l16 hitachi cuts out

[smoke]

I'm glad someone mentioned the zero vac at the distributor, emission thing. I ALWAYS run manifold vac to my distributors, not ported. Vac advance at idle not only makes them idle better and increases throttle response, it will also idle at a cooler temperature.

[datzenmike]

Yes but don't everyone run out and do this or you will ping under load. The distributor is set up to work properly this way. Idle would probably like an extra 5 to 8 degrees of advance but it may be too much too fast for above idle with a base timing of 12 degrees. The vacuum can on the dizzy must be adjusted.

[smoke]

No diff, under load you have the exact same vacuum as you do when it's ported it only changes at idle. Once you open the port, it acts exactly the same. This is the difference, as you can see on the chart, the only time there is a change is when you close the throttle and shuts the port. There are some exeptions, over time, a handful of manufactures used venturi vacuum to run the vacuum advance, much like the way a vacuum secondary works, but, it's pretty rare. But on most, once your distributor receives vacuum from any throttle input at all, it can't tell where the vacuum is coming from, it acts the same way, just not at idle, because it shuts it off.

 

 

Also seen in this as a plain old vac gauge. One is the gauge hooked to the ported vac advance port, the other is hooked to straight manifold vacuum. As you can see, the only difference is when the throttle plate is closed.

 

 

 

 

 

[datzenmike]

Yes

 

The thing is that the ported vacuum isn't instantly ON at a set point above idle. It 'gradually' adds vacuum to the distributor. The Hitachi carb does not have a hole but a very small thin vertical slot in the wall of the carb that the throttle plate opens past, maybe 1/8" long. At some point in the increasing RPMs above idle the mechanical advance begins to kick in. Some as low as 900 RPMs.

 

With full manifold vacuum and an early in mechanical advance you may get pinging is all I'm saying. You may have to delay or slightly limit mechanical advance. Simply decreasing the initial advance a few degrees to prevent this will rob the high RPM total advance.

[smoke]

Well, I am speaking without actually directly testing the Hitachi carb on a Nissan engine, but now you have my curiosity up and I am going to go out and test it soon. But, Most carbs, it acts just like on on off switch. To find out the Hitachi carb did a more advanced version of it would really not surprise me in the least though. However, I will still say that under a heavy load, as in next to no vacuum, it won't make a difference, due to no vacuum going to the advance, even if it's hooked right to the manifold. The case where that would not be the case would be venturi vacuum rather than manifold vacuum. But the placement of the port on the Hitachi, it's getting manifold vacuum.

[smoke]

Also, if you're building ANY manifold vacuum at full throttle, you have something wrong, like way too small of a carb or a restriction.

[datzenmike]

Agreed at WOT it's all the same.

 

If manufactures like no vacuum at idle to reduce emissions it's only reasonable that they also like to delay advance as much as they can get away with. California carbs (and some others) won't allow vacuum advance until the motor is warm and there are also built in delays in the hose.

[smoke]

Yeah, the 80s were a bad time for emissions. Ford even retarded camshafts. They always consider idling to be the worst for the environment, namely, sitting in traffic. Both GM and Ford had the vacuum advance set up so it would give you full manifold vacuum when the engine was cold (so it would idle) but when it warmed up, it would switch to ported advance.

[RatVonDude]

I just chucked mine in the ocean, I hated that f@cking thing. 

Sounds like an air leak

[datzenmike]

Yeah, the 80s were a bad time for emissions. Ford even retarded camshafts. They always consider idling to be the worst for the environment, namely, sitting in traffic. Both GM and Ford had the vacuum advance set up so it would give you full manifold vacuum when the engine was cold (so it would idle) but when it warmed up, it would switch to ported advance.

Nissan was different. They used dual points to delay the spark 4-6 degrees when cold and in certain gears. Later L20Bs had a thermal vacuum valve that only allowed advance when warm and the Z series motors had a vacuum leak in the vacuum advance line that was closed by a thermal valve when warm.

[smoke]

I just chucked mine in the ocean, I hated that f@cking thing. 

Sounds like an air leak

Your Hitachi? Yeah, I think they get a bad rap for being picky and acting weird if everything is not just right. A lot like the old GM quadrajet, you will find so many who just despise them. But, a qjet that is tuned perfectly is really about as close to fuel injection an American carb ever got, get one thing out of whack though, and it can be a real turd sandwich.

[smoke]

Nissan was different. They used dual points to delay the spark 4-6 degrees when cold and in certain gears. Later L20Bs had a thermal vacuum valve that only allowed advance when warm and the Z series motors had a vacuum leak in the vacuum advance line that was closed by a thermal valve when warm.

Yeah, I bet plenty of the guys who designed the engine to begin with started to cringe when they had to start making vacuum leaks and retarding timing. But, they were doing what they could to get it to pass at the time. Today they have that pretty well down with engine management. Of course, I still have yet to figure out how it's better for the environment that my friends brand new diesel truck gets LESS than half the mpg of my 04 diesel. 

[smoke]

This might have warranted a new thread, but since it is touching on the topic at hand, I figured I would keep it here. 

 

I went out and hooked up my vacuum gauge to my truck which has a L18 and the only smog stuff left is pretty much the ported vacuum advance (which I don't use). Now, first off, Mike was 100% correct, the ported vacuum on these is NOT just on or off. I have been working on domestic shit all my life and that's just the way the are. I should have known it would have been better on Nissan. My readings are as follows. 19 inches at straight manifold vacuum, warmed up, regular idle. No surprise there. On start up, cold, with the fast idle running, I was surprised to find a steady 4 inches of vacuum at the ported fitting. Not surprised by the presents of vacuum, just of how little. On a domestic, as soon as the throttle blade opens that port, you have the same as straight manifold vacuum. This right here told me Mike is right, but I am curious about this shit, so I went on.

