Once you go triples , you never go back…: )
**
Two remarks here, Gordon; the specs given for advance setting is usually tied to a given rpms - and of course specific to the fitted set-up. Ie, was the advance specified to 1000 rpms? Also, the initial setting is done with vacuum disconnected - it is very important that the specifics are followed…
Secondly; the initial setting is done by turning the distributer body - once set the distributor is clamped, and is not to be altered. All changes in advance are done automatically inside the distributor - by centrifugal weights and vacuum capsule.
Your post seems to imply that further turning of the dist body was used to obtain more retard - after the initial setting. This is wrong if the setting was to right specs - though some tweaking is ‘permissible’ using the specs given as a baseline. I suggest you recheck advance - and indeed watch advance changes with rpms and vacuum inputs. It may reveal that the specs your using are incorrect…
As for the noted condensations. Firstly; using manifold heated air to the air intake is basically an anti-icing device - preventing ice forming in the carbs. Another factor is that mixture alters slightly with air temp; if temps vary so will mixture - so precise carb adjustments should be done with intake temps as near to the expected on road temp as possible…
Further; as air passes through the carbs air gets very cold, which spreads to the surroundings. Which means that that when the engine stops and air stops flowing; the petrol and air humidity in the mixture remaining in the carb will condense on the surrounding surfaces.
The amount of condensation will vary from ‘nil’ to quite a lot, depending on conditions before shut-down. This is perfectly normal and of no concern - it will evaporate as engine heat spreads throughout during engine cooling down…
Not to be confused with fuel leaks, of course. Fuel level is kept constant in the carb bowls by needle valves operated by carb floats. Adjusting float levels is a standard preparation before carb adjustments and carb synchronisation. If fuel levels are different in the carbs, it complicates adjustment and synchronisation. And if carb levels are excessive, the carbs will leak - and the engine will run fat…
As an aside; if fuel pressure is very high, it may overcome the needle valve - resulting in excessive fuel levels…
Frank
xj6 85 Sov Europe (UK/NZ)
**
Thank you Frank for the primer on the carburetor operation. I have been a pilot for 50 years and am familiar with carburetor heat on airplanes (however I have not flown an airplane with a carburetor in almost 50 years). My planes since 1976 have both been fuel injected engines. That having been said, as long as I have been working on old cars, it has never occurred to me that the exhaust manifold heat in automotive carburetors is to prevent icing. Makes perfect sense, just never connected the reason for airplane carburetor heat to automotive carburetor heat. Seems so obvious now. It is cold here today so I will make sure the air cleaner exhaust manifold heated air vacuum divert valve is working properly.
I think I finally got the timing correct on the car. It runs very well with no spark knock. The book calls for setting the timing to 5 degrees static before tdc. Then with the car running and at exactly 1,000 rpm the advance should be 10 degrees. If it is not, then adjust the vernier. Problem is there is no vernier on this distributor. When I use the static timing, the car is a little advanced at 1,000 rpm. My only setting is rotating the distributor. My tach may not be exactly accurate as it tends to bounce around and changes with lights on etc. I understand I may have a grounding problem with the tach. Anyway, either static or 1,000 rpm, it spark knocks under heavy load. I only have to move the distributor a little bit (about 2 degrees at 1,000 rpm) and under very heavy load it no longer spark knocks. Points gap is proper so I think this is the best I can do. Engine runs very smooth at idle, water temperature needle is over the “o” on the word “normal.” The mixture is set at 2 full turns off of full rich. Lifting the carburetor piston over about a half inch causes no rpm increase and at 1/2 inch of lift rpm drops off quickly. Up to 1/2 inch no noticeable reduction, but no noticeable rise either. Both carburetors act exactly alike. Air balance between carburetors, measured with the air flow metering device placed over the carburetor air inlet is very close to equal. Full acceleration from 30 mph after Model 12 transmission has down shifted from third to second is smooth and does not feel inhibited all the way to just over 60 mph, so if mixture is lean, it is not by much.
