Should have read 3000rpm not 300!
The degrees are on the crank not the dizzy. The Jowett DM2 is normally limited to 10deg max advance. but this wears to give upto 15deg at dizzy. I rebuilt the wear with weld when I rebuilt the race dizzy on the Jup. That was tested on the rolling road for max power over 12 years ago. This Jav dizzy has been reconned professionally'! Car is run with Vacuum advance.
Anyway took the car for extended test today after checking distributor with timing light. The static setting was 5 deg before and 3000rpm 24 deg. this was what I had set to after a road test a few months ago.
The car is now not overheating so much with the super unleaded in the system.
I first tried half turn advance and did not get any pinking but it did seem to overheat a bit more and did misfire on full throttle up a hill.
I then reduced the advance by one turn and then another half turn on the micrometer which is about 3 deg so bringing the it to 2 deg BTDC static and 21 deg flat out, (which is what the Jup is set to).
I took it for a 10 mile 65mph drive between these changes along a straight road with some long hills. I had my temp gun with me and am now a lot happier with the temps. Still at 100c at the head; but drops to 85 at top of radiator. The car cools down quickly when you reduce speed below 50mph.
So that is it. The petrol I think is the culprit combined with too much advance. The faster flame of the ethanol in modern petrol needs to some retardation (3deg) from the petrol of 5 years ago.
I am now going to retard the Jup as well as it is both pinking occasionally and running hotter than it used to.
The following article may explain the petrol pump problems. Perhaps a sagging diaphragm. Will check next week.
Lobsided Jowett not balanced at all.
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Last edited by Forumadmin on Sun Jul 05, 2009 11:19 am, edited 3 times in total.
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WHY DOES MY CURLEW RUN BETTER ON THREE YEAR-OLD STALE PETROL? FROM THE JUNE JOWETTEER----
Great to hear that the shackles are off and we can once again ‘talk dirty’ (or, as the better - and cleaner - half says: “talk turkey!). This is a question that should bring out the technically knowledgeable, so I will open the batting:
The engine starts immediately on this brew, ticks over with the even reliability of a steam engine, runs without any pinking or loss of performance, and starts readily when hot. Comparing this with new petrol and not changing any settings, starting is the same and the tick-over starts off fine, but an irritating little ‘flutter’ and hesitancy sets in as the engine warms up - a very minor, but noticeable change and the tick-over has increased when hot. The running performance is unchanged; however a little piston rattle can be heard when changing from a trailing or light throttle setting on the transition to more load. Hot starting takes more turns for the engine to fire up. The engine is as near correct as it is possible to get, with a ‘new’ old stock carburettor, new Champion N5 plugs, and long reach adaptors; new rings, gudgeon pins, and valves, were supplied by Jowett Car Spares (unashamed advertising plug!) - so why does old stinking unleaded petrol work better than new petrol?
When our cars were designed and produced, there was little leaded petrol (BP Ethyl). Most motorists that wanted a bit of ‘pep’ and cooler running, mainly chose Cleveland Discol which contained some alcohol content that made engines appear to run smoother, and this gave the impression of improved performance. I haven’t seen any practical test data to prove this; maybe someone out there has, and it would be interesting to see this in our magazine, if it exists. The way that manufacturers got around the anti-knock problems was to run with low compression ratios of around 4.0/5.0 to I, and the petrol hovered between about 75 to 85 octane rating. Thus, with the long strokes employed in most popular engines together with heavy pistons, many having a fourth skirt ring, there was little chance that the ‘rat in a drain pipe’ could wobble about much at revs that were just a tad faster than the Flying Scotsman.
The burn time in these engines in comparison to today’s products was long; the spark being generated in an alcove above the valves required the flame path to rush across the head, pop around the corner, and cause a bang in the cylinder. To enable this relatively gentle push to occur, the re doubtable Mr Joseph Lucas, erstwhile ‘prince of darkness’, provided a magical piece of equipment that automatically fore told when the spark should occur to enable the most efficient running of an engine from tick-over to about 1,500rpm. This was the predicted spark advance to suit most compression ratios, petrol fuel, and strokes of the day; it was all done by bob weights and springs - no smoke and mirrors here, and the system served us well without question... Until now?
