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MG TD TF 1500 - Running VERY Rough

My car was running fine for two weeks. Yesterday, I noticed a "trucky" sound, almost like there was a hole in the exhaust. (The exhaust system is new.) Then, it started running VERY rough. If I gave it too much gas, it would almost stall, but if I didn't keep giving it gas, it would also almost stall. I limped home at slow speed, and let it cool down overnight. Tonight, I tried again. It stalled almost immediately. I richened the mixture on both carbs, and it ran but very very roughly. On accelerating, it shook and made a backfirish noise. Applying the choke would stall it. I swapped the fuel pumps out, with no change (it's a MkII). I checked the fuel filters, they are clean. I tightened the fuel lines; no change. The plugs looked blackened (new Champion N5C's),so i replaced them with new NGK BPES's. No change. There is 4" of gas in the tank.

The car ran like a top two days ago! My next possible moves are to check the screens at the fuel line fittings at the tank, to add gas, and to rebuild the carbs (the jets and needles were adjusted and new cork seals were added two weeks ago; the carbs were then adjusted and synched).

Any suggestions?
Ira Spector

Ira,
Silly question...but check for a "leak" around the intake manifold.
Possibly a cracked carb spacer...if you just did exhaust...maybe you stressed it?
David 55TF 1500
David Sheward

Ira,

As SU-guru, Lawrie Alexander, is wont to say, "90% of the problems with SU's are caused by Lucas electrics". I'd take a serious look at the condensor.
Bud Krueger
Bud Krueger

Ira

The point about electrics is well-made. I have found the gas side of the engine to be robust and reliable, the electrics are a disaster. Look at the thread on coil failure on this board and check the whole HT system and the weak points on the LT side, including the "Z" insulation washer on the distributor and the condensor (which are very hard to come by by the way - the Octagon Club in UK has a supply of the correct ones).

All the best!
Paul Joachim

Take your car at once to my mechanic in Charlotte , North Carolina. You will never see your car again so it will not seem such a severe problem. Dave.
capdave

Ira,
spend some money on electronic ignition, and a few bob for a sports coil. Forget about the other things.
It's quite true that Lucas distributors are f**d.
Yann
Yann

Hi Ira, sounds like too much fuel, not too little. Check to see that there is no problem with the air getting to the carbies ie blocked air cleaner if you are using a cartridge or too much oil if using oil bath if you have topped it up in between use. The timing may have also slipped if the bolt was a bit on the loose side. This will cause a trucky sound if the timing is seriously out, as well as poor performance, backfiring etc.

Good luck,

Paul.
Paul van Gool

Hi everybody! Thanks for the suggestions! Since two out of the first three suggestions were to check the condensor, that's what I did first tonight. Replaced it with the old condensor- car now runs great! Sure enough, the NEW condensor had failed. Carbs now do need readjustment; this will wait until I rebuild them. Saved by a 35 year old part!

By the way, the spark plugs cleaned up with some CRC contact cleaner spray.

Many many thanks!!

Ira
Ira Spector

The symptoms are very like those you get with a sticking float needle, due to wear or dirt. All SU's are prone to this problem, and its very easy to fix. The simplest way to see if it is the cause is to take the float bowl lids off and see if either has no petrol (gas) in the bowl. If not, disconnect the float lid from the fuel line and blow through the entry hole with the fork hanging loose-it should be free, but if not this will usually free it. If it won't clear, take the whole needle assembly out and wash it in petrol.
It may have been the condenser that was your problem, but it may be that the float needles cleared themselves. Whatever, if you get a sticking float needle, the car is running on one carb. and only through two cylinders, which makes it sound terrible and lose all power, so any of you who suddenly get these symptoms, try the check above.
John Dutton

John,

Good point. I did rebuild the carbs with new jets and needles last weekend.

Ira
Ira Spector

This thread was discussed between 22/08/2001 and 31/08/2001

MG TD TF 1500 index

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