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Thread: Vapour Lock

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    Yoda
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    Vapour Lock

    The following query appeared on another site. We would very much appreciate comment, recommendations.

    Within the last couple of years my Roadster's been experiencing vapor lock. I've had the car since the early 70's and up until now, it's never had this problem. It happens after the motor and compartment reach full operating temperature and I shut down for several minutes. It typically takes about 20 minutes or so until the engine and carbs cool a bit to restart. Now, when I shut down, I open the hood just so it doesn't get even hotter from soak-back, (the rise in engine temperature after the motor stops running, which naturally stops circulating the cooling water through the block). I'm thinking it's the new gas with methanol. Is anyone else having this problem? If so, any remedies out there?

    -kdls

    Hello Dom! This has been an unbelievably hot summer - going for a record July here in SE Pennsylvania with over a month of temps close to 35C. I think this will be the norm in future years.

    SO, I have seen lots of TR owners, both 4 and 6 cyl. engines tend to install heat shields. This was a hot topic (no pun intended) of discussion at this year's TRA. All you have to do is look at the proximity of the exhaust manifold to the float bowls of your SU carbs. This isn't something you might be concerned about in 1950's Great Britain, considering their very mild summers! Also, I wonder if modern fuel formulations are more prone to vapor lock, that-is, comparing 1950-60's leaded gasoline to current unleaded, 10 percent ethanol mix, which one has the lower boiling point. Does anyone know?

    Frank

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    Jedi Warrior justin_mercier's Avatar
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    Re: Vapour Lock

    Ethanol has a low boiling point, and fuels with ethanol such at E10 gas at low pressure can boil as low as 190 degrees to cause vapor lock. It's not a problem in fuel injected vehicles because the higher pressure of the fuel gives a higher effective boiling point, but in our older cars, it can be more of a problem, and the gas can boil out of the float bowl when the engine bay heats up after shutting down.

    (the boiling point of pure ethanol is around 175, this is why distilling alcohol works, since it's lower than that of the boiling point of water)
    Justin 'Tharkis' Mercier
    1976 TR6 Hunter Roadster - CF56244U http://www.hathawayhunter.com
    1977 TR7 - ACW15899UA
    Former owner of 1977 TR7 - ACW16812UA
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    Yoda poolboy's Avatar
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    Re: Vapour Lock

    Here in the DEEP South I've had my share of fuel percolation problems.
    Most vulnerable is an attempt to restart within the interval of time between 5 and 20 minutes after a thoroughly hot engine is shut down.
    Less than 5 minutes there doesn't seem to be enough time for the manifold heat to get the gas in the float chamber boiling. Longer than 20 minutes seem to be adequate time for the manifold to cool down enough to lessen it's effect.

    Now I'm talking Summertime, temperatures in the 90's and an engine that has been shut down following a 20 mile highway run..That's been my test conditions.
    My attempts to find a cure involved 3 phases:
    1) ARE heat shield installation
    2) Same heat shield with rerouted fuel lines
    3) Same heat shield but with 2 layers of insulation on the top and bottom of the heat shield floor plus returning to the stock routing of the fuel lines.
    The last attempt resulted in a complete cure and has been that way for the past 5 Summers and 2 different TR6's
    DRIVE 'EM IF YOU GOT 'EM

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    Yoda Gliderman8's Avatar
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    Re: Vapour Lock

    Have you given any thought that the problem may be a bad ignition coil?
    Coils can overheat; excessive temperature may affect conductivity of the ignition coil, thus allowing it to carry less current until it cools down.
    A coil swap is easy enough to do, and will tell you pretty quickly if the one you replaced is defective.
    Elliot
    Central PA
    1973 TR6 Damson Plum / Biscuit interior, HVDA 5-speed, Good Parts Hubs
    1976 TR6 White/Biscuit interior SOLD
    Nostalgia isn't what it used to be.

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    Yoda poolboy's Avatar
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    Re: Vapour Lock

    That wasn't my problem, Elliot. Don't know about the others.
    DRIVE 'EM IF YOU GOT 'EM

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    Yoda Gliderman8's Avatar
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    Re: Vapour Lock

    Quote Originally Posted by poolboy
    That wasn't my problem, Elliot. Don't know about the others.
    My post was in response to Franks original posting.... I did not see your post until after I hit the "submit" button.
    Elliot
    Central PA
    1973 TR6 Damson Plum / Biscuit interior, HVDA 5-speed, Good Parts Hubs
    1976 TR6 White/Biscuit interior SOLD
    Nostalgia isn't what it used to be.

