Zedyone_kenobi

nope, I forgot about that, but I have tried that before. Funny though, I have no idea if it helped or not.. I do not remember.

Well went for a test drive, and it is still popping through the exhaust. I will recheck everything balance wise, and mixture wise in the morning. I will also probably change needles, even though I do not think it will make a bit of difference.

about 2 seconds is what it takes to push them up. What I did find that both my screw valves that act like a damper in the SU oil are both exactly .348" plus or minus many half a ten thousanth. Very close to each other. I took off the first carb dome today and cleaned the begezzus out of it. I used some gun cleaning towlettes and a good thin plastic pushrod. I cleaned every where there is metal to metal in close proximity. It went together and the piston acts like a mirror at all times to the rear carb piston with the exception of one thing. WHen I push the piston ALL the way up, it took the front piston a good 4 or 5 mississippi's to come down.. while the back one dropped right away. In an any other position, the pistons dropped identically, but all the way up, the front SERIOUSLY lagged the back. This may explain why my car only stuttered, at high rpm, at part throttle, and while changing throttle positions. At wide open throttle it would just go open and not have to adjust... So long story short, I took everything apart again and cleaned it up including the oil that was from the overfilled front SU oil reservoir and whala, the pistons fall at the same rate even from the very top of the stroke. I got my stock SU needles in but have not touched them yet. Only going to change ONE Thing at a time. I have high hopes that this may have fixed things. Perhaps my tolerances on my piston and dome are such that any liquid contamination at all was making it hang up. This is going to be interesting. If this does not work, I will let you guys know, and then get that O2 sensor installed ASAP. I will also try the NO SU oil trick and see how it acts.

Great advice! Thanks Captain! Just so you know my SU's are very hard to push up and they do leave a noticeable dent in your finger. Check valve okay. My standard needles have arrived, but I am going to try to clean the damper and dome more thoroughly today. That really seemed to help out yesterday. It was Steve91tt idea, and I think it paid off. I ordered an innovative O2 wideband yesterday as well. I will get that welded in and the guess work will be over when it comes to what is happening with my carbs.

Just want to thank steve91tt for coming to the house today to give me a hand. Just to update the thread. Steve took the dizzy with his pertronix out and we put it in my car and ran it with the same problem surfacing. Then we checked a different coil and it still happened. However, steve then suggested that we take a look at the pistons and the SU domes for cleanliness. Well they had some varnishing on them but nothing too serious. I cleaned them off and reinstalled them (first time the domes have ever been removed since I bought them from Z therapy). The car ran better with no popping until about 5500 rpm. Very clean running We also think we have the problem narrowed down to something in the domes, as the car will hold an rpm with little fuss, but the second I change the pedal position, it starts to sputter and pop out of the exhaust. Since I am VERY confident now that I was wrong thinking it was a timing issue, I am convinced it is a carburetor issue. Which means the time has come to increase the amount of data we have to work with. I will place an order for a real time wide band O2 sensor and we can further diagnose this issue. The O2 sensor will come to be more useful WHEN I get my triples one day, so it is money well spent.

Great work!!! keep up the momentum! I think you have a real fun project on your hands. Enjoy the drive man!

I checked my fuel lines and they are peachy. They are supple and are holding their shape well. I have not touched my float levels. I have ordered a standard OEM set of SU needles AND a set of float bowl gaskets from Z therapy so when I tackle the float levels I will be ready. copy that on the timing chain. I forgot my mechanics there. One more reason to check to see if the valves are adjusted correctly AND if the timing chain has any stretch. Can fix both at the same time. By the way, while I am thinking of it. I would think you should check for timing chain stretch while the engine is hot. But I have not checked. Is that the case.

MY car has 71k original miles on it. Since I am thinking that my issue lies not in my carbs but in my timing somehow,I was wondering if my timing chain may have some stretch in it, which is not allowing me to time it right. But I am not sure if that would make me run advanced or retarded. I will have to think about it. Nevertheless, I need to pull my valve cover and check to see where the heck I am when it comes to timing AND valve lash.

Merry Christmas guys, and happy new year. My God bless each and every one of you with health and happiness in 2012

I will check for you, but remember I had it recurved, cleaned and had new bushings/bearings installed. , so it is nothing like stock any more. Still I wish I had an extra dizzy just to see what a stock one would run like. I need another data point. Just for kicks I installed a brand new in the box set of NGK plug wires and a new cap. Still does the same thing. These plug wires have a 5 kOhm reading, were as my taylor wires had a 0.740 kOhm reading. Car ran exactly the same. Last thing I did was advance my timing to 17 degrees static and I will see how that runs tomorrow. I have yet to hear any pinging so I will do that. If that fails I will order a new valve cover gasket and take a look at my cam shaft. It is possible that I may have a worn lobe, but I honestly think that is highly unlikely.

tomorrow morning first thing I am going to do a compression test... I did one 3 years ago, but we have to check it off the list.

