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MG TD TF 1500 - Understanding the vapour lock?

I'd like to try and understand the problem and possible solution to this continuing problem.
Before I'm politely redirected to the archives can I say that I have read them but I'm trying to work something out, so please bear with me for a bit?
I think it's agreed that the vapour lock occurs when the fuel in the float chambers evaporates usually because of the sighting of the float chambers and carbs above the exhaust manifold?
But since the resulting vapour is lighter than the fuel which will eventually replace it, then why doesn't the fuel, pumped under pressure from the fuel pump, displace the vapour either into the inlet manifold or out through the overflow pipes on the top of the float chambers?
If the problem is then that the new fuel simply evaporates as soon as it enters the float chambers then surely the process of 'new fuel replacing vapour' would continue until the float chamber is cooled down enough helped by relatively 'cold' fuel being pumped through it? And if there is a vapour ‘lock’, where does this ‘lock’ occur? The rough running can be reduced considerably by pulling out the choke.
The reason that I ask these questions is that about 18 months ago I fitted a new SU pump and for about a year until the points went, I had no problems with starting when hot, which had previously been a problem.
After fitting new points in the pump the problem has returned and I’m beginning to wonder whether fuel pump pressure is the problem/solution because there is no increase in pump activity when this 'vapour lock' situation occurs and to my mind there should be.

Any views would be most helpful as would a simple explanation as to how to set-up the fuel pump after fitting new points.

Mike
Mike Christie

Mike - First, let me quote a paragraph from an article I wrote (but has not yet been published) regarding vapor lock:
Fletcher Millmore (a frequent contributor to the Bulletin Boards and Forums) also tells us that "True vapor lock is a result of the fuel on the inlet side vaporizing as the pump drops the pressure on the suction line (inlet side of the pump). It is easily avoided by putting the pump as low and as close to the fuel source as possible”, which is the reason that MG went to a pump mounted in the back of the car by the fuel tank instead of in the engine compartment as on the T series and earlier cars. Additionally “for all pumps, it is desirable – to – essential to have the outlet above the inlet to avoid trapping vapor in the pump chamber”.

"I think it's agreed that the vapour lock occurs when the fuel in the float chambers evaporates usually because of the sighting of the float chambers and carbs above the exhaust manifold"

Not so, what you are experiencing is a different kind of vapor lock that occurs in the carburetors. More specifically, it occurs as the result of fuel boiling and vaporizing in the channel between the float chamber and the jet in the carburetor. This results in a pocket of vaporized fuel in the channel. While this pocket of vaporized fuel is a higher pressure than the surrounding fuel, the pressure is not sufficiently high to push past the fuel in the jet (with the needle at its lowest position) or to push past the fuel in the float bowl, but the pressure is sufficiently high to keep the float pushing hard enough against the needle valve thus keeping the pump from pushing any fuel past the valve.

As you can see from the above, the result is that no fresh fuel can be pumped into the float chamber to cool the existing hot fuel in the float bowl. Even if the pump could pump additional fuel into the float bowl, there would not be sufficient "cool" fuel to offset the heat concentrated in the carburetors. One thing that can relieve this situation is to push the tickler pin in the float bowl lid a couple of times until there is a squirt of fuel, either through the over flow line or past the tickler pin (a reason to keep the tickler pin in place?).

"I’m beginning to wonder whether fuel pump pressure is the problem/solution because there is no increase in pump activity when this 'vapour lock' situation occurs and to my mind there should be".

There is no increase in pump activity because the needle valve is being pressed hard against the seat by the float being pressed up by the high pressure pocket of boiled fuel. Were this a classical vapor lock ad described above by /Fletcher Millmore, with the fuel being vaporized on the inlet side of the pump, the pump would be chattering away as though the fuel tank were empty.