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    Yoda poolboy's Avatar
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    Re: Vapour Lock

    I thought so, Elliot, since they were so close, but I did want to take the opportunity to get that out of the way, at least in my situation.
    DRIVE 'EM IF YOU GOT 'EM

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    Yoda
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    Re: Vapour Lock

    I really appreciate tour comments. Well it seems like the heat shield would be a potential solution for a TR250/6 engine/fuel line routing and Strombergs. But, Dom and I are focusing on the TR3A.TR4 with SU's. I hope that Randall and George H will chime in since they constantly see in high temp conditions in CA and AZ.

    El, no Dom did consider the coil but that has been ruled out.

    Later, Frank

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    Yoda dklawson's Avatar
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    Re: Vapour Lock

    My suggestion is to bypass originality. Consider a rear mounted electric fuel pump below the gas tank.

    All my British cars have electric fuel pumps (either as stock or as a replacement for mechanical) and none of them suffer vapor lock. Like Poolboy I live in a very hot climate where vapor lock is a possibility.
    Doug L.
    '64 Morris Mini Cooper-S 1275
    '67 Triumph GT6 Mk1

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    Yoda poolboy's Avatar
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    Re: Vapour Lock

    I imagine a lot of us have the same contributing factors to contend with, Frank,. high ambient temperatures, proximity of float chambers to hot manifolds and the lower boiling points of alcohol blended fuels.
    On occasion seems a lot of those factors may converge.
    DRIVE 'EM IF YOU GOT 'EM

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    Darth Vader Don Elliott's Avatar
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    Re: Vapour Lock

    During VTR at Valley Forge in 2007, I had all kinds of "vapour lock" problems and I traced it to the fact that USA had recently 10% ethanol added, whereas here in Canada, we didn't have it yet. So I changed the rubber hose that feeds the float bowls and I've had no problems since with any type of gas in over 14,000 miles. The rubber hose on mine is the braided stainless covered one with the banjo fittings. I had a hydraulics repair shop make it for me with modern rubber and it's been fine ever since. They told me they would have made it out of teflon but didn't have that size in stock.

    BTW, it was Randall you suggested that my 50 year old rubber hoses were probably expanding (swelling) inwards because of the ethanol and this caused the blocking off of the fuel flow.
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    Re: Vapour Lock

    Quote Originally Posted by Don Elliott
    During VTR at Valley Forge in 2007, I had all kinds of "vapour lock" problems and I traced it to the fact that USA had recently 10% ethanol added, whereas here in Canada, we didn't have it yet. So I changed the rubber hose that feeds the float bowls and I've had no problems since with any type of gas in over 14,000 miles. The rubber hose on mine is the braided stainless covered one with the banjo fittings. I had a hydraulics repair shop make it for me with modern rubber and it's been fine ever since. They told me they would have made it out of teflon but didn't have that size in stock.

    BTW, it was Randall you suggested that my 50 year old rubber hoses were probably expanding (swelling) inwards because of the ethanol and this caused the blocking off of the fuel flow.
    Don: yes now I remember You and I spent time together at that event. Thanks for reminding me.

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    Great Pumpkin TR3driver's Avatar
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    Re: Vapour Lock

    Quote Originally Posted by angelfj
    Also, I wonder if modern fuel formulations are more prone to vapor lock, that-is, comparing 1950-60's leaded gasoline to current unleaded, 10 percent ethanol mix, which one has the lower boiling point. Does anyone know?
    There seems to be no simple answer to that question. Basically the refiners used to be able to control it within a fairly wide range, to whatever they thought would work best for their customers, local climate, time of year, etc. But now the EPA dictates a fairly small range (still adjusted for time of year and climate, IIRC). And since a lower boiling point helps reduce pollution (better fuel vaporization during a cold start) and modern cars don't have problems with vapor lock; I am guessing that the refiners tended to keep the vapor pressure lower before the EPA started dictating to them.

    I've definitely had troubles with percolation, though perhaps not quite as severe as the OP. I could almost always get it started by holding the throttle to the floor and cranking much longer than usual (to clear all the vapor out of the intake manifold). Then I'd usually have to hold the throttle slightly open to keep it idling until I could get back on the road.

