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Dirty Dist cap at rotor and advance question

Posted by jonathan.lipkin

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Dirty Dist cap at rotor and advance question #1
jonathan.lipkin jonathan lipkin ., Long Island, USA 1972 MG MGB 2012 Volkswagen Passat	Posted: July 04, 2012 12:02PM Registered: 2 years ago Posts: 448

Starting to tune my B after working on the suspension. Car runs roughly at idle, and since most carb problems are in the distributor, thought I'd have a look. First thing I noticed was that the vacuum advance ran from the inlet manifold, not the carbs as I thought it should. Second thing is that when I disconnect the advance tube and suck on it, the distributor doesn't advance, so I'm going to try to clean the top plate. Finally, I noticed that the cap is dirty at the contact for the rotor. Points, plugs, cap, rotor and condenser are new, as are the HT wires. Do I need a new coil?

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Re: Dirty Dist cap at rotor and advance question #2
rdmgb77 Robert Davidson Grand Rapids, Michigan, USA 1977 MG MGB	Posted: July 04, 2012 12:08PM Registered: 7 years ago Posts: 892

Unless the coil is failing, resulting in difficult starting, hesitation in running, all manifested in a tach that will fluctuate, the coil should be ok. They either work or they don't syndrom. They tend to fail quickly leaving you stuck on the road. As far as the dirt that sounds like some arcing could be occuring causing some carbon buildup. You may have a ruptured diaphram in the vacum advance.

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Re: Dirty Dist cap at rotor and advance question #3
RKM Richard Marcks Palm Desert, CA, USA 1973 MG MGB	Posted: July 04, 2012 12:08PM Registered: 4 years ago Posts: 760

Manifold vacuum should be correct for 1972.

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Re: Dirty Dist cap at rotor and advance question #4
jonathan.lipkin jonathan lipkin ., Long Island, USA 1972 MG MGB 2012 Volkswagen Passat	Posted: July 04, 2012 12:11PM Registered: 2 years ago Posts: 448

Thanks for the quick responses

In reply to # 2110930 by RKM Manifold vacuum should be correct for 1972.

There are ports on each carb that are blocked off with a bit of hose, just behind the butterfly shaft. There is also a metal tube coming off the side cover of the engine block. Should these be connected to create a negative pressure in the crank case?

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Re: Dirty Dist cap at rotor and advance question #5
rdmgb77 Robert Davidson Grand Rapids, Michigan, USA 1977 MG MGB	Posted: July 04, 2012 12:15PM Registered: 7 years ago Posts: 892

I think if the very early B's the crankcase just vented straight out to the atmosphere. In the later years the vent went to the carbs. I am not totally certain in your case, but I do think there should be a coupling of vent lines to go to the side cover vent tube. Others with a car of that vintage will chime in for sure. Do you have a picture of the carb setup. I assume they are HS-4's.

Edited 1 time(s). Last edit at 07/04/2012 12:16PM by rdmgb77.

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Re: Dirty Dist cap at rotor and advance question #6
mac townsend Fairfield, CA, USA	Posted: July 04, 2012 01:45PM Registered: 7 years ago Posts: 18,132

If sucking on the hose doesn't move the breaker plate, the vacuum diaphragm is likely "perished". Removing the plates, cleaning, and lubing can't hurt (and there is a chance the restriction is gunk in the bushing).

72 should have HIF carbs without a vacuum port. If the distributor has not been replaced with an earlier one, then manifold vacuum is what that distributor expects. (when vacuum signal and advance unit are mis-matched it results in some very interesting problems.<G> winking smiley

. Now it is possible for someone to retrofit a later distributor with an earlier vac advance which throws a wrench in the earlier statement.

Black stuff around the carbon brush inside the cap could simply be wear on the brush. Cleaning it out with brake cleaner should do the trick.

BTW, Jeff has some killer distributor caps...a new item...with BRASS contacts instead of aluminum. Combined with his extremely high quality rotors, his selected points, and other components you are looking at the worlds best MGB tune up kit.

1973 Roadster. A nice 50-footer!
SUs, Datsun 5-speed
MGB Tips and Tricks: www.mgrescue.com

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Re: Dirty Dist cap at rotor and advance question #7
jonathan.lipkin jonathan lipkin ., Long Island, USA 1972 MG MGB 2012 Volkswagen Passat	Posted: July 04, 2012 05:08PM Registered: 2 years ago Posts: 448

Yes, HS4s. I'll post a setup photo tomorrow.

Thanks

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Re: Dirty Dist cap at rotor and advance question #8
B-racer Jeff Schlemmer Minnesota, USA 1958 MG magnette 1971 MG MGB "POS" 1973 MG Midget MkII 2006 Dodge Charger "Daytona" 2008 Ford Super Duty	Posted: July 05, 2012 08:08AM Registered: 6 years ago Posts: 12,514

A '72 should have HIFs with float bowls at the bottom of the carbs instead of the outsides. Either way, in 1971 the ported vacuum line was eliminated. It IS common for your vacuum advance to tear the diaphragm. If its not working, disconnect and plug the line!!!

jeff@advanceddistributors.com

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Re: Dirty Dist cap at rotor and advance question #9
jonathan.lipkin jonathan lipkin ., Long Island, USA 1972 MG MGB 2012 Volkswagen Passat	Posted: July 05, 2012 08:59AM Registered: 2 years ago Posts: 448

Most definitely HS4s. ID plate missing from the engine block, so can't identify it. Looks like #2 is not firing, and has gas smell. Going to re-check points and spark to that cylinder when it gets back from front end alingment. I'd guess because gas is getting into the cylinder that it's not valve lash?

Another - is the ground wire in the dist special in some way? Mine was pretty corroded, so I bent back the pins on the plate and connector and replaced the wire. Moss lists a new wire for sale, so I was wondering if there was something special about it.

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Re: Dirty Dist cap at rotor and advance question #10
B-racer Jeff Schlemmer Minnesota, USA 1958 MG magnette 1971 MG MGB "POS" 1973 MG Midget MkII 2006 Dodge Charger "Daytona" 2008 Ford Super Duty	Posted: July 05, 2012 03:07PM Registered: 6 years ago Posts: 12,514

Just because gas gets into the cylinder doesn't mean its getting in at the right time, or getting out... Valve adjustment is the first step of a proper tune-up.

The ground wire just needs to be extremely flexible and pliable so it doesn't break when flexing constantly.

jeff@advanceddistributors.com

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