I filled the gas tanks last night. Some wetness on the bottom of the front carburetor piston this morning, but no pooling. Your description of fuel condensation on the carburetor parts at shutdown combined with the tapped holes holding the long bolts for the carburetor float bowl being tapped all the way into the carburetor throat, means that any condensation that drips on to the carburetor throat can find its way along the bolt threads and out on to the outside of the carburetor float bowl, which is what I have been experiencing. No similar experience on the rear carburetor. Anyway, this morning after yesterday evening’s drive home in very cool weather and after driving to the hangar this morning at both times no gas on the bottom of the float bowl and none in the throat of the front carburetor other than slight dampness on the bottom of the piston. I will let the car sit a few days and see if anything shows, but maybe it is all finally fixed. All the upper engine oil leaks seem to also be finally fixed and a couple of leaks along the oil pan gasket have been fixed. Only oil leak appears to be small leak out of rear seal. Engine has never in almost 50 years been this dry.
Thank you for all your patient help.
Gordon
Hi Gordon - I have multiple Federal spec series 1’s and have played with this set-up extensively. The car I mention here was neglected for years and when this happened I hadn’t yet found all the kinks. Here is a possibility. Firstly that port to the vac retard is only gonna get fuel into it if there is unburned fuel on the engine side of the carb bridge. Something that I experienced when I lived in NJ during the winter created this exact circumstance only much worse to the point that it flooded the carb immediately after shutdown.
My 73 was stored outside as usual one cold night. I went outside in the morning and started her up - it was sunny out but the car’s fuel tanks were still shaded by trees as I warmed it up. Immediately I drove to the bright sunny gas station to fill up while the bright, warm sun warmed my fuel tank area. Shut the car off, filled the tank, tried to restart, it wouldn’t fire. Quickly I found that the carbs were flooded with wet fuel. I also noticed a trickle of fuel out of the charcoal canister in the left wheel well. This is what happened:
Fuel in the tanks was very cold and the vent-line to the charcoal canister was clogged. When the sun hit the cold tanks the fuel and vapor expanded forcing the fuel in the lines into the carbs flooding them as well as forcing fuel through the clogged vapor line - actually opening it up to some extent. I cleared the flood and blew out the vapor lines and it never happened again.
Moral of the story - you could have a clogged vapor/vent line.
~Mike
72 XJ6 (x2)
73 XJ6
85 XJ6
84 XJS
**
The vernier adjustment is mentioned as an easy fine tuning device, Gordon. If absent; the fine tuning must be done with further turning of the distributor body. Ie, if you read 12 deg instead of spec 10, you need fractional turning of the dist body counterclockwise…
Just to clarify; ‘static’ adjustment means setting the advance with the engine stationary. And ‘dynamic’, engine running when checking advance, is done with the vacuum disconnected - unless otherwise specified, of course…
With vacuum connected the advance will depend on the dynamics of the dist fitted and the vacuum source. So using the pertinent vacuum source is essential - I trust your makeshift arrangement is discarded?
I would like to know what happens to the advance a 1000 rpms with and without the vacuum hose connected to the dist - and indeed the hose’s vacuum with throttle closed in normal idle. This will offer clues to the dist’s characteristics - which may have some bearing on various issues…
As an afterthought on the carbs; if the ‘O’ ring mentioned was leaking; it might draw air out of the carb bowl. This will limit the amount on fuel delivered through the jet, causing the engine to run lean - which would lead to backfires.
But while wrong ign timing may cause backfiring; knocking is uniquely related to too high ign advance. And it is quite right to back of ignition, turning the dist body, if knocking is experienced. However; timing settings are specified by factory to ensure that knocking will not occur with the engine compression is to specs and fuel octane rating is as specified for the timing set…
The factors mentioned by Mike is relevant for fuel issues; though when fitted the vacuum connection to the charcoal canister should be connected to the crankcase ventilation system - and canister overflow may drain into the carb throat…
You have indeed done a thorough job and deserve a complete solution to your issues…
As an aside; carb icing occurs at high humidity - below freezing the air humidity drops steeply, cold air contains little water. Actually, the ice forms around the throttle, interfering with fuel flow - injected system are less prone to power loss as fuel delivery is not depending on the airflow through a carb…
Frank
xj6 85 Sov Europe (UK/NZ)
First, All I have been off line for the last two weeks while I had to actually work at my jobs. Hate it when that happens.
