Chickenman

I highly doubt it's a valve problem... and your mechanics tale of having to adjust the one valve to .013" never did make any sense at all. That's a wild goose chase IMHO. It's going to be either a fuel or ignition problem that is affected by heat. What is the temperature gauge reading when in Traffic and the problem occurs? More likely fuel. Having to pull the choke lever on when it gets hot indicates engine is running out of fuel. Could very well be vapor lock. Can you take a few clear pictures of your engine. I want to see a few things. Some good shots of the carburation and fuel lines and fuel filter would be very helpful. Take a few general pictures of ignition system and wiring as well. BTW... do you have the factory heat shield in place under the carbs? Edit: You need to find a different mechanic IMHO. Your Porsche " expert " has some strange ideas or you are not understanding him. Either way, these are simple engines and any decent mechanic should have it running like a top by now.

Choose the right components, blue print the engine and a good port, polish with three angle valve job and a " stock sounding " and " looking " L24 can be very fast. It doesn't mean what inside is " stock " at all.... for a 1972 engine that is. Lets see: An early block .040 over with Flat Tops, an E88 head ported and polished with large valves. Fully balanced and blueprinted, 1970 Euro intake manifold with early SU's massaged by some of the SU guru's of the day ( Or larger SU carbs off a Jag ) , early Camshaft ( I think an E88 was the best... if my memory is correct ) . Or a mild Autocross grind, around 268 - 270 degrees with some added lift. You wouldn't notice any idle " Lope " with a mild enough cam. A nice set of headers or an early non-emission exhaust manifold into a mandrel bent 2.5" exhaust system. Yeah that would make some decent power. I ran a similar combo back in the late 1970's and early 80's with my ICSCC D - Production 240Z. We used to give the C - Production Porsche 911S 's a real hard run for the overall win. NHRA Stock class is also a prime example of what can be done with " Stock " engines. They make much more power than the factory engines with stiff restrictions on modifications for the class.

It certainly wouldn't hurt to rebuild the calipers as ZH mentioned.16 years is a long time ago, especially if they were sitting. Buy new seals for all of the calipers. While they may not be leaking, the seals may have lost some of their " elasticity " and may be allowing one side to drag on the rotor. It's a common problem with old seals. They are cheap and you can buy them direct from WilWood. Summit and Jegs also stock them. You may also need to polish the bores due to corrosion. Even a slight amount bof corrosion in the bores will cause a pistoon to stick slightly. That will cause a pulling situation. Hand polish with " Crocus " cloth ( Also called: " Machinist cloth". 2,000 to 3,000 grit ) soaked in brake fluid. Hand polish the Caliper pistons as well with the same material and procedures. If the rotors aren't brand new, get them turned so they are flat and have a good surface finish. Modern pads are sensitive to pad deposits on the rotors. If you change pads brands you should surface the rotors, unless the pads have a special " break-in coating " that will scour off the old pad deposits off of the rotors. Semi-metallic pads aren't sensitive to this, but a lot of " Ceramic " pads and Carbon or Polymatrix pads are. What pads do you have in there? I'll tell you right now from experience that most of the WilWood " Street compounds aren't that great ". They do tend to grab right or left. Especially in the rain. Fortunately the Superlites and Dynalights have a huge selection of pads to choose from. Hawk HPS compound is a decent Hi Performance street pad. Suitable for any street use and Autocross. PFC also makes a good Hi Perf street pad for these calipers. If you run Track days you should go with a dedicated set of proper Race pads and a spare set of rotors bedded to those specific pads.

