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RE: Dist. replacement. - hesitation

Subject: RE: Dist. replacement. - hesitation
Date: Tue, 5 Feb 2002 13:35:59 -0500
Well guys,

I got so many replies, I'll have to sort them out.
Most votes went for the too lean mixture (whatever the cause).
As I do not have an electronic timing light, I'll have the vacuum advance
checked latest.

To answer Paul's question my engine is as standard as possible using normal
filters, however as the car has been defederalised from Californian
standards this is a special case. 
Paul triggered me to the needle topic. The '71 BGT still has its original
engine 18GK high pressure no OD.
After having it defederalised according to the Porter How to ... manual what
needle type should I use? I purchased new needles from the local MG spares
shop Octagon Spares - the guy is well knowledgable on MG's and has been the
Dutch MG Car Club Adviser on MGB, so at these days about 8 years ago I
trusted him. 
(don't know needle type now as they are inside the SU's) 
Please advise needle type. Carb is the original HS4's with spring loaded

A quick and dirty trick of course is to have the both SU's slightly adjusted
a bit richer, but I'd like to have the engine well tuned.

The tuning job btw did not include any replacements...

The backfiring is in the carbs. I once saw it and the family just was
looking to the car's first start and then the bang came - wow afterwards the
family had much more respect for the GT!!!!
When the backfire happens, I can feel it on my throttle pedal.
When backfiring happens, I saw no changes on the rev counter.

Vernier adjustment is the 2nd serious attempt, keeping in mind what the
original position was of course.

Next thursday I think the weather is o.k. to do some testing.

Looking forward to the needle advise.



'BGT coughing sometimes when cold

-----Original Message-----
From: David Littlefield []
Sent: Tuesday, February 05, 2002 6:31 PM
Subject: Re: Dist. replacement. - hesitation

CHECK YOUR IGNITION ROTOR.  You said you recently had a tuneup, which
like means the rotor was replaced.  I had a defective rotor that gave me
similar symptoms and I've since learned there is a large batch of them
out there.  The offending rotors are pear-shaped (no counterbalancing
"tail") and were made by Intermotor.  Some bear the Lucas name, as well.

An easy check is to put the old rotor back in and see if the problem goes

David Littlefield
'62 MGA MkII
'51 MGTD
'74 MG Midget vintage racer
'88 Jaguar XJ-S

On Tue, 5 Feb 2002 10:39:39 -0500 writes:
> Thanks Paul,
> Looks like the first - when the choke is pulled more and longer, 
> there is
> much more power, but then the engine roars heavily @ 1500+ RPM when 
> you wait
> for the first traffic light.
> The backfiring also occurs when the engine is running at "normal"
> temperatures and the outside temperatures are at freezing level or 
> lower.
> How should I correct this?
> Is the vacuum advance timing involved in this?
> How should I check the vacuum advance mechanism?
> Last saturday we had 15 deg. Celcius and great sunny weather, so 
> driving the
> GT was a pleasure. 
> The wedding of the Dutch crownprince Willem Alexander with his 
> Argetina wife
> Maxima was a great event also by this  most exeptional temperature.
> Never in a hundred years the 2nd of february was so warm.
> As lucas is my best friend, I'll check the ignition wiring anyway, 
> but I'm
> convinced the wiring is fine. The problem is to reproducable and 
> shows no
> irregular occurences, which is typical for electrical problems.
> Cheers,
> Hans
> -----Original Message-----
> From: []
> Sent: Tuesday, February 05, 2002 3:58 PM
> To:;
> Subject: Re: Dist. replacement. - hesitation
> Could be a couple of things, Hans.
> Could be weak on pick-up i.e. not enough damping hence enrichment 
> when the
> throttle is opened, easy to check by pulling out the choke when the
> hesitation is happening and seeing if you suddenly roar off into 
> the
> winter's gloom.
> Could also be a fractured wire inside the dizzie, being disturbed 
> when the
> points-plate twists under vacuum change.  Can be verified by 
> removing and
> plugging the vacuum line.
> A Scimitar GTE I had nearly gave me heart-failure several times by 
> cutting
> out or severe hesitation just as I pulled out of a side-road onto a 
> main
> road.  In that case the ground connection to the points plate was 
> simply by
> sliding contacts rather than a flexible wire, and these contacts 
> were known
> to get iffy over time.  The cuire was to install a flexible wire 
> inside the
> dizzy, and that completely cleared the problem.  The MGB has that 
> wire
> anyway, but it can fracture, as can the points wire.
> Cheers,
> PaulH.
> ----- Original Message -----
> From: <>
> To: <>; <>; 
> <>
> Sent: Tuesday, February 05, 2002 10:11 AM
> Subject: RE: Dist. replacement. - hesitation
> > This hesitation triggered me:
> > Since I have my BGT the engine shows some hesitation when the 
> accellerator
> > is pressed. This is felt best when this is done slowly when going 
> at a low
> > speed and low revs. It always occurs when going faster from a 
> stable
> speed.
> > Especially when the engine is cold it is at worst.
> > When hesitating then the engine sometimes backfires in the 
> carburattors.
> > When the engine comes to speed >2200 RPM the hesitation is over.
> > The engine is recently tuned by a knowledgable guy.
> >
> > For the rest the car drives well.
> >
> > Dear list what is your opinion?
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