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MG TD TF 1500 - Fuel Filter(s)

How many fuel filters/screen are on a '53 TD? I know each bowl lid has a screen and I know the pump has a filter at the bottom. Any others?

Also, to check the pump filter, the diagram from Moss shows it on the bottom of the pump. Do I just remove the bottom nut on the pump and withdrew the filter? How much fuel, if any, should I be prepared to catch when I do this?

Sorry to be so dense, but asking is better than disaster.
L Karpman

Don't forget the one in the fuel tank. Bud
Bud Krueger

Thanks Bud. One more question.

The car's fuel pump has always ticked for a few seconds before starting, especially after sitting for a day or so. Now that I have this dying at idle situation, I notice that the pump won't tick at all, and sometimes just once or twice after sitting for days. The car runs fine at RPM, but as soon as I let off the accelerator and it decelerates to idle, it dies. Is it possible that the pump is not delivering duel when first turned on, or at idle, but IS delivering fuel at RPM?
L Karpman

Larry - the float bowls hold the fuel, and when you turn off the car the float bowls are theoretically full. When you go to re-start and turn on the key, it's normal for the pump to tick once or twice, just to show it is working and to add a small amount of fuel to the chamber. When the car has sat for a while and fuel has either leaked out or evaporated, the pump will tick more, as it fills the float chambers.

There is plenty in the archives about checking the fuel pump; if your car has ticklers on the float lids the pump should tick when you depress and hold a tickler. Have Dave Dubois rebuild you a spare - electronic - pump in case yours goes bad.

Tom Lange
MGT Repair
t lange

Thanks Tom. That's just the issue. There have been many times recently where the car has sat for weeks and when I turn on the ignition, the pump has not ticked at all. That's the part that is a new phenomenon. That is why I am suspecting the pump. The question is, is it possible for the pump to deliver fuel at RPM, but not deliver fuel when first turned on or at idle, perhaps due or clogging in the system, electrical issues (grounding),etc.?
L Karpman

Larry, you might also want to see my recent thread "Float Bowl Needle Valves" although it turned out the needle valves weren't the problem. Switch on resulted in several ticks then nothing. I disconnected the outlet line from the pump and hooked up a hose to a catch can. Same results - several ticks than nothing and no fuel flow. In my case I found a totally blocked in-line fuel filter which I removed. Switch on resulted in steady ticks and steady fuel flow. Ninety miles today with out a burp or a studder. That included twice shutting the car off and leaving in in direct 85+ degree sunshine for 15-20 minutes. Instant restart and no studders. It's running so good I'm getting worried.

Jud
J K Chapin

Larry, maybe I'm jumping out of my knowledge base, but let me try this. Hopefully Dave D. will correct me. It's the working against pressure that causes the pump to stop pumping. Generally, when an engine has been sitting for a bit there is a bit of a gap that is created in the fuel line. The pump comes on to fill this gap. If you are not seeing this initial bit of pumping it could well be that your needle valve is rigidly closed, so, there is no gap in the fuel. Engine motion can very well unstick the needle valve. I think I'd make a go at new needle valves. Bud
Bud Krueger

Bud. I just replaced the needles the other day with new Gross Jets to no avail.
L Karpman

Jud. I've been reading your thread. I had an in-line filter I removed many years ago. In fact I had a hard time understanding what filter you removed until I realized it must be an add on. The only filter I have not checked is the pump filter itself, and that's next.

So, until that time, my question remains "is it possible for the pump to deliver fuel at RPM, but not deliver fuel when first turned on or at idle, perhaps due or clogging in the system, electrical issues (grounding),etc.?"
L Karpman

"So, until that time, my question remains "is it possible for the pump to deliver fuel at RPM, but not deliver fuel when first turned on or at idle, perhaps due or clogging in the system, electrical issues (grounding),etc.?" "

Larry - Welcome back to the BBS, we have missed you. To answer your question, the SU pump ticks over when ever the diaphragm reaches the bottom of it's stroke, causing the points toggle to throw over. When that happens, current is supplied to the coil, pulling the diaphragm up and opening the points. If there is back pressure from a full float bowl, needle valve stuck, or a clogged outlet circuit from the pump to the float bowl.

The other thing that will stop the pump from running (ticking) is a clog on the inlet side of the pump. In this case the pump will stall in a current on condition and the pump will quickly overheat (feel the coil housing to see if this is happening), The most common thing that will cause this situation is debris from the tank, either at the internal filter in the tank, or the filter in the pump. A lesser common clog would be in the fuel line between the tank and the pump. If someone placed a high efficiency modern filter between the tank and the pump, that filter can clog on much finer particles than the existing filters and stop the pump from running.

