Zedyone_kenobi

UPDATE: I performed several vacuum related tests yesterday. More data, for those who are still with me. I Tee'ed into my manifold vacuum near the power brake tap. Warmed up I am solid steady at 17 in. I fiddled with the timing a bit so that may be why I am off from the 19 or 20 I had last time. When I drove the car, I saw nothing unusual with the vacuum readings as I moved along. Very steady all of the time, and responding to my inputs form the throttle as you would expect. When the popping happened, the vacuum was steady and the needle did not jump around. So I pulled it into the garage and sprayed carb cleaner around the gaskets, and no change was noticed in RPM Lastly I moved the SM needles flush with the groove in the bottom of the piston (although I know the FSM says otherwise) This make the car super rich at idle and it really struggled to hold a 500 rpm idle with so much fuel going through her. But the problem still happened. the LAST THING TO try with the carbs is to weigh down the pistons more so it is harder for them to rise as suggested before. I may try to hook up my GoPro camera under the hood with a flash light to see what the pistons are doing if I get sporty. I truly think my car is not getting the fuel it needs. THis is the reason: I got her up to 5000 rpm and she was popping like mad. I held her there at 5000 rpm still popping and with the ARF at the mid to high 16's. I yanked down the choke all the way this time and she went to 12.5 and took off. THat would seem to indicate that the needles are NOT rising ENOUGH! I have a sneaky suspicion that this is a far more mechanical issue than just carbs. But I am about ready to crush this problem with my wallet and a phone call to Datsun Spirit!!!!

I vote for an epoxy covered floor....HAHA It is what I use and it makes sliding very easy. Also, I will second card board. It makes it VERY easy and provides some cushioning.

Agreed When I redid my inner fender, I used a tube of stuff called plastic metal. It made the repair so very easy. I also recommend www.automotivetouchup.com they can match your OEM color VERY close. I have a thread on here somewhere that shows my inner fender repair. I had 13 or so holes in there from an AC install I removed.

Okay first things first. The distributor vacuum advance should be connected to the little vacuum nipple RIGHT BEHIND the front SU. The proper location for the large line coming out of the valve cover is the orange air cleaner. The hose from the crankcase that exists the block right below the dizzy should plug into the PCV valve on the balance tube. I will check out my three way vacuum valve to see where they are hooked up. One is definitely the expansion tank, I think one is the air cleaner, and the other is the small tube coming off the crankcase vent

Shouldn't there be a throttle lever next to the choke lever on the center console.

I need a moment. This is not fair. I had your car as a screen saver for a while.

Yup, 2 new sets of NGK's.

I asked Z therapy about the floats and Steve said they were spot on. Also bad floats would also show up at WOT, not just part throttle. I spent the night cleaning connections and hooking up a vacuum gage inline with my manifold. I had to run a line all the way into the cabin from under the hood, but that should suffice. My wide band responds to changes in the idle mixture screw immediately. I was running about 11:1 when I sent them off, and Steve said that his car would stumble badly off throttle and would lean out terribly the way I had them set (2.5 turns from the top). He said he went to a hair over three turns out and he drove his car for 100 miles just like that with no issues at all. I did not touch the carbs when I bolted them up. I went from running 11:1 at idle when I sent them off to 10:1 at idle due the extra turn or so out. Problem is exactly the same. OR at least similar enough I cannot tell the difference. The thing is if I run it 5 turns out, the engine will not run it dies. I would be willing to try a points type distributor if I had one Captian. I would be willing to buy a Mallory Unilite at this point as well. But I do not think it will make a bit of difference accept to lighten my wallet further. Although I do plan on running a Mallory for this engine build I have planned... Hummmmmm

Okay, I will ensure everything is cleaned and making good contact, but I am sure it is. The little flexible fabric looking wrapped wire in the distributor that goes from the housing to the pertronix plate may be dirty. I will also check to see if my coil is getting enough voltage as I drive it. More wires coming out of the hood! going to look like an over instrumented test mule before I am done!

Okay, I have checked the electrical schematic, how would one go about finding where the ignition is grounded? The coil gets its power from the tach, which gets power from the ignition switch. A weak spark could cause my issue, just need to check every ground in the ignition circuit. This is refreshing,as this is something new!!!