Frank, my manual did not mention anything about removing the vacuum line when I was setting the timing at 1,000 rpm. Makes complete sense to do it, just never crossed my mind. I checked the timing without the vacuum and at 1,000 rpm. At 1,000 rpm I am at 6 degrees advance and the book says should be 8 degrees so I am about 2 degrees retarded. With the vacuum line connected I am at about 10 degrees advanced. The vacuum at idle (650 rpm) is about 18 inches and drops to 0 when the accelerator is quickly opened. If I ease it open, it initially drops to 0 the settles back below 10 inches if I only have the throttle open a little bit. Under very heavy load the car barely spark knocks (very close to no knock). Under normal loads and when I fully accelerate and the transmission drops down one gear, there is no knocking all the way to 60 mph. If i move the distributor to any advance at all, the engine will spark knock, so I think I have the timing advanced as far as it should be advanced. It is far better running than it ever has been.
As to the “T” in the vacuum line, I have left that in place. The front carburetor still leaks gas along the center back bolt holding the carburetor bowl in place and that comes from the fact that the the threaded bolt hole is drilled right into the carburetor throat right behind the where the piston would touch if the needle were to be completely removed. This occurs about 10 minutes after engine shutdown. I am guessing this is from fuel condensing on the bottom of the piston and eventually dripping into the carburetor throat and down the bolt. The rear carburetor does not do this.
The “T” in the vacuum line does not affect operation of the vacuum retard. Think of it this way. If you cut a vacuum line, install a “T” and then plug one leg of the “T”, there is no effect on vacuum delivered to the distributor. This is effectively all I have done. I run a vacuum line from the front carburetor vacuum connection that is just on the engine side of the carburetor butterfly to what would be the upside of the top (straight) part of the “T.” I run a short vacuum line from the opposite (lower leg) of the “T” and cap it with a neoprene cap. The horizontal leg of the “T” is connected to the vacuum line running to the distributor. This set up has no affect on vacuum delivered to the distributor, however by making the length of the vacuum line going to the distributor long enough to have an upward curve before the line descends to the distributor, any gas that leaks through the fitting on the bottom of the carburetor on the engine side of the carburetor butterfly cannot get to the distributor and damage the vacuum retard diaphragm. I think this a really good set up that prevents gas that leaks for whatever reason from the vacuum fixture on the carburetor. Until I completely solve this leaking at engine shutdown, this set up protects the vacuum retard (and the distributor) from being invaded by gas.
Rust free Mike,
Thank you for your response. I did check the vent and using lung power blew back through the line to the tank. I could hear bubbles in the tank so I presume the line is clear. I did, however, find the vacuum line to the engine crank case had slipped off the carbon canister. I will more carefully check the carbon canister system when I return home next week.
This has been an adventure and I so much appreciate everyone’s comments and patience.