A few years ago I noticed that both my Model-9 1934 Sunbeam and 1936 Inter national Norton motorcycles began to rattle on full advance. By easing back the magneto advance lever slightly, all serenity re turned without any detrimental effect on performance. Clearly something had changed; it was the pump fuel: both engines preferred non-supermarket Texaco. We all know that the fuel producers provide summer and winter grade fuels, and on a motorcycle the advance and retard lever is your engine’s friend - and this can also apply to non-auto advanced cars. Modern lead-free fuels are, in most cases, a higher octane rating than our engines were designed for; they bum hotter and quicker than the old grades and are lighter and more ‘flarey’ to suit modem short-stroke high compression and high revving engines which demand a fast fuel bum rate. This raised the questions: Were these new fuels having a detrimental on my ‘travelling time warps? And are the fuels of today suitable for seventy- plus year-old vehicles? And if not, then is there anything that we can do to improve matters?
The first thing to do is find out what has changed; we know that the fuel has, and I won’t bore you with excessive bedtime technical reading of fuel specifications, but at a practical level determine the actual working change in simple terms.
Using the single-cylinder 490cc 79xlOOmm Norton engine as a model, the Lucas magneto has an advance range of one inch (25mm) of piston movement. Ignition advance for petrol fuel in 1936 was 1 1/l6ths inch points opening before t.d.c.; ditto best running in 2008 is half an inch points opening before t.d.c. The difference between the years 1936 and 2008 indicate that 3/l6ths in. of advance is not required, thus indicating the increased volatility of modern fuel. Should an engine be run over-advanced? The whole engine will be overstressed; normally the first part to fail is the big ends and other parts will also suffer i.e. mains, little ends, rings, and pistons. The reason why modem cars are not affected by filling with varying fuel products without any discernable effect is due to the inclusion of a knock detection system within the management box. We don’t have management boxes on our engines so we rely on our ears for any signs of distress. Those of us that have the Lucas auto-advance unit have no recourse to manually adjusting to the engine’s natural advance curve to suit a particular grade and make of fuel.
It is of some concern that there is indication that the engine is not entirely happy with modern fuel in lieu of not being able to change the advance range. In order to reduce the octane rating and volatility of the fuel, I have reverted to adding two- stroke oil; this slows the rate of combustion- the amount added can be found by experiment. It has the added benefit of providing valve and upper cylinder lubricant; the Jowett instruction book recommends the use of upper cylinder lubricant and the two- stroke oil provides a low carbon ‘finger print’ smokeless burn.
New fuels containing increasing amounts of ethanol are extensively aggressive; these fuels have turned the inside of my Norton’s petrol tank which was sealed with Petseal in the late 1 980s and remained hard until last year, into a gunge-filled mess which I cannot remove. The dual tube rubber petrol pipe fell off the union under the weight of the fuel and it has expanded to twice its natural size into a sticky mess at the union connection. Additionally, the zinc plating on the magneto cover has etched off where petrol has dripped onto it, and the primary chain guard paint is sticky and lifting where petrol has come into con tact with it after forty years of not having nay problem, including using petrol for cleaning and degreasing.
This is a wake-up call to all of us with vintage vehicles. It shows that these new fuels could cause extensive damage in the way that they bum; they do inflict dam age to rubber components that were petrol rated, and put plated and painted finishes at risk. Rubber seals and fuel pump diaphragms could be subject to unseen deterioration, and unexpected failure could result. The FBHVC have issued the attached statement regarding fuel topics. I will be contacting them to ask a number of questions relating to technical risk to historic vehicles, and why warnings relating to corrosion and damage to finishes and components were not advised at points of sale before these new fuels were introduced, and whether damage costs can be recovered. Any further observations would be of interest; meanwhile we state the usual disclaimer regarding the use of upper cylinder lubricant - it works for me, but the modem petrol doesn’t.
-Ian Thompson, Datchet
The FBHVC relevant comments, summarised from their Newsletter, read as follows:
• At concentrations of less than 5%, there is no obligation for the petrol pumps to be labelled at the point of sale, so petrol can be sold with between 0 and 5% ethanol. Ethanol is hygroscopic so manufacturers should have been adding corrosion inhibitors to it before blending with petrol. Ethanol changes the volatility of the fuel which, although it can give some benefit to cold starting, it is at the expense of increased problems of vapour lock and hot starting in susceptible vehicles. Corrosion could be a problem if no inhibitors are used.