^ above is linked from a 13 year old thread. http://www.classiczcars.com/topic/1382-backfiring-should-i-be-concerned/#entry482317 Ok. So you never did get back to me in the other ( this ) thread when I asked for clarification on how loud the back fire from the exhaust was. That's the problem with starting or discussing the same problem in numerous threads and scattering information all over the place. People can't follow what you have done. And it is really bad form to revive 13 year old threads from someone else and expect people to follow what you have done. George, please stick to ONE current thread!! However, from your latest description it sounds ( no pun intended ) like you have a fairly big backfire as you describe it like a " Gunshot". Is that correct? Most cars with a bigger cam and properly tuned will pop or sneeze through the exhaust. That is perfectly normal. What is NOT normal is a big Gunshot or Shotgun backfire. That type of backfire is usually caused by air leaks into the exhaust system. What happens is that you always have some " over run " with carburetors on deceleration. This means that partially un-burnt fuel gets blown out of the cylinder on the exhaust stroke. Higher duration cams such as your Shneider 274 add to the problem due to the greater valve timing overlap. By itself, this partially burned fuel is not a big problem.... but add some extra Air into the mix via an exhaust leak and and it can create an explosive combination. Most people don't realize that exhasut leaks work both ways. The exhaust gases flow " pulses " blowing exhaust gases out of a bad joint... but also sucking fresh air in on the Negative pulse. So any leaks in the exhaust side needs to be located and fixed. 1: First thing that comes to mind is that you removed some of the emissions control parts. If exhaust manifolds had air injection plugs did you plug the system off properly. Note that the air nozzle threads are NOT a standard pipe thread size. Brass or steel Pipe fittings will fit if you force them in... but they can leak air. That can be enough to cause backfires. 2: Look for any broken studs, blown exhaust gaskets or cracks in the exhaust manifold/header. All are sources of air leaks and can cause backfires. Check tightness of all nuts and bolts. 3: If you still have the factory manifold, check for broken studs or blown gasket. Check that the fasteners are tight. Any signs of black carbon or white markings around exhaust parts can be signs of an exhaust leak. 4: Check the rest of the exhaust system all the way back to the tailpipe. Best to do this on a hoist. Look for leaks at pipe joints, cracks or holes in mufflers. Big backfires can blow the seams in a muffler. Then the problem gets worse. Black traces from leaking carbon will usually be a clue.

See reply at: http://www.classiczcars.com/topic/52702-attempted-to-tune-su-carburetors-but-still-backfiring-on-intake/#entry482353 George. Stop making multiple threads on the same topic. People can't follow what you've done. It starts to get really annoying and multiple threads on the same problem are generally against most Forum rules.

Problem is finding one of those 240Z AC pots. Then you still have to plumb in one of those Ruby Goldberg electric/vacuum combo valves, which can be finicky. The other issue is that George has a bigger camshaft in his car ( Shneider 274 ), and the vacuum servo/pot system doesn't work well with the low manifold vacuum caused with a bigger cam. It all depends on how much manifold vacuum the engine pulls. The bigger camshafts also cause the idle to be pulled down more when the AC kicks in ( if no AC kicker is used ) . How much depends on the engine and camshaft combination.

I have a fairly large cam in my 280Z ( Shneider 280 duration ) and I have to run it at 1,000 to 1,100 RPM for idle speed. No issues at all..... until the AC kicks in I have AC as well, and with the low manifold vacuum caused by the big cam the factory vacuum AC kicker doesn't work very well. I've really had to tweak things to get the AC vacuum kicker to work. Even then it's not satisfactory and doesn't work properly all of the time. I'm going to an electric solenoid on my 280Z to keep the idle steady when the AC kicks in. On a 280Z though it is easier to retro fit an electric solenoid in place of the factory vacuum pot than on a 240Z. There are already mounting points and brackets on the manifold and the throttle linkage has a " Leg " for the solenoid to press against. The first solution of mine for your 240Z may be a bit too complicated. There are other solutions that may be simpler. Edit: George. I can't remember at this point, ( there's been too many posts ) but don't you have a bigger camshaft in your car. A 274 degree duration one I believe?? Ah yes. Found the post where you mentioned you had a Shneider 274 duration cam. That does make a difference to idle quality, How much depends, but my 280Z with a 280 Shneider is rather finicky with the factory AC vacuum kicker. That's why I suggested the electric solenoid. http://www.classiczcars.com/topic/51548-ngk-bp6es-spark-plug-burn-color-ok/#entry470480

^ That is just one thought for mounting. I can think of at least 3 others off the top of my head. 1: You could mount the solenoid above the main throttle push-rod and have plunger contact the plastic end cap directly. Mount may be a bit difficult but you could bolt to Intake manifold. Properly designed ( with an anti-rotation lug ) a single stud on the Intake manifold would work. 2: Mount the solenoid so that it actuates the throttle at the Bell-crank on the Firewall 3: Mount the solenoid inside the car so that it actuates at the accelerator pedal linkage. Use you imagination. Lots of possibilities. It doesn't have to be pretty at first. Just functional and strong. Now get your butt in gear and start thinking!. Just do it!! Edit: Once you have a prototype made, you can take measurements off it and get a CNC machined parts made for a relatively small cost. Lots of online CNC shops and 3D printing these days. Free Cad software as well: http://www.emachineshop.com/ http://www.emachineshop.com/machine-shop/Custom-Metal-Brackets/page382.html https://www.google.ca/search?q=CNC+fabricated+brackets&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwik5K361bzJAhXJoogKHYB6DocQsAQIJw&biw=1232&bih=615

