Welcome to our resource for MG Car Information.
MG TD TF 1500 - Fuel Pump Location
|I am planning to re-locate my fuel pump to the rear of the car. The fuel pump would then be gravity-fed by the fuel tank, would be in a much cooler location and the under-hood fuel routing would be fully pressurized. The fuel system should then be much less susceptible to vapor lock. Has anyone accomplished this modification?|
|Corey Pedersen 1951 TD #7169|
|Seems to be a lot of work to modify the system. Never heard of anyone doing this before. I guess originality doesn't fall into play. Why not just ad a facet pump back by the tank and leave the original where it is?|
Anyway, here's a shot of the pump location on my TF. Once covered up, their a bear to service! I wish mine was under the hood/bonnet like yours! You also don't have to crawl in the dirt in your clean duds to service the pump. I don't like mine where it's at! PJ
|Corey, I had a 77 midget that would vapor lock as soon as the outside temperature reached the 80's. I left the mechanical pump on the engine and added an electric in the rear and never had any more issues, so I agree with Paul.|
|Richard Taylor TD3983|
|Corey, for what purpose? The only place I have ever heard of vapor lock being an issue on these cars is the under hood area, down stream of the pump...which is the pressurized portion of the system. Regards, tom|
|Shouldn't be to hard to do Corey unless you want to keep a stock pump. I'd probably leave the stock one in place also and just cut in a Faucet pump near the the tank. |
Probably some value as starting with the mid TF most future MG's got the pump located near the rear axle. Not a fun location to work on for sure.
If you think you don't like where it's at now Paul, wait until you get the tub on it. I had to do this again in a hotel parking lot in Kansas in 107 degree heat without the assistance of Dan, Gene and the floor jack and stands.
|L E D LaVerne|
|Actually on mine, I'm going to fabricate a hidden removable door in the side curtain box floor to service the pump, as indicated in the photo if needed, and not have to crawl in the dirt! I didn't opt for the original floor to service the final drive as it can be serviced from below, normally done in the shop and driving in rainy weather, I understand it leaks. The floor gets fabric covered. PJ
|My TF has had the pump relocated to the firewall! My plan is to install a facet or similar where the pump was originally mounted.|
|J E Carroll|
|I run a "slightly relocated" facet pump in the rear.|
Can actually be easily removed/replaced by removing just the rear tyre. My fuel filter is located just the other side of it there as well. (on outlet side).
Have a "Lucas" pump I have considered putting in the bonnet as a back up.
I run a "cut off" switch for the pump so was going to just replace the toggle with a "on-off-on" so I could switch on the fly.
|Cory - Granted, a fuel pump at the rear of the car is less apt to have a problem with vapor lock. That said, I have not heard of any TD having a vapor lock on the inlet side of the pump (the place where vapor lock would form due to the fuel being under vacuum at that point). If you are suffering a vapor lock issue, it is most likely in the channel between the float bowl and the carburetor jet. This is usually caused by heat soak when the car is parked on a hot day after being driven sufficiently to get the carburetors (directly above the exhaust manifold) quite hot. A fuel pump in the back of the car is not going to cure this problem. |
If you want to put the SU pump in the back of the car, you will have to get a high pressure pump (2.7 - 3.8 psi) such as the SU AZX 1331 or an aftermarket pump with about the same output pressure. At 1.5 psi output pressure, the low pressure pump that you have mounted on the firewall of the TD would be hard pressed to deliver the required amount of fuel to the carburetors. I would suggest a Facet or other after market pump for this application (much cheaper than the high pressure SU pump). If you insist on a SU pump for the back of the car, use the AZX 1331 or AZX 1332 (depending on the polarity of the car) and see the attached picture for mounting and plumbing the pump.
Dave S. - Lucas pump? The only pumps Lucas makes are fuel injection pumps for modern cars (a bit to high a pressure for the SU carbs). I suspect that you mean a SU pump. If you are going to install a backup pump, I would suggest the Facet pump as the backup, unless you have an all electronic SU pump - a points style SU pump will very likely not work for you when you need it due to the points having filmed over due to non use.
"I run a "cut off" switch for the pump so was going to just replace the toggle with a "on-off-on" so I could switch on the fly."