• Any tank sealant manufactured in the USA should not be affected by ethanol as it has been in American petrol for some time. To avoid problems, customers should check that any such product does indicate it can be used with fuel containing ethanol. Many seals have a ‘memory’ and may leak when introduced to ethanol when they are old. The same type of seal may not leak when new. Particles resulting from the breakdown of tank sealants and moving through the fuel system may also cause problems, although these would be for a finite time (until it has all been washed through). A solvent is available to remove existing tank sealant, Epoxy Remover made by Tank Cure.
However, the active ingredient in this product is methylene chloride, a.k.a. paint stripper, which is the subject of a proposed ban.
At present the number of problems reported is small in relation to the number of vehicles which could be affected. The FBHVC will be monitoring the situation closely and would like to hear from anyone who is experiencing problems, giving full details of the vehicle concerned. If the situation is seen to be more widespread, then the Federation will look into the possibility of further research.
Great to hear that the shackles are off and we can once again ‘talk dirty’ (or, as the better - and cleaner - half says: “talk turkey!). This is a question that should bring out the technically knowledgeable, so I will open the batting:
The engine starts immediately on this brew, ticks over with the even reliability of a steam engine, runs without any pinking or loss of performance, and starts readily when hot. Comparing this with new petrol and not changing any settings, starting is the same and the tick-over starts off fine, but an irritating little ‘flutter’ and hesitancy sets in as the engine warms up - a very minor, but noticeable change and the tick-over has increased when hot. The running performance is unchanged; however a little piston rattle can be heard when changing from a trailing or light throttle setting on the transition to more load. Hot starting takes more turns for the engine to fire up. The engine is as near correct as it is possible to get, with a ‘new’ old stock carburettor, new Champion N5 plugs, and long reach adaptors; new rings, gudgeon pins, and valves, were supplied by Jowett Car Spares (unashamed advertising plug!) - so why does old stinking unleaded petrol work better than new petrol?
When our cars were designed and produced, there was little leaded petrol (BP Ethyl). Most motorists that wanted a bit of ‘pep’ and cooler running, mainly chose Cleveland Discol which contained some alcohol content that made engines appear to run smoother, and this gave the impression of improved performance. I haven’t seen any practical test data to prove this; maybe someone out there has, and it would be interesting to see this in our magazine, if it exists. The way that manufacturers got around the anti-knock problems was to run with low compression ratios of around 4.0/5.0 to I, and the petrol hovered between about 75 to 85 octane rating. Thus, with the long strokes employed in most popular engines together with heavy pistons, many having a fourth skirt ring, there was little chance that the ‘rat in a drain pipe’ could wobble about much at revs that were just a tad faster than the Flying Scotsman.
The burn time in these engines in comparison to today’s products was long; the spark being generated in an alcove above the valves required the flame path to rush across the head, pop around the corner, and cause a bang in the cylinder. To enable this relatively gentle push to occur, the re doubtable Mr Joseph Lucas, erstwhile ‘prince of darkness’, provided a magical piece of equipment that automatically fore told when the spark should occur to enable the most efficient running of an engine from tick-over to about 1,500rpm. This was the predicted spark advance to suit most compression ratios, petrol fuel, and strokes of the day; it was all done by bob weights and springs - no smoke and mirrors here, and the system served us well without question... Until now?
A few years ago I noticed that both my Model-9 1934 Sunbeam and 1936 Inter national Norton motorcycles began to rattle on full advance. By easing back the magneto advance lever slightly, all serenity re turned without any detrimental effect on performance. Clearly something had changed; it was the pump fuel: both engines preferred non-supermarket Texaco. We all know that the fuel producers provide summer and winter grade fuels, and on a motorcycle the advance and retard lever is your engine’s friend - and this can also apply to non-auto advanced cars. Modern lead-free fuels are, in most cases, a higher octane rating than our engines were designed for; they bum hotter and quicker than the old grades and are lighter and more ‘flarey’ to suit modem short-stroke high compression and high revving engines which demand a fast fuel bum rate. This raised the questions: Were these new fuels having a detrimental on my ‘travelling time warps? And are the fuels of today suitable for seventy- plus year-old vehicles? And if not, then is there anything that we can do to improve matters?
The first thing to do is find out what has changed; we know that the fuel has, and I won’t bore you with excessive bedtime technical reading of fuel specifications, but at a practical level determine the actual working change in simple terms.
