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MG MGB Technical - Stalling Occurrences

1977 MGB, Weber 32/36 DGV, 25D points distributor rebuilt by Advanced five years ago, sports coil. The car has run for several years without issue.

An otherwise perfect ride was interrupted by two stalling occurrences. One occurred while waiting to leave a gas station after filling up with half a tank. The second was five miles later when letting off the gas at a stop sign. Neither felt like gas starvation because there was no moment of poor running... the engine just stopped. In both cases the engine immediately restarted.

After beating it home by the shortest route, in this case an interstate at 65mph for 10 miles, I have not been able to replicate the situation. The engine starts, idles as normal, and returns to normal idle after running at speed.

I hate the idea of waiting for it to happen again, but I also don't want to change out parts without being sure I'm addressing the issue. My suspects include the sports coil, the condenser and maybe a crummy tank of gas although I'm doubting it.

Another possibility is that I had a backfire through the Weber carb a couple weeks ago and a few instances of momentary hesitation when running at speed, so I turned the mixture screw in about half to 3/4 turn on the Weber. Maybe I leaned it too much and need to adjust from scratch.

Any ideas are most welcome before I give in to an urge to make changes in parts and adjustments. Thank you for your time.
Brian Denis

When I had that type of stalling, though on my Wolseley, it turned out to be a loose battery terminal.

The dynamo kept the car running , until I stopped and the revs weren't sufficient to generate power, so stall.

Herb
H J Adler

Ah, hadn't thought of that one Herb, I'll check that out in the AM. Thanks!

Pardon the pun, but I'm "leaning" to the Weber mixture adjustment being the culprit. I checked the current setting and it's less than a turn from bottoming out. Tomorrow I'll go through the setting sequence and hope that solves the problem. Could be the DCO (dumb current owner" has made a few adjustments over the last few years which cumulatively added up to cause this problem.
Brian Denis

Brian. My 79 has pretty much the same set up as yours. You say the Weber is a half turn from bottoming out. That is way lean. I had similar issues with mine last year.

Try the following:

Check the nuts that hold the intake and exhaust manifolds to the head. Mine had loosened up over time as well as the nuts that hold the Weber to the intake manifold. Major vacuum leak.

Check the color of the spark plugs. Mine were white. If they are white, you are running too lean. The plugs should be tan to brown in color.

So after resolving my vacuum issue by tightening the manifold and carburetor nuts, I reset the carburetor. The car starts up quickly from cold, smooth idle and pulls through the gears much better. The spark plugs are a light brown in color now.

Cheers

Gary
79 MGB
gary hansen

Brian,

I had a similar problem with my 77. Here is a link to the discussion. I didn't get a definitive fix, but it is a thread full of likely problems/solutions.

Charley
http://www2.mg-cars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=71&subjectar=71&thread=201507192051226143
CR Huff

I'd have said far too few occurrences to warrant doing anything at all at this stage, and possibly mucking something up in the process.
paulh4

Gentlemen, I appreciate the interest in my problem.

I went through the Weber setup process and now the mixture screw is set 1.25+/- from the bottom. After two cruises I haven't had a repeat of the issue.

Gary the mixture screw was set way too lean, and the plugs were white. Cumulative tweaks over time is my best guess on how this happened.

Charley, I remember your post when it was running and you had some of the most knowledgeable contributors participating. You're right, some great stuff in there. Hopefully your car is reliable at this point.

Paul, I wasn't comfortable doing nothing because it was a three day holiday weekend here and if I got stuck waiting for a flatbed it would take forever. Adjusting the Weber was low risk. I would have successfully fought the urge to change out parts based on scant information... but it wouldn't have been easy!
Brian Denis

This thread was discussed between 27/05/2016 and 31/05/2016

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