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MG MGB Technical - MGB virgin

Hello all just bought a 78 GT and getting to grips with these wonderful little cars. Picked it up in Liverpool onWednesday and drove down through Wales to get the ferry in Holyhead (I live on the west coast of Ireland). Everything was going great until Colwyn Bay when it developed a backfire through the exhaust. Stopped for lunch and when I restarted it was fine for a while but every 10 miles or so would start to lose power and backfire. Kept it going until15 miles or so from Holyhead when it gave up and I ground to a halt on the A55. I had no tools so was completely b*********ed but after about 20 minutes managed to get is started again. Limped into Holyhead and bought a screwdriver in Lidl. Checked fuel to the carbs, no problem there, had a good spark on the leads so got on the ferry and crossed to Ireland. When I reached the other side the problem had apparently cured itself and I drove the 150 miles home without a misfire!! The car is now going OK, running a little lumpy and a bit hesitant at low revs but basically OK. Any ideas as to what I should look at. It has the old style points fitted. Delighted with car otherwise, very clean example and retro fitted with chrome bumpers.
Hmm McMahon

I would suspect a fuel problem such as dirt in the pump filter or even the pump itself.Some mgb's needed a fuel cap that was ventilated. try running with a loosened cap or when it does it again go to the cap and loosen it. If you hear a woosh it means you are in need of a vented cap.
Then if that fails I would look for a replacement condensor.some of the new ones are no better than an old one. I always keep ,an old one that worked as a spare.
Sandy
ss sanders

I always recommend the same for new owners and that's buy and read the Driver's Handbook, do a staggered 36k-mile service (of the whole car) whilst regularly driving the car on reasonable length journeys, the full and proper service of the whole car will find and help to prevent problems as will regular use throughout the year, there are many dry, sunny, salt-free opportunities throughout late autumn and winter (if you have to use salt over there on the roads(?))

note; this is not a Haynes type manual see below (Ref: 0053) - http://www.mgocshop.co.uk/catalog/Online_Catalogue_Handbooks_5.html

as you *might* have already discovered new made parts are not always the same as the originals and some are p*ss poorly made such as some ignition, electrical and many parts with rubber in (any new parts fitted?)

for ignition parts go to the Distribution Doctor - http://www.distributordoctor.com/

Ashley Hinton for various parts - http://stores.ebay.co.uk/ashleyhintonmgparts2002/

for servicing set up of the engine then check/adjust - tappets/CB points/plugs/timing/carb mixture - in that order

if you have to adjust any item in that chain then you’ll also need to check/adjust all the items that follow it in the chain

there are loads of excellent John Twist videos to help you - http://www.youtube.com/user/Universitymotorsltd#g/u

plus an excellent site for MGBs is regular poster Paul Hunt’s –
(Spanners) http://www.mgb-stuff.org.uk/hammertext.htm

doing things as they crop up doesn't prevent further issues and means the whole car might not be running as well as it could or should do


Nigel Atkins

Thanks for the advice. Will certainly get a copy of the manual and start to go through the car step by step. Was thinking of changing to electronic ignition. Do you think this is a good idea?
Hmm McMahon

A very practical upgrade - the only downside being there are too many to choose from! Graham
Graham Moore

Hmm, (?)
the 36k-mile service/check up listed in the relevant Driver's Handbook will cover just about most items or if you can you can get this book at a sensible price, sometimes on ebay for around £10, (might have a few typos in specifications) – MGB Step by Step Service Guide (Porter Manuals) –
http://www.amazon.co.uk/MGB-Step-step-Service-Guide/dp/189923800X

I think electronic ignition is a great idea but bear in mind if you put an igniter unit into the top of the dissy it still leaves the rest of the dissy probably well worn, I've read that the dissys were out of tune within a few years of the cars leaving the factory so you can imagine they wouldn't get better with decades of use so I'm a big fan of a 123 fully electronic dissy

the units that fit in the head of the dissy have delicate leads and have to be installed carefully or the wires will get scuffed or chaffed inside or outside the dissy cap and cause problems, most blame the unit rather than the poor installation of the unit

there are some inexpensive units that some have found to be faulty from new

but I'd never suggest spending money on upgrades or improvements (unless a part or components has to be replaced anyway) until at least 12 months of regular use on reasonable length journeys all year round, otherwise you might need that money for unexpected distress purchases or spend