yes, brand new cap and rotor. Well less than 4 month old and 400 miles. I advanced my timing to 17 degrees static now which should yield me about 36 degrees total advance. Which I think is plenty. I did order new float bowl gaskets today and some OEM factory needles. We will see how they act if I need them. Today I experimented with my mixture. It still pops profusely at part throttle, Here is an interesting tidbit. As long as the rpm is increasing it seems to barely notice anything, but when I slowly creep up on about 4000 rpm, it spits and sputters if I hold it there. How about some SU help here. During acceleration the pistons rise, but when I reach the tail off of the acceleration, I would think the bowls would drop. Could my bowls be dropping way to fast, causing lean spot? OH I run standard issue SU oil that MSA sells. No idea what weight it might be. It came in a clear bottle called 'SU oil'

wow, less than one turn! My car would not even run like that... amazing how different two mostly stock cars are..

motorman, glad to know there is somebody else chasing this issue. Were you popping out of your exhaust? Can you tell us your stats? What initial static timing are you running? Max advance? Are you seven eights turn form full lean? Or are you 7 to 8 turns from full lean? You lost me at your mixture screw setting? Also is your motor stock? The more data points the better. OH, I forgot to mention, I only run 93 octane Chevron in my Z.

Welcome welcome! I do wish you the very best luck in your search. I hope you find one that lights your fire as much as your first Z's did!

copy that, I checked mine out. Mine flows in the direction it is suppose to flow. I cleaned it up and reinstalled it. Today I may be grounded. It is pouring rain out side all day and I may not get a chance to go for as spin. Sort of irresponsible to do wide open pulls on a wet road! So here is where we are at. Carbs are at 2.5 turns from full lean. All my choke cables do return to the right spot. Needles rise and fall with no binding what so ever I have good fuel pressure Timing is at ~15 BTDC Vacuum Advance is installed but not hooked up PCV valve is clean and operational NO vacuum leaks of any kind These are my symptoms: Car starts idles and drives perfectly up to about 4000-4500 rpm Under part throttle of any kind that takes me above 4000-4500 rpm I get popping and misfiring through the exhaust Under wide open throttle in second gear anyway I can get the car to pull all the way to redline without hesitation With the vacuum advance hooked up The part throttle symptoms are still there and may be worse What I have tried: I balanced the carbs 2 different times, they are spot on I checked PCV valve I installed new plugs I installed a new fuel pump I totally rebuilt my entire fuel system I had my distributor rebuilt and recurved to european specifications New Z therapy carbs with SM needles I have run with the vacuum advance and without it I have tried timing from 8 degrees to 15 degrees I have run a jumper from the battery to the coil bypassing the tach to see if the old tach is messing up my power to the coil What I have not tried yet: I have not tried to advance the timing more I have not swapped out my distributor or pertronix to see if that is at fault I have not done a valve adjustment I have not run more than 2.5 turns out on my carbs I have not looked at my float levels since I bought the carbs I have not bought a wideband to get real answers once and for all (after christmas I promise!) What I am planning to do! When it dries up, I am going to make a hard full throttle run on a long stretch of road, and then stop and pull the plugs immediately before the evidence is lost Analyze the results and make changes I may go more rich/lean by a quarter turn I will place an order today for stock SU needles from Z therapy and a set of float bowl gaskets. I will buy a wideband O2. NGK makes a nice one for less than 300 bucks. If I get desperate and I am convinced my fuel A/F mixture is close, I may play with timing more. Am I missing anything guys? Can you give me any more advice? I certainly appreciate all the ideas. This is truly a tricky problem.

nope, I have not done that...But the engine does not act like it is that far out of time. When I did my valve job 2 years ago I noted in my journal that the timing mark appeared to closely coincide with the TDC. But I can always double check. A wide band will have to come into play eventually. So man variables to consider. I have to be able to concretely nail down some of them with data.

I can do a valve adjustment Friday. I am taking off that day. Can anybody with a stock 71 tell me what kind of max advance they are running with the stock cam at say 3000 rpm? I did not touch the timing today. I am still at about 15 degrees static. Max around 32. As I was yesterday. By the way folks, thanks VERY much for the help. I usually try to be the one helping others, but now I really need the wisdom of the Z gurus.

Ah, I never really looked that hard into that. Yup, That goes to my crank case ventilation, check, PCV valve is new when I got the carbs. I removed it and it rattles when I shake it... I will check to see if there are some diagnostic checks I can do on it.

There is nothing at all on my balance tube. It was all taken off when I got my total Z therapy treatment. Another piece of the puzzle. I went out for a drive today after work and fiddled a bit more. Set the carbs at 2.5 turns out which is where they were at, NOT 1.5 turns out, I misspoke earlier. As I wanted to be sure I checked them and set them to the 1.5 turns out from all the way up and the car would not idle. I knew that was wrong as my car always had an awesome idle. So I put them back to 2.5 turns and BAMMO, rock solid idle again. Also, the popping only occurs at part throttle at around 4500 rpm. At full throttle it pulls hard to 6500 rpm no issues. Interesting problem!