Using the single-cylinder 490cc 79xlOOmm Norton engine as a model, the Lucas magneto has an advance range of one inch (25mm) of piston movement. Ignition advance for petrol fuel in 1936 was 1 1/l6ths inch points opening before t.d.c.; ditto best running in 2008 is half an inch points opening before t.d.c. The difference between the years 1936 and 2008 indicate that 3/l6ths in. of advance is not required, thus indicating the increased volatility of modern fuel. Should an engine be run over-advanced? The whole engine will be overstressed; normally the first part to fail is the big ends and other parts will also suffer i.e. mains, little ends, rings, and pistons. The reason why modem cars are not affected by filling with varying fuel products without any discernable effect is due to the inclusion of a knock detection system within the management box. We don’t have management boxes on our engines so we rely on our ears for any signs of distress. Those of us that have the Lucas auto-advance unit have no recourse to manually adjusting to the engine’s natural advance curve to suit a particular grade and make of fuel.
It is of some concern that there is indication that the engine is not entirely happy with modern fuel in lieu of not being able to change the advance range. In order to reduce the octane rating and volatility of the fuel, I have reverted to adding two- stroke oil; this slows the rate of combustion- the amount added can be found by experiment. It has the added benefit of providing valve and upper cylinder lubricant; the Jowett instruction book recommends the use of upper cylinder lubricant and the two- stroke oil provides a low carbon ‘finger print’ smokeless burn.
New fuels containing increasing amounts of ethanol are extensively aggressive; these fuels have turned the inside of my Norton’s petrol tank which was sealed with Petseal in the late 1 980s and remained hard until last year, into a gunge-filled mess which I cannot remove. The dual tube rubber petrol pipe fell off the union under the weight of the fuel and it has expanded to twice its natural size into a sticky mess at the union connection. Additionally, the zinc plating on the magneto cover has etched off where petrol has dripped onto it, and the primary chain guard paint is sticky and lifting where petrol has come into con tact with it after forty years of not having nay problem, including using petrol for cleaning and degreasing.
This is a wake-up call to all of us with vintage vehicles. It shows that these new fuels could cause extensive damage in the way that they bum; they do inflict dam age to rubber components that were petrol rated, and put plated and painted finishes at risk. Rubber seals and fuel pump diaphragms could be subject to unseen deterioration, and unexpected failure could result. The FBHVC have issued the attached statement regarding fuel topics. I will be contacting them to ask a number of questions relating to technical risk to historic vehicles, and why warnings relating to corrosion and damage to finishes and components were not advised at points of sale before these new fuels were introduced, and whether damage costs can be recovered. Any further observations would be of interest; meanwhile we state the usual disclaimer regarding the use of upper cylinder lubricant - it works for me, but the modem petrol doesn’t.
-Ian Thompson, Datchet
The FBHVC relevant comments, summarised from their Newsletter, read as follows:
• At concentrations of less than 5%, there is no obligation for the petrol pumps to be labelled at the point of sale, so petrol can be sold with between 0 and 5% ethanol. Ethanol is hygroscopic so manufacturers should have been adding corrosion inhibitors to it before blending with petrol. Ethanol changes the volatility of the fuel which, although it can give some benefit to cold starting, it is at the expense of increased problems of vapour lock and hot starting in susceptible vehicles. Corrosion could be a problem if no inhibitors are used.
• Any tank sealant manufactured in the USA should not be affected by ethanol as it has been in American petrol for some time. To avoid problems, customers should check that any such product does indicate it can be used with fuel containing ethanol. Many seals have a ‘memory’ and may leak when introduced to ethanol when they are old. The same type of seal may not leak when new. Particles resulting from the breakdown of tank sealants and moving through the fuel system may also cause problems, although these would be for a finite time (until it has all been washed through). A solvent is available to remove existing tank sealant, Epoxy Remover made by Tank Cure.
However, the active ingredient in this product is methylene chloride, a.k.a. paint stripper, which is the subject of a proposed ban.
At present the number of problems reported is small in relation to the number of vehicles which could be affected. The FBHVC will be monitoring the situation closely and would like to hear from anyone who is experiencing problems, giving full details of the vehicle concerned. If the situation is seen to be more widespread, then the Federation will look into the possibility of further research.