The reoccurrence of the problem after your having rebuilt your pump could be just coincidence of higher ambient temperatures, different formulation of fuel that changes the vapor pressure, or perhaps not getting the pump adjust properly after replacing the points (or crappy, after market points - the ones from Burlen Fuel Systems, though higher priced, work much better than the after market ones). The addition a heat shield between the manifold and the carburetors minimizes the problem, but doesn't completely cure it. A proper setting of the timing for the engine will make it run cooler, resulting in less heat build up in the engine compartment. Finally, make sure the slats in the grill are opened up sufficiently to allow the air to flow through the radiator and engine compartment. The only other thing that will help is to get some 50 year old fuel that doesn't vaporize so easily (this would have its own set of problems if such existed). Cheers - Dave
David DuBois

Maybe this will clear up some of your confusion. Think steam. Boiling fuel releases vapor, like boiling water does. The pressure in fuel lines could end up being quite powerful. The float bowls are vented, but boiling fuel will push against itself in the wrong direction, messing up the fuel flow. Or the fuel may have vapor bubbles in it which I would suggest makes the mixture lean, explaining why your car runs better with the choke out somewhat.

Considering steam powered locomotives, cooking with pressure cookers, the temps under the hood in some locations, and the boiling point of gasoline, maybe all of this will connect to make vapor lock easier to understand.

Modern cars don't have as many problems with all this stuff because of high pressure fuel injection.
Tom

Thank you David and Tom, your explanations were clear and very helpful.
But, given that I can't (won't) move the pump to the rear of the car is there any modification that allows the build-up of vapour pressure to be released?
My carbs have never had the tickler pin you speak of David and am I right in thinking that this pin simply presses on the float when depressed?
If depressing the tickler allows fuel into the bowl by physically overcoming the pressure, (or allowing the pressure in the chamber to vent) what would be the effect of drilling a small hole in the float chamber top to release the pressure in the bowl? (The vent pipe outlets are below the bottom of the float chambers on my car.)
Or since the pressure lock in the channel between the bowl and the jet prevents the fuel from flowing, wouldn't lowering the jet by pulling the choke thus open the gap between the needle and the jet and allow the pressure to escape? And if that is so then maybe the solution is to pull the choke and leave it out when parking and then to turn the engine over without the ignition to 'flush' the vapour, before starting?

Tom, if the pressure pushes against itself and the bowls are vented then why doesn't the pressure vent? If there was pressure in the fuel lines wouldn't this pressure have the effect of opening the needle valve into the float chamber which then should vent, especially if the fuel in the float chambers had reduced because of heating? Or is the problem that there is no top vent in the float chambers? (See above).
There seems to be at least a couple of places this pressure should vent, so why doesn't it. I can see the problem in a sealed container, but the system isn't sealed. The pressure cooker analogy is good except that in my pressure cooker there is a valve, calibrated by weight vs pressure, that keeps the pressure in the cooker constant, if I lift the valve then the pressure in the cooker will never build up. If the car runs better for the minute or so when the choke is lowered then isn't this because the pressure is vented? And once venting commences then the vapour will be replaced by new fuel, since in this case the vapour and the fuel can both be considered as liquids and a flow will occur?

To run through the bits I should check:- the timing is OK; the slats on the rad are OK; (I have an electric fan in place of the original and providing I keep this on in very hot conditions such as returning from the French European event 18 months ago in a traffic jam at 30 degrees on the Paris peripherique, all is well.
The fuel is the same, or as far as I can tell; the points are Moss/SU replacements; and I have both a heat shield and spacers between the carbs and the manifold; no luck with old fuel. It's just that recently the problem has re-occurred and I'm wondering why, especially since the only change is new points.

Thanks again.

Mike.
Mike Christie

It seems to me that there are a substantial number of us who don't experience this vapor lock problem. I wonder why? Or, why not? Right after getting my car on the road I did experience some symptoms that were very similar. I was taking very short, not far from home runs as shakedown cruises. This was in the summer with ambients in the 80's. If I shut the car off after a run that was far enough to allow the engine to warm up it would restart immediately with no problem. However, if I shut if off long enough to have a snack, or a chat with a friend, it was a different story. It was difficult to start and would run rough most of the way back to the garage.