I will check the ground as best I can. I can honestly say I have not checked every ground on the entire motor. I will pull up a schematic to see where the ignition is grounded and see where I may be losing something. I get into the high 16's and 17's when it pops madkaw. I will measure my resistance through the coil again, but I am sure I hooked it up right. I think my coil is 3 Ohm so I bypassed my ballast resistor, but I will double check.

Not sure how I would do that? I have checked that my coil is getting 13+ volts, and I have tried two different coils. I guess I could wire in a voltmeter to the coil while I am driving. Not sure how I would measure spark intensity though As far as attachments to the coil, I do not have any capacitors attached to my coil or dizzy at all. I am using a Pertronix flamethrower right now. And I am bypassing my ballast resistor.

Well just looking at the cam lobes will tell me when the valves are closed but it will not tell me when TDC is on each cylinder. Not really sure it matters, as all I am really measuring is make up flow, but everything I have read says put it on TDC. Also, for those who have done a leak down test, did putting 100 psi in the cylinder spin the motor over.

Blue, you thinking is very logical. I actually ran with my brake booster plugged off at the manifold and this still happened. Did the same thing with my PCV valve blocked off and the same thing happened. I also checked the check valve in line with the booster,and it pasted the FSM check. I am just about ready to pull the head off the darn thing. I know there is lots of build up on top of all the intake valves. It is not unreasonable to think that I may have a burn valve. But I would think that would show up on a compression test. Still, I have replaced and swapped just about every single part I can think of. I am not so ham fistted at tuning that I think I have something that out of whack. I am going to do my vacuum runs tonight if it is not pouring rain. But not sure what I will do with the data. If I show my vacuum dropping off as my rpm rises under part throttle, what do I do? I will do the spray can of carb cleaner around the sealing surfaces as well and listen for rpm changes. If that does not show anything, well, then folks, I am going to admit defeat. The last test I will perform is the leak down test. Not sure how I am going to find TDC on cylinders 2-6 though. My plan is to run the engine until it is hot. Pull the plugs disconnect the coil remove the valve cover rotate the engine until it is on #1 TDC do leak down test on #1 Not sure how I am going to find TDC on #2-#6 though. I could stick something into the cylinder that is long and thin and when it stops moving down and starts going up I will know I am close. Guess that can work. But it will not be exact, it will only be close One question I have is when you put 100 psi into the cylinder, do you have to keep the engine from turning over?

Doradox, I hear you, and to the best of my knowledge, I do not feel any hesitation or missing at all right up until it starts to pop and stutter. If I never revved the engine past 4500 rpm I would not ever even know I have an issue. To add more weight into the lean camp, my plugs look light brown when I pull them out, not the nice dark patina you want to see.

Blue, the car can rev to 7000 rpm without any issues stationary, and revs pretty freely... This phenomena only happens under load and only on part throttle. With the throttle opened 30% in 2nd gear I get to darn near 5000 rpm before it happens, in 3rd gear with the throttle opened 30% I get to about 4500, in 4th gear with the throttle opened 30% I get to 4000 rpm. THe harder the car has to work against a mechanical load, the sooner the AFR hits 16+:1 and starts popping and the car stops accelerating. But if I am currently popping and stuttering, if I floor it, I go strait to 12.8:1 and all is right with the world.

yessir. I have three sets of brand new rotors and caps! haha I still need to perform the carburator cleaner spray check. But I am saving that until after my vacuum round. I am getting desperate. How desperate you ask? I have already called Rebello and Datsun Spirit about an entire rebuild, from oil pan to valve cover. I can leave nothing to chance. That 2.7 purist motor Rebello has is looking VERY tempting right about now! Then again, I would really love to tear it down myself and rebuild it with my own two hands.

