240ZMan

I had to travel for work for a few days, so no time to work on the Z. Hate it when my work life interferes with my Z life ;-). You guys asked some questions, and this thread has gone on long enough that I feel I should summarize what I've tried. <b>Configuration:</b> 73 240 with E31 head, N33 manifold, 72 3 screw carbs, Pertronix electronic ignition and coil. Everything else is stock <b>Issue: </b> - Engine won't pull past 5k rpm in any gear at WOT with the air cleaner assy on. - If I back off the throttle just a little, it will pull higher, but it's not strong at all. - It will rev past 6k in neutral. - If I remove the airleaner and cover, it revs a few hundred rpm higher before it stops increasing. - If I remove the aircleaner backplate, the engine will pull past 6k, albeit more wheezing, than pulling. - I live at around 6,000 feet elevation. <b>Things I've checked and tried:</b> - new distributor cap and rotor - timing is set to 8 degrees advance at idle which is as far as I can go before pinging. - full advance comes somewhere around 2-3k rpm (don't remember exactly where) and is around 30 degrees - all new rubber fuel lines (needed replacing anyway) - bypassing mechanical fuel pump and running with electric only - raising and lowering fuel float setting - running with choke on - adjusting mixture to excessive rich, and excessive lean - throttles open fully when gas pedal is floored - cleaned pistons and needles and ensured that both needles are seated at the proper height. - pistons move up and down with no sticking - dampers properly filled with Marvel Mystery oil - carbs balanced with UniSyn - One needle is slightly bent at the tip but does not stick at all (spoke with Steve at ZTherapy and he didn't think that had anything to do with this). - compression ranges from 145 - 160 cold <b>Next steps:</b> - I ordered new needle and seats for my floats as one showed lots of wear and I have an intermittent idle problem when it's hot out. I'm going to put those in this weekend, although I dont' expect that to make a difference. - When I put the E31 head on I made sure that the crank tdc mark was accurate, and that the cam timing was correct as well. I was surprised that even though my timing chain has 200k miles, it didn't show stretch. Hence my cam gear is on the #1 setting. Still, I keep wondering if something is off and I plan to try the #2 setting this weekend as well. - I haven't adjusted the valves, but the mechanic who sold me the head said he had adjusted them shortly before taking the head off. I'll probably do the adjustment this weekend as well. - I suppose I could buy a new set of needles and nozzles. I asked Steve at ZT and he really didn't think that was the issue. I want to respect his opinion given that his company sells them, yet he didn't advise I do it. Other than that I think I'm out of ideas. (Does this qualify as the longest thread yet?)

Garret, I am familiar with synching the carbs and have followed the procedures from both the Haynes book and ZTherapy video. At this time I have both carbs turned out 3 turns, although I can't sense any difference from 2 1/2. But with this issue I figured I'd go a little extra. Much more out and the idle becomes erratic. I've gone back and reset the throttle to full open when floored. Didn't expect any change, and didn't get any either. Question to all: Could there be some issue with using the 73 N33 intake manifold and the 72 carbs? Otherwise I'm thinking I either: 1) replace the needles/nozzles wiht a set from ZTherapy or 2) buy another set of carbs from eBay. Don't like either approach as I feel like I'm beginning to throw money at the problem without understanding it which has never worked for me in the past. Still stumped. Daniel

Garret, I used the second way as you described it to mount the needles in the pistons so I think I'm ok. Before that one of the needles was so low that even with the nozzle turned all the way in (closed) I was too rich. On your question about running without the aircleaner, the problem was better in that I could pull to 6k (but not past it), but to your point, it was weezing, not at all strong. The engine is also vibrating a lot above 5k, but as I've never been in another Z I don't know if this is normal or not. I'm encouraged to hear you and others say I should be able to pull to 6k and beyond as I'm excited to unlock this car's potential. But this is becoming a rather frustrating problem as I'm just about out of things to try. Daniel

I do have some small vacuum leakage on the throttle shafts (spraying carb cleaner at idle causes a slight decrease in idle speed). The aircleaner is an early one with the lever to move between winter and summer. The carbs are 3 screw roundtops which I was told by the original owner are supposed to be '72s. Head is an E31. Beyond that all is stock.

I just recently had the head off, and when I was putting it back on, I thought I might need to move the cam gear to the #2 or #3 postition to account for chain stretch. But when I put it back on in the #1 position, the notch on the gear was to the right of the mark on the tower, just like the book and ZTherapy's video say it should be. So I'm going on the assumption that the cam timing is good.

Just tried one more thing (one of the advantages of working from home on a slow day). I adjusted the gas pedal stop so that when fully floored the throttles open a little bit more than 5 degrees shy of fully opened (when they hit the stops). It pulls a bit past 5k now, but still stops reving completely after that unless I lift slightly on the throttle. Seems to me that I'll need to really further reduce the throttle opening to get the revs to climb which will reduce power - which seems pointless and not a strategy I want to follow any further. Sor right now I have 2 theories: Theory#1: For some reason my needles/nozzles combination doesn't flow enough fuel to meet the peak demands of the engine. With the aircleaner on, the horns enhance airflow and the engine runs out of the incremental fuel it needs around 5k rpm and simply stops increasing revs due to an excessive lean condition. When I back off the throttle a little bit I reduce the airflow and the mixture comes back to more normal and the revs climb a little further. When I remove the aircleaner completely, including the back plate, the lack of airhorns means the peak airflow of the engine is reduced and hence the fuel flow just barely meets the needs of the engine (I say barely because it really doesn't even want to pull to 6k as the power is falling off so badly). I'm assuming it's not a carb setting as I tried running with the choke on and it made no difference. Theory #2: There is a resonance between my airhorns and the carbs right around 5k rpm at full throttle that limits airflow. Reducing the throttle a little changes the resonance point and allows the engine to rev past that point. If theory #1 is right, then I suppose the solution would be to get new needles/nozzles. If theory #2 is right, then what is unique about my situation to cause this. And how do I solve it? So 'm wondering what others think of my theories.

Well, the saga continues, but I've finally tracked down the culprit. I checked my dizzy and cleaned it up as well. It's an "11". The vacuum advance moves without binding and the mechanical weights can be moved without any binding I can feel. I also tried setting the floats significantly lower. None of this made any difference. Then I tried making a run without the aircleaner including the backing, attached. In other words, just the mouths of the carb breathing straight out. PROBLEM SOLVED!. Just for grins I put the old stock '73 aircleaner with square horns back on the problem returned. This is very strange because I know I never had this issue with the old aircleaner. I also noticed from experimenting that with the aircleaner back on, if I kept it floored in 1st gear until the engine "settled in" at around 5k, and then lifted the throttle just a bit, the engine would rev higher! I could get it to pull to 6k, albeit the power was falling off at that point. So I went back and checked that the throttles are opening properly with the pedal floored. I'm using a mirror in one hand a lifting the cylinder with the other and from that perspective they look horizontal. But I'm suspecting that this is either 1) an optical illusion perhaps?, or 2) there is some resonance with the aircleaner on AND the throttle in a specific position that doesn't occur when the airhorns aren't there. I tried backing the linkage off a few turns and took one more pass. I don't think that was enough and by then it was too late to drive at redline ;-) So I have backed it off another 5 turns and will drive it later today, as well as enlist the family one more time to floor the pedal and check the throttle position. My concern is that in order to get the throttle set to let me pull the full revs, I'm going to limit the opening during the entire rev range below 5k. And I'm surprised that this is so sensitive. I'd think that others would have experienced this before me. I'm all ears to hear what others think!

Thanks Rolf and Victor for the feedback. I'm going to focus my attentions next on the timing. The dizzy I have is a used replacement and I know nothing of it's history. I'll open it up tonight and see what there is to see. I'm also suspicious of possible binding on either the mechanical or vacuum advance. To Rolf's suggestion, I'm sure the timing mark on my pulley is accurate as I just had the head off and had the chance to get everything set right for TDC. One question on the issue of dizzy advance: I notice at idle that if I pull the vacuum hose off the dizzy the timing doesn't change one bit. This is different from any car I've ever owned where it was important to remove the vacuum line and plug it. Also, if I put the hose up to my tongue I can feel some vacuum, but there is no change in idle speed if I leave the hose open to the atmosphere. I'd expect the idle speed to rise a little as the mixture leaned out.

Rolf, Don't take this wrong way, but I'm glad I'm not the only one with this problem ;-) How did you advance your ignition so far and not have detonation? I tried 10 degrees advance at idle and found I had significant pinging at lower revs (and couldn't tell at higher revs because the other engine noises are too loud). I can only imagne what 20 would be like! Thanks, Daniel

Good question Garret: when I went richer it didn't want to idle well and I didn't notice any other difference. Going a turn leaner didn't make any difference that I noticed at all. I'm running whatever needles were in the carbs when I bought the car with the 72 roundtops. I'm going on the assumption they are stock. Is there some way I can tell?

If anyone is still with me, here's the latest: Per the suggestions above, I've gone back and checked that my timing is still solid at about 7 degrees at idle (which is all I can do before I get pinging), that my throttles are opening all the way, and I used inline6's technique to set my float level (which meant that I raised the level a little more than 1/8" on each one). Also swapped the old distributor cap and roter back in. None of this has had any affect on pulling past 5k (with one exception below), but the good news is she runs great from idle up to that point:-) So here's some new inputs: I was worried I was not getting enough fuel. Although I have both a mechanical and electric fuel pump, I usually leave the electric off as it's rather noisy (I put a switch in case I need it). I wondered if perhaps the mechanical was somehow restricting the flow so I routed the fuel line to bypass it and run entirely on the electric. That made no difference. However, I took a run with the air cleaner cover off (base plate still on) and found that the power now didn't fall off until 5500 rpm and it was more gradual, although I think still too steep. Also, while running at >5k at wot, I heard a few loud pops, almost like backfires, until I upshifted. It was always between 5000 and 5500 rpm. Just to refresh, I have an early aircleaner on my 3 screw SUs with the 73 intake manifold and an E31 head. The rest is a stock 73 240. And the airfilter is pretty new and looks clean. I put the air cleaner back on and went out to get a burger. On the way back I experimented with turning the mixtures a full turn richer and a full turn leaner. Neither helped, but immediately after I set them back to normal, when pulling back onto the road at WOT in first gear, the power didn't fall off until after 6k rpm. It only happened that once, and then 2nd gear gave me the usual "rev limiter" at 5k. But clearly there is something intermittent here. One last thing, as I was adjusting the float levels, I notice that rear needle valve stuck once. I took it apart and the sides of the needle show some wear that appears to correspond to the size of the hole in the seat. The front is fine and doesn't show any wear. So, what you think? I'm leaning towards buying a rebuild kit from ZTherapy to get to a "known state", but hate the thought of spending the money if it isn't necessary. Sorry this has dragged on so long, but as you can probably tell, I'm pretty stumped!

BadDog, Did you get this sorted out? I have just about the same setup you do and could shoot some pictures this weekend if it would help. Daniel

Just got back and tried an experiment on a deserted road. Instead of upshifting when the power fell off, I just left it in gear and held my foot down. The revs stop climbing right around 5k and just stays there as if there was a rev limiter. When I did the same thing in 2nd gear, the same thing happened at the same RPMs. Power up that point is good, not like it was starving for fuel. Besides, if the fuel supply couldn't keep up, I'd expect the power to drop off more gradually, and after a sustained WOT. Not at all what I'm experiencing. Any other ideas?

Good suggestion to check the throttles opening fully. I checked this about a month ago and did have to adjust the linkage a bit but I'll check it again this evening. I did check that the chokes are all the way up several times this weekend so I don't think that is my issue this time. What's got me puzzled the most is that prior to me tuning the carbs I could pull past 5k. The power was falling off, but it didn't just drop off a cliff. One more thing, I live at 6500 feet elevation. Of course, that hasn't changed since the tune up either ;-).

This weekend I received the ZTherapy video on tuning the SU carbs (I have 3 screw round tops on a 73 240 with an E31 head). I followed his procedure to do the tuneup, just short of taking the bodies off the manifold. From 1000 rpm to about 4800 rpm all is great now. But at idle if the engine isn't fully warm (and I mean from driving, not just as indicated by the temp gauge) there is some hesitation when first cracking the throttles a small amount at idle. This was never there before. Also, when accelerating at full throttle, just before 5k rpm the power falls off. I don't mean gradually, it's almost as if there is a rev limiter it's that sudden. Feels like it's not getting enough fuel. I have both a mechanical and electric fuel pump and have changed all the fuel line hoses and filter as well (hoses needed changing anyway - I think one piece was the original 30 year old stuff!). And prior to me tuning the carbs the sudden drop off didn't exist. The two main changes I made with the carbs apart were to reset the floats (both were a bit more than the .55" recommended in the video) and to set the needles with the shoulder flush with the piston (They weren't even close). I've checked the plugs and they look really good, the best they've looked in a long time. I have them gapped to 0.040 as I'm running a pertronix ignition with their 40kV coil. So I'm looking for some suggestions on the power falling off a cliff at around 4800 rpm. Thanks in advance. Daniel

So last night I cleaned all the pieces up and reassembled. T tried to spin the needle in a drill and straighten it, but I don't think I made much of a difference. I did get it a bit straighter by pressing it on the wood bench with my hands (didn't want to use any tools and risk scratching it.) Interestingly there doesn't appear to be any sticking at all. I really think the needle was bent when I pulled it out and has been that way for some time. I guess I'll see how it works when I get the rest of the engine together and fire it up.

That's an interesting suggestion kmack. I may try it. You also mentioned replacing the choke nozzles. I've not heard of that part before. Where is it and what does it look like? Thanks, Daniel

Attached is a picture of one of the needles from my 72 SU carbs. I'm worried about the bend at the bottom. I was very careful lifting the cylinder out and don't think I did it, but I guess that how it happened probably doesn't really matter right now So what do I do now? Try to bend it back? Ignore it and put the carb back together after I clean it? Replace the needle? (I've heard that they are hard to get...) Daniel

I have a '73 240Z with the stock ignition system that I want to upgrade to electronic ignition. I've seen this discussion before, but still have a few questions that I'm hoping someone in the group can help answer. 1. What are the merits of going to a 280z distributor vs. adding a new pickup to my existing distributor? 2. Does anyone have experience with the MSD 6A and Crane XR3000 units? The MSD seems more popular, but the Crane comes with a kit to replace the points on my existing distributor, and is also cheaper. 3. How important is it to replace/upgrade the coil? 4. Should I expect any issues with my stock plug wires if I do all these upgrades? The rest of my engine is currently stock except for carbs which are 72 SUs. Thanks, Daniel