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 MGA - MGA Running Rough

Have a 1956, 1500 that is cosmetically in great shape. engine was rebuilt >26 years ago...but runs absolutely great. Last month, needed to replace the starter as the power wasn't getting to the starter motor. Car turns fine now , but I have a problem getting her to fire unless I choke full. Not unusual, but when I get her started, I can usually ease up on the choke when she warms up. Not now, when I push in the choke, she runs very rough until the engine stops. Fuel is getting there as the float bowls are full, and I checked the spark on the plugs seeing a fine spark on eah one. Plugs are actually pretty clean, with a tan colored plug. My first step will be to replace the wires, cap, rotor, etc.. Any thoughts on this diagnosis?
Jim

Jim, The choke linkage is probably not returning the jet when you push in the knob.

Before you do anything else inspect the jets.

Push the choke knob all the way in. Remove the chambers and measure how far the jet is down from the jet bearing, then reach under the carb and push up on jet. It shouldn't move up any further.

Could be the return spring on either of the brass levers, worn linkage, a bad cable or a problem with the jet assembly.

Fred H

Jim,

Remember to make alignment marks on the vacuum bellhousing and the carburetter body, so that the bellhousing can be replaced in the same position.
If both bellhousings are to be off at the same time they should be marked "front" and "rear".
Some SU's are made with factory markings, but if you engine has been running well in the past you should use your own marks.

Mick
Mick Anderson

You gentlemen really think this is fuel? I had it fired up yesterday with lots of backfire and missing at high and low idle now....
Jim

Jim

Were all 4 of your plugs the same colour? - no soot on numbers 1&2?

The reason I ask is that I had similar symptons a month or so ago and I discovered that the coupling for the throttle spindles had come loose. Effectively, one carb (the rear) was trying to do the work of two. The front carb remained at idle.

Or, scenario 2, it may just be that the 2 carbs are badly out of synchronisation.

Don't forget to ensure you have oil in the dampers.

Steve
Steve Gyles

Steve, thanks for the advice. I check the dampers..looked good. The reason I feel the carbs are in good sync is because this spring she ran well. I jsut figured I have never touched the wires, distributor cap, rotor, condensor, points since I have owned the car....circa 1981!!! But I will check that linkage again....make sure it is lubed...and throw in a new set of wires, cap...etc......Thanks again!
Jim

"I can usually ease up on the choke when she warms up. Not now, when I push in the choke, she runs very rough until the engine stops"

"I have never touched the wires, distributor cap, rotor, condensor, points since I have owned the car"

Since the only thing you've changed is the choke setting, it makes sense that you should look there first. It's very common for those jets to hang up. Don't check the linkage until you've removed the chambers and inspected the jet levels. they should be about .070" below the level of the carb body bridge when the choke is pushed all the way in. Now move the choke knob in and out and see what the jets do.

You may have another problem, but since you,ve used the choke, look there first.

PS If you removed them when you replaced the starter, are you sure the plug wires are in the correct order?
Fred H

Jim, its quite possible that the advance weights in your distributor are starting to stick in place, not allowing your timing to advance and retard properly. That will cause a rough idle, since you never know where your timing will be when you come back down to idle. Its easy enough to detect the problem with a timing light too.
Jeff Schlemmer

You say you need the choke on, even after it is warmed up, and if you push the choke off even after it is warmed up, it runs rough and dies. Does it do this only at idle, or is it rough at all speeds with the choke off. If it is only at idle, it could be a vacuum leak allowing too much air and a lean mixture at idle.

Jeff Schultz

My bet is a vacuum leak, and a pretty big one to boot. Check to see if all the manifold and carburetor bolts ara tight, that it hasn't lost a core plug from the end of the intake manifold, and no missing plugs in the top of the intake manifold.
Barney Gaylord

See the thread "MGA stalling - need help". I am having difficulty relating the choke problem to the starter replacement?
By the way, you should disconnect the choke cable, or at least slacken the clamp bolt, before checking the jet height. When clamping the choke cable, the slack in the choke operating levers has to be taken up first on the front carb, and the interconnecting link adjusted for length to take up the slack in the rear linkage.(but only the slack, no more)Then your choke knob should only come out about 1.5 inches max from the dash.
P. Tilbury

This thread was discussed between 19/08/2006 and 21/08/2006

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.