I'm a retired EE and was working in Polaroid's Engineering Quality Laboratory at the time this was going on so I started analyzing components. What I discovered was that the (new) condensor had a unbelievable coefficient of capacitance vs. temperature. It seemed that was happening was that, after shutting of the engine and air flow, the condensor would warm up due to the heat of the engine compartment. The capacitance changed by enough to severely affect the ignition. Replacing the condensor solved the problem.
Bud Krueger

Bud: What is the brand and source of the (new) condensor that you used?
Ed
Ed Eastman

Mike
If you truly have a vapor, the following will not help but I will share anyway. A while back after the TD warmed up it would start missing and eventually stop. I discovered the ignition points would close or almost close afer warm up. The retaining screw would work loose, thus allowing them to close. I offer this b/c of the connection with your point change - you may want get another set and see what happens.

Tim
tw hager

Mike - Drilling a hole in the float bowl lid is not the answer. the reason that newer float bowl lids don't have the tickler pin is that it provided a hole in the lid that is lower than the entry point into the overflow, resulting in any overflow coming out at that point and dribbling on the hot exhaust manifold - my parenthetical comment "(a reason to keep the tickler pin in place?)" was intended to be tongue in cheek. Because the vapor bubble is in the passage between the float bowl and the jet, the pressure as near as I can tell, is just high enough to press the float against the needle and keep fuel from entering the float bowl, it is not sufficient to push past the float and the fuel around it in the bowl. the reason I say this is that one time when I had a particularly bad episode with this problem, I was pushing the tickler pin, to no avail, when suddenly there was a spurt of fuel from around the pin and the problem went away. Puling the choke out is certainly one method of clearing the problem as you noted in your original post - anything that will move that bubble of vapor out of the passage will clear the problem. Another help would be a spray bottle of water that could be used to cool the arm (and passage) between the float bowl and carburetor. So too, would be using a procedure that was common in the hotter areas of the US in the 50s when the cars were new, removing the bonnet side panels for summer driving. Unfortunately the problem has become worse in recent years with the reformulation of fuel to make it burn cleaner. Even the shift between summer and winter formulations makes a difference, particularly if one experiencing some hot days before the change over from winter to summer formulations.

Bud - I think that your experience with the capacitor in the ignition system is not uncommon. The ignition capacitor is cheap, low tolerance device that is rather prone to failure or change in value. I was always advised to look at the old points when replacing them and if there was very little metal transfer, leave the old capacitor in place as it was the correct value for the system and, having survived for some good amount of time, it would probably not fail. My experience is that if an ignition capacitor is going to fail, it is shortly after it has been installed (this is certainly not to say that they won't fail over the long haul, just that they are more apt to fail when new). Cheers - Dave
David DuBois

Bud,

People are less apt to do careful tune-ups today, I think because we are so used to our modern cars that the tune-up has become both a neglected skill, and a skill that requires practice. With only one car in the family which really benefits from yearly ignition service, it can be hard to keep one's hand in as it were. A careful tune-up, as Dave D points out will go a long way to preventing overheating of the engine, and hence vapor lock. I think that people are tending to run these cars more for show and don't realize that (again as Dave D points out) the radiator slats are meant to be very open.

Our little TDs and TFs are different enough in nature from modern cars that some of the skills in maintaining them have to be carefully nurtured... or things can quickly go haywire. I speak from experience. I'm one of those fellows with a set of ignored points which caused more and more difficulty with starting and low speed running. I was rescued eventually by Dave Zyp as he set them for me using a matchbook cover for a feeler gauge at a GOF in Duluth. It was truly amazing the difference made with such a simple procedure. I had literally lost all of my trouble shooting skills over a period of years of little use of my car. I resolved then and there to become a better caretaker.

This BBS goes a long way to keeping us all aware of our responsibilites and helps us greatly in becoming better caretakers. Just take a look at the owners manual for our cars and see the myriad of tasks one is supposed to do at regular and frequent intervals. It is amazing.

warmly,
dave
Dave Braun

A 'Tune Up' should still be a 'clean up' most of the time. Clean plugs, points and fuel pump points....never, never, never touch the carbs!!!!! There is very little to wear and when they are tuned, they are tuned. (ok, top up with oil)... More people get into more trouble with their little flat end screwdrivers and the carb adjustors!!!
(and the matchbook cover worked in the 60's to set gap, and if you just pull it though, it cleans as well)
gblawson (gordon)- TD#27667