Gordon
**
While the standard ign timing procedure is with the vacuum disconnected, Gordon - your test shows that you have an ‘advance’ dist. It’s the logical answer to the ignition advancing 4 deg when vacuum applied. The 6 deg advance with vacuum disconnected is purely centrifugal - usually about 4 deg with the more common 800 rpms specified…
Of some interest is the advance reading, with and without vacuum, at the prescribed 650 rpms - it may tell something interesting about the dist advance curves, vacuum and centrifugal…
Your vacuum readings at various throttle settings is somewhat bewildering - it differs from the usual ‘ported’ vacuum characteristics. Which are ‘0’ vacuum with the throttle closed and varying with throttle opening. With direct manifold vacuum connections, unloaded; vacuum will be stable at up to 18" Hg in various throttle settings - but will vary with engine load for the same throttle settings. However, for any ‘advance’ set-up; high vacuum with the throttle closed is not harmful…
However, carb spigots are designed to effect the necessary vacuum to the dist. And given original configurations, carb and dist, it should be a matched pair - with the required advance response. So the only question is simply to get the advance set correctly; with or without vacuum connected…
However, your procedure with testing advance setting, using knocking as a reference - is fair enough when in doubt. The rule of thumb is that if the engine knocks briefly under heavy constant load, like climbing a fair incline with increase pedal and not downshifting, and no knocking in the other scenarios you describe - is a fair confirmation…
That such tweaking is necessary either means that there is some anomalies relating to the dist and vacuum connections or indeed unclear initial setting specs…
You are of course right about the ‘T’ connection; a plugged stub will not affect vacuum readings - I simply misunderstood the set-up, sorry…
Then again; there is something abnormal with your front carb; there should be no ‘unadjustable’ passages between the carb bowl and the airflow through the carb. Any such passage will interfere with mixture, and it will be difficult/impossible to adjust the carb to correct mixture through out the rev and load range. and may well lead to other symptoms…
Frank
xj6 85 Sov Europe (UK/NZ)
**
Frank,
The distributor is a retard vacuum system not an advance vacuum system. Look at the pictures with my March 17 reply to you. The black vacuum line goes to the distributor side of the fixture meaning that when vacuum is applied, the distributor retards. This is also confirmed by the fact that with the engine running at idle, when the vacuum is removed from the distributor, the engine rpm rises about 300 rpm.
What is confusing is that if I remove the vacuum line from the distributor (and cap it) and then set the rpm to 1,000 rpm, then the timing should be at 8 degrees, but I am set at 6 degrees to keep spark from knocking. If I reconnect the vacuum line, the engine will slow to 700 rpm so I have to increase the throttle to set the distributor advance with the rpm at 1,000 rpm. When I do this the timing is at about 10 degrees without changing the distributor position. I need to re-check all this when I get back so that I get the advance numbers exactly correct, write them down and then transmit them to you. I wrote the numbers from memory yesterday so may have messed them up.
I agree that there is something a little odd about the front carburetor, but the leaking fuel is for a very short time and in a very small amount. I can run the fuel pump all day without the front carburetor leaking so it has to be some sort of condensation, but the back carburetor is not leaking at all. Eventually I will figure it out.
Gordon
In a message dated 4/16/2018 5:54:39 AM Eastern Standard Time, noreply@jag-lovers.com writes:
Triples are oversold: for the VAST majority of street driving, properly-set up ZSs, with thr secondary flutterblies removed, work juuuuust fine.
Not quite the eye candy, but…not that much difference in horsepressure, until the engine reaches Ludicrous RPM(c)…
Hi again Gordon,
Have you considered a ripped diaphragm in your front carb’s Bypass Valve? Usually you can tell if your bypass valves are torn because it’s hard to get the idle down but if only one is bad and you have a functional vac retard capsule that might be disguising the problem. The bypass valve is supposed to only work during high depression on overrun. If it’s torn fuel and air completely bypass the butterfly meaning that carb could be running rich. You can test it with a vacuum pump - if you can’t pull a vacuum on it it’s bad.
This might also explain your timing issues as well because the front carb controls the vacuum retard capsule. Definitely worth a look IMHO.
~Mike
72 XJ6 (x2)
73 XJ6
85 XJ6
84 XJS
Wiggles that’s the problem, the triples are sooooo easy to keep up and balance, they breath ALOT better than the strombergs but that double butterfly and the manifolds and the cross overs, once removed the car losses 200 lbs of junk and overall runs so much better, you must be down 30 hp with the 175s?
**
That’s all well and good, Gordon, but you said that ign advances from 6 to 10 deg when the 18" vacuum is connected. And if that is not vacuum advance…??