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Keith Andrews
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Profesionally doesnr mean it has been done right...even pros have been known to resize sintered bushes with a reemer...causing short life.This Jav dizzy has been reconned professionally'! Car is run with Vacuum advance.
VA...now we are in a completely different ball game, just like a carb is '2 in 1 ' or an idle /mixture screws, totally indepenant of jets. power valves , accel pumps....so the same exists with the Cent dizzy and the VA curve.
I assume you have a timing light, crank marked with degrees upto about 45/50 and a manifold Vac gauge under the hood AND inside the car...and a vac advance pump....these also double as 1 man vaccuum brake bleeders.
Does it work off ported vac or manifold vac...ie is the port above or below the carb butterflys.
VA has nothing to do with power...it should only kick in at part to cruise throttle enabling economy to run on lean mixtures at cruise...AND if manifold vac, low intial cent advance for easy start, but kick in when fired up, advancing (cent+VA) for a smoother idle
Hence why a track engine doesnt need a VA Find out what the manifold vac is at open road cruise, the VA should be full in at this vac...
.if manifold vac Advance, at idle (no VA attached and blocked) the VA should also be very near or full in.
You also need to find out how many degs are in the VA...
Take the rpms up till dizzy is full in then connect the VA, the difference between these readings will tell u that.
PS and much of the other posts above I have covered previoualy in old post regarding bradford engines, compression, timing and old english pool fuels...I have just skimmed thru, there is a note about etinols in fuels flashing faster...they do not...higher the octane the more advance required, higher the compression, the less advance
And running high octane in a low compression engine is a total waste of time...
The more advance the "better" the engine "feels" but that is all it is , a different engine note giving that impression.
Also a lot of what im saying goes against the grain of us guys who grew up with our '1600 ford crosflow boy racer cars' and mk1 zephers
Some 35 yrs ago I got into some serious Formula ford racing, then off roading and street/strip drag racing...Everything I believed got thrown out the window, and untill I changed there was no way I could compete.
My Spelling is Not Incorrect...It's 'Creative'
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You may be interested in a period article supplied by Leo on fuels. I have yet to fully comprehend how this explains the overheating; but I think it does.
See https://jowettnet/forum/download/file.p ... &mode=view
See https://jowettnet/forum/download/file.p ... &mode=view
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Centrifugal advance adjusts spark timing for an increase in speed to allow time for air/fuel mixture to burn efficiently. However, when the vehicle is cruising under light load conditions, ie not hill climbing, the fuel intake is reduced and the fuel charge will be at lower pressure at the spark point. These conditions result in a slower burning time and further ignition advance is required.
To achieve this, use is made of the fact that there will be a relatively high vacuum in the inlet manifold under light load and less vacuum under heavy load when the throttle is opened wider.
Conditions under which the vacuum system comes into operation are worthy of note:
(a) At tickover speed, the degree of vacuum in the inlet manifold is large, since the throttle butterfly is nearly closed. Vacuum advance does not occur, however, because the butterfly has not exposed the vacuum tapping hole
(b) When cruising on the flat, the engine is on light load and the throttle only partly open. The vacuum is still large and is transmitted to the diaphragm of the advance unit. Ignition advance occurs
(c) When the engine comes under heavy load the driver presses the accelerator pedal and opens the throttle. The vacuum is reduced considerably, allowing the vacuum unit spring to return the contact breaker baseplate to the original position. The degree of advance is then fixed only by the centrifugal advance mechanism.
It is thus possible if the vaccum unit is not providing enough advance when 60mph cruising the ignition advance is not enough and overheating will occur. This is contrary to what I observed. But then the vacuum advance could have been giving too much advance, which as I previously stated I have found to also cause overheating on another engine in the Jupiter. That time the extra advance was caused by worn centrifugal stops.
Anyway worth another check that the VA is adding the 10degrees of advance at the crank. Note VA units have different strengths as I found when I sorted the dozen distributors collected off different Javelin engines, most of which seemed to be different. I will try to find the article I did 15 years ago on them!
To achieve this, use is made of the fact that there will be a relatively high vacuum in the inlet manifold under light load and less vacuum under heavy load when the throttle is opened wider.
