You shouldn't have to regularly go through the full set-up, once done
properly and not fiddled about with afterwards I find both ignition and
carbs keep their tune very well, sudden faults not withstanding. However
sudden and wide ambient temperature variations can necessitate small
adjustments of mixture, but this should only be noticeable as a slight
change in idle rpms, nothing more drastic than that. If you have checked
the points dwell as well then you have probably eliminated any ignition
problem, which is thing to do first before tackling the carbs. However if
the tach flickers with the backfiring it *is* an ignition LT problem. Also
clip a timing light onto each plug lead and make sure the flashes remain
regular during the misfiring. If the car runs OK when warmed up I would
check the choke mechanism - a little difficult on HIFs as the actual
enrichment occurs internally unlike the HSs.
Personally I don't see how you can use the Colortune on a twin-carb MGB as
you either need two or have to keep swapping one between cylinders 1 and 4
(or 2 and 3). This is because the carbs are inter-dependant (i.e. dependant
on each other) and a change to one will usually require a small compensating
change to the other, and vice-versa.
----- Original Message -----
From: "Marc Siegel" <smarc@abs.net>
To: <mgs@autox.team.net>
Sent: Tuesday, June 24, 2003 3:34 PM
Subject: How to diagnose poor running?
> I'm in need of some advice (how unusual...) to diagnose a problem I'm
> having. My '80 MGB with the dual HIF setup I installed had been running
> great. Over the last two weeks, it's gotten difficult to start when cold,
> and runs rough, spitting and backfiring until it warms up really
throughly.
> Then it runs mostly ok.
>
> I checked plugs, cleaned & regapped, swapped out cap and rotor with new.
> After work today, I'll recheck the timing as well.
>
> I was thinking I should just go through the whole set-up procedure again.
Is
> that a normal occurance to have to do that?
>
> Also, I'm considering the purchase of a Gunson Colortune. Are these
useful,
> especially for a novice?
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