MG stalling hot

[Dave Sherman]

Found it! Cracked vacuum elbow at the EGR valve. Had to chuckle a little when I had to describe to the Autozone guy what a vacuum elbow was, but fortunately he remembered where they were. Somebody suggested cleaning the EGR valve, which is actually a maintenance item. When I put it back in it occurred to me to check that the EGR and vacuum advance would hold a vacuum, and when I put the Mityvac on it, I heard it hissing from the elbow. Running much better now!

 

[ctrcbob]

If the rubber carb diaphragm is perforated, air bypasses the throttle valve causing erratic idle.

Funny you should mention this.
I had many BMW Motorcycles. One started running terrible. Most BMW “Airheads” use Bing Carburetors. Took the carbs apart and found one had a small pinhole in the rubber diaphragm. I had a roll of very thin “Mylar” tape, so I cleaned the diaphragm, cut a very small piece of Mylar and covered the pin hole.
It worked. Never had a problem with that carb again.

BTW, I still have that roll of Mylar tape somewhere in my shed.

 

[michaelluscher]

SU makes an upgraded solid state fuel pump these days?

 

[Wrenchturner44]

Dave, I take it you have since checked the "rest of the vacuum lines"......yes?

 

[Dave Sherman]

Dave, I take it you have since checked the "rest of the vacuum lines"......yes?

Yes, if I put the Mityvac on the carburetor end, it's all holding a vacuum. EGR valve opens, and the vacuum advance advances.

 

[Wrenchturner44]

Excellent news Dave. Enjoy your piece of British Leyland motoring history. Beware of the Mr. Lucas though, he is always hiding between the electrons.

 

[Dave Sherman]

Well, the issue has returned. It's back to not wanting to idle when I've been driving it for a while. Runs fine along the road and if I give it gas it's fine. Last time it was a vacuum leak, but if I put the vacuum pump on the vacuum lines, it's not leaking. Tonight it did something different though, and now I'm wondering if it's ignition related.

Was sitting at a light, it was idling so slowly it was close to stalling for several seconds. Was about to feather the gas a little to get it back up, but without touching anything, it suddenly started idling normally. Got back to my driveway to let the wife get out, same thing. It was idling slowly, close to stalling, and like flipping a switch it's instantly idling normally without touching the gas. While it's doing this slow idle and nearly stalling I can get a whiff of the exhaust and it's richer than normal, so I'm wondering if it's misfiring.

It has a Pertronix ignition, relatively new cap and rotor, and the wires aren't very old. The coil is original though. It gets pretty toasty which makes me wonder if it's getting flaky. Got a new coil on the way, I figure if it doesn't fix it I'll have a spare anyway. Any thoughts?

 

[wings&wheels]

Check your coil resistance. Had same symptoms and it was a failing coil, but you say newish cap and rotor. I once replaced the cap and rotor on my Tr6 a while back and it quickly developed a random miss which was traced back to the cap, despite looking ok, being manufactured off to the point where the rotor was contacting some of the terminals in the cap, flinging metal shavings around. Don't underestimate the garbage out there...

 

[Dave Sherman]

Think I made an improvement, at any rate. Got a new coil, and after driving it around until it was good and warm, it wasn't stalling and stumbling at stops like it was before. I did make one silly mistake though. Don't go to Amazon for parts for your vintage car. Guess I was thinking "It's an ignition coil, it's not rocket science.". What arrived was a good 1/8" larger in diameter than the original, and wouldn't fit the mounting bracket, though it showed as a match. Moss Motors to the rescue, which came with a new bracket.