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MG MGB Technical - Idle gremlin

67 BGT with original engine. Runs nice, typically idles just around 950 smoothly. For some reason, it will all of a sudden idle at around 500 and will stall out if I don't blip the throttle. This will happen about once a week. Car is warm when it happens. Will do this for 10 or so minutes and then go back to normal idle.

No air/vacuum leaks around the carb. All hose connections are tight. Fittings are snug. Butterflies are tight and there is not foreign material that is holding them open.
Bruce Cunha

Bruce,

Carburetors are mechanical devices and given your statements I don't believe it is fuel related, unless your heat sheild is poor. I would be looking at the distributor, rotor, coil, anything that could shift under heat.

warmly,
dave
Dave Braun

Is it one cylinder stopping (listen at the axhaust)? If so could be ignition. Other than that could be vacuum leak coming and going. Unless you do your tests when the problem is happening you won't find anything wrong. Debris holding a butterfly open would cause a *high* idle.
PaulH Solihull

Dave and Paul

Appreciate the feedback.

As it happened again today, I was thinking if it could be something getting hot and expanding to make a leak. I will do some additional checking next time and see if cylinders are all firing. Does not appear to affect the running of the car, so a bit odd for a miss in a cylinder.

Hey Dave. What do you charge for a carb adjustment for the B? A nice drive to your area might be just what I need. I would love someone to go over my carbs and timing to assure I have this running as well as it can.

You did magic on the TD.
Bruce Cunha

Check the operation of your PCV valve. If it is in need of service, it can cause some unusual problems. RAY
rjm RAY

Your issue reminds me a heating pipe bracket screw onto inlet manifold that was just slightly unscrewed but with a rubber gasket below it, made me mad to fix it out.
Guy RENOU

I will check the PVC tonight Ray. That is one I had not thought about but your post brought back memories of similar issues I had with that in my old 68. (of course that had all the pollution control, not just the PVC.)
Bruce Cunha

Bruce, Let's hope that it is something as simple as that. RAY
rjm RAY

Bruce,

I charge by the hour ($30). I think the last set I only had to adjust was 1.5 hours with the 'victim' doing most of the work ;), they were HIF.

Tune up should include setting valves, checking compression, setting timing, checking dwell. If it has been a while since new wires were installed, those break down with regularity. Put an ohm meter on them and look for similar readings. Then moving onto fuel; check float level, mixture, carb balance, idle RPM, advance at 3500 rpm, and then recheck dwell. That would take about 3 hours.

I'll buy the steaks and the beer! The garage is open 'cause the B is at Mikes where it is much more convenient to do the body work. We fabricated and installed a lower front quarter today, so we are close.

warmly,
dave
Dave Braun

Dave

Send me your home e-mail (new computer and all my e-mail addresses, went by by. That sounds like a good deal to have someone walk me through setting the B up. I think things are close, but I always wonder if I have it set as well as it really can be.

Bruce Cunha

This thread was discussed between 06/06/2011 and 09/06/2011

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