Zedyone_kenobi

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.

pics of the tach?

That is awesome advice, and my sincere apologies for not including details... I run a Pertronix Flamethrower coil Advance Distributors rebuilt Dizzy that was recurved to close to european specs Vacuum advance plugged up. Pertronix electronic ignition installed. Taylor 8mm plug wires New NGK plugs I am running with a balast resistor with a jumper wire across it. I was looking for a wiring diagram of the 71 to find the tach to coil relationship. I have a 73 FSM, but I know they may be a bit different than the 71. Just for reference, I have a spare tach in my parts bin... but have not checked it out. Your suggestion is fantastic zkars. I will give it a try when it stops raining here. May be a couple of days. As we are getting a down pour lately.

That depends.. do you have all the lines from teh tank to the evaporator back there? When I redid my evaporator tank, I no longer had room for 6x9's back there...

I ask this as I am chasing down a very predictable miss and back fire out of my exhaust around 4000 rpm. I have been playing with mixture ratios and timing and the more I do this, the more I think they are acting just fine. Everything in the fuel and ignition portion of my car is less than a year old. Now I have seen my tach on some days just go nuts and peg at 7000 rpm when I am slowly idling in traffic, but it always returns, and there are other times when I floor it and the tack needle just swings insanely fast upwards 5x the speed my engine can actually rev. Most of the time my tach does behave normally, but it does act pretty funny above 4500 rpm often. So, I always thought my engine was not running well and my tach was showing it. However, I am starting to think that maybe my tach is causing my coil to miss fire and that is sending a lot of unburnt fuel into the exhaust causing the popping. Has anybody had any experience with this. I may try to locate the wire going from the coil to the tach, and disconnect it and then see what happens. This has been a fascinating problem to track down. And electrical problem would explain SO much with the behavior of this missfire.

I have a very recently rebuilt dizzy form Advance Distributors. I run 14 degrees static timing and max out at about 35 degrees with mechanical advance, I have tried this with both the vacuum advance on and off, and still get teh same results. Perhaps my pertronix is going bad. I have a brand new pertronix coil as well. Part of me thinks this very well may NOT be carb related.

My gosh Healy, you have had some beautiful cars!!! You got a think for the convertibles eh

UPdate, as I was starting to troll on Healy Z's thread. I used a colortune to see where I was in my mixture, and low and behold I got a nice pretty blue flame at idle. when I gave it gas I get a very orange color that never quite gets to blue again. I think I am still rich, but I am also starting to suspect other things. My dizzy is practically brand new from a professional rebuilt with new bushing/bearings, etc. All the advance weights actuate very well. I have the Vacuum advance blocked off, as I had the dizzy recurved to match the european specs. I still need to find a wideband O2 sensor that can be read real time. Then I know for sure what is going on at higher rpm.

I do have a go pro camera that could be used for this. But i would need an extreme amount of light under the hood to make it work. But it could be fun. I assume this is all under load we are talking about Blue. I find the SU a very fascinating carb. I have read quite a bit on it and I do understand its function for the most part. What kills me is when I installed these carbs from Z therapy, they performed flawlessly to 6500 rpm. I have since had my dizzy rebuilt and recurved but nothing extreme. I somehow think this is not fuel related any more. My SU's are fresh off a Z therapy rebuild and they look and feel amazing. The car idles and performs FLAWLESSLY below 4000 rpm. But its a backfiring wall at that point.

Hooked up my colortune in the number 1 position last night, dimmed the lights in the garage, and started her up. I had already warmed the car up by driving it for 15 minutes prior to this. When I walked around the car to see if I could see any flames, it was a beautiful light blue. When I revved the engine it turned very orange/yellow and bright! So, initial diagnosis. My idle mixture is pretty darn close, and any throttle input is met with extremely rich conditions. I tried holding the throttle in a fixed location, and the flames never went back to blue, but stayed orangish. I will try using the screw to hold the idle dead steady and make a note what happens. Well whatever I am I am not far off. So leaned it out a 1/4 turn and went for a drive. Car drives flawlessly up to 4000 rpm. Then as predictable as clockwork, it pops and stutters badly out of the exhaust. I am starting to wonder if my oil level is wrong or maybe I need a different viscosity SU oil. I checked my needles and they fall straight back into the jet smooth as butter. I know I have good fuel pressure, but I have not checked my float levels, but like Bruce says many times, They were set from Z therapy a year ago, and I see no reason why they would have changed. So I am going to keep playing with this as best I can. I will try to make a video of it working...if I can find my camcorder.

Yes, I will MOST definitely plan another trip for next year... i the warmer months. It will be more grand this next time, I guaranty it.

do you pop from the exhaust or form the carbs?

OOOOh data with a reference measurement.. now we are talking!!! Add a few more sensors in there, and we will start getting in to NASA levels of measurement rigor. Ask me how I know!

That band is not color related Healy Z the color of the flame is due to heat, leaner mixtures run hotter (whiter), while richer mixtures run cooler (more orange) I do not think you will go orange/blue/orange. I get my colortune tomorrow.. we can talk over the phone if you like and we can compare results and try out ideas. remember you cannot tune one carb totally independent of the other. The balance tube dictates you will get some cross talk. I have a testing arrangement in my head in mind, but I really look forward to playing with this toy. IN the end, I can easily see myself getting a portable O2 sensor, and getting fittings welded into my header. But this seems to be a great first shot. I want to echo what Blue has said in countless posts... reading your plugs is an irreplaceable tool...to knowing what your engine is doing. It is the equivalent of drawing blood and running labs. Plugs do not lie. I just need a whole day to mess with this, and I am hoping to have a week off of work to play with my colortune. Healy, PM me your phone number and we can chat if you like with our colortune experiences!

Yeah, so cars are in essence, really good for trees.

I would think this tool would be ideal. You have to set SU's fuel mixture at idle anyway, so it should get you pretty close. I ordered a colortune this week. I am hoping that at night with the lights off, I will get a good color reading. I just want it a bit blue. I still think I am running rich as I am popping out of my exhaust anywhere above 4500 rpm. That may be my needle though. I checked my records and I have SM needles in my rebuilt carbs. That may be too rich for a stock engine.