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MG TD TF 1500 - Help, It won't idle!

Gentlemen

I'm having some difficulty with the old 'Lady' Have changed the fuel pump, coil, points, dizzy cap, rotor arm, condenser and needles, jets and seals on the carb and still cannot get the TD to idle without stopping (It runs fine above 2000rpm). It can't be anything to do with vapour lock because it is simply too cold here in the North of the UK at the moment! Anyone have any ideas? I keep cleaning the plugs and still they get covered in carbon in a short space of time which would indicate a rich mixture but if I lean the mixture out further I cannot get the engine to start. I'm currently running 'lean needles' to see if this makes a difference, but sadly it doesn't help.
Just to make sure, when you replace the ignition leads how do you correctly determine which lead from the dizzy goes to cylinder No 1, just in case I've lost the plot!! (again!!!!!!)

Sorry but I'm still learning about all things electrical!!

Thanks

John
J Clack

The rotor points to the wire about to get the spark.

John
John Redman

john, did it SUDDENLY develop this problem? if so, i would lean (pun intended) towards fuel supply or electrical. if this happened after a carb overhaul i would look at float level. i was chasing an idle problem myself on my car..i overhauled the carbs including reshafting and rebushing the throttle body, and i discovered one float level was too low. so low it ran lean and made it impossible to synch the carbs and get engine to idle properly. let us know what you find so we all can learn. regards, tom
tm peterson

There are other ways, but here's a direct way of determining when you're at TDC for cylinder #1. Take off the valve cover. Turn then engine over by hand until the pointer is in line with the notch on the pulley. Try to move each rocker arm for cylinder #1. If both rockers are free to move -- you're at TDC for #1. If they're not free, you're at #4 so go around another revolution and try again. Now take off your distributor cap and see where the rotor is pointing. That's where your plug wire for #1 should be connected.

You may have very sloppy throttle shaft bushings. Check the archives for more information on this subject. A way of showing it is to spray an aerosol, such as carburetor cleaner at ends of the throttle shafts while the engine is running. If the shafts are sloppy, the engine will bog down.
Bud Krueger

You can also determine TDC on cyl#1 (=closest to the front of the engine) by doing what Bud says, but with a difference:
Remove spark plug from cyl#1, and put your (or your helpers') thumb on the hole. Turn then engine over by hand until the pointer is in line with the notch on the pulley, if cy#1 blows you have compression and the right TDC (and then as John says the rotor points to cyl#1)
Willem van der Veer

Oh, about the idling: I would also look carefully at the float heights, too. And maybe you should (re?)check if you fitted the jets and seals correctly.
Willem van der Veer

Also, make sure the air cleaner isn't restricing air flow. Many of the oil bath air cleaners get "over tightened" and block air flow.

Evan Ford - TD 27621

I have similar issues. One area I'm confused about is the correct dowel to use in setting the float levels. Some say 7/16, others say 3/8. My car is a very late '53.

Thanks,
Tom Balutis

There can be many variations in the carbs that make setting the float level by depth below the cap very inaccurate. The method I've used for years is to remove the pistons and look doen the jet. Adjust the float lever until the fuel level is approximately 1/8 inch below the jet bridge.

Cheers,
Lew Palmer
Lew Palmer

Thank you all for your input, not had any success yet but I have rechecked the float heights and all seems OK and also checked that No 1 lead does go to No 1 cylinder!

The manual describe setting the jets by turning the nut one 'flat' at a time. I can turn the nuts 4 to 6 flats without any noticable difference. Also when running (without the air filter assembly on) there is a sporadick blowback (it sound like a 'shrp' crack through the carbs) and a 'popping noise' from the exhaust.
More suggestions are most welcome!

John
J Clack

John, have you checked for worn throttle shafts?
Bud Krueger

Bud

I'll pull the carbs off later and investigate the shafts.

Thanks

John
J Clack

John, you don't have to do that. If the shafts are worn and leaking it means that air is being pulled in at that point, i.e., after the needle/jet. The quick test is to spray an aerosol, e.g., carburetor cleaner, onto the ends of the throttle shafts, right against the body of the carburetor. Do this while the engine is running. If you have an appreciable air leak the liquid will momentarily block the air and the engine speed will change, and may even stall. Check both sides of both carburetors.
Bud Krueger

John, When did this start? Was it sudden, gradual, or had you done any work on the car right before this started? It shouldn't need lean needles unless you are at high altitude. A black, sooty plug can also indicate bad ignition. The history on this would help solve the problem. George
George Butz

John;; What Lew was saying is that even though you have set the float level using a rod is that the level can still be off. It all depends what thickness the washers are that you have used to mount the float body to the carburetor. The best way to verify level is to remove the damper and turn on the pump. Look down into the hole in the jet and see that the fuel level is actually 1/8" below the bridge,(aluninium ramp in body intake)This is the only way that you can be certain of actual fuel level. I have used that method for 30 years. Also check that you have the carbs balanced, valves and timing adjusted. Then you have the requirements to adjust the jets.I use a propane torch to gheck for throttle shaft leaks. With the car outside only start car and open valve on torch. Do not light it but play the fumes over the shaft to carb area and listen for an increase in speed.This will indicate wehter you have worn shafts.
Sandy
Sandy Sanders

Thank you for all very much your input.

I took the carbs off and pulled them appart and cleaned them (just in case). Someone in the past has re-bushed the throttle spindles so no leaks there.

I'm going on vacation this weekend so will try Sandys method for adjusting the floats next week.

I have replaced the needles back to the standard ones and turned the 'jet nuts' back two complete rotations (is that correct?) and will try again next week.

I'll also check to see if i'm getting a good spark before starting any adjustments.


Again my thanks to you all.

Kind Regards


John
J Clack

John,

Lew's (and Sandy's) method of checking float height works. It helps to have a small scoop or syringe to remove the fuel if it is too high, readjust the float and let it pump up again.

The T-Reg T Series Handbook says 3/8 inch, but that seems too low, so I always went with 1/8. Next time I see Lew I'm going to ask him if he knows if that's a typo, I can tell you that my car never ran right with the fuel 3/8 inch below the bridge.

I've been doing it this way since '79, but in that time I've only done it three times. Takes a few tries, but once done it is good for a long, long time. A set of original needle valves, body washers, and floats are the only combination which the original 7/16 inch bar adjustment between float lever and top of float bowl seems to work on. We tried the old way on Gary's carbs with the new needle valves and lever arms and got no where.

I ususally start six flats down, which would only be one turn. Make certain your needles are installed the same on both cars (hard shoulder flush with bottom of piston.)

Again, in my experience, if your throttle shafts aren't leaking, and your carbs are clean, and once worked fine, the problem is probably somewhere else. Carbs get blamed for a lot of troubles which are more rightly assigned to ignition.

warmly,
dave
Dave Braun

This thread was discussed between 27/08/2006 and 01/09/2006

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