I wish you were right my friend. I just tried the ultimate overkill ignition test tonight. I left my old dizzy on and installed the newly reset carbs from Ztherapy. Started right up and idled great as always. Drove well below 4000 rpm as always, but again, I was leaning out and popping at part throttle as the rpm reached north of 4000 rpm. So I got out of the car and hooked up the vacuum advance. Drove the car again, with exactly the same results as before. My dizzy is free inside to move, I tested the VA diaphragm and it help vacuum just fine. So Now I was ready for the swap. I installed a brand new pertronix into my D611-54 dizzy, put on a new cap/rotor, and installed it sans VA hooked up. Drove it again, and whala. Same thing. NO change at all. My first dizzy was timed to 17 deg BTDC with and without VA .. .leaned out at part throttle Second dizzy was timed 11 deg BTDC w/o VA ... leaned out at part throttle I am ready to write off the ignition has anything to do with this. I have tried Three pertronix, Three distributors, 2 coils, and anywhere from 7 deg BTDC to 17 deg BTDC, with and without a VA. It was getting late so I did not want to annoy the neighbors, but all the VACUUM gage stuff is next. I will try to see the following: I will see if the VA nipple is pulling adequate vacuum while driving to operate the VA I will see what my manifold vacuum is doing when this leaning is going on vs WOT I will get back you guys on that. Then I will perform the leakdown test on all 6 cylinders

Well you can have a vacuum leak from the intake to head, the PCV tube on the balance tube, and the power brake booster line on back of the manifold. One sure fire way of checking the float level is to hook up a clear tube on the bottom of the fuel bowl. Unplug the coil, and crank the motor over. Then go look to where the level is in the clear hose. You should be a certain level (22mm) if I recall (check the FSM) from the joint between the cap and the fuel bowl. Adjustments of the float is done by slightly bending the tang that contacts the float needle. If you live in a cold weather area, the lines help heat up the carbs faster. I live in houston, and like yourself I removed my coolant manifold lines.

Yes I checked valve lash. Nothing is crazy out of whack or lose. Hard to say for sure, as it was not hot and it was not cold. More warm. But the feeler gages felt within the realm of acceptability. I have a dizzy in there with a working vacuum advance. It is just plugged up. When I get her running tonight hopefully (I installed the carbs last night) I will be able to play with timing again with AND without vacuum advance. On top of that I have another OEM distributor that has not been recurved with a NEW pertronix, new cap, and new rotor, and new wires, I may swap that in, set it 5 BTDC and give that a try. I will flush out the ignition part of this thoroughly by the end of this weekend. Although, keep in mind, I already swapped dizzies with somebody else and this problem still existed. So this is one last ditch effort to run this to ground on the ignition side. While I know no two engines are the same, but many other people have run without a vacuum advance and high static initial timing without any issues. So part of me thinks this is something more clever. A leak down test will give another data point, as will the vacuum readings

UpDATE: Had a talk with Dizeasedz and he suggested I do a leak down test. I have acquired a leakdown tester today and will try to get that hooked up tonight to see what I find. PS-It was great talking with you Guy. Thanks for all the VERY helpful advice on the engine build. I will be in touch soon to discuss that further.

I will be interested to see how this one compares to the one I am running. Thanks for that. I had forgotten about that post from a while back. I will see if I can get a picture of the weights stamped inside as soon as I can.

I have a 71 240Z an this is not the OEM distributor to my knowledge. My car came with a D615-52 which is currently on the car (but recurved from www.advanceddistributors.com). I have no idea what this came from. It was an ebay find that was just too inexpensive to pass up. I have ordered a new pertronix to put in it and new taylor wires to keep for another build I have in mind. Which year, make model came with a D611-54. Any idea?

I have an infrared heat gun that I use to measure, well anything from the temperature of my grill, to the air coming out of my vents. My question is with your heat shield under those triples is there enough room to touch the pipes. I mean I guess there is since you did it, but VERY cool Nice use of science. I agree with steve, time to buy another diagnostic tool!

Thanks Adam, I am not even running my vacuum advance at this point. I am relying totally on mechanical advance. Well I got my carbs back last night, and I plan to put them to the test. After I get the car back together and I do all my other trouble shooting, if it still does this I am going back to timing. I picked up a newly rebuilt D611-54 single point distributor. I ordered a new pertronix, more new wires (I wanted red ones anyway), new cap, new rotor, new vacuum advance and will try timing from scratch again. I know that distributor is not OEM for my car, but it should work well enough.