New member introduction and a problem

[sdyck]

Hi just became the proud owner of a 1972 240Z its a little rougher around the edges than it looks in the picture

My plan is to keep it on the road during the summers and work on bigger projects through the winter. There are a number of things that need addressing right away, a new brake booster for starters. I need to give it a good tune for starters, check the compression etc. I have a little experience with SU Carbs but they ones I fooled around with was on my Dad's old MG and he always kept it in tip top condition.

I'm going to follow this post up with my first question,

Thanks,

Steve

[sdyck]

So my 1972 240Z pictured above runs reasonably well and doesn't seem to be blowing any smoke. I still have to do a compression test and tune up, but have an issue that I'm not familiar with.

I took off the air cleaner cover and its full of carbon, obvious blow back from the carbs. (see pictures below). I've been having run-on issues that I attributed to a brake booster issue as well as the previous owner was running on regular unleaded. The engine rpm was going up when I put my foot on the brake, due to a vacuum leak at the brake booster. If I keep my foot off the brake and with premium gas the car doesn't run on. Could the carbon be from the run-on?

The other issue I've been having is popping on deceleration. No full-on back-fire, from what I've read that could be an exhaust leak at the header. I took a look tonight and some of the bolts were loose so I tightened the ones I could reach. I noticed one bolt missing as well, I'll need to get the car on jackstands to get underneath to reach some of the bolts. Could this be the cause of the carbon in the air cleaner.

Thanks in advance for any help!!

Steve

[Carl Beck]

Hi Steve:

What you are seeing in the Air Cleaner - is very common. Did you notice that hose running from the Valve Cover to the Air Cleaner? I think at least part of what you are seeing is blow-by from the valve cover. Not all of it but enough to put a fine mist of oily air in there that helps trap other dirt on the surface. You see it build up around the air horns -because that is where it is sucked into a turn of direction in the air flow. {it is also an indication that the previous owner wasn't keeping up with routine maintenance}. Just clean it out with some carb cleaner & a rag.

Then keep an eye on oil consumption - you may have some failing valve stem oil seals. Another common problem with 40+ year old engines.

Secondly - STOCK - the 240's have an anti-backfire valve and associate linkage on the intake manifold. It is there to prevent the SU's from slamming shut suddenly, when you lift off the throttle. In which case you get a suddenly rich air/fuel mix and a backfire. {or is it suddenly lean? its late and I can't think - anyway another known and common problem}. Running too thin an oil in the SU's can add to the cause as well - as it doesn't dampen the closure as it should.

Special note - the above Backfire problem - should actually be reduced when you remove the Air Injection system. But it isn't eliminated..

Carbon build up on the tops of pistons - also seems to be common - if the cars aren't ran regularly and as hard as intended. . There are additives and other products that can do a reasonable job of cleaning the piston tops off - if used consistently. But that is a common cause of run-on as well.

Yes - you should have a heat shield under the crab's. Especially with headers.

Over-all nothing major and the car looks pretty good.. Drive it like you stole it…the more you run it the better it will run.

good luck,

Carl B.

Edited August 18, 2014 by Carl Beck

[siteunseen]

Nice car. My air filter housing looks very similar maybe worse.

[FastWoman]

Welcome! Nice 240!

You asked, "Could the carbon be from the run-on?" I think it would be the other way around. Usually run-on is caused by carbon accumulation in your cylinders, which raises the compression. That's why higher octane gas remedies the problem. But it's only a remedy, not a cure.

FAIW, octane ratings nowadays are not the same as octane ratings back when the car was manufactured. I don't know a lot about them -- how they differ -- but I do know that an 87 octane gas today is equivalent to a higher octane rating from back then. I don't know what 1970's 91 octane that Datsun recommended would compare to today. Perhaps 89? As long as you don't get knocking you can use any grade of gas. I use 87 in my '78 280Z. It works fine. My engine is happy with it, so there is no reason to use higher octane.

Anyway, your engine's intolerance to regular gas is probably more of a symptom than anything else. Your engine seems to be running rich, hence the carbon accumulation (check your plugs to confirm -- probably black) and the boost in RPM when you engage your leaky brake booster (which leans the mixture). I suspect if you correct the lean condition, your engine will slowly burn off the carbon by itself. Until that happens, run the higher octane gas. Eventually, after your engine cleans up, you should be able to run 89 or even 87, unless your head was shaved to raise compression or something.

If you do confirm a rich condition, correcting it will involve practicing voodoo on your SU carbs. You can find experienced voodoo practitioners on the carb board on this forum.

[sdyck]

Wow thanks for the detailed responses, good to know I don't have a major issue.

I will look into a heat shield, judging by how tight things are in the intake/exhaust area I may need to take the carbs off to properly tighten down the headers.

Next steps will be to fix a coolent leak. That short rubber coolent pipe near the fire wall is leaking, tightening the clamp made it worse. I hope the size isn't odd so I can just pick up a length at my local auto zone.

After that I'll check compression, check the condition of the plugs, check timing, adjust points, adjust valves.

Then I'll report back.

Thanks again,

Steve

Edited August 18, 2014 by sdyck

[bartsscooterservice]

Check ignition timing, It should be around 17c ( a little over the 3rd mark in the pulley ) and make around 650 rpm ( maybe you can not reach that rpm because the idle on the carbs is not set right ).

[JGREEZY]

Make sure to check all of your hoses going to your heater core. I just had the small one that is on the core itself blow, it was pretty dramatic when it blew, it spewed hot coolant and steam inside on the passenger side. Not trying to scare you, but it is worth going through the trouble of removing your A/C blower to really check all your hoses out. If it blows it'll burn your passenger. Glad my wife wasn't with me. I can just here her now "GET RID OF IT!"

[sdyck]

Thanks for the advice JGreezy. I got the leaking hose off tonight and bought a replacement to install tomorrow night. The old one was pretty weak and stretched out and cracked. When I went to the store the 1/2" looked to small but the 5/8ths was too big. obviously the old one was set to fail which tells me I need to replace them all. I've been looking for a source for lengths and diameters but can't find a single listing. Does anyone have a source?

Thanks,

Steve

[rossiz]

motorsportauto (MSA)

Welcome To Motorsport & The Z Store! Nissan-Datsun 240Z-260Z-280Z-280ZX-300ZX(Z31/Z32)-350Z-370Z Parts!

is a good resource - i replaced all my heater hoses, inside the cabin and outside. the ones on the inside were hard as rock and a small crack would have meant sudden and catastrophic failure for sure. there's a fitting that's attached to the firewall with screws and a rubber grommet - the hoses clamp to it on either side. easy to remove and clean up. on the inside it's a bit of a pain to get up there - blower fan comes out, heater core is behind the console. get used to being upside down w/your head under the glove box... easier if your seat is out, gives you a bit more room to work.

in general, it might be a good idea to attack each system, one at a time, replacing rubber hoses that are even vaguely questionable. cheap to do when ya got it all apart and saves a whole lot of pain vs. waiting for things to fail (which they will, eventually)

have fun - looks like a really cool car!

[JGREEZY]

These guys look like they have some cool hose options Hosecandy | Build Your Own "Jaw Dropping" Custom Hoses. you can also check out JEGGS, and SUMMIT. for braided lines

[JGREEZY]

I agree with rossiz I took my seat out and removed the blower. But I got carried away and removed the whole A/C system EVERYTHING. I'm going to take out the heater when I get the car back. I'm not going to be driving it in the winters anyway unless it's dry out. and I got a bee-nee for that .