I sometimes offer some of my non-technical, non-mechanical notes for those new to classics, which most who get them ignore, I know this by the posts they put up later with problems which should have been avoided, if you want a set just email me
Nigel Atkins

Hi Nigel, did wonder about just replacing the igniter and came to the conclusion that for an extra few quid I would replace the whole dissy. Over next few weeks will hopefully get to grips with MG mechanics. Took it for a run this evening & on the m'way and ran very well at speeds up to 70/80. Bit spluttery at low speeds round town & when cold but maybe this is normal?
Hmm McMahon

Hmm,
er, a fully electronic dissy like a 123 is more than an extra few quid to an igniter head

do bear in mind a cheap part or component that is faulty from the start or soon goes faulty or never fully works correctly is an expensive part or component as it's robbing you of performance, reliability and fun with your car and you'll have to pay a second time to replace it

if you think about buying one of these kits with fully electronic dissy, plugs and HT lead set then think at the price something must give - I know at least one BGT owner that said the HT leads were poor

for HT lead set you can fit and forget got to a British manufacturer that only sell by phone order via there web site because they don't want to upset their customer who they make leads for for them to put their names on 'performanceleads' not cheap but not very expensive but good value - http://www.performanceleads.co.uk/

and no of course it's not normal that it seems ok at higher speeds but is spluttery at town speeds or when cold

but

you are making the newbie mistake wanting to fiddling with the carbs when there are much more important system to check on the car first

if you must fiddle about then see my previous post for the order you should do it in

have you check the fuel supply to the carbs, is the engine bay fuel filter dirty, is there dirt in the fuel bowls, floats operate correctly, needles and seats clear and operating correctly, is there oil in the carb dashpots

what new parts have been fitted in the last year say, have the carbs been fiddled with by the previous owner

I offer some non-technical, non-mechanical notes that give pointers to general care of the car, not repairs but prevention, if you want a copy of the set just email me, almost no one follows them, I know as they put up threads with problems that prevention would have, er, prevented

nigel atkins (one word, lower case) at bt internet (one word, lower case) dot com
Nigel Atkins

Throw some Isopropyl alcohol in the tank sounds like you got water in your fuel. Commonly known as dry gas here. Cant hurt...my car runs as you describe when moisture gets in the tank!

Goodluck! :-)
Steven Devine

Check that the carburettor butterflies have been replaced with earlier flat ones - this is unlikely to be your problem but won't help.

A '78 came with spring valves in the butterflies that do nothing for tick over or gas flow into the carbs. HS4 butterflies are the ones you want and fit your HIF4 carbs. This is the cheapest improvement you can make to a UK spec later MGB.
John Prewer

Hmm? not sure what that's short for. Anyway, welcome to the weird world of MG. Where abouts are you? I'm in Limerick 0866061228. Mine is a Mk1 1966, so quite different in detail, yet very much the same.
I have had most of the problems over 7 years, so feel free to call.
I also drove from the UK but from the Norfolk Coast to Liverpool, then over to Dublin, then down to Limerick. My only problem was binding rear Brakes.
I think it's a fuel problem you have. Did you fill up in UK or was there fuel in her? She may have been sitting unused with a low tank & got Condensation over time? Old Fuel also goes off. Fill up with Shell V Power wher ever you can get it. If she ran better later, had you fillrd up? If you still have an original head, you may need an unleaded additive.
Millers do a good one, or Castrol Valvemester + is also one of the best.
Enjoy.
B.
B. G. Griffin

First thing to do in a case like this is look at the tach. If that's leaping up and down it's an ignition LT problem, and that will cause backfiring, whereas intermittent fuel starvation won't. A bad condenser won't affect the tach but will also cause backfiring. However they usually either work or they don't.

Whilst a 123 is 10 times the price of an electronic trigger there are vendors of the latter that supply is as part of replacement conventional distributor - more than just the trigger of course but still a lot less than the 123.
Paul Hunt

This thread was discussed between 22/06/2014 and 25/06/2014

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