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MG MGA - Pig to start when cold

My A is a pig to start when cold. engine is completly rebuilt (not by me).
Fitted new correct plugs , rebuilt carbs and fitted correct new needles, adjusted choke linkage and set to its richest setting.
Checked points gap and set timing to 7.5 dgs btdc fitted red distributor arm.
Fitted geared starter motor and one 12v battery so it turns over quite fast.
Checked polarity at coil.
When its started it ticks over fine, and runs and pulls really well.
If i start it with a whiff of easy start after 20 seconds i can turn it off and it will restart first pull on the starter and then its ok all day, its just when its cold it just wont fire.
Thoughts , weak coil? have not changed plug leads yet. Or could it be low compression, If i do a compression cheack what should it be. If camshaft timing was out by one tooth would that lower compression?

Thanks Roy
R Mcknight

I think in cases like this you just have to be methodical and write down a list of likely causes e.g. coil, condenser, compression, stale fuel, etc.,etc. and eliminate them one at a time.
I had a problem recently with poor idling performance and I included,amongst others, low compression on my list so I bought a gauge last week. Hopefully it won't cost you 20 to cross out every item! My figures, by the way, were 160 +/- 5 psi so that was one item I eliminated........................Mike
m.j. moore

Roy. I found an MGA to be more reliable that my American vehicles in the winter in Wyoming. The MG would start when my Chevrolets (an Impala and a Corvette) would not.

The first thing I would do would be to remove the suction chambers from the carbs and put the choke in the released position. Use a set of dial calipers (or just estimate) to determine how far the jets sit below the bridge. Then, pull the choke to the on position and reexamine the depth of the jets. There should be a quite visible difference between the raised height and the "on choke" height. If not, you are not enrichening the mixture as the engine needs to start.

The coil lead can be checked for a good, fat spark by removing it from the distributor cap and holding it near the block while cranking. If the spark is weak, either the coil or the lead may be at fault. If the spark is good, check for spark at each spark plug lead. If you have good, strong sparks at the leads, the ignition system should be sufficient to start the car from cold. Weak spark indicates distributor cap problem, rotor problem, or spark plug lead problem.

What leads are you running? Copper wire or silicone/carbon fiber? The latter can break down with age, internally, and look good from the outside while providing too much resistance in cold weather.

My website, www.custompistols.com/ had an MG section which has a tech article on how to inspect the ignition system and spark plug leads. It would help you to go through the systems in an organized manner. Paul Hunt's website, "The Pages of Bee and Vee" have some good info on carb set up and trouble shooting.

Les
Les Bengtson

The holes in the brass choke linkage are almost always ovalled and you get far less travel than you would new. Have you brazed and redrilled all the holes and removed all of the slop from the linkage? You may not be getting as much choke action as you think.
Bill Spohn

But some of the holes were designed as oval!
Art Pearse

Roy with most starting problems you start with the ignition system and then onto the fuel system. However in your case i would second Les's suggestion that you check the choke adjustment first. The chokes on these older SUs are sometimes difficult to get to work properly because they are old and worn.

The choke works by moving the jet (which is the brass tube around the needle) downwards. It should move down at least 6mm which enriches the mixture. It's very easy to think that the choke is working but the jet isn't going down so it won't start easily. The linkage may be worn (oval holes) that prevent this from working correctly. Check this out and let us know how much it's going down when the choke is pulled out.

Andy
Andy Preston 1

Hi Roy, how often do you use your car? I often experience the same problem as you but use my car very sporadically. Last week I decided to drain my car bowls and fill them with fresh fuel from the local gas station. The car started immediately leading me to think that my problem is stale fuel.

Regards

Steven
S HILL

Replacement of the coil on my TR3 did the trick for me.
Tom Going

Andy (and Bill),
The holes are not oval when new, just oversize as a design feature, I believe. I have fitted new brass linkages when the holes have become too worn. (I can't weld brass, except on a monkey when the weather is very cold!)
Peter.
P. Tilbury

Hi Roy , i was having the same problem very frustrating then i looked at the John Twiss video on U-Tube on starting the MGA , full choke and foot on the floor and away you go , this seems wrong to me but it works ,make sure that you are getting full choke with help from a third party under the hood

cheers Colin & good luck
c daly

I've seen quite a few MGA choke linkages that had so much wear that when you had the cable pulled all the way out, the jet barely moved.

Brazing the holes and redrilling, or Peter's method of simply replacing the parts (the Moss bits are reasonably priced but have no idea on fit and quality) should get you back to stock.
Bill Spohn

There is one hole in the choke arm that is intentionally oversize from new. It is that way to allow initial motion of the mechanism to give fast idle before choke. If you weld and drill or bush that hole for minimal clearance, you will get immediate choke along with fast idle, not good.

For adjustment, the first requirement is to pull the choke arms up considerably before securing the cable end, taking a lot of slack and free-play out of the mechanism. If you don't do that, pulling the choke knob full out may do nothing.

Pity the Workshop Manual does not do a very good job of detailing choke and fast idle adjustments. For more information see here: http://mgaguru.com/mgtech/carbs/cb102.htm
Barney Gaylord

This thread was discussed between 10/04/2013 and 14/04/2013

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