Mike; Thanks for prompting one of the most in-depth discussions on vapor lock that I have ever been privileged to read. Understanding the mechanics of a issue is essential to most of we problem solvers-BUT... before this progresses far beyond a crappy running TD, how about trying a fresh pump on the car and see if the issue disappears? Heck, I'll send you one of mine if you like. If the problems disappear than lets see why new pump points started all the hassle-if not then you have one less possibility to cloud the waters. Given the circumstances you describe, a loss of pressure or volume resulting from the change you made certainly sounds likely-and lower pressure always equals lower boiling point. Send me an address if you need to borrow a pump-2 new ones on the shelf in my shop. Hang in there Dan
D.R. Craig

Dan - I can state with absolute certainty that the fuel pump is not the cause of this type of problem. The fact that the pump is not clicking when this problem occures is proof that the needle valve is shut off, not allowing any fuel to be pumped into the float chamber. The reason that I can state this with so much assurance is that we just drove out TD a hundred miles today to our local register's noggin & natter. After letting the TD sit for 20 minutes or so while we checked in and got our stuff into the room, I went out and started the car to move it into a parking spot. While it started right up, it would not run unless I kept the accelerator pressed down and then only just barely coughing over. Using Mike's technique, I pulled the choke all the way out, the engine immediately sprang to life reving right up and then setteling down to a nice idle after releasing the choke and the fuel pump was again chattering away as it should. How do I know that the points on the weren"t stuck, keeping it from running? The pump is an all electronic pump from Burlen Fuel Systems - no points to stick.

Folks, this is pure and simple a case of a vapor bubble in the passage that keeps the float pressed up hard against the needle valve and not allowing fuel to be pumped into the float bowl. Something has to be done to release the bubble (kind of like burping a baby), either by pressing the float down with the tickler pin until the bubble is displaced, pulling the choke on all the way or cooling the fuel passage to condense the fuel back into a liquid state. I don't know of any way of avoiding the problem with today's fuels. All of the suggestions - heat shield, proper tunning, radiator slats opened up will all minimize the problem, but will not cure it completely. We have ot recognize that we are driving cars that were built nearly 60 years ago, with engines that were designed nearly 80 years ago and carburetors that are at least 60 years old. None of these items were made with the fuels of today in mind. In fact the T series cars were designed to be run on pool petrol available right after WWII, a fuel that was barely one step up from kerosene and didn't vaporize anytime the temperature got above 80°F. In the 34 years of owning and driving our TD, I have seen things go from now problem with vapor lock in the ambient summer temperature the Puget Sound region of Washington State (very mild) to a problem on hot summer days to today when it happened in an ambient temperature of the upper 40s after runing the car hard for 100 miles. Cheers - Dave
David DuBois

Maybe if you are experiencing vapour lock you could use a ceramic coating for your exhaust manifold (such as Jet Hot). This will lower your under bonnet temp and it will minimise your chances of vapour lock.
Regards, Richard.
R Payne

The following is not to argue with David DuBois' experience at all, but the fuel pump can cause a "vapor lock" situation. Several years ago I suffered this problem, even in moderate temperature, and went through all the fuel line insulation, carburettor heat shields, tune-up, etc. I had checked everything mentioned and was down to the fuel pump. I did a flow test on the fuel pump using clear tubing into a bucket. The test was intended for timed delivery measurement, but I immediately noticed a stream of very small (I couldn't bring myself to say tiny) bubbles in the fuel stream. Subsequent finding was a pin hole in the diaphragm of the fuel pump. Apparently these bubbles collected into one large bubble at the float passage, although I never had carried the thinking that far.
New pump corrected the "vapor lock".

Dallas
D C Congleton

Dave; Very certain that you have far more experience with SU fuel pumps than I ever will. Your described event seems to validate the presence of an internal vapor lock within the carbs during the hot soak period-much the same as Mike describes. Help me understand what shuts the pump off-isn't it a matter of line pressure vs spring tension on the plunger?
What I am suggesting to Mike is simple backtracking-if you change something and have a poor result, why not first reverse your path and see if the issue is resolved?
Mike; Since you already have an electric fan,how about using it in an "after blow" mode? May vehicles run the electric fan for a period of time after shut down to help alleviate high underhood temps that occur during the hot soak period. Just thought it might be an interesting experiment. The ceramic coating is also a worthwhile investment when you have the time-looks good,too. Dan
D.R. Craig

