NapZ in a 320

[LKPar1270]

Wasn't sure whether to post here or in the 720 area, but since I have a 320, chose here.  I have a z24i in my 320 which, as I'm quite 'old school' I discarded the ego and installed a Weber 32-38 progressive carb.  The question I'm dealing with is the vacuum advance is too much for cold running.  In the mornings when cold the detonation is bad enough that it sounds like loosing a rod.  Retarding the timing isnt any help as I've move it to 5° and with only a little help in reducing the knock, but severely degrading warm running.  I'm looking for a way to limit the amount of vacuum advance.  I see the advance module has an area that is filled with some sort of epoxy.  Are these things adjusted by manufacturer and then sealed?  If so, I could remove that seal and adjust to my liking?

[datzenmike]

The Z24i has a CAS (crank angle sensor) that needs the EFI to work so what distributor did you put in there.

[LKPar1270]

I used a distributor for an '86 z24, it was new.

[datzenmike]

 Pull the vacuum advance hose off and see if it goes away. I doubt the vacuum advance is doing anything.

 

Check that the intake AND the exhaust side plugs are firing. Possibly only one side is working. Put an old plug in any intake and exhaust side wire and hold against the head or anything that is grounded. Have someone start the engine. Got spark?

 

The correct timing advance is 3⁰ with engine at operating temperature and the idle speed near 700.

[LKPar1270]

Already did all this.  With vacuum disconnected the knock is gone.  With it connected and timing light on, engine cold, you can watch the timing climb as the knock increases.  I'm getting about 20 to 24 degrees of advance from the vacuum advance.  The knock is almost undetectable when the engine is up to temperature.  If I could get hot air to the air cleaner it would probably only last a few minutes but there's no room to shield the exhaust manifold and get the hot air to the intake side of the engine.

[datzenmike]

 

 

There are three sorts of ignition advance.

1/ Initial advance is set by adjusting the distributor and it is permanent at 3⁰ and is always there

 

2/Vacuum advance is load dependent. When driving, the more you step on the gas the less vacuum advance there is. There is no vacuum advance at idle. Almost no advance at full throttle. Maximum advance can be as high as 25 degrees.

 

3/Mechanical advance or centrifugal advance increases with engine speed. There is none below 700-800 rpm and it maxes out above 2,500 RPM at about  25- 28 degrees. 

 

 

Are you saying 20-24 degrees of advance at idle??

 

What happens if you pull the vacuum advance off at idle? 

 

 

[LKPar1270]

I am very well aware of how a distributor operates, I totally understand the advance mechanisms.  I've been working on cars for atleast 50 years, built 2 from ground up.  I thought I needed to explain what was happening for your benifit.  I will find a way to limit the vacuum advance, just thought someone on here knew if the vacuum advance was adjustable before I tear into it.

[datzenmike]

 

 

 

So at what point do you get 20-24 degrees? What RPM?

 

The vacuum advance is connected to the port on the side of the 32/36, correct?

[LKPar1270]

That's correct. V A comes on just after idle and fades at about quarter throttle, just as it should.  On cold engine with no preheat on the incoming air makes for a lean mixture.  I know I can get by with maybe 12 degrees of the vacuum advance, but the 20 or more is more than this engine's configuration can stand.  I will go ahead and pull the vacuum advance module off, open that plugged hole and see what's in there, hoping it's a set screw to adjust the amount of pull it has.

[datzenmike]

During cold operation the choke would be on, forcing a rich mixture. That's the point of a choke. Is your's set up and working??????

 

Adjusting the vacuum canister is not fixing the actual cause. This should work as it is.

 

Where do you have the vacuum advance connected to on the carburetor????

[LKPar1270]

Obviously you don't know if its adjustable.  Just an fyi, everyone on this site are not ignorant.  Thanks for helping those that are.

[Stoffregen Motorsports]

Ok, this is a perfect example of why limiting the centrifugal advance and adjusting the spring tension on the weights is a good idea. By re-curving the distributor, you could still run the vacuum advance or delete it, but either way, there would be zero danger of too much advance at any given moment in the curve.

[datzenmike]

The thing is this is a Z24 distributor on a Z24 so it should be working and not need adjustments. In fact I doubt it can be adjusted. If it's sealed that should tell you that it's not expected that the owner should ever have to adjust it.  I'm expecting something is not connected properly something over looked. 

 

If the vacuum advance is connected to the intake vacuum this would explain the high signal.

[Stoffregen Motorsports]

The internals of any distributor can't be adjusted, unless it's a Mallory, but they can be modified.

 

This is basic tuning. Performance tuners don't leave anything untouched or at least unverified. Distributor curve adjustments are as old as the internal combustion engine. It was quite common in the '50s through the '80s as a means of doing exactly what we are discussing - getting the engine to run properly with no pinging and with optimal power/economy. My friend has a vintage distributor curving machine in his shop, though it's just for display.

 

So all due respect, I would not look at a part and say, well, it's stock, so it must be ok. Get in there and tweak on it until you get the results you desire.

 

But yes, I would also look for an actual problem before I dive into any modification.

[Charlie69]

On 11/8/2022 at 9:44 AM, LKPar1270 said:

Obviously you don't know if its adjustable.  Just an fyi, everyone on this site are not ignorant.  Thanks for helping those that are.

How does a person posting help for your situation know you mechanical ability? 

[datzenmike]

On 11/8/2022 at 8:44 AM, LKPar1270 said:

Obviously you don't know if its adjustable.  Just an fyi, everyone on this site are not ignorant.  Thanks for helping those that are.

 

Missed this post. Not adjustable as far as I know and have never seen or heard of doing this. No way to take apart or if they are it's set at the factory and never intended for the owner to do it. Adjusting the advance is like taking pain killers for broken leg but not fixing the actual cause of the pain.  

 

On line diagnosis is like a doctor having to do the same but not being able to actually see the patient. Info is filtered through a third party and so a lot of extra questions need to be asked, often repeatedly, to get the complete story worked out.

[Stoffregen Motorsports]

Many aftermarket domestic distributors have an advance that can be metered/adjusted with a set screw down inside the vacuum tube nipple. It's basically an idle adjustment screw. While Nissan/Datsun never had this, they have been in use for years.

 

This still doesn't explain why the OP is having the problem in the first place. My guess is the cause is related to using parts that are not original. Trial and error are the best way to get mismatched parts to work with each other.

[datzenmike]

Weber 32/36. Has a vacuum advance port that should read zero at idle. The vacuum advance plunger begins to move at 2.75 to almost 4 inches of mercury again depending on model, and the total advance varies from 10 to 25 crank degrees depending on model.

 

The Z distributors ('84 at least) start mechanical advance at idle which is 650-750 depending on model. This is why setting the idle is critical. If this problem shows up when engine is cold it has to be assumed the choke is on and it may have a fast idle.

 

 

 

LKPar1270 can you supply the distributor part number if possible?? It is stamped on the outside of the case and begins 22100-????? Probably will say D4K or D4N or D4R followed by two numbers a - and two more numbers.