I did that on our MGB (after having to change out a pump on the shoulder of I5 in Northern California) and it works great - no need to even pull to the side of the road. I have found that my backup pump works great - in 10 years I haven't had a pump failure - just like our whole house backup generator - haven't had a power failure since it was installed. Cheers - Dave
SU was what I meant. (Lucas? oops)
I always carried a spare Faucet type in the boot.
Last year when "Grace" (Drive Away Cancer 53 Austin 100) was here we put my spare on her. John left me an SU. He had been burning though those at an alarming rate but the spare they had shipped him had threaded couplers. John had converted the Austin to take in line fittings with hose clamps as they were easier to swap out on the road.
The Austin used dual pumps but they had been burning up every couple of days. Last I heard he had gone with a second Faucet type and they were both working with no failures. Not sure "why" they were burning out ...but Grace was pretty much in need of a full re-wire from what I saw.
|I haven't had any problems with the car. This just seemed like a logical and easy upgrade. In view of the feedback I think I will leave well enough alone!|
|Corey Pedersen 1951 TD #7169|
I not only relocated it for all the benefits you mentioned but also added a Facet, with separate switches under the dash, and it has saved us a number of times.
They are each mounted on a separate fitting under the tank, for a reason. I installed a cheap sediment bowl with valve that provides a reserve of about three quarts (if I had to, I could stop and unscrew the valve farther) to feed the SU pump. The Facet taps right off the bottom of the tank so I can switch to that reserve in seconds, if it ever dropped that low. I calculated there's about 3 gallons from the time the gas tank idiot light stays on solid, to that last reserve. I installed an obnoxious green LED as an incentive to refill SOON.
They both tee into an adjustable pressure reducing valve, mostly to keep the Facet pressure under control, so there's only about 2 psi to the single carb (supercharged). I should probably crank it up a bit.
There is one minor drawback, and then maybe you'll appreciate the importance of a backup pump! As the pump is in a lower location, the pressure to the floatbowl is now reduced slightly due to the head pressure the pump has to work against. Won't matter right? I think it does in extreme heat with ethanol rich gas...
A few weeks ago we drove to GOF Central, cruising around 70mph average, 500+ miles each way, in temps bordering 100F, with long delays creeping in construction zones! We hit stations displaying ethanol content as high as 10%, but 15% is now permissible. Reminds me of my old fuel injected Saab that vaporlocked on gasahol at 85F! Anyhow, as we're cruising at 70 with the footwell scorching our feet (in spite of 4" dryer vent air conditioner) the engine would stall and the air/fuel ratio meter dropped completely off scale lean- no fuel. I'd reach under that dash and hit the facet and it'd fire right back up. It happened so frequently, both directions, I finally just left the Facet on and gave the SU a well deserved rest. There's nothing wrong with the SU, as we just ran it to the Alden British Car Show, and that was well over 500 miles round trip, much of it in 80-90F temperatures, sometimes in excess of 80mph.
Bear in mind, unless you're really smart and run the line on the left side of the car, the fuel line will still run up the firewall behind the exhaust, where I'm sure temps must exceed 250F, well above the boiling point of gasoline. I ought to insulate the fuel line, but really like the looks of that stainless tubing . I did run flexible stainless tubing over all the exhaust pipes,(sort of reminiscent of Duesenburg exhaust plumbing) but that didn't really seem to beat the heat. I swear, when the boost jumped up around 4psi, I could feel the temp rise in the footwell, and it is pretty well insulated (no carpet yet)! I should carry a noncontact digital temp gauge to measure it.
I've never seen this trick anywhere else, but when we got this TD umteen years ago, the PO installed 1 1/2" SUs with a return line to the tank. The siamesed banjo fitting he used on the front carb was slightly plugged for the return line. I might just have to dig that old banjo fitting up and try that.
The switches under that dash also serve as a poor man's antitheft system, but my wife would curse me out if I shut them off and she stalled out a block away!
|JIM NORTHRUP SR|
|Jim - It looks to me like you have a Harting pump rather than a SU. Those are good pumps, but when they fail, that's it, there are no replacement parts for them.|
Having a return line to the tank makes it easier to regulate the pressure. Cheers - Dave
|Jim, is that a 3.9 banjo rear out of a MGB? If so, how do you like it's ratio? PJ|
Tis an MGB rear, for the ratio and the wire wheel splined adapters. Cruises 60mph @ 3000rpm... 80mph @ 4000rpm. Vast improvement over stock for cruising. We run older Moss Magnacharger and wouldn't recommend it without a blower. Still a touch high gearing, even though the chart indicates 65-70hp max around 5500rpm, the engine is running way far below peak horsepower. At 60mph, the engine needs less than 3psi boost and puts out approx 40hp; at 80mph, 4-5psi cruising, about 50-55hp.