Finally, the lack of power to the pump or a bad ground can cause the pump not to run.

For troubleshooting tips for the fuel delivery system, see the article, Fuel Delivery Troubleshooting Guide in the SU Fuel Pump Articles section of my Homepage at: http://homepages.donobi.net/sufuelpumps/

For Bud - You got the sequence correct :-) Cheers - Dave
D W DuBois

Thanks Dave. If I read your post and articles correctly, the answer to my question is - NO, if the pump does not run or is intermittent at idle it will do no better at RPM with throttle applied. Correct?

Do you (or anyone) know the size of the pump filter bolt head, and do I need to remove the pump from the TD to pull the filter?
L Karpman

I removed my pump filter easily and with very little fuel spillage with the pump inmtalled. The filter brass nut took a large Whitworth wrench but I don't recall precisely which size it was. I can check and let you know.

Jud
J K Chapin

Jud: The size would be helpful as I can't get any of my Whitworths to grab it. May be due to the narrow clearance between the nut and the mounting plate. Don't know for sure as I can't stand on my head :-)
L Karpman

I'd like to reiterate my problem for those that may be following this thread. The problem is simple, the solution may not be.

Basically, the car runs fine at RPM over 800. It revs fine, runs smooth, etc. It just won't idle on it's own.

The car ran just fine as of one month ago. It's been sitting since. It starts fine, and with pressure on the pedal it runs fine. With pressure off the pedal it dies. I have changed nothing on the distributor (petronix kit), the coil, the plugs, the wires, timing, etc. I have only put in new Gross jets in the float bowls, but that was after this problem began.

I have checked the filters in the bowls, and getting ready to check the pump filter. As I said, the car runs fine, but only with pressure on the pedal to keep the RPM's up. Pressure, off and it dies.

I may be chasing a rabbit down a hole just concentrating on the fuel system, so I'd appreciate any and all input as to other possible causes. Thanks.
L Karpman

Larry - The wrench size for the filter plug is 3/8W.

"the answer to my question is - NO, if the pump does not run or is intermittent at idle it will do no better at RPM with throttle applied. Correct?"

That is not necessarily true. The more fuel that is used from the float bowl, the faster the pump will run in most cases. The SU fuel pump is an on demand type of a pump - there is a return spring (called a volute spring) behind the diaphragm, which determines the output pressure of the pump - in the case of the TD the output pressure is 1.5psi. If the float bowl is full and the needle valve is closed, the spring behind the diaphragm cannot push any fuel out of the pump. Once fuel is used from the float bowl and the needle valve can open, the volute spring in the pump can push more fuel into the float bowl. The faster the fuel is used from the float bowl, the faster the pump will run in an attempt to keep the bowl full.

"Basically, the car runs fine at RPM over 800. It revs fine, runs smooth, etc. It just won't idle on it's own."

This sounds like a carburetor adjustment problem rather than a fuel delivery problem. You may want to talk to Dave Braun at dave@dbraun99.com Dave is the carburetor expert on this forum. Cheers, Dave

D W DuBois

Thanks once again Dave. Very clear now. What is perplexing is how the carbs may come out of adjustment just sitting in the garage? I'll get this filter out first just to eliminate that possibility, then proceed from there. Too hot in the garage during the day, so I'm a night worker now :-)
L Karpman

Dave beat me to it (he probably knew and I had to conduct an empirical test) but 3/8W fits the pump filter plug. Also, when I said "I removed my pump filter easily and with very little fuel spillage " I should have mentioned that at the time I had both the inlet and the outlet side of the pump disconnected.

Jud
J K Chapin

Larry,
Check the points on your pump,,,
The following is from the other thread about dying at an idle

>>>>F. W.,
If your carbies have tickler pins, watch them as the car is ideling,, if there is a fuel delivery problem, the pins will go down until it stalls from lack of fuel.
ALSO, listen to the fuel pump as it is ideling,, it should periodicaly tick as it pumps fuel, I have seen a pump not operate at idle, but work fine as the car was moving. This was because the points needed to be reset, and all it took was the extra vibration of the moving car (or vibrating engine)to make the pump work! Once the car stopped moving, the pump also stopped.<<<<

SPW


Steve Wincze

Larry, another indicator is your ammeter. In neutral, take your foot off of the brake and set the hand brake. Watch the ammeter when the engine is idling. You can readily see the flicker of the needle when the pump operates. Bud
Bud Krueger

Thanks again folks. Steve: No tickler pins. Can't listen to the pump at idle, as the car won't idle. Also, I doubt with my bad hearing that I could hear the pump tick over the engine noise. It sputters and dies immediately after I take my foot off the pedal. I have checked the float bowls numerous times after this, and the bowls have fuel in them.