Thanks again for all the comments and help.
Dan that was a very kind offer and if I lived in the US I'd certainly take you up on it. I have the old pump which is my running spare, but the problem pre-dates it. I do leave the fan on if I park and if I leave it on long enough, about half an hour, the problem goes away because everything is now cool. I often open the bonnet on the exhaust side when I park. Because I've installed a 5 speed box, the fan has to be offset to the right which means that most of the 'blow' is over the exhaust, which helps.
I’ve thought about the ceramic coating, I’ve also thought about putting louvers in the top of the bonnet, but it rather spoils the effect.
I've not considered the condenser, I'll check that.
David, I take your point about the hole in the float chamber top and petrol, so what about a small, I'm talking sowing needle size, down through the top of the float chamber bolt. Because of the size of the hole, the path of least resistance for the fuel would still be through the overflow pipe?
Another solution, going back to the pressure cooker analogy, would be for a tiny weighted valve allowing air pressure but not fluid pressure?
Given that lowering the choke clears the lock, I'm going to try leaving out when I park. I'll let you know if it helps.
Are there any fuel additives to reduce the effect of vaporisation, or is this reverse technology?

Mike.

Mike Christie

Who was it who said,"90% of the problems with carburetters is electrical"?
Geoff Love

Dan - "Apparently these bubbles collected into one large bubble at the float passage..." That won't happen unless your overflow/vent tube at the top of the float bowl is clogged (in which case you would have other problems). the fuel comes in at the very top of the float bowl, above the level of fuel in the bowl, this acts as a vapor separator with the fuel pouring down on the top of any fuel in the float bowl and the air from the bubbles going out through the vent, as does the air on top of the fuel in the bowl as the level raises. In your case, where there was a leak in the diaphragm, the pump was in fact the problem. Wat you experienced was more of a classic vapor lock as described by Millare Filmore in my opening post. The leaky diaphragm will allow air to collect in the pump body and if there is any back pressure on the pump the air inside will just compress and decompress as the diaphragm moves up and down, disrupting the pumping of fuel.

You are correct in your assessment that the pump is shut off when the pressure in the outlet line equals or exceeds the pressure of the volute spring in the pump. What is happening in the situation we are discussing, is that the bubble of vapor forming in the passage between the float bowl and the carburetor is pressing upward on the fuel in the float bowl causing it to rise and push the float harder against needle valve - sufficiently hard that the pressure of the volute spring cannot overcome it.

Richard's suggestion of jet hot coating of the exhaust manifold is a good consideration. Anything that will reduce the heat build up in the engine compartment will help this situation. Since the jet hot coating is both on the inside and outside surfaces of the manifold, it purportedly allows the exhaust gases to pass through the manifold quicker, thus having less time to transfer the heat to the engine compartment. There have been reports on this BBS about this helping with the vapo lock situation.

Mike - "...so what about a small, I'm talking sowing needle size, down through the top of the float chamber bolt. Because of the size of the hole, the path of least resistance for the fuel would still be through the overflow pipe?" Even a small hole is going to allow some fuel to escape, although perhaps not enough to cause a problem. If you really want a tickler pin, the boss, where is was originally installed is still on the float bowls but it has not been drilled out and you could just drill it out, get the pin and spring from Moss Motors and install it. I have never remove the tickler pins and closed up the hole on the carbs in our TD because I haven't had a problem with fuel poring out, onto the hot exhaust manifold (the tickler pin/spring set that Moss supplies also has a small seal with it that seems to close off the hole quite will when the pin is not being pressed down). Other people are bothered by the fact that there is a hole there, below the outlet level of the overflow tube, some have claimed that they personally know of engine compartment fires resulting from fuel escaping from said hole.

Your pressure cooker analogy is flawed because pressure is pressure, whether it is air pressure or fluid pressure - both of them will lift the weight if it becomes greater than the weight.