I have to overhaul the original engine which is 1466cc and have a Fanelli roller lifter cam cut for street supercharged which reportedly affords very strong midrange, which is where we cruise. Really looking forward to feeling how it pulls then!
Haven't needed to look at it for so long, forgot which went in... had a number of pumps to choose from so selected the cutest one. Its been very reliable, until the hot cruise to St. Louis brought out the transient fuel starvation. Have debated about upping pressure setting or even removing pressure regulator, but it has run perfect for the last few weeks, even when wife is cruising at 80mph.
I like the idea of the return line for providing a steady stream of cooler fuel, rather than a standpipe of superheated gasoline waiting to vaporize in the line or float bowl. The return would vent vapor back to tank quickly if it were to form.
|JIM NORTHRUP SR|
|Jim, I have a 3.9 banjo out of a wire wheel MGB with perfect hubs. I bought it for the gears, but now I'm thinking 4.1, minimum 4.3 for this 1500 of mine. It has a 4.8 in it now. PJ|
I would hesitate to put a fuel pump in an enclosed area. On a hot day, even the slightest leak could create a fire hazard.
Underneath if it leaks there is less risk.
|Ira Spector (PA)|
|Ira, The fuel pump is in the factory location and is exposed to the elements, the trap door I mentioned is only to service same should the occasion occur, without crawling under the car and adding more fun to a drive as these lucky fellas are doing! PJ|
|Jim, your observations re: the rear mounted pump substantiate my theory. If fuel vaporizes anywhere in the fuel line, including the short stretch in the engine compartment upstream from the stock pump location, a rear-mounted pump should continue to move fuel (both liquid and vapor) through the line. Any fuel vapor in the line should travel to the carburetor and be exhausted through the overflow tubes, thus preventing a vapor lock condition.|
Is it advisable to simply add a pump to the fuel system at the rear of the car and deactivate the front pump? That would retain the same fuel line pressure, and allow the front pump to serve as a reserve.
|Corey Pedersen 1951 TD #7169|
|Corey, you seem pretty intent on doing the mod, but in regard to mg td's the pump location will make no difference in regard to vapor lock. TD's vapor lock issue is not on the supply side, but on the pressure side. moving the pump further aft will not change that on the TD's.|
i only post this in regard to the vapor lock issue, you may have other reasons to relocate your pump. if your main reason to relocate the pump is to prevent vapor lock, you maybe disappointed in the results.
it is your car. i make no judgements, modify it as you see fit. regards, tom
|Tom, how can we be certain of the vapor lock location? Vapor lock may be occurring in the upstream side the stock pump near the exhaust manifold, in which case the use of a rear pump would be beneficial.|
|Corey Pedersen 1951 TD #7169|
|"TD's vapor lock issue is not on the supply side, but on the pressure side. moving the pump further aft will not change that on the TD's."|
Tom, vapor lock does not occur on the pressure side of the pump. Being under pressure raises the vapor pressure, requiring more heat to get it to vaporize. That said, I agree with you that moving the pump to the rear of the car will not cure the vapor lock in the T series cars as the vapor lock is inside the carburetor (channel from the float bowl to the carburetor jet) and this is not affected by the fuel from the pump being under pressure - all of the pressure is relieved once the fuel gets inside the float bowl. Cheers - Dave
|Interesting that the TF pump is located in the rear. Does anyone know what that design change was made?|
|Corey Pedersen 1951 TD #7169|
|dave, perhaps this is a semantics issue..i consider anything downstream of the pump "the pressure side of the pump" and anything upstream of the pump the "suction side". i did not say vapor lock occurs in the "pressurized portion of the fuel system". i believe we are talking about the same thing. perhaps my meaning would have been clearer if i had used the terms upstream and downstream in reference to the pump location to describe where vapor lock occurs in the TD fuel system. regards, tom|
according to the service parts list the change came at TF chassis 1500 on engine 31536.It is pig to work on without a trapdoor but I have never had a vapour problem even driving in southern Spain in the height of summer.
