean that it is time to get new carbs? or should i try cleaning them again and see if the problem persists?

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I'm not a great plug reader and I could definitely be wrong but.....,

Plug 1 - closest to 'normal'

Plug 2, 3, 5 and 6 - rich fuel or weak ignition

Plug 4 - wet (oil/fuel/water, not firing??)

Comp test looks ok in that all the cylinders are about the same pressure.

Maybe try pulling #4 ignition wire and seeing if engine rpm changes (dead plug or bad wire?). If no change, suspect plug/wire/dist cap for spark.

If you can afford, I highly recommend ZTherapy carbs. I had to wait about 2 years to save up, but hands down one of the best things you can spend your money on. Throttle shaft air leaks and other 'weird' conditions are totally taken out of the equation.

More knowledgeable members, please correct my errors.

Edited by mlc240z
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Zedyone - I agree with you on the validity of this plug check, but I was under the impression that Crazyoct's car was not able to out on the road confidently at this point. Using this assumption, I figured that this was better than nothing. I should have been more clear!

Crazy, I have very little knowledge on these SU's, but I am agreeing that you have some leaks which could be ALL of your problems or not. Are your floats set too high? High floats will cause flooding on most carbs that I have worked on.

Since you are using a not-explosive spray to find the air leaks, you could be also loading those plugs up causing misfires leading to the plugs getting fouled -except for #1! I dont have an answer for that one!

As far as new/rebuilt carbs, I would not advise you on that. More Z - SU experienced folks would be much better than me!

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during the most recent float setting i have noticed that the front carb requires to be a few turns richer than what it had been before i set my floats. i'll check em again maybe I wasn't putting enough pressure on then inlet tube. Also if my floats were set too high wouldnt that mean that i would have to be running leaner on the adjusting nut and not richer?

here are what the spark plugs look like right now, just pulled them not 5 minutes ago


and yeah there is no way that i can take my car out on the road i just noticed that i snapped a brake line.

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an hour ago I took off the carbs and looked for anything that seemed out of place, and noticed that the backside of the butterflies, the back side of the piston, and the entrance of the intake manifold were damp with fuel. Note: the engine was sitting for 5 hours at this point. So I wiped it all down, pulled the floats and checked their levels still 24mm. checked all of the bolts and nuts to make sure that they were all tight, they were.

took a bit of coercing but she finally started to sputter, and while they were chugging away i pulled out the #4 spark plug, nothing happened. I pulled #2 and there was a drop, then it died.

It seems that with all of the tests that I have done, the issue is indeed with the carburetors; and more specifically the vacuum of the carbs.

solution send the carbs in to get a complete rebuild, get a new set of SU carbs, or buy some triple weber dcoe 40s.

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