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MG MGA - Engine dying

Folks,

Maggie May the MGA is having a hard time idling when cold. In particular its dying when I take my foot off the gas for an extended period of time like when approaching a stop sign.

I'm suspecting its the oil in the carbs, which I replaced last summer with straight 30 weight.

Since its still quite chilly in michigan I thought I'd try a 20 weight or so. what's the best way to get out the old oil? Just stick a paper towel in the opening to suck it out?

Tysen
Tysen

Tysen

Try a bit of plastic tube and suck on it, or use an old washing up liquid bottle and fiddle the tube onto that.

Correct dashpot oil for the A is SAE 20.

Checked carbs balance and mixture? Things change with the seasons...

Pete
Pete Tipping

I suppose the best way to remove the damper oil with the carbs still on the car would be to use a syringe. I've used one of my kids old infant medicine syringes to remove excess brake fluid from the master cylinder. Works great.

Good luck,
M.D.
'57 coupe
M. D.

1. are the plugs fouling form a rich mixture?

2. check the achives but, I think an erratic idle due to engine temp might be caused by a vacuum leak at the carbs, possibly worn throttle shafts.

3. I don't think it's the dashpot oil which is there to give a slightly richer mixture when accelerating.
Fred H

Hi Tysen. I agree with Fred that the damper oil is likely not the cause of your idling problems. In fact, if your MG was running well, and the idling problem "just started happening", chances are that the carburettors are not the problem at all. SU carbs that are set up correctly, seldom have sudden ailments. It is more probable that you have an ignition fault of some kind. Im not ruling out a carburettor problem, just saying that it is not as probable. Good luck. GLenn
Glenn

Tysen, since the car had been sitting for a while check your choke linkage and make sure that the jets are moving all the way up against the stop when the choke is released, they tend to get sticky when sitting. Is your engine getting up to proper runninng temp? If you have a 160 deg or no thermostat the engine may not be getting warm enough. To empty the dashpot take out the three screws, remove it, and turn it over to drain. I vote with the others, I don't think the dashpot oil is your problem.
John H

Tysen:
Has Maggie May ever idled properly in cold temps or is this something new?
If not, the carbs may not have been set up properly and it may be something as simple as an idle screw adjustment.
Not trying to sound condescending, just not wanting to overlook the obvious.
If they were properly setup, then I would agree with the others, I think it is unlikely to be the oil in your dashpots.

Clayton
C. Merchant

Ok, I will defer to the greater experience represented here.

Here are the symptoms.

When the engine is cold it requires a constant foot on the gas to keep the revs up. This is the point that it can die if I suddenly take my foot off the gas, the revs just drop and drop to nothing.

After it warms up it idles just fine, but up noticably in revs than when cold.

Any thoughts?
Tysen

Hi Tysen. As stated previously, try checking that the choke linkage is working properly, and the jets actually raise and lower properly when the choke knob is pulled out or pushed in. ( a drop or two of oil on each of the jet tubes isnt a bad idea) I would aslo check the carburettor mixture settings. If the carbs are set too lean, the engine could die when cold. Also check the carb idle speed settings, and also check the fast idle setting. Additionally, make sure that the carb throttle spindle clamps are tight. If one of the clamps is loose, you could be opening the throttle on only one carburettor. You might also want to check for vacuum leaks around the carburettor mounts and the throttle spindles. If you check the carb settings, and everything is correct, then I think you need to look at the ignition system next. Good luck, Glenn
Glenn

As I recall, here is a cam in the idle linkage with three holes for different climate conditions. Is this hooked up properly and is it functioning? Does the choke linkage increase the idle when the choke is on? I believe that the small cam gives different idle increases.
John

Hi Again Tysen. Another thought: If your carbs havent been apart for some time, you might want to remove both carburettor dashpots, and clean the inside bores thoroughly. Any dirt or grit will prevent the pistons from rising properly. This could fuel/air mixture problems also. Glenn
Glenn

If you also have problems starting in cold weather, then it is probably the choke linkage. If it starts fine, but just idles to slowly until fully warmed, then possibly just the fast idle adjustment, or maybe the linkage between the two carbs is loose and only one is being held open by the fast idle screw. Another possibility is an air leak either from worn throttle shafts, or a break somewhere in the vacuum advance line.


Jeff Schultz

During my first winter of MGA ownership, I experienced similar symptoms. I eventually determined that, despite the cold weather, I was using too much choke during warm-up. When I backed off the choke a bit, the car would idle fine. You might try that once to rule it out as the problem.

Regards,
M.D.
'57 coupe
M. D.

Tysen,
Go into your wife's kitchen and get a turkey baster. I'm talking about the big eye dropper thing. It will suck up th eoil fine.
Mike Parker

...then clean it REALLY well before you put it back in the kitchen draw, and DON'T tell your wife. Don't eat any more turkey either...

M.D.
'57 coupe
M. D.

Tysen, if it idles and runs fine after it warms up, there's nothing wrong with the carbs themselves. I would still check to see of the jets are returning to normal position, it's just something to do all the time, especially if it's running kind of lumpy (rich).

My experience is with Triumph TR3 and 4 carbs, so there may be some small difference in the linkage setup. But previous posts make it sound very close.

The fast idle cam that comes into play when you pull the choke should be your cold idle adjustment. I set mine so the cam starts to work before the jets pull down. So when you start it, you have choke and fast idle, then you almost immediately push in to where you have very little choke, but still have a faster idle. You drive away after less than a minute, maybe right away. After a few blocks, you push in a little more, maybe all the way depending on if you have to come to a stop or not. Sometimes I need a bit more idle than I thought, but it usually dies before I come to a complete stop, and letting the clutch back out and a quick rev, along with a little more choke. At this point, I'm not pulling the jets down, just touching the cam to the idle stop a bit.

On mine, there are 3 holes in the idle cam to kind of get the combo right. I appreciate the new cars and their ability to start and idle great without even touching the pedal, but I get a little smile each time I do it myself for some reason.
Tom

As some of you poets will remember from a recent thread I had a lot of trouble with my engine running when cold. Difficulty in getting all cylinders to fire evenly and an even idle was non-existant. Ran reasonably ok when warm.

Turned out to be the balance between the 2 carbs. The rear one was doing all the work as the throttle spindle connector between the 2 carbs had slackened slightly, allowing the carbs to gradually get out of syncro.

Worth a check along with all the other points raised.

Steve
Steve Gyles

Thanks to all!

This will give me something to fiddle around with over the weekend. (like I need something else)

One item nudged a slow memory cell for me. When I first got the car and was exploring the engine bay an inadvertant, and very slight touch to the vacuum pipet caused it to separate from the distributor. I did some looking up and discovered that it was missing the clamp at to the head and the mount on the manifold. It was simply staying up by itself and would vibrate to all hell. The vibration had caused a stress fracture at the distributor. At that time slow idle was off and was immediately better when repaired.

Well I never got around to replacing the clamps last year, so I now suspect that its the same thing all over again.

Your collective assistance is always appreciated.
tysen

Tysen ,

May be did you discover it by yourself after all
"very slight touch to the vacuum pipet caused it to separate from the distributor"
And the main gap between idle and running resides in vacuum advance, provided your jets return home at switch off.
Renou

This thread was discussed between 27/03/2006 and 28/03/2006

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