Ray TF 2884
|My take on the vapor lock issue...and I'm certainly no expert. Seems to me the majority (if not all) of the vapor lock problems are related to "heat soak" after running. Almost never during running. With the close proximity of the float bowls to the exhaust manifold, it makes seems that's the main issue. |
Apparently not a big deal on the TD until modern gasoline formulations came along.
Not so on the TF. With a more compact engine bay it has more direct heat radiation from the side panels and bonnet. The spacers on the carb manifold help but moving the pump to the rear took the away the possibility of any vapor lock away from the pump.
Would this help on a TD? Perhaps but I doubt it would solve the issue.
Later MG models such as the B addressed this with larger carb spacers and more specifically an asbestos backed heat shield between the carbs and the exhaust manifold.
I'd reckon that one of the heat shields I've seen on a few TD's would do a far better job of eliminating the vapor lock problems.
Just my take.
|L E D LaVerne|
|My car is currently on my lift, I am in the process of wiring it and my car has a three-piece easily removable rear floor. I don't see any downside, so I'm going to add a rear-mounted pump to my existing fuel system. I plan to install an ON/OFF/ON switch to the pump wiring circuits, which will allow me to select either pump, and which can serve as an anti-theft device.|
|Corey Pedersen 1951 TD #7169|
|the only downside is the time spent if your goal is to eliminate vapor lock. since this is a hobby our time working on these cars is free anyway. modify your car as you see fit. regards, tom|
|Tom - You and I probably are talking about the same thing. Classic vapor lock (fuel vaporizing in the fuel line on the inlet side of the pump, due to the fuel being under a partial vacuum on that side of the pump) is not the issue here. As LaVerne has stated the problem is heat soak in the carburetors (LaVerne, I have had a vapor lock while the car was underway, but it was only one time and that was under extreme conditions). Because the problem is heat soak, a heat shield is of minimal help because there is no air movement to carry the heat from a hot exhaust manifold away. I put a heat shield on our TD when I restored it some 20 years ago.|
LaVerne - You are correct when you stated "Apparently not a big deal on the TD until modern gasoline formulations came along." In our area (Puget Sound region of Washington State), we would often have the problem on the first hot day in the early spring because the fuel at the stations was still the winter formulation. The problem would go away later in spring, when the fuel companies started dispensing the summer grade fuel. Now days there is not winter/summer formulations because now that all gasoline fueled vehicles are fuel injected, with the fuel being delivered to the engine under a relative high pressure - in fact, I would not be surprised if the fuel of today is formulated to vaporize even more quickly that the fuels of days gone by.
The vapor lock that is occurring in our cars is the result of the fuel vaporizing in the passage between the float bowls and the carburetor jets. This vaporization results in a bubble that keeps a constant pressure on the fuel in the float bowl, such that the fuel is being pushed up, shutting off the needle valve. This can sometimes be relieved by pressing down on the tickler button in cars that still have the button operational, and can always be relieved by pulling the choke out.
Believe it or not, the MGA suffer from the same problem, in fact there was an extremely long and comprehensive discussion on the MGA board a couple of years ago for anyone who wants to dig it out of the archives and read it. Because of the engine compartment configuration of the MGA, they also had a problem with the vapor lock (in the same area as on our cars) when the car was being driven. Some of the MGA people have cured the problem by utilizing a 3" bilge blower to force more air through the engine compartment. Following their lead, I have gotten a 3" bilge blower for our TD and am trying to figure out exactly where to mount it and how to duct the air to blow on the carburetors when the car is parked. I have come up with a control circuit that will monitor the temperature on the arm between the float bowl and the carburetor jet on the rear carburetor and turn the blower on just few degrees below the temperature where the problem occurs and then turn the blower off when the temperature drops. At present, I have attached a thermocouple probe on the arm and will monitor the temperatures at that point to determine where to set the on and off points of the circuit controlling blower (see the attached picture). The problem is that we have passed the hottest time of our summer, so I am now having trouble getting the car to vapor lock when parked (we should all have this problem).