 

Once fast idle was off, the port gave zero vacuum (normal). But, when I cracked the throttle slowly, vacuum rose slowly and was very dependent on throttle position. In other words, you could steadily increase it or decrease it with throttle input. I could run it up to 17 inches, probably 19 if I wanted to keep screaming it. 

 

However, if you crack the throttle fast from idle, like really fast, you get next to no advance at all. As a matter of fact, I could snap the throttle and have it rev without the needle even budging off of zero. The way they have this works on normal driving with light load. Anytime, you give it a hard(ish) take off or have a little weight, you are not going to get vacuum advance.

 

I go for a drive with the gauge hooked up and it's the same deal, anytime you are under a load of any kind other than light cruise, it goes to zero. Now, with straight manifold vacuum, I clearly have more advance in like 80% of driving, but if I put a load on the engine, it still goes to zero, just like the ported did. At light cruise, like doing 55 mph on flat ground, there is a little difference between ported and straight, but only about 1 inch. 

 

For this next part, keep in mind that my engine is bone stock, stock compression and so on. Mine hooked to straight manifold vacuum never pings. If I actually carried a load in this trucks bed and pulled it hard to get rolling, it would drop from the 19 inches to zero, the ported source would also be at zero. At this point, you are operating on mechanical advance only, which would be the same for both ported and straight sources. When you are hard into the throttle, it will be the same on both ported and straight sources. The big differences on this is at idle and easy stop and go town driving. The way I have mine routed to full manifold vacuum, it's getting more advance in situations like this than ported would. On my engine, in my truck, it runs MUCH better like this. It's a very lean fuel mixture and it likes more lead time to get a proper burn at low speeds and idle. The factory of course knew this, but a retarded engine makes more exhaust heat (more heat in general) thus lowering NOx emissions. 

 

My truck runs fine with it hooked to ported, but is just much more 'snappy' with straight manifold vacuum. That and the idle is smooth as glass when compared to ported (but both are pretty smooth). I think this is a case by case sort of thing, what works great for me, may not for you. However, it's a cool thing to try, because it's not like buying a different carb or a cam. Just a few minutes of your time, if you don't like it, you can switch it back in like 10 seconds. Nothing "bad" will happen on a short test drive.

[danfiveten]

Meh dont mind it here, gives me more to read :)

 

And i wish i could chuck mine into the ocean, thats the problem with having a well known preserved 510, have to keep her original, so the ocean gets nothing from me..(damnit)

[smoke]

I can swing by and have a look at it sometime if you like. I'm not tooooooooo creepy.

[RatVonDude]

Your Hitachi? Yeah, I think they get a bad rap for being picky and acting weird if everything is not just right. A lot like the old GM quadrajet, you will find so many who just despise them. But, a qjet that is tuned perfectly is really about as close to fuel injection an American carb ever got, get one thing out of whack though, and it can be a real turd sandwich.

I'm sure, off the lot, that thing worked like a Swiss watch.

Most half wits ( such as myself ) by pass all the re-directional hoses through that painfully annoying blue steam tray.

This may have been Datsuns attempt at smooth riding luxury and fuel economy. I always think of that seen in the Brady Bunch where the drivers ed teacher pulls out an egg and puts it on an orange cone. The Hitachi, in perfect form, may of done well in this situation, a hopped up racing carb would def knock the egg off the cone.

A stock Hitachi is perfect for L.A traffic.

[smoke]

I feel ashamed to know EXACTLY which episode of the Brady bunch you're talking about.

[RatVonDude]

L.O.L !!!!!!!!!!!!!!!

[danfiveten]

So took her again tonight after adjusting the idle and throttle and mixture, hesitation off the line sitll there, doesnt do it at steady throttle, only when you get on the gas.  its only doing it once it warms up, not when its cold, but once it warms up, boom starts having issues?

 

I have some black plug wires i had put on when trying to figure out the old issue with stalling on the old carb, because theyc ouldnt get ngk's in saying they were on order from factory only, so i just found a set online and ordered, think it could be the plug wires?  When i tried to do the timing it seemed very erratic. 

[smoke]

If it does not do it when cold (choke close) then you probably have a lean transition point once it opens.

[danfiveten]

So what you suggest smoke?

[smoke]

My first thoughts on it would be too low of a float level or not enough of a pump shot. I noticed though you said the timing seemed erratic, does that mean it was jumping around at idle?

[danfiveten]

When using the timing light it would  show the marks and dissapear, and then seemed off constantly, i got it to a point between 10-15, i just felt like it wasnt right, and still isnt right on timing. I ordered ngk wires today, these wires were just some generic ones i threw on because i didnt know how old the old wires were when i had the issue where she wouldnt even move under her own power with the old carb.  I figure process of elimination right? I know fuel pressure is right and good pump, new ngk plugs, crappy wires (will have good ngks in by friday) rebuilt carb, next is distrutor but it seemed fine.  Just weird it only does it when its cold, i dont notice any issues, and then once warm BOOM, issues when getting on the gas. Also when driving under 30 mph she feels weird when on the gas, like somethings dragging? or pulling on her from behind.  

[smoke]

That helps. I think I'm going to stick with this being a timing issue. Like not advancing like it should.

[datzenmike]

Try turning the idle mixture screw out. (richer) Not so much that the idle quality is bad just closer to the rich side than the lean side, See if that helps get you past that 'spot'.

 

Make sure your accelerator pump squirts right away and there is no pause.

 

Try a very slightly higher idle speed like 850 or so.

 

Pull dizzy cap off and vacuum hose off carb. Suck on hose and cover end with tongue... rotor should turn clockwise about an inch. It should not return until you release it. If it fails to turn (stuck) or returns (leak)