[Mgs] MGB Ignition Idle

[Richard Lindsay]

   Good advice Joel, and congratulations on your long ownership! Here are a
few more hopefully helpful ideas now surrounding your words. You wrote,

> I\we installed a Petronix's ignition...

   I did the same on both my TD and TR3b, and plan to do so on my TR6. The
issue with all of these cars was unstable slow idle timing. No electronic
trigger system alone would solve that problem.
   My original assumption was wear and therefore slop in the distributor
bushings, but that was not the case. The bushings were fine. The bits that
were worn out were the pivot holes and posts in the centrifugal advance
mechanisms. I observed the same problems in all three cars. There was
nothing for it but to replace the distributors. Okay, perhaps some of the
worn out bits could have been replaced if parts could have been sourced,
but since the holes AND posts were worn, I bought new.
   Like Joel I opted for Pertronix brand but purchased the whole
distributors. What an incredible improvement! I know owners often change to
electronic ignition trigger modules for reliability but I changed the
complete distributors for ignition timing stability. After upgrading, my
TR3b would idle smoothly at 500 rpm! (But I set it as per the manual.) The
TD would actually idle below 1500 rpm, which it wouldn't do before. :-P
   As I implied above, my next upgrade will be for the TR6, but that has to
wait until after paint. The coin chest is running way too low. Joel also
wrote,

>...and had Mr. Johnson rebuild the HIF4 carbs replacing the throttle
> body shafts.

   Yet another wise choice. Joel went on to say...

> To determine if your throttle shafts are leaking, start car and at
> operating temp, spray some carb cleaner around shafts.
> Any change in idle RