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MG MGB Technical - Vacuum advance

Hello,

I rebuild my engine(after a conrod bearing failure) and now adjusting ignition, carbs ect. I checked and adjusted the timing dynamicly with a strobe light.(10deg @ 1500 rpm)
Checked the Haynes manual and found out that an 18V890 engine should have a 41695 distributor. When i checked the distributor which was renewed by the previous owner not so long ago, i found a 41610 model.

Before the rebuild the engine ran well. Now it feels like it has not all the grunt when accelerating. When i drive 100km/hr, it runs well and i also checked the plugs and these are brown so this looks good.
I checked the vacuum advance and the difference with and without is approx 25deg. The Haynes manual says it only differes a few degrees.

My questions are: does the "wrong" distributor have a lot of influence and what about the vacuum advance, is it normal?
Thanks in advance

Best regards
Peter
Peter

Peter,

One approach that I highly recommend is to obtain or borrow an adjustable timing light and a reliable reference tach. With these two tools you can check what advance you are getting at the various engine speeds provided by the manual. Fundametally, this is what you are interested in, and will provide the best performance regardless of what number is stamped on the side of the distributor. Lots of good stuff in the archives. This is approach I have taken and car has never run better.

Cliff
Cliff Maddox

Cliff,

Thanks for your reaction. I do have a reliable reference tach but what is the difference between a normal strobe light and an adjustable timing light?
You are right, i am looking for the advanve at various engine speeds. I will have a look at Paul Hunts side. This is very extensive and he may have something on distributor curves.
Regards
Peter
Peter

The dialed timing light is an amazing tool. No matter what the rpm, you point it at the lines and then turn the dial until they line up. Then you simply read the dial for the correct timing at that speed. Or, you can set the dial for a certain advance and then turn the distributor until they line up.

I helps to find tdc and with a little white or yellow paint, enhance the lines or better yet, make new ones in a spot that can be easilly seen from the right side of the engine bay.
Fred H

Peter,

Paul Hunt's site has all the info you need and is what prompted me to get an adjustable light for tuning. The non-adjustable lights are next to useless, but the adjustable models are invaluable. Lets you verify advance at all engine speeds as per the manual.

Cliff
Cliff Maddox

Fred, Cliff,

Thanks for your reaction. I will buy one and currently there is another thread with this subject. Earlier this week i had a look at the gunson's web-site to look at their exhaust analysers and carburateur synchon adjusters.
Any of you have experience with those? Now i roughly set it up, then go for a run and look at the state of the spark plug, then re-adjust it again, go for another run and re-check untill i am satisfied.
With my 2 cilinder motorbikes, i can synchronise these well with listening to it but with the 4 cilinder it is difficult and i also have an 8-cilinder B which is even more difficult.

Thanks
Regards
Peter
Peter

Peter,

The distributor you have,45D 41610, is the generic replacement that was (is?) sold by Lucas. The advance curve on this is very mild. When I replaced my distributor with a 41610 I had to set the strobe advance to at least 20 degrees BTDC at 1000rpm (with vacuum disconnected) for it to run even halfway decent. I finally got new springs and recurved it.

Cheers, Doug
Doug Keene

Doug,

Thanks for your reaction. I gave it a little more advance and now its running much better. I also synchronised the carbs better and modified the non-original air filters which let some air in not coming threw the filters.
Regards
Peter
Peter

This thread was discussed between 26/09/2003 and 29/09/2003

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