landmizzle

Plugs and wires are in good shape. However, just to be sure, I put brand new NGK plug wires and NGK B7ES plugs in today. No difference. The NGK B7ES plugs are a step cooler than the NGK6ES that I had in before. These plugs were recommended by Rebello Racing whom did the rebuild on the engine.

Since I'm still running the stock coil that is rated at 1.5 Ohms, I believe that I'm supposed to run the resister which also is rated at 1.5 Ohms. This gives a total of 3 Ohms on the ignition circuit. Removing or jumpering the ballast resister removes it's 1.5 Ohms from the ignition circuit. To prevent premature point wear, 3.0 Ohms are required for the ignition circuit. You're correct that I currently don't have points so I don't have to worry about frying them. But, with only 1.5 Ohms in the ignition circuit (from the coil itself), it's my understanding that I could ultimately fry the stock coil too. Of course I could install a 3.0 Ohm coil and jumper (or remove) the ballast resister so that I would not fry the coil. However, I suspect (but haven't confirmed) that doing so, would reintroduce 3.0 Ohms to the ignition circuit and consequently the hesitation issue. If running only 1.5 Ohms resistance in the ignition circuit won't do harm to the stock coil, than my current configuration is fine. However, it's still a band-aid for the symptom and I would prefer to figure out what's going on. That way I could go back to points if I so choose.

I am familiar with that thread. I don't believe that I have the same situation since replacing the Pertronix unit with points makes no difference. It really comes down to jumpering the ballast resister. That is the only thing that seems to make any impact. As I mentioned in my other tread, I've gone back and forth between points and the Pertronix unit, replaced the coil, replaced the ballast resister, replaced dizzy, replaced fuel pump, etc. The car actually runs great except for the 4.5K + RPM hesitation. Jumper the resister and it shoots right on past that mark and will rev to nearly 7k pulling pretty nicely through 6K. Unjumper the resister and you're back to square one.

Hi all, After a long trouble-shooting session (literally over a year...) I've determined that the high rpm (4.5 K + ) hesitation issue I've had is ignition based (weak spark or too much resistance?). I can make the symptom disappear (or nearly so) by jumpering the ballast resister next to my coil. My '72 240Z currently has a Petronix ignition on it with the stock coil (1.5 Ohm) and ballast resister. I've gone through a long session of replacing the dizzy, fuel pump, coil, adjusting a/f ratios, and carb float levels in an attempt to resolve the high RPM hesitation. What it has finally come down to is that if I jumper the resister, I get much better performance, if I live it unjumpered, the hesitation returns and non of the aforementioned adjustments and replacements make any difference. See this thread for all the gory details : http://www.classiczcars.com/forums/showthread.php?41414-Mid-Range-RPM-Hesitation I believe just running the resister jumpered is not the best thing for the car. I understand that the Pertronix unit might be ok, but the coil might ultimately fry. If that's the case, I really would like to trace the problem down. I'm assuming that by removing the resistance of the ballast (by jumpering it) , I've removed enough resistance in the ignition circuit to allow it to function normally. Therefore, there must be additional, unintended resistance in the circuit. Unfortunately, I'm not much of electrician and don't know where to be begin in tracing this down. Any suggestions? I'm also guessing that installing a 3.0 Ohm coil and bypassing the ballast resister will not solve anything since the same amount of "coil based" resistance will be introduced into the circuit. Does that seem correct? I do have a multi-meter as a tool, but, I'm far from an expert in using it. Any suggestions would be greatly appreciated in it's use and how to resolve my ignition issue. Best Regards, Landmizzle

Hi all, The longer test drive confirmed that the 4500 rpm + hesitation was mostly gone with the ballast jumpered. There was still a little flat spot in the power range but it was much less pronounced. Now it seemed more like a tuning issue (A/F, SU damping oil, etc..). I emptied the SU damping oil which was ATF and reverted back to straight 20w. Next test drive the car performed better especially upon acceleration. Revved nicely to 6000 rpm, and wasn't as flat in the powerband, but still could be better. I don't recall if I mentioned but the stock engine has been rebuilt to a 2.8 stroker by Rebello Racing about nine years ago. Consequently, she likes to breath a little deeper. I have a spare air housing that I cut openings in on the top surface to allow more air flow. I placed that on the car and took her for another drive. Nice! She really picked up some steam in the upper RPM range now. Still may need to adjust the A/F or put in SM needles, but all in all much better than before. So, just to confirm that the ballast jumpering was the main "fix", removed the wire that was connecting the +/- poles. Symptom returned. I took the ballast off and inspected it more closely. There's not much to it. A ceramic housing with a thin coiled spring enclosed. The spring is attached to two bolts with washers and the bolts protrude up through the housing and are what various ignition circuit wires attach to. There was some tarnish/rust on these bolts and washers so I took a Dremel to them and cleaned them up. I then cleaned all the connectors on the ballast. Unfortunately, non of this helped. The 4500+ hestitation will persist if I don't jumper the ballast. So, on one hand I'm happy, the car drives much better. Actually it drives like it's supposed to. On the other hand, I'm perplexed that the ballast has to be jumpered even after the cleaning. I'll go ahead a get another (they're cheap), just in case I'm missing something and the cleaning wasn't enough. So, it seems clear to me that this essentially came down to a weak spark issue (as many of you suggested) and that the ignition circuit has too much resistance in it unless the ballast is jumpered (which of course removes the resistance of the ballast). If a new ballast doesn't resolve the problem (without the ballast jumpered) then there has to be additional uncalled for resistance elsewhere in the ignition circuit. Of course I'm getting ahead of myself here, but the fact of the matter is the car did not need a jumpered ballast in the past to run properly. So while my fix works, it is a band aid. It's a band aid that prevents me from going back to points if I wanted to. I'm thinking maybe it's time to close this thread and open up another one that focuses just on the ignition/weak spark issue. While this issue is not closed, I feel much better. At least now, I see the logic (for the most part) of the problem. I've learned a lot in this process and want to thank everyone that took the time to post replies and put up with my ignorance and sometimes thick headed nature. If anything, this ordeal has reinforced the importance of being open minded, make limited changes during trouble-shooting, and probably most of all, continuity of approach (don't let long time spans occur in between trouble-shooting sessions).

Hi all, Did two things this morning. First pulled the spark plugs and gapped theme to .34 (they were all at .31 ~). Then I jumpered the ballast resister. I'm running the Pertronix ignition right now with the a stock spec coil so I think this is safe to do. If I were running points, it's my understanding that this configuration would eventually fry the points. Took the car for a quick trial run and the flat spot at around 4500 and beyond is gone! I was able to wring her out too 6000 rpm without issue. Nice! I'm going to take her out for a longer test drive and I'll report back, but I'm so jazzed right now I wanted to put up a quick post.

Hi beermanpete, Ok, I think we can rule out the fuel pump of fuel pressure. I hooked up he fuel pressure gauge as you suggested by taping it to the outside windshield while I drove around. Fuel gauge showed no change even while the hesitation was occurring. I'll really check the fuel lines below the bowls to the nozzles, but the last time I looked at them nothing seemed unusual.

Hi beermanpete, Yes, the engine was running at 1000 rpm. I actually ran another test today and put an external tach on the engine. With the rpms reading ~1100 rpm on both the inside and external tachs, I got repeat flow rates of 6.5 cups/min or 3.25pts/min. Just under the 3 3/8 pts/min called for. If I race the engine, the fluctuating readings stabilize and I typically get 3.1 psi front and 3.5 psi rear, but the pressure does not rise. Fuel did not look foamy or bubbly. The return fuel line is certainly thinner than the fuel line to the carbs. Not sure if the end orifice is too big on the return line. However, it would not have been something that changed since before this issue began. Thanks for the response!

Hi all, Just for comparison, I put the old fuel pump on and got the following readings; Front= 2-3 fluctuating psi Rear= 3.1-3.4 fluctuating psi Note: both would stabilize by giving slight input to throttle shaft. So, all-in-all, slightly lower readings than the new pump. BTW, with either fuel pump, pinching the return line either removes the fluctuating reading or slightly raises PSI (<.5). I then put the gauge directly on the output nipple of the fuel pump and got a steady 3.5 psi. BTW, answered my own question regarding the tube length coming off "T"; I shortened them and saw no change.