I can see an easy spot right away. You have a vacuum pot that is connected to the carb linkage and that vacuum pot is not being used. I would utilize the vacuum pot's mounting point as a base for the electric solenoid. Note that the linkage on there is designed to pull up, so you either have to mount the solenoid upside down or change the direction on how the linkage operates. Miniature bell-cranks are great for this type of job. You have a variety of mounting positions and you can change the direction of travel easily. A circular bell-crank would be ideal. Get them at Hobby shops that sell RC Cars, Helicopters and Planes etc. RC Cars have some very strong and well made parts. So do Helicopters, although more delicate. https://www.google.ca/search?q=RC+plane+bellcranks&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjq2LHG0bzJAhWINIgKHUi0DIAQsAQIKg&biw=1232&bih=615 https://www.google.ca/search?q=RC+Car+bellcranks&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwi_jc7U27zJAhUY9mMKHSeXCk8QsAQIGw Now you are going to have to fabricate a mount. That may involve welding, cutting or fabrication skills that you may not have. So find someone who does ( Other car enthusiasts.... not regular MECHANICS at a shop ) Local Metal artists and Hobbiests are also a good source . Prototype can be an ugly bodged together piece, Doesn't matter as long as it's strong. You can make it pretty afterwards.

I suggested that same part to George way back in July. Same link. But George chooses not to listen to the advice given here and just continues to ask the same questions over and over again. He's now got three threads going on this, but refuses to take any initiative on his own. I'm done with offering him advice. Waste of time...

George... this is the third thread you've started on the same subject. And you've already gotten a reply to this question. http://www.classiczcars.com/topic/51811-servo-diaphgram-and-control-valve-for-ac-on-a-240z/#entry481823

What part of: " You'll have to fabricate a mounting bracket " is not clear? The supplier you called did not understand what you were trying to do, or you did not explain properly that you were going to custom fabricate a bracket for the solenoid. It's a simple on/off 12 volt solenoid that can be made to work on ANY car with a little bit of thought and a minor amount of skill.... If you called up the supplier and say something like: " Will this Chevy solenoid work on my 1972 Datsun? "... of course they will say no. If you say: " I want to buy this solenoid and adapt it to fit my car. I don't really care that it's not made for my car." Then you should get an entirely different answer. Like: " Yes sir...will that be MasterCard or Visa? " Hell... I had 1968 Mini Cooper parts on my 1973 Camaro. You sometimes have to MAKE things work on 40+ year old cars. It's not all plug and play.

Cringe...not a good idea IMHO. Roller bearings inside tranny's don't like shock loads like that. Yoke would have bottomed on main shaft and transmitted all those Hammer blows directly to the tranny main shaft bearings Check the tail shaft seal as well. It could have been damaged.

OP: If you do confirm that pump is operating, you may have to add more fuel than 5 gallons to get the fuel pump to prime. You may have an " air-lock " in the fuel line. Since the later models fuel lines are at the top, the F/Pump may not be able to create enough suction in the line to prime itself and start a siphoning action. It's not a problem with " In Tank " pumps as they will prime with low fuel. But with external pumps, if you lose the prime in the fuel tank to fuel pump line, it can be an issue. If pump works, then fill fuel tank to top. Or have a helper pressurize fuel tank with compressed air while you crank the engine. You will need a fairly large volume of air and you will have to close off the hose to the " Vent Reservoir tank "

Reading the OP Signature line it looks like he has a 1978 280Z. OP: Is that correct? 1977 and 1978 280Z's have a fuel tank that is different than the earlier style that ZedHead shows in post #8. From the parts manual, it looks like the fuel line connections are on top of the tank. OP: Can you confirm this? With fuel lines on top of tank, fuel has to be drawn out by vacuum from the fuel pump. 5 gallons in the tank may not be enough to have fuel flow " up and out " by tilting the tank or even pressurizing it. You would need a very large volume of air to maintain flow, and all vent lines and fuel filler tube would have to be closed off. Picture of 77 - 78 Fuel Tank. Note that the fuel lines appear to come out of top of tank:

You may find that size in Hobby shops that sells parts for RC Cars, Planes and Helicopters/Drones.