Conditions under which the vacuum system comes into operation are worthy of note:
(a) At tickover speed, the degree of vacuum in the inlet manifold is large, since the throttle butterfly is nearly closed. Vacuum advance does not occur, however, because the butterfly has not exposed the vacuum tapping hole
(b) When cruising on the flat, the engine is on light load and the throttle only partly open. The vacuum is still large and is transmitted to the diaphragm of the advance unit. Ignition advance occurs
(c) When the engine comes under heavy load the driver presses the accelerator pedal and opens the throttle. The vacuum is reduced considerably, allowing the vacuum unit spring to return the contact breaker baseplate to the original position. The degree of advance is then fixed only by the centrifugal advance mechanism.
It is thus possible if the vaccum unit is not providing enough advance when 60mph cruising the ignition advance is not enough and overheating will occur. This is contrary to what I observed. But then the vacuum advance could have been giving too much advance, which as I previously stated I have found to also cause overheating on another engine in the Jupiter. That time the extra advance was caused by worn centrifugal stops.
Anyway worth another check that the VA is adding the 10degrees of advance at the crank. Note VA units have different strengths as I found when I sorted the dozen distributors collected off different Javelin engines, most of which seemed to be different. I will try to find the article I did 15 years ago on them!
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I cameacross the 1953 articule several yrs ago when looking into fuels/octanes etc
A couple pints to note
1/the blends where very different back then, as this was before the abolution of British Pool fuels
2/the methods of measuring and the octane ratings are ery different to todays stds and cannnot be directly related.
3/Lead in fuels along with the y2k computer bug would be the 2 biggest legal scams of the 20th century.
The above post on the VA is a very good description
A couple pints to note
1/the blends where very different back then, as this was before the abolution of British Pool fuels
2/the methods of measuring and the octane ratings are ery different to todays stds and cannnot be directly related.
3/Lead in fuels along with the y2k computer bug would be the 2 biggest legal scams of the 20th century.
The above post on the VA is a very good description
Yes...there is enough advance in the cent not to cause overheating when the VA is not working...assuming the cent is advancing within a 'ball park' correct advance.It is thus possible if the vaccum unit is not providing enough advance when 60mph cruising the ignition advance is not enough and overheating will occur. This is contrary to what I observed.
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Having retarded the ignition (back to TDC static to help the overheating issue) the engine now is difficult to start when hot. Not completely proved that by rewinding the change though!
Searched web and found this.
Not that a Javelin has a long intake manifold.
The car does start if I hold the throttle wide open when pressing the button. Note DELLORTO carbs.
Went to a Mini car show yesterday and was tempted to put the Javelin on the rolling road they had there. However, really need to do it where the gas analyser and ignition are hooked up to the computer driving the dyno.
http://jowett.net/forum/viewtopic.php?t=1184
and in particular
https://jowettnet/forum/download/file.p ... &mode=view
Searched web and found this.
--- The last thing I have to say is that new reformulated gasoline
with lots of ethanol in it causes old cars with carburetors to have
trouble starting when they are hot because it evaporates so quickly.
It is best suited for a fuel injected engine were it is under a
constant pressure, and not a system like the 2CV with a very
long intake manifold where it can be subject to vapor lock with
hot weather or when the engine gets hot.
----
Not that a Javelin has a long intake manifold.
The car does start if I hold the throttle wide open when pressing the button. Note DELLORTO carbs.
Went to a Mini car show yesterday and was tempted to put the Javelin on the rolling road they had there. However, really need to do it where the gas analyser and ignition are hooked up to the computer driving the dyno.
See the other threadTo produce peak power the mechanical requirement is for peak cylinder pressure to occur at the same crank angle under all operating conditions. Through testing that angle turns out to be between 15 and 20° after top dead centre (TDC). Any earlier than that and there's either too much power lost to rising cylinder pressure before TDC, or a risk of knock. Any later than that the pressure front chases the piston down the bore rather than forcing it down.
The mechanical system, having a fixed geometry, works the same regardless of operating conditions. The same cannot be said for the chemical reaction it harnesses. Combustion speed of an air/fuel mixture is dependent upon numerous factors, some set during engine design time, a lot that vary during operation and some that vary even under steady state conditions. Indeed, just like snowflakes, no two combustion cycles are the same. Fortunately, the cycle-to-cycle variations can be safely ignored, as can some other factors, but most cannot. It is important to identify the physical controlling factors when changes are made to a stock engine so that an initial advance curve can be determined. The other factors, let's call them environmental factors, have to be accommodated in operational controls or at least safeguards provided to ensure the engine does not operate outside safe ignition limits.