The change in rpms with and without vacuum; did you clamp the vacuum hose when disconnected? With a vacuum leak introduced, rpms will increase - it is air that dictates engine rpms. Within reason; idle rpms do not vary very much with ign timing.
Idle setting and ign timing is two separate operations. Ign timing is set at specified rpms, with (usually) vacuum line disconnected. Both with vacuum advance using either manifold ('European) or ported vacuum (US). When the ign timing is set to specs - the vacuum is reconnected. The timing is then correct, and timing changes when the idle is set to specs is of no interest…
Whether ‘retard’ or ‘advance’ vacuum is used does not alter the general procedure - the only variations are rpms and vacuum connections, described in the specs. The variations relates to dist dynamics - and specs are used specifically to match these items to engine requirements. If the engine knocks excessively with the spec settings; something is wrong - whether setting procedures. or the specs are given for a different set-up…
Tuning the ign timing on trial and error basis is perfectly legitimate - but if doing so and getting satisfactory engine responses; the actual advance is of only academic interest…
As an aside; all the xk engine have the same basic requirements for ign timing - but different set-ups are used for ‘special interests’. The ‘European’ set up is designed for maximum engine power…
As for the carbs; there is no way of knowing if fuel is only leaking into the carb with the engine stopped. For all we know; the fuel may leak into the airflow while running, distorting fuel mixture…?
Frank
xj6 85 Sov Europe (UK/NZ)
**
Frank,
Let’s start over. With the car at idle, if I remove the vacuum from the distributor, the engine speeds up about 300 rpm, which makes sense if the vacuum is retarding the spark. Now with the vacuum connected and setting the engine speed to 1,000 rpm, the advance at 1,000 rpm is about 10 degrees. When I remove the vacuum, the engine speeds up about 300 or so rpm, so when I adjust the throttle down to 1,000 rpm, the advance drops to about 6 degrees. When the vacuum was removed and the engine speed increased, I am sure the advance moved up, but slowing the engine down to 1,000 rpm dropped the advance to about 6 degrees. The reduction in engine rpm from from reducing the engine speed from about 1300 rpm to 1,000 rpm reduced the advance more than the increase at 1300 rpm resulting in about 6 degrees advance at 1,000 rpm. Now that I write this down, I am not sure this makes sense either. But I am doing all this from memory. On Sunday I will run all this again. This time I will put my vacuum gauge on a T fitting in the line so I can read the vacuum in the line with the line connected to the distributor. I will also write down the rpm/vacuum/advance for all these scenarios so that we have good data. What would really help is if I had an electric rpm gun so that I am not relying on the engine tac (which is erratic anyway). I will see if I can purchase one before Sunday.
Gordon
In a message dated 4/17/2018 5:07:50 AM Eastern Standard Time, noreply@jag-lovers.com writes:
Ah…not even close…
Again, if the secondary butterflies are removed, and the crossover circuit blanked off, I doubt that the engine is down any appreciable amount of power, till it hits 4000 rpm, or so.
I drove a well-tuned ‘66, and an equally well-tuned and modified ‘69 (as above), back-to-back. The ZS was just as zippy, till it hit 4000-4500: only then was their any perceived lack of power.
**
Again, Gordon - we have to make sure that it is not the vacuum leak that increases the idle; clamp the hose when disconnected…
Ignition timing has little influence on idle rpms - to vary the rpms more than marginally, a large change of timing is normally required. The designed control of any petrol engine is varying the throttle to control air flow - any air leak will increase idle rpms, more or less depending on the size of vacuum leak…
What you say is that at 1000 rpms, vacuum disconnected; the advance is 6 deg - with vacuum connected it is 10 deg. Ie, connecting the vacuum increases advance by some 4 deg at the same rpms - which to me indicates a vacuum ‘advance’ set-up…
At 1000 rpms, vacuum disconnected, only the centrifugal regulates advance, and 6 deg is about normal when using the ‘European’ settings - using manifold vacuum. With the usual US ‘ported’ vacuum the normal setting is 17 deg - but the characteristics of this ported vacuum is that it is about ‘0’ with the throttle closed, but varies with throttle setting…
While the centrifugal advance exclusively depends on rpms; the vacuum varies with rpms and throttle settings. Using manifold vacuum the dist ‘reads’ the amount of air going into the cylinders, the higher the vacuum the less the cylinder fill - which is important for the ign timing/knocking relationship.
