If the tach instantly drops then it is definitely the ignition LT circuit
i.e. ignition - coil - points/capacitor. If the ignition warning lamp came
on then it is 12v going off the white or brown./white circuit for some
reason i.e. ignition switch or ignition relay. If the ignition warning
light stayed off (and it normally works!) then it is the 12v feed to the
coil, the coil itself, points, or capacitor. The coil can go open circuit
as it warms up, then 'heal itself as it cools again. The capacitor could be
short. The wiring inside the distributor could have frayed and be
grounding. Check that you have 12v both sides of the coil with the points
open, and ground one side and 12v (or 6v if it is a ballasted system) the
other when they are closed.
PaulH.
http://freespace.virgin.net/paul.hunt1/
or if that doesn't work try
http://194.168.54.52/paul.hunt1
-----Original Message-----
From: James Nazarian Jr <James.Nazarian@Colorado.EDU>
To: Skye Poier <skye@ffwd.com>
Cc: James Nazarian Jr <James.Nazarian@Colorado.EDU>; MG Nuts
<mgs@autox.team.net>
Date: 10 August 1999 18:55
Subject: Re: MGB Ignition
>The fuel pump is good, I just rebuild it a few months ago. The problem is
>a sporadic ignition problem. 99% of the time the car runs great but
>occasionally the ignition will loose spark literally for a second or two
>and then it will instantly return. When driving you can feel engine die,
>tach drops and car is slowed by non firing engine that is still in gear.
>Then everything returns to normal just as quickly. If you weren't paying
>a lot of attention most of the time the problem is so brief that it feels
>like a backfire through the carbs.
>
>James Nazarian
>'71 B roadster
>'74 BGT bastardization with big alluminum heart :)
>
>On Tue, 10 Aug 1999, Skye Poier wrote:
>
>> I assume it turns over but doesn't start. You didn't mention. Does it
>> seem to "try" to catch and then fail?
>>
>> I read somewhere "90% of electrical problems with the ignition, aren't".
>> Very true. Try this just in case:
>>
>> Disconnect the HT lead from the coil at the cap end and lay it near
>> a ground. Remove the cap. roll the car in 4th so that the points
>> are closed. Turn on the ignition and use a screwdriver to open the
>> points. You should get a healthy spark from the end of the HT lead.
>> Turn off ignition, reconnect HT lead and cap. Remove one or more
>> spark plug leads at the spark plug and lay them on the block. Have
>> someone turn over the car and look for sparks.
>>
>> .. or my hunch ..
>>
>> It sounds more like a fuel delivery problem.
>>
>> Take an bottle, pull off the fuel line just before the carbs and stick
>> it in the bottle. Turn on the ignition. If you don't get gas: hooray,
>> you have a bad fuel pump.
>>
>> Skye
>>
>> --
>> 1966 MGB The MGB Experience __,__\__ Safety Fast!
>> GHN3L-70307 http://www.mgb.bc.ca/ (_o____o_) MGOFR 1.375
>>
>
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