It will probably well into summer of 2014 before I have this all worked out and installed. I will keep you all updated with my progress and information on how to duplicate my set up. Cheers - Dave
|Dave DuBois,I did that on our MGB (after having to change out a pump on the shoulder of I5 in Northern California) and it works great - no need to even pull to the side of the road. I have found that my backup pump works great - in 10 years I haven't had a pump failure - just like our whole house backup generator - haven't had a power failure since it was installed. Cheers - Dave|
Boy does that sound familiar! Installed a whole house automatic gen set also and no power failure since. Pretty expensive insurance policy though. Grin. PJ
|"Boy does that sound familiar! Installed a whole house automatic gen set also and no power failure since. Pretty expensive insurance policy though."|
Yes it is expensive insurance, but considering the last time we lost power, it was out for 3 days and on the third day, the temperature inside the house was 41°F even with the fireplace going full out - 41°F is the temperature inside a refrigerator - and we decided that was enough, we were not going to go through that again, regardless of the cost. Cheers - Dave
|Hi Dave, you said:|
"The vapor lock that is occurring in our cars is the result of the fuel vaporizing in the passage between the float bowls and the carburetor jets. This vaporization results in a bubble that keeps a constant pressure on the fuel in the float bowl, such that the fuel is being pushed up, shutting off the needle valve. This can sometimes be relieved by pressing down on the tickler button in cars that still have the button operational, and can always be relieved by pulling the choke out."
I've never quite understood how this could be a problem -- seems to me the pressure in the jet tube would be relieved through the jet and the bowl vent. The jet is more or less open to the atmosphere (albeit with the needle occluding most but not all of it) and the bowl is open to the atmosphere through the vent -- no place for pressure to be contained. What am I missing?
And of course as you mentioned, any vaporization that might occur between the pump and needle valve in the carb would just be pushed along by the pump and vented at the bowl....
That's not to say that *something* isn't going on -- I've had hard starting some times after heat soak but I always assumed it was flooding from fueling boiling out the jet and running down the intake tract.
|In my experience, the vapor lock issue raises it's ugly head most often right after shutting down, and then expecting to start up within a few minutes. The fuel line soaks up heat and the gasoline has an oppurtunity to vaporize, especially on the suction side of the pump. That's why the fuel pump will chatter like crazy, trying to pump vapor. I've dumped|
cold water on the line, or wrapped wet rags around it; also have whipped the adjustable wrench out of my pocket and loosened the line to the carb to let it bleed vapor & gasoline into a rag or paper towel to reprime the pump.
The positive pressure in the fuel line downstream should raise the boiling point enough to feed the carbs flawlessly.
I will point out again, the lower position will reduce the pressure at the carbs, but just a touch.
It wasn't until we were cruising for hours at 70mph in 95F+ degree air temp, running a supercharger, that we experienced loss of fuel feed. A quick switch to the Facet instantly revived the engine every time. I let it occur over and over, to see if the Facet made the difference... every time. As I mentioned, I have a pressure reducing valve inline, which might have contributed to the problem, but I believe the old pump isn't putting out near the pressure the Facet does.
We ran many hundreds of miles in the last 2 weekends, with temps barely hitting 90F, and it never recurred.
One major factor is the alcohol % with different fillups! Government has now raised the limit to 15%, which is distressing a lot of manufacturers.
Two fuel pumps; don't leave home without them!
|JIM NORTHRUP SR|
|never heard the rapid clatter of the fuel pump after the classic "hard run quick stop scenario", which are the only times i have ever had vapor lock. the times i have experienced vapor lock in that situation a pull on the choke always cured the issue.|
i cannot speak to jim's experience. my 11 years experience does include a 3.5 hour drive on a 98 degree day in rush hour traffic on the expressway on the southside of chicago..one hour of which was stop and go traffic..mostly stopped, with the engine running. not a hint of vapor lock during that sit on a smoking hot concrete expressway with only the original 4 blade fan providing any airflow through the engine bay. regards, tom
|Rob - "I've never quite understood how this could be a problem -- seems to me the pressure in the jet tube would be relieved through the jet and the bowl vent. The jet is more or less open to the atmosphere (albeit with the needle occluding most but not all of it) and the bowl is open to the atmosphere through the vent -- no place for pressure to be contained. What am I missing?"|
It has been a bit of a mystery to me also. I happened to be fussing around under the hood after driving some distance in hot weather. Since we were home and the car was in the garage, I wasn't thinking about the vapor lock issue but after a couple of minutes I happened to see a spurt of fuel through the tickler valve on one of the carburetors and that was when it hit me. About the only scenario I can reasonable come up with is that a bubble was forming in the channel between the float bowl and the jet. I suspect (but don't know for sure) that the needle being all the way down in the jet allows a bit of pressure to build up, just enough to keep the needle valve shut. I do know that if the car won't start, pulling the mixture knob out will allow the car to start. Keeping it out long enough for fuel to cool things down a bit will keep the car running until everything settles down. My suspicion is that when the car is stopped after a good hard run in ambient temperatures of 80°F and above gets everything in the engine compartment hot enough that when the car is shut down heat soak elevates the temperature in the above mentioned channel sufficient that a bubble forms.
