MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Power loss under load - help please

This I know is such a common problem but I am completely stumped and need some help please.

My TD has no power when the engine is under load. In fact it cannot get past about 20 miles an hour.

Background. The car has been running well all summer but I thought I should check the tappets which I did and set them to 15 thou as per John Twists Youtube recommendations. None of the tappets needed much adjustment and I thought no more about it.

Car would not start after adjusting the tappets and I had no sparks at the plugs. I had obviously disturbed something. I swapped out the "accuspark" electronic points system and put the original points back in and the car immediately started but ran rough. I bought a new "accuspark" system and the car runs and starts well at idle with nice fat sparks on each plug.

However I took her for a run up the road and she falters badly under even a slight load.

With no load on the engine she runs OK and can rev ok but after a minute she starts to falter.

Plugs one and two are a bit sooty but have always been like this (I have never had to use choke to start her). Plug 3 is a bit wet and at idle when disconnected the revs do not alter. Plug 4 is ok.

I did a compression check a month or so back and (at that time) I had really good compression.

There may be a host of red herrings in the above sitrep but I thought I should give you the whole picture.

So the question is what am I missing here? She revs well in the garage but not when I take her up the road. Was it something to do with the tapet adjustment or has another problem appeared? What causes power loss under load?

Thanks chaps

Ray
Doctor Bob

Fuel filter at the tank is one cause of that problem. I got my car altogether and had same problem. the tiny screen the the rear filter would suck up dirt/debris when you put the pedal to the metal and would not go. idled fine . cleaned out tank and filter and no more problems. Just a thought..
Tom Maine

Check the fuel filter in the bottom of the fuel pump.

Jim
James Neel

Also check the filter screens (where the fuel line attaches in both carburetors. If you are getting debris in any of the filter screens, especially the one in the tank, check the tank for rust problems. You might to also check the timing on the ignition. Cheers - Dave
D W DuBois

Doctor Bob,
How old are your plug wires? Obviously you disconnected them to pull the plugs during the tappet adjustment,, Maybe the spark is jumping from one wire to another now? (under load)

Are you positive that the plug wires are reconnected to the correct firing order ??

SPW
Steve Wincze

Check also the condition of advance weights & springs under the points. Check timing @ 3,ooo rpm with timing light with advance curve. Should be TDC at about 30 degrees advance.
David Sheward 55 TF1500 # 7427

Hi Bob,

I had a Mark 2 Jag which idled well and (as I remember) revved ok in the garage but wouldn't "go" on the road. It turned out to be caused by a seized distributor advance mechanism.

Similar symptoms were experienced by my wife's mini and my brother's MGB V8. They both had blocked mufflers!

Both of these things are rare but do happen. Good luck with your diagnosis.

oTCagonally, Bob Schapel
R L Schapel

If removing wire from 3 does not change idle, that cylinder is dead. Re-check plug wire order, change that #3 plug, and maybe recheck the valve adjustment on #3.
George Butz

Thanks for your advice everyone.

I checked the fuel filters and cleaned them all. Some material came out the one I have near the tank connected to the backup facet pump but not much.

I measured the flow of fuel to the carbs and I can get a pint pumped to the carbs in 45 seconds so I am confident I have fuel getting to the carbs OK.

I am 100% sure I have the leads connected correctly and I have high quality "bumble bee" multi strand copper wire in them.

I then looked at the timing and connected my strobe to cylinder 1 cable. It flashes on the pulley notch right by the pointer. When I rev her to about 3000 revs the pulley notch moves (if you know what I mean) less than an inch. I thought it should move something like 30 degrees on the pulley am I right?

Thinking I might have an advance problem..I pulled the distributor apart and found the weights a bit sticky and started to polish them on my bench polisher. I was polishing the small pivoting cam that goes on the top of the weight and attaches to the spring and like an idiot wasn't holding it tightly enough and it flicked out of my hand and is lost somewhere in the garage.

This means that I am in a worse position that when I started! I am so cross with myself.

We are going on holiday in her next week and I have to get her fixed by the weekend.

All I need is the little cam that is less than half and inch long but the Moss catalogue doesn't specifically list it.

Not sure what to do now.
Doctor Bob

All I can offer is to search the garage again, with a magnet in all the usual suspect spots and then look in the impossible spots or how in the heck did it land here?

When I'm really in a bind to find something I engage my wife's help. It seems she can locate anything if given a sample or picture - sort of a visual bloodhound.

Someone in your neck of the woods must know of a distributor shop that can overnight a part or exchange distributor.

Good luck.
JE Carroll

http://www.distributordoctor.com/distributor_advance_weights.htm
mog

The stock TD has about 25 degrees of advance, the pulley is 3.75 in diameter, so each degree is about .031 inches. 25 degrees of advance is therefore .77 inches on the pulley.

With a rebushed distributor to steady the action, the XPAG will tolerate 8 degrees BTDC static timing which is about .25 inches before the timing mark on the pulley. The advance will go to about 12 degrees at idle, and 32 degrees all in at about 3500 RPM, which is about 1.05 inches on the pulley.

Make sure your timing isn't jumping around which would indicate a worn shaft, and the advance is as I describe it, or your advance springs and stop may be worn.

Of course all this is moot if that cam stays AWOL.
Dave Braun

Thanks all for your advice and help on this.

She is back up and running again.

Even managed to find that little part from the dizzy that the bench ploisher hurled across the garage. Only took me 4 hours to find it - but at least I have a nice tidy garage with all the nooks and crannies vacuumed and neatly arranged.

After a weekend of swapping every part of the ignition system it was fuel related in the end as Dave suspected.

Not filters but a Sunk float!

Thanks everyone



Doctor Bob

Sorry

I am not giving proper credit where it is due...it was fuel related as Tom Maine, James Neel and Dave suggested.

All the other tips such as leads, timing, advance weights etc were very much valued and appreciated.

Amazing place this forum

Thanks chaps.
Doctor Bob

Sorry for sending you on an "under the bench" adventure!
Main thing is she's up & running!
David Sheward 55 TF1500 # 7427

This thread was discussed between 23/08/2014 and 26/08/2014

MG TD TF 1500 index

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