What this means is that to ensure the peak cylinder pressure occurs when it can do the most work, the flame front has to be initiated at the correct time. Unfortunately, this time varies, and because we are talking about a rotating machine, so does the angle. Because a cylinder charge takes a particular amount of time to burn and the engine speed varies, so then must the point at which combustion is initiated in advance. A typical ignition advance curve is shown in figure 1.
The major factors affecting ignition timing requirement are volumetric efficiency, engine speed and burn rate. Volumetric efficiency, or VE, is an expression of how much of a lung full a cylinder gets for each breath. As it turns out, a full cylinder burns faster than one that is only partially full so any improvements to VE also affect timing. Improvements to cylinder head ports, inlet manifold or camshaft improve VE at certain rev ranges so the ignition timing must also be changed to suit.
http://jowett.net/forum/viewtopic.php?t=1184
and in particular
https://jowettnet/forum/download/file.p ... &mode=view
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The Javelin did make it to Goodwood as you have read elsewhere on this forum. But it is still overheating on motorways or consistent driving over 50mph.
Unfortunately, a slight leak on the o ring on the bypass meant I could not prove that the car was not using water. But I suspect (or hope) not. Another test run should prove that.
Anyway the car ran on proper 4 star lead replacement petrol supplied by Lord March (that smells so different to normal pump fuel) the whole weekend and on the way back. So I do not think it is a petrol issue.
If no water is being used then I am going to give it another series of head gasket tests, before finally throwing in the towel and rebuilding another engine.
Unfortunately, a slight leak on the o ring on the bypass meant I could not prove that the car was not using water. But I suspect (or hope) not. Another test run should prove that.
Anyway the car ran on proper 4 star lead replacement petrol supplied by Lord March (that smells so different to normal pump fuel) the whole weekend and on the way back. So I do not think it is a petrol issue.
If no water is being used then I am going to give it another series of head gasket tests, before finally throwing in the towel and rebuilding another engine.
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Re: Lobsided Jowett not balanced at all.
As was said in the Javelin Sump thread, this saga still continues.
Having changed the main jets for bigger ones the car was taken for a test drive; but on the way back suffered a major loss of power. Having been otherwise engaged on the SC Jupiter the fault finding had to wait. Anyway after checking petrol pump and changing it, checking ignition coil and changing it, checking distributor and changing it, I eventualy went back to rechecking the carbs, only to find the main jet had come out. But the good thing is the test drive with the 'old' distributor which has optical electronic ignition seems to have reduced the temp.
This was on a test run after I had picked up Neil Hood from the station in the Jav Taxi who is over from Australia and was collection tickets from me for the Festival of Speed.
I will at some stage check the curve on the brand new distibutor that had been fitted... I will also fit some temp sensors on the heads and oil cooler when I get the chance.
But for now it is all hands on deck to get it looking pretty for the Vintage at Goodwood show in August where it is is one of 10 cars of the decade on display.
Today I took the rear wings off and attacked some rust that was bubbling through from the rebuild in the mid 1970s. I cut out the rust and welded up the holes. Awaiting Chris to see how we go about the paint touch up.
Having changed the main jets for bigger ones the car was taken for a test drive; but on the way back suffered a major loss of power. Having been otherwise engaged on the SC Jupiter the fault finding had to wait. Anyway after checking petrol pump and changing it, checking ignition coil and changing it, checking distributor and changing it, I eventualy went back to rechecking the carbs, only to find the main jet had come out. But the good thing is the test drive with the 'old' distributor which has optical electronic ignition seems to have reduced the temp.
This was on a test run after I had picked up Neil Hood from the station in the Jav Taxi who is over from Australia and was collection tickets from me for the Festival of Speed.
I will at some stage check the curve on the brand new distibutor that had been fitted... I will also fit some temp sensors on the heads and oil cooler when I get the chance.
But for now it is all hands on deck to get it looking pretty for the Vintage at Goodwood show in August where it is is one of 10 cars of the decade on display.
Today I took the rear wings off and attacked some rust that was bubbling through from the rebuild in the mid 1970s. I cut out the rust and welded up the holes. Awaiting Chris to see how we go about the paint touch up.