Zmanco

I can see flex in the shaft and some small movement between the shaft and the bushings. However, I took that into account when I set the linkage by taking up the "slack" before adjusting. I probably should replace the throttle shaft and bushings, it just hasn't made it to the top of my budget yet Do you think that would be the source of this noise? All 3 covers list "TIPO: DCOE2". Below that is "No. 4F" on the front carb, and "No. 4K" on the 2 back ones. What is the significance of the differnt letter (F vs. K)? Perhaps the jetting as shipped from the factory?

Having just fnished swapping the toyota 4x4 calipers, let me take a shot at answering IdahoZ's question. Slotting and drilling should not change the diameter or thickness of the rotor, so the answer is yes, you should be able to use them with the '79-85 12S calipers. Note: I just upgraded from the S12 calipers with stock rotors to the S12W and '84 300ZX vented rotors. I also used 300ZX pads which give a little more surface area than the Toyoto ones. Although I haven't had a chance to take it out on the track yet, I've found the brake response to be more linear than before. I'm sure some is due to new rotors and pads. If you are going to upgrade the rotors and calipers anyway, I'd recommend going this route. About the only extra expense is the spacer which I got from Modern Motorsports for about $135 shipped. To Jon's comment up top, you can get away without switching to the 15/16" master cyliinder, but the pedal becomes rather long, and it just diddn't feel right. Also, my size 12 feet were hitting the gas pedal during braking now and then. A little scary when you're still in gear!

I just checked the carb balance. The front was off about 1/3 of a unit on the synchrometer at about 2500 rpm so I adjusted that. On the run afterwards I noticed that the sound was louder. Hmm, louder with the air cleaners off, that doesn't sound like detonation. So I tried going up a hill in 3rd or 4th at around 1k rpm. The sound is still there, and completely regular, like what a cracked exhaust manifold would sound like. There is none of the randomness that I have heard in the past when my old engine would sometimes ping. Based on this I'm pretty sure it is NOT detonation. That would explain why retarding the timing to zero (from about 13 where it is now) didn't make the slightest bit of difference. I'm not sure why it sounded louder last weekend when it was so hot. Perhaps it was just me expecting it to be worse due to the heat, or perhaps whatever is making the sound in one of the carbs just does it more when it's really hot. I'm thinking I'll swap the bigger cam in and while I have the carbs off take a close look for anything strange. While I have the head off, are there any tell-tale signs of pinging I would see if it really was detonation? Dan, Jon, Drax240Z, does this make sense to you?

I know they are in balance at idle - i've verified it several times with the syncrometer. When I had my SUs I used the fast idle screw to balance them at part throttle and there was a slight difference from idle. Tonight I'll rig up a stick on the throttle and test it to see. Thanks for the suggestion Drax240Z.

Jon, the webers are pretty close to done. I have an O2 sensor and can tell that I'm not lean when the detonation occurs. The only time I ever go lean is during the transition from idle circuit to main, and after the last change to the idle jets it's barely noticable. I'm probably going to go up one size further on the idle jets, but was waiting until I put the new cam in before making any more changes. As you know, it's not cheap experimenting with weber jets Do you think this is part of it? I had read that being lean can make detonation worse, but it was so loud last Saturday that I figured going a bit richer wasn't likely to solve it. Perhaps that's a bad assumption?

No, there is no vacuum advance connected. I installed the webers shortly after I rebuilt the engine with this combination of flat top pistons and N42 head. When I had the DGV carbs on, I never heard any detonation. Immediately after I installed the webers I began to hear what sounded like faint detonation when the throttle is partly opened, say between 20 and 50%, and only at low revs. Even when I retarded the timing to the point that the carbs were spitting and backfiring (front firing?) there was no change in the sound. That's part of what has me confused. But last Saturday it was very warm, close to 100 ambient, and I heard the detonation louder, and over a wider range of throttle. That's what convinced me it was really detonation and not some other strange sound. BTW, it doesn't have that somewhat random sound that I'm used to hearing. It's a more regular sound that rises with engine speed. Very strange. Does any of this make sense?

I noticed you typed "ring" and I typed "rings". The search engine built into this site isn't quite as sophisticated as Google and so it thinks those are 2 diferent words and hence you get different results back for each. You have to anticipate the different ways the term will be used and search on them all. Glad you found the Deves, I've heard nothing but good things about them.

Deves makes a good set of cast iron. Google "deves 280zx" and you'll find a few stores selling them. PS. I know you won't want to hear this, but you could have found your answer yesterday by searching this site. "piston rings" would get you close, and "piston rings source" even closer.