WHat PVC system? I do not think my car has one? All great advice Leon. I am running SM needles and I adjusted my carbs per the SU video, finding the highest idle possible. 1.5 turns form full lean is not out of the ball park is it? I get a nice pretty blue flame from my gimmicky colortune with that setting. Still, I can always check for vacuum leaks, easy enough, and look at my valves ( which I did actually adjust about 2000 miles ago! haha) All my original tubes are hooked up to the air cleaner as the factory had them. I will take her out for a drive and try to fatten her up a bit. I have exactly 2 turns clearly marked on my car so that will be a easy spot to reference. More news in about an hour.

yup, my wires are all reading very low .55 Ohms or therebouts. coil wire included... I tend to agree with you doradox. It would seem that as close as my car is to 'normal' that something else may have been going on. I need to verify that my proposed solution is in fact the answer. I will also try to hook up a jumper from my battery to my coil to see if my tach is in fact causing any goofiness... I will need to go for a drive today to verify my settings on my car and see if I can eliminate the popping with the addition of more timing. ( I am going to try to run 17 BTDC without a vacuum advance as the european dizzies run) Steve, I read many of your other posts about timing. IF the stock OEM Datsun 240Z in 71 could theoretically achieve 47 degrees BTDC I would think that hoping for high 30's would be reasonable. If there was a way to check to see if my pertronix was funcitoning properly I would do it, I have no other dizzy to swap out with it and I have not had points in my garage ever. I bought the car with the pertronix in it. I have to admit, even though I read all the negative things said about the colortune, I wanted to try it anyway. Call it curiosity maybe. But having used it, I can tell you it would be far more useful for a car that cannot idle well in the first place and that is about it. For a car like mine that is faultless below 4000 rpm, it was just a toy that I plan to play with my lawn mower with now. Everytime I put the colortune on my car I get a nice blue flame.... but I am an engineer, who really prefers quantifiable results. Not pretty colors. Shame on me for not listening. Yes, I will look into a o2 sensor now, just for kicks. also you all should note that I have a new fuel pump putting out almost 4 psia and a new fuel filter and a completely new set of all fuel lines.

Okay an update for any who care.. I was messing around with my colortune and came the realization that it does in fact give useful information, but really only on a gross setting at idle. I would not trust it beyond that. AN engine will react differently under load, so revving up to at idle to me is not an indication on mixture ratio whatsoever. However, with all the mucking about I did, I decided to start from scratch. Again.... I checked my carb balance and verified it was good at both idle and 3000 rpm. Next I set the A/F mixture knob to two turns form full lean. Third, I started it up and found the highest rpm at 1.5 turns out form full lean, so I leaned it out a half turn. Checked the static timing and max advance (folks get a digital timing light so you can do this, it is very critical) Static timing was close, but my max advance is only around 32 degrees, where stock you could theoretically get to 47 degrees, but realistically only got to about 40. I decided to advance my timing to close to what the european spec cars run ( 17 degrees) at idle. I could only turn my dizzy to get 15, but went out and gave it a try, and low and behold the popping was gone at 4000 rpm. Instead it was moved up to 5500 rpm and then only barely. Methinks I need more total advance. I will try to hook up the vacuum advance again and see if I can eek out more timing out of it. I Car feels FAR better now by the way in all gears. I should also note that I have a custom curved dizzy. Do not try to run your stock dizzy at 17 degrees BTDC as your mechanical advance and your Vacuum Advance will put you into a dangerous place.

Dave I would budget in for new oil pump as well. I cannot possibly hurt. And it is a bit of extra safety for you. The price for a bore seems a bit low, but I would check to see if they could clean the block in a bath and chase all the threads for you. I have no idea at all what kind of power that will make...

Got home from work a bit early, and decided to try out the jumper, to no avail. Maybe it was better, but if so not by much. However, I did do some more digging. I decided to rebaseline everything. I pulled off my air cleaner and rebalanced the carbs. They were of course unchanged and dead nuts on. Then I started with the MR 2 turns from full lean I proceded to go half a turn toward the lean side and the idle picked up dramatically.. AHA!!! this is good. Then I went another half and it dropped a bit, so about 1.5 from full lean is my sweet spot. Next, on to timing. I had it set for 12 degrees BTDC at idle per my dizzies rebuilders request w/o the vacuum advance. However, I am reaching max advance at about 2800 rpm, which is not bad per say, but the most I am getting is 32.5 deg BTDC. I should be closer to 40. I maxed out my dizzies advance and got it to 15 BTDC. I took it out for a drive and I was able to rev almost to redline before the popping out of the exhaust happened. I think I just need to dial in a few more degrees of total advance, maybe hook up the VA again. Seems timing is my most likely culprit.