I am hoping to get some data this week. We are going to some friends on Wed, which is supposed to be a 80°F+ day and the route is mostly uphill on a 4 lane highway so I can push the car hard and then get some temperature readings on the channel between the float bowl and the jet, during the time we are on the road and after shut down - hopefully after a good heat soak. I will keep you all posted.
Jim - what you are describing is the classical vapor lock, where the fuel vaporizes on the inlet (suction) side of the pump. This is the reason that a high pressure, SU fuel pump was put in the rear of the cars, starting with the TF.
This was just received from our friend we are to visit this week:
A guy needs a camel to go out into the desert and get an oil lease signed. He goes to Habib's camel rental and gets set up. He gets on the camel and goes around the corner. The camel stops, lays down and lays on the ground, quivering. The guy runs back to Habib and says, "Hey, there’s something wrong with your camel! I think he’s dying!" So the man and Habib arrive at the camel, who is still on the ground, quivering.
Habib walks around him a couple of times, and then gives it a boot in the gut. The camel blows a fart, stands up and is ready to go.
Habib turns to the man and says, "Ah, vapor lock."
With my apologies - Dave
|Wouldn't you think a heat shield, as on a MGB, would help the heat soak problem somewhat? Be a fairly easy job to fabricate one. PJ|
Installing a 3" Rule or similar Bildge blower is on my list of things to do this summer,,, but I was going to just put an on-off switch on it,,, If i was going to be away from the car for up to 45 minutes, I would just turn it on,,, any longer, it would cool on it's own,,, or,,, use the old standby method of pulling out the choke,,,
When I first got the TF vapor-lock was a big problem.
After about the third time coming home on rollback and/or trailer only to have it start when it got home, I got serious about finding a cure.
(Even tried kicking it, as Habib recommends! LOL)
Heat shield (acquired from flebay) was 1st thing I tried. No difference.
After joining this site and searching archives decided to do everything others mentioned including:
Replaced rubber fuel lines on carbs with stainless steel.
Replaced smaller manifold carb spacers with correct ones.
Sent carbs to John Twist for rebuild.
Sent exhaust manifold to Jet-Hot for treatment.
Reassembled without heat shield.
Something worked as I have not had VL Problem since.
(+12 years now)
My "gut" feeling is Jet Hot did the most for solving the problem, as there was a noticeable difference in operating temperature.
As a child my father hated driving his TF in 4th of July parade because we would have to stop on the route several times for about 15min and he would shut engine down. "His cure" was to put dry ice in burlap and warp the carb bowels with it. It worked.
This dawned on me about the 3rd time with mine so I carried a couple of those "cold snap packs" in my car before I got mine sorted.
Last time I used that trick was at a gas station leaving a British car show on another TF. That one would not start even with choke fully engaged. I got a note from that guy a few months later telling me he did ONLY Jet Hot treatment to his car and the problem went away.
|Paul - I have a heat shield in place already. Problem with the heat shield is that if there is no air flow through the engine compartment the heat from the exhaust manifold has nowhere to go but up, heating the the heat shield and the carburetors. |
Dave S. - I would try the Jet Hot treatment on the exhaust manifold except the manifold in our TD has a perfect, original aluminized finish on it that I really don't want to change it. That, and I have heard from some others that the Jet Hot treatment didn't cure their problem. It is still an option if the bilge blower doesn't do the trick. Cheers - Dave D.
This thread was discussed between 12/08/2013 and 19/08/2013
MG TD TF 1500 index
This thread is from the archive. The live forum is active now.