Thanks for the pictures Spotfitz. Looks like it's a vacuum solenoid. With my webers and their poor idle vacuum, I'm thinking I need to go with an electric. A parts counter guy suggested that early 80's Fords, such as their big sedans, might be a good source for it.

That's the first time I've heard that. Does it mount on the firewall? Any chance someone has any pictures?

I have the stock (dealer installed) AC in my '73 and it's really only effective when driven at speeds above 30 mph. At idle there are two issues: 1) the stock engine fan doesn't pull enough air over the condensor to keep it the air in the cabin cold 2) in stop/start driving the underhood temp goes up and when the compressor kicks in, coupled with the carbs getting hot, the engine doesn't like to idle. You can increase the idle speed to compensate, which helps some, but that means that on a cool day you're idling around 1100 rpm. Despite that I do think it's worth it. And if you can find a better solution for the evaporator under the dash I'd be very interested! BTW, has anyone come up with a good (simple) way to increase the idle speed when the compressor kicks in on carburated cars?

I'm guessing that your idle mixture is just too rich. You might get away just turning the idle mixture down to lean it out, or you might have to go down a size or two on the jets. But without an exhaust gas analyzer you're going to be doing this trial and error, and I'll guess that you are only allowed one more try at the test station. I very much doubt that the multiple spark ignition will make that much of a difference. Perhaps you can find an indendent shop that specializes on early british cars, or even early Hondas and Toyotas. They ran on carbs, and the analyzer is the only way to set them to pass. Look for a mechanic who is in his 40s or 50s. Younger than that and he probably has little experience with carbs. That's where I'd put my efforts. Good luck!

Bryan, not sure what you mean here. The mechanical fuel pump bolts to the head, not the block. The N42 head has an opening for a mechanical fuel pump, the N47 does not.

How far off were you on the unburned HC at idle?

If your goal is to get the car to pass emissions, then I'd suggest you find someone with an exhaust gas analyzer who can tune the car to meet the test levels. Basically they put the probe in your exhaust and then can set the mixture to get to a passing level. I had to do that when I bought my Z. It drove like crap, but I only had to go a few miles to the test center. I drove right back to the mechanic and he set things back to make it drivable again. If you're looking to put a new ignition in, then maybe you should try it. But if your carb is set too rich, which helps with drivability, then I doubt there's anything you can do with the ignition system to get it to pass.

Short answers: yes, yes, yes. Better to use an intake manifold gasket for the early 70-73 since you're using carbs. You will probably have to swap the dizzy mount from the L24 to the L28.

I had heard I might have detonation issues, but so far (1500 miles) I haven't been able to hear any although I realize that's not the best method. But I have been listening closely, driving with the windows up on the really hot days trying to hear it. Perhaps it's because I live in Colorado and do most of my driving above 5000 feet? Or maybe because I've limited my total advance to about 34 degrees? Paul, I really value your advice and I'm not trying to argue with you. I'm just trying to compare what you're saying with what I'm experiencing with this engine. Perhaps I'm missing something else?

Yasin, you might ask the cam shop what they recommend. I just sent my core up to Delta Cam to be reground. They say that for the grind I chose, .180" lash pads are all I need. So I've gone and ordered a set. I'll know more when I actually get it all assembled and check it out, but they say that they've done enough of this grind for Zs that it should just bolt together. We'll see

Why don't you just get your existing flywheel lightened? I had my stock L28 lightened from 23# to 16.5# using just a lathe (to keep the cost down). Everything came off the outer edge where it matters most. Going any further would have required machining and more $$$. Including resurfacing and rebalancing the total cost was about $120. That's about the same weight as the Maxima flywheel, and if you figure you'll still need to get the used flywheel resurfaced and pay for shipping, I doubt you'd save much if any money with the Maxima.

If you assume that the diameter of the combustion chamber where it touches the head gasket is the same as the bore of an L28, then it's about 1.5 cc. In the real world it's probably a little less.

I just went through this same issue a few weeks ago. The general concensus was that the ring manufacturer is the one who specs the end gap. Usually it's a function of diameter, for example: gap = .003" per 1 inch of diameter. In my case I was using ITM pistons and rings (not sure if they're related to your ITC) with a top moly ring, not chrome. The manufacturer was no help with end gap, so in the end I went with .014" for the top ring and .012" for the second. FWIW, my N42 was bored .030 over.