    Installing Joe's heat shield has all but eliminated the hot soak problem on my TR3. I did have one incident this weekend (took a several hundred mile road trip with the wife), but I think it was electrical rather then fuel, because the engine kept cutting in and out like turning the key on and off. I'll have to spend some quality time looking for a bad connection (or maybe going back to the previous 1.5 ohm coil plus external ballast).

    Two other things that may have had some small effect: I finally got a decent controller installed for the electric fan, which turns the fan on whenever the water pump intake gets above the set point (probably around 185F but I haven't tried to measure it yet). And I leaned the mixture about 1/2 flat from where I normally set it.
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Great Pumpkin TR3driver's Avatar
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    Re: Vapour Lock

    Quote Originally Posted by dklawson
    My suggestion is to bypass originality. Consider a rear mounted electric fuel pump below the gas tank.

    All my British cars have electric fuel pumps (either as stock or as a replacement for mechanical) and none of them suffer vapor lock.
    This perhaps merits a comment. "Vapor lock" is when the fuel vaporizes inside the suction line to the pump, causing the pump to not be able to deliver liquid fuel to the carbs. While the problem is real, I have never experienced vapor lock on any of my Triumphs. Using an electric fuel pump mounted near the tank is an excellent way to prevent vapor lock (since now the fuel in the lines is under pressure, making it much less likely to vaporize), but of course introduces other potential problems of it's own (including having fuel pressure when the engine is not running).

    My Stags came with electric pumps mounted in the rear, and I went for several months having to occasionally stop and thump the pump to get it working again. Brought back fond memories of riding around with my buddy in his MGA and the battery cover off, just so we could whack the pump without getting out of the car

    But the problem Frank posted is almost certainly not vapor lock. Even if the fuel in the lines did boil after parking, the engine would still start on the fuel in the bowls and run for a few seconds (until it used up that fuel). Very likely the OP's problem is "percolation", fuel boiling inside the carburetor and taking the mixture way rich (aka "flooded"). An electric fuel pump will not help with that (and may even aggravate it). However, a heat shield will definitely help, and many British cars came with one as stock.

    Here's a shot of the heat shield going in on TS13571L. Easy project, would have taken less than an hour if I hadn't found other things to attend to at the same time. Once the carbs and filter are installed, the heat shield is pretty well hidden from view. If it was painted to match the inner fender, it would look right at home. (On my car, anything shiny under the hood looks out of place )

    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Yoda dklawson's Avatar
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    Re: Vapour Lock

    Your point is well taken and I can see that fuel boiling in the bowl(s) could/would find its way out of the jet and into the manifold.

    The heat shield will certainly help with radiant heat and many of the cars I have had used carb heat shields. Our Spitfire came without the heat shield. To protect its single carb I bought a sheet of the fiber blanket material with aluminum backing. I formed that blanket around the header and up behind/under the intake manifold to provide a degree of protection for the float bowl. It cost less than header wrap, seems to have worked well in place of a proper heat shield, and fortunately it has not become nasty looking.

    The electrical SU pumps can go a long time before needing points cleaning and adjustment but I too have memories of using a piece of 2x4 to knock the fuel pump on a friend's MGB to get it going. However, when installing an electric pump on a car that originally had a mechanical pump I doubt most people would install an electric SU. Facets are much less expensive and can be fairly reliable. There are also a couple of Carter pumps that are popular. Recently I have seen a number of people using Airtex pumps. All less expensive than the electric SU.
    Doug L.
    '64 Morris Mini Cooper-S 1275
    '67 Triumph GT6 Mk1

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    Luke Skywalker
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    Re: Vapour Lock

    Frank I wish I could help with this problem but I've still not started the TR3 engine. My car when finished is going to by like yours as being original. I am going to install a ARE heatshield and not worry about any judging. You can't be judged if the car is not there. My TR6 has this problem all the time, but I have not installed any type of shield. Our gas runs 15% ethanol and comes out of the pump around 100 degrees. It's best to fill up in the mourning so you get what you pay for.
    Keith D
    1974 TR6 been the owner of this car for 37 years.
    1956 TR3 car is being restored.

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    Yoda
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    Re: Vapour Lock

    Not the same car, but I ran into this with the Mercedes on the roadtrip. Every time I stopped I opened the hood and I bumped the idle up some.

    +1 or +5 or whatever the count is on adding a heatshield.

  18. #18
    Yoda
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    Re: Vapour Lock

    Here's an interesting article from my good friend Alec Pringle ,TR Register - UK
    Attached Files Attached Files

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