As for my experience this weekend (we are back home by the way, we had to leave early today as we have a formal dance to go to tonight), I am considering that the carburetors in our TD are quite old (we have had the car for 40 years and the carbs were old when we got it), so I am considering having them overhauled by one of the carburetor gurus here in the US or getting a new set. It will be interesting to see if this has any effect on the situation. As I said yesterday, I tried Mike's solution of pulling the choke out and found that the this relieves the vapor lock almost instantly, so I will rely on this method until I get the carbs worked on. Mike, I would be a bit concerned that pulling the the choke out on shut down would allow the fuel to be pushed into the carburetor while the car was not running. If this happens the fuel will pool in the intake manifold, causing an excessively rich air/fuel mixture and could cause hard starting. Do let us know how that works for you.

I think that by pooling all of our experiences and the results of our experimentation may finally come up with a solution solution eventually. In the mean time, we have a work around that apparently works. I know what is happening and why it is happening, but I don't know what the perfect solution is yet. Hopefully, our collective wisdom and experimentation will come up with a good solution.

"Who was it who said,"90% of the problems with carburetters is electrical"?" Probably the people who make the carburetors :) Cheers - Dave
David DuBois

Thanks Dave; Appreciate the explanation-I see the area in question on the carbs. Needs either a means of keeping the area cooler or perhaps some sort of internal vent tube to safely relieve the vapor pressure in that passage. Maybe a piece of capillary tubing routed from the passage to a point above the fuel level inside the bowl-small enough to not interfere with fuel flow thru the transfer passage or disturb operation of the float in the bowl. Just a thought.
By the way, the air bubbles were observed on Dallas' car-I've never tried the clear line routine. Certainly could be useful for an inexpensive diagnostic tool.
Keep us posted on what you observe from your temporary solution.
Dan
D.R. Craig

How about a windshield washer type spray directed at the problem area on the carbs? Water in summer, that blue stuff isn't flammable, is it?

I don't see why a pressure cooker analogy would be flawed. Steam (OK, fuel vapor) pressure can get quite high, overcoming pump pressure.

I think the problem lies more with the fuel aerating in the float bowls and passages to the jets. But it's just my theory, and it doesn't bother me enough to expend a lot of energy fixing it. Just a quirk for these machines that I've learned to appreciate (live with?).

Next summer, maybe I'll carry a spray bottle along to cool carbs after a frustrating heat soak. Right now, ice and snow are never more than a few steps away, but I never need to cool the carbs in the winter.

I don't think leaving the choke pulled out while the car sits will help.

Another thing that newer cars do to help this is, they have a return line to pump excess (and warmed) fuel back to the tank. A steady stream of fuel through the lines and air through the engine compartment while we're motoring lets our old cars run fine. But the heat soak of sitting after a long run or a parade (!) will give us fits unless we put in a modern system. I'm not gonna do that.

Tom

A friend couldn't get his Jag 120 to start after shutting off hot... we used the ice from our drinks to cool the float bowls and it started right up!
gblawson (gordon)- TD#27667

David,
If pulling the choke breaks the vapour lock in the chamber between the jet and the bowl, and pressing the tickler breaks the vapour lock in the float bowl, why is there still a problem? Or is doing these two things before starting the solution?
Mike.
Mike Christie

Mike - "If pulling the choke breaks the vapour lock in the chamber between the jet and the bowl, and pressing the tickler breaks the vapour lock in the float bowl, why is there still a problem? Or is doing these two things before starting the solution?"

These two procedures, along with Gordon's ice, work fine, but are what I would call a work around rather than a solution. It may well be that these two "work arounds" are the best solution that there is, in which case we live with it. I would just like to keep track of people's efforts to come up with a permanent solution that can then be posted on a convenient web site (or several) for everybody to use. My wife is currently working on producing a web site for my fuel pump work and I would be glad to devote space for this effort as a start.

Tom - "I don't see why a pressure cooker analogy would be flawed." - Perhaps flawed was a wrong choice of words, what I was trying to point out that a weight over a valve, like used on a pressure cooker, will lift for any over pressure situation, be it vapor or fluid. Mike was looking for something that would vent off vapor, but not fuel and the weighted valve (any safety valve essentially works this way, using a spring for the weight) lifts and will allow the escape of either, resulting in the spray of fuel released in the engine compartment, which we don't want.