That is another reason I am looking for possibilities other than the pump. There is fuel available to the engine, and it still dies. I have not driven the car in months and absolutely nothing has been changed as far as carb settings, or anything else. So I have to look for every other possibility why the car is dying at idle when pressure is taken off the pedal.

I have been looking for a bad component, as nothing has changed from week to week while the car has been sitting in the garage. Starts,idles and runs fine (without driving) one week, next week it dies at idle. I just started with the pump as possibility, but with thought if there is fuel in the bowls, pump working properly or not, the car should idle until it needs more fuel. At least that's my thinking right now.

In any case I'll run a flow test after I check the pump filter just to be sure, but right now I believe the problem is elsewhere, unless I'm totally wrong in my thinking (which for me is always a strong possibility :-)

L Karpman

You're right Bud. Thanks! Had to hold pedal to keep about 900 RPM and about every 2 seconds the ammeter flicked. More than ever, I think the pump is not the issue.
L Karpman

Larry, what engine idle speed are you looking for? Would your engine continue to idle at 900? Bud
Bud Krueger

Larry, If you had to hold the pedal down to maintain 900 RPM, it sounds as if your idle adjustment screws on the carbs is way out of adjustment, Thus it dies at idle, but runs fine at speed.
Lew Palmer

I have had to hold the pedal down to make it idle at all. Once pressure is lifted the engine stumbles and dies. Several weeks ago, and for years, the car idled fine at 800 RPM.

I just tried the idle screw again, and if I set the screw to idle at 800 RPM now, it will idle but hunt between 800, and 900 RPM and idle very poorly. Set over 1000 RPM, it will run smoother, but "hunt" also and have terrible "dieseling" on shut down.

Open to any and all advice.
L Karpman

After a while of fiddling, there's nothing I can do to get it to idle smoothly on it's own at 800 RPM. At 1000 RPM it's fine, but with run-on at shutdown. Probably (I hope) due to the carb plate being open too much at 1000 RPM. Shutting it down by putting it in gear and slowly releasing the clutch will have to do for right now. Looks like a carb adjustment is in order. Now I have to pull out my books and go step by step. But for the life of me I cannot figure what changed with the car just sitting in the garage over time. Thanks to everyone for their input.
L Karpman

Problem solved! ( I think)

Turns out the culprit in my problem was ME! I had been fiddling with the idle some months back and I was turning each idle adjustment screw equally. Well I discovered after a re-read of of tech info that I was turning the fast idle screw on the front carb by mistake. It had been about 5 years since I adjusted the carbs, and my memory of the front screws was 180 out. Naturally this upset the sync of the carbs.

I decided to re-sync the carbs and loosened a nut on the rear carb connector clamp, and checked to make sure only the rear part of the rod moved when the throttle plate was lifted. All was good. Then, I remembered that I had a scheduled Dr. Appointment, and so I decided to re-tighten the clamp. I then ran into an odd situation I have never experienced before (before meaning the one time I synced the carbs when I replaced them about 5 years ago. When I tightened the nut "tight" it bound the throttle shaft so when I lifted the lever, it stayed in the position I lifted it to. I did not fall back down. I loosened the nut again, but this time it was too loose to keep the front carb shaft connected.

I re-tightened the nut a little bit more, and all was well. Next day I started the car, with a little pedal as I always do, and the shaft once again stuck in the upper position. I loosened the nut a bit an once again - too loose! I again found a happy medium so the shaft would operate normally. So my questions are these: Is it normal for the shaft to stick if the nut is too tight? Is it normal to have to find a "happy medium" in tightening the nut? Or, is there something amiss with my connector shaft? Thanks as always in advance for any assistance.
L Karpman

Larry, no it's not normal. There's a good chance that you may have the couplings configured wrong. Check your manuals for a good image of the carburetor linkage and see if you have them connected up right. There's agood set of images in NEMGTR T-Type Restoration Handbook in the "Back to Basics" section. Bud
Bud Krueger

Bud. I don't have access to that document, but here's a pic of how mine are connected.


L Karpman

I just re-tightened the nut fully and it seems to be OK. Don't know what caused it to stick before. I'll see what happens tomorrow. Is there any lube required anywhere on the shaft?
L Karpman

OK, fixed the throttle shaft linkage sticky problem. The rear portion of the coupling band closest to the throttle lever had no clearance between it and the lever. The rear metal was bent outward slightly (how it got that way remains unknown). Loosened both nuts and slid the band slightly away from the lever, re-tightened, and all is well. Still waiting for a cooler day to re-sync the carbs though. We're in the 100'sF again.
L Karpman

This thread was discussed between 16/08/2014 and 23/08/2014

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.