The copper colored valve seal in the center is an A-Series ( Datsun A-12 ,A-13, A14, A-15. A-12a ) . It's a good seal and gives a bit more clearance to the valve spring retainer when a higher lift Cam is used. The other two silver colored seals appear to be some kind of aftermarket seal. Possibly a Ford V6.

You're welcome. I got switched on to Trimetal bearings when I ran Vandervell Bearings ( from the UK ) way back in the 1980's on my SBC Race engines. Very high quality bearing. Vandervell is now part of the Mahle group. http://www.vandervell.co.uk/ Clevite is also part of the Mahle group and is apparently using the Vandervell Trimetal design. http://catalog.mahle-aftermarket.com/na/home/index.xhtml

Something doesn't sound right at all. I'd get a different set. If memory serves me correct #1 and #7 have the wider shells and top and bottom always match. . #2,3,5 and 6 are slightly narrower. And of course #3 is the center thrust bearing. Clevite Trimetals are a very good bearing.

Dry startups after extended storage are always a big concern on Vintage cars. Anything that can be done to get oil pressure to the parts quicker is helpful. Your pre-oiler or an Accusump is a very good idea. Other things that can help: Synthetic oils have a big advantage over Dino oils during storage. Synthetic oils will cling or soak into the metals on a molecular level and provide added protection ( over Dino oils ) during long storage spells. It's an important point on Vintage cars or Specialty cars that may not be driven for months at a time Of course you have to wait until the rings are seated ( on a new build ) till you start using Synthetics. The oil sending unit location for your pre-oiler is very good. Goes straight to the main oil gallery and the bearings should get the oil first. Recommended location by Accusump. It's the bearings that I worry about more than Camshafts when the engine is sitting on a stand for a long time. Turning the engine over by hand ( on the stand ) won't damage the camshaft, ( as long as you used proper cam proper lube on it and the " Parkerizing " on a new Cam also helps protect it ) but the Main and Rod bearings are susceptible to being damaged by getting " wiped dry". It's why some bearings have a sacrificial layer of dry lubricant on them. When the engine is all installed and ready to go... remove the valve cover, pour some fresh oil directly over the camshaft, then bolt things up again. That will provide extra protection till the oil gets up to the spray bar on the initial startup. After the camshaft is broken in ( 20 minutes at above 2,000 rpm minimum ) the delay of oil spray to camshaft is not as critical, and in fact, once the oil galleries are initially filled, they tend to remain filled. See explanation below. A note on oil filters. It is important to use the proper oil filter on our cars. Because the filter sits sideways on the engine, the factory filters feature an " Anti-Drainback " valve. This prevents the oil galleries from draining down when the engine is shut off. Some cheap oil filters don't use an " Anti-Drainback " valve or have one of very poor quality. Buyer beware!! ( BTW, the factory Nissan filters use a high quality Silicone ADB valve ).

Those plugs look fine. The red is just an additive in modern gasoline. Personally, I wouldn't worry about a pop, burble or mild backfire on decel. Probably just normal. BTW... a backfire ( from exhaust ) means different things to different people. To me, a backfire out the exhaust is like a shot gun going off. Pops and burbles are normal..... and most cars with higher compression and larger duration camshafts will do that. They add " character ". Shotgun type backfires are not normal.

I found another supplier for high quality Head-lite Relay upgrades. The nice part is that these are Plug and Play for any vehicle. I'm thinking of getting these for my 1976 280Z. MSA doesn't supply 280Z kits. http://www.ceautoelectricsupply.com/h4headlightrelaykits.html

Thanks guys. I thought I`d gone crazy. So the page layout has just changed. ??? Yep, Keyboard was set to English ( Canadian ).... but I didn't change it. Very strange... ??

This is a bit of a strange one. I used to have an Online parts link that I use all the time, but it has either changed appearance or disappeared. Can anyone confirm if the following Link has recently changed it`s appearance. I swear there used to be an Index panel with a drop down list on the left hand side: http://www.carpartsmanual.com/datsun/Z-1969-1978 Or does anyone have some more links to Nissan Online Parts catalogs É ( and why in tarnation are Question marks now appearing as an É )

I use Synthetic Silcone grease on those ball joints. The synthetic does not turn " Waxy " from exhaust heat like regular petroleum grease. Super-Lube from Synco works well. It's good for Plastic and metal. Product #21010. Works great on Slot Car gears as well!! http://www.amazon.com/Super-Lube-21010-Synthetic-Blistered/dp/B000BXKZQU