"I don't think leaving the choke pulled out while the car sits will help." - This will help if it open the space between the hole in the top of the jet and the needle by lift moving the top of the jet to a position of the needle that is small enough that the fuel will move through. I just today received an e-mail from a gentleman monitoring this exchange to report that he is experiencing a similar problem with his TD only instead of a vapor bubble forming and building up enough pressure to shut off fuel delivery from the fuel pump, he noticed that fuel was percolating up into the carburetor throat and running down into the intake manifold when the engine was shut off. This is a different manifestation of the same problem and at the same time shows how pulling the choke out far enough to lower the jet will solve the problem (although it may result in an over rich situation, making for hard starting. In this case, opening the throttle wide should get enough air in to lean out the mixture and get the car started).

"Next summer, maybe I'll carry a spray bottle along to cool carbs after a frustrating heat soak" - This is another work around like Gordon's that should work fine.

Keep the ideas and experiments coming folks and maybe we can come up with a permanent solution. Cheers - Dave

David DuBois

OK, a couple of short tests today not in an ideal situation as the temp was only about 8 degrees here in the UK, but leaving the choke fully out when parked made starting the car after about 10 minutes a dream and there was virtually no 'rough' running.
What I noticed was that after turning on the ignition, but not starting the car and with the choke out, I could hear the pump chattering away so clearly there was a flow of petrol to the float chambers and possibly beyond. I pushed the choke in before staring the engine.

David, going back to some sort of vent at the top of the float chamber, would it be possible to use the tickler hole for some form of small float. What I am envisaging is something like an 'I' bar with a small wooden/cork float fastened/glued to the bottom of the 'I'? This would allow the vapour to escape but would float up and close the hole if the chamber over filled with fuel.
It has also been suggested that as prevention is better than cure, could we insulate the float bowls by manufacturing oversized covers filled with a insulating/heat dissipating material?
Mike.
Mike Christie

Just to make my last post clear and to complete the range of tests - I tried leaving the choke in when I switched off and then restarted the engine after about 10 minutes, and it ran quite rough for about 20 seconds.

Mike.
Mike Christie

Mike - "as the temp was only about 8 degrees here in the UK"

Please tell me that is 8°C - at 8°F your fingers should freeze to the choke knob. 8°C would be around 42°F over here, which is about the temperature here Friday when I experienced the problem with our TD.

Regarding the tickler pin, Mike, would you e-mail me directly as a reminder and I will take some pictures of the tickler pin sets that are available now. They may well do the job as they have a seal with them. I have those in the float bowl lids on our TD and have not had a problem of fuel coming out the holes. I am doing battle with a new laptop computer trying to get it set up (a vastly worse task than working on a TD) right now and may not remember to take the pictures without a reminder.

Interestingly, between the time we got our TD in 1974 until I tore it down for restoration in 1982, I don't remember ever experiencing this sort of a problem here in the cooler climate of the Puget Sound area of Washington State. After finishing the restoration in 1987, I noticed that we would have a problem on the hottest days of summer only. Since then, it has been a more and more common experience, the worst being two day ago, when it started playing up at a relative cool 40 something degrees F. Since I know that the gas companies in the US have a summer and a winter formulation for the fuel they sell us, the winter formulation being one that vaporizes at a lower temperature I have to conclude that the problem results from fuels that are formulated for todays vehicles, which are almost all fuel injected. Cheers - Dave
David DuBois

Hi Dave,
You have mail.
Mike
Mike Christie

Mike - Your e-mail never arrived. Try either ddubois@sinclair.net or SUfulpumps@donobi.net
Cheers - Dave
David DuBois

I have beat this one to death over the years in the archives ...so I won't bore everybody again with the details and my "IMHO's" ....but the "quick re-cap #1:
JET-HOT works!
Re-cap #2: "pre JET-HOT days" (what Dad did in the 50's when they would talk him into using his TF for a parade) : DRY ICE!
The "modern equivalent" of DRY-ICE : Cold "Snap Packs" from the drug store! (I still carry a couple of those in my car and have saved a few "LBC" owners a tow bill when finding them dead on the side of the road after a car show!)
Cheers,
David 55 TF1500 #7427
David Sheward

This thread was discussed between 15/02/2008 and 25/02/2008

MG TD TF 1500 index

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