With ported vacuum the ign timing/knocking relationship is ‘read’ a different way; the amount of air going into the engine uses throttle position - but deviously. Using the fact that vacuum increases with air speed; suitable placing the vacuum orifice in relation to the throttle edge will give required information to the dist for advance purposes. However, the vacuum read-out from the port must match the distributor in use - and the initial ign timing is specified accordingly…
So the interaction between the centrifugal and vacuum advance is complex, but with a matching pair of dist and vacuum tap-off - after the initial setting of ign advance; the pair gives the proper advance for any load, rpms and throttle settings…
Plotting the centrifugal advance curve is straight forward - just read advance at various rpms with vacuum disconnected. Likewise, plotting the vacuum influence just requires reading the total advance with vacuum connected - and subtract the centrifugal advance. negative if vacuum retards the advance. However, the advance changes while the throttle is moving is more complex as several factors are involved. These are data not generally available beyond manufacturers; there are few data given to the public for the various dists. But data are always interesting…
Indeed, With no data available, or using the available data gives a ‘wrong’ result, ie knocking’; trial and error like you have done, is perfectly legitimate. However, the wrong combinations of porting and dist may have unnoticed drawbacks…
As an aside, the complexities applies to the fuelling with carbs; the speed of the air past the jets dictates how much fuel is ‘sucked’ into the air stream (actually; forced from the carb bowls by the ambient air pressure). With CD carbs; using a vacuum operated needle to vary the jet orifice, considerably simplifies carb construction…
Frank
xj6 85 Sov Europe (UK/NZ)
**
I will run all this on Sunday and report what happens. I did plug the vacuum line when I removed it from the distributor so that the rpm increase was only a function of removal of the distributor retard not open vacuum leak.
**
It’s odd, Gordon - it implies that you can vary idle at 1000 rpms by some 300 rpms by altering advance 4 degrees. I have never experienced anything even near that…
Still; 4 deg more advance with vacuum connected than disconnected doesn’t figure as vacuum ‘retard’…
Frank
xj6 85 Sov Europe (UKNZ)
**
Sorry I have gone missing for the last weeks so not responsive. When I returned from being gone for three weeks, found the brake reservoir empty and a puddle of brake fluid under the car. Turned out the master cylinder was again leaking at its interface with the vacuum boost. SNG Barrett has no replacement or re-built units and said they had not had them in years. They turned me on to White Post Restorations in White Post, Virginia (One Old Car Drive, White Post, Virginia (540-837-1140) who re-sleeved and rebuilt my brake master cylinders. They also repair vacuum boosts. Anyway the new unit is installed and I finally got all the air out of the master cylinder and brake lines resulting in the best peddle firmness I have had in years. I also finally got the air conditioner working properly after installing a filter and a new expansion valve. First time in almost 50 years the air conditioner actually cools the car.
I still have the 10 minutes after stopping gas leak out the bowl bolts of the front carburetor and having to run the car about 2 degrees retarded static from where my book says for a US Car (#6 5 degrees BTDC) and about 2 degrees retarded at 1,000 RPM. I know I owe Frank some date and hopefully I can get to that this week. The car is running very very well at the moment, so if I can solve the gas leak, this car will be great to drive and enjoy.
I know I’m jumping in here really late in the game, but I am surprised that if your main issue is engine knock, or pre ignition, that no one has suggested that you look at your sparkplug heat range and perhaps switch to a colder plug.
Whew, that was a long winded sentence.