MGB MGB Ignition Timing

[Old and In the Way]

Can anyone tell me how much I should retard (or advance) my ignition timing to reduce run on after I turn off the switch? I have a '70 B/GT, European model, although I don't think it has a high compression engine. I have static timed to about 8 degrees BTDC, using 93 octane unleaded. Run on after shut down is too much. I picked up at Craftsman timing light with variable advance, but I'm not sure what I should dial in. Thanks for your help.

 

[PAUL161]

My 72 is set at +15 degrees, vac advance disconnected and hose plugged while setting. Hook up after. It runs great!

 

[eschneider]

8 degrees should be about textbook.

15 degrees is good for performance, and good to know you should be able to go that high.

If you are running twin SU's and still having issues after timing, check carb synchronization. If you're running a weber downdraft, your decel valve might be leaking.

just some thoughts.

 

[Old and In the Way]

Thanks for the suggestions. Carbs are synched, points are properly gapped, plugs are clean. Found a plug wire that had touched a metal cable and burned through the insulation. That could be a problem, but it isn't missing at lower RPM. The car has about 50,000 miles on the original distributor. Is that about time to replace, assuming it wasn't properly lubricated before? The 3500 mark makes me think that the vacuum advance isn't working. I pulled the advance to time it, plugged it and replaced it when I finished. Can't figure anything other than distributor wear (just had to be the most expensive item, didn't it).

 

[100DashSix]

You can test to see if the vacuum advance is working by sucking on the end of the line connecting to the unit--it should hold a vacuum. My distributor's vacuum and mechanical advance weren't working, and I had the whole unit rebuilt by Jeff at AdvancedDistributors.com (on the advice of people from this forum). It works and looks great now, and I didn't feel it was that expensive to have done.

The problem I had that prompted it, however, wasn't run on but misfire at speed. It's a 74 MGB with a downdraft weber, I'm running at 15 deg. BTDC.

 

[tdecell]

100-6, at what rpm's did you adjust your timing? I have a 74b with 32/36 Weber and have been playing around with timing to get rid of stumble on initial tip in.
Trey

 

[100DashSix]

Actually, tdecell, I set it at 15 degrees static timing, but the car still has a very noticeable stumble; I got a nice timing light, so I'm going to set the timing and will tell you what I used and if it solved the problem.

 

[Bugeye58]

[ QUOTE ]
You can test to see if the vacuum advance is working by sucking on the end of the line connecting to the unit--it should hold a vacuum.

[/ QUOTE ]

Perhaps more importantly, while sucking on the hose, make sure the advance plate is actually <u>moving</u> . Just because the diaphragm holds vacuum doesn't meen that the advance plate isn't frozen in place.
Jeff