Hi all, For all you imploring me to measure the fuel flow rate and pressure, you'll be happy to know that mission is accomplished. Now, I'm not sure how accurate the measurements are. Here's why. The the rubber fuel lines are 5/16" but the nozzle on the pressure gauge I have is smaller, maybe 1/4". So I had to use a "T" adapter that would accommodate the different sizes. Rear carb had 3.4 psi while the front was running 3 psi. I believe specs call for 3.41-4.27 psi. So I'm on the low side (especially the front) assuming the my readings are accurate. I'm a little concerned that the readings are being affected by the T as the readings went down on the front when I used a T with a larger ID opening for the connecting fuel lines. I went to measure the fuel flow next by measuring the flow from the individual carb lines. The readings averaged out to be 2.5 pints/min rear and 2 pints/min front. Looking at the FSM and it called for 3 3/8 quarts/min! Or 1600cc per min. I then measured the flow from directly past the fuel pump and averaged 3 pts/min. Still low! I then realized that there has to be a mistake in the FSM. 1600cc does NOT equal 3 3/8 quarts. It equals about 3 3/8 Pints! Even with correct conversion, I'm a little shy of the proper flow from the fuel pump. If the measurement is supposed to be from just before the carb, than I'm really low. I'm a little surprised that the flow and PSI are not meeting specs as the fuel pump is brand new. Measuring from the fuel pump would rule out any obstructions between the pump and the carburetors (as far as fuel flow), but I'm not sure if that's where it's supposed to be done. Thoughts? I'll probably pickup a new pump locally if I can, but I might try putting my old pump back on just to see the results I'm also curious if the length of lines might be having an effect on the measurements. For example the length from the T to the gauge is probably 12"(this is also the thinner 1/4" line). The connecting fuel lines to the T probably span 8" to 10". Of course these shouldn't really affect the fuel flow reading which is low also.

Hi Blue, I pinched off the fuel return line for about a minute and noticed no difference in how the engine was running at idle. What should I be looking for? I did pull off the rubber hose from the steel return-line and fuel was squirting out at what appeared to be a constant pressure.

Hi, I know some people have reported issues with the Pertronix, but I've ruled that out in that I get the same symptoms even when I run points.

Hi Steve, Yes, the float inlets appear to work fine.

Hi all, Still at this.... At this point, I've gotten very good with adjusting the float level bowels. I do not believe the issue has to do with a low fuel level in the bowls. Nor is it the "last chance" filters in the lids of the float bowl as air and gas flow freely through them. At this point I've; Replaced the distributor Replaced fuel pump. Replaced coil Adjusted fuel level to specs. in bowls. Performed fresh tune-up, plugs, adjusted valves, cap and coil. Pertronix is currently installed. (switching to points does not change anything) I have NOT actually checked fuel flow with a gauge as I don't have one. May be my next desperate act will be to purchase one. However, I may have stumbled on a clue, maybe. I mentioned earlier that the mechanical advance appears to work because when I blip the throttle I can see the timing advance with a timing light. This is still true. I'm wondering though if there is a problem with the vacuum advance. The car drives the same whether I run with the vacuum line attached to the dizzy or not. So, I'm thinking the vacuum advance is not kicking in. Any thoughts on this? Vacuum at the dizzy line is 6" Hg. Vacuum at the center vacuum port on the intake is about 11-12" Hg. Are these numbers normal? I maybe totally off here with the vacuum idea, but it seems reasonable. I agree it still could be fuel flow issue, but with the new pump, I think it's less likely. BTW, had my old Z mechanic ( he's retired now), look at the car. He put a compressor on the fuel line from the engine bay going back to the tank and air flowed cleanly as we could hear bubbling coming from the tank. He checked the dizzy, needles for straightness, fuel level in the nozzles, and fuel filter and noticed nothing amiss. I didn't want to abuse his courtesy and so we left it at that. Any ideas?

Hi all, I'm still dealing with a high rpm issue, but I'll leave that to another thread. What I would like to know is the float level for 1972 carbs; I hear that they are not the same front and rear. I believe the typical level ('70 and '71) is 23 mm measured from the bottom of the lid to the fuel level with the floats in the fuel bowl. Measuring from bottom of lid to fuel level (using clear plastic hose from fuel drain and aligning it up against side of bowl.) I can get a level of 1 inch (25.4 mm) pretty easily for both carbs. Is this close enough? I'm getting pretty good with the whole procedure, but it's still fairly time consuming. Unfortunately, so far, all my attempts to reduce the fuel level a few millimeters results in the level going too high and gas overflowing. If an inch is good enough, I would rather move onto other issues to trouble-shot my high rpm hesitation issue. It feels like I'm chasing a phantom goose trying to get get that last 2 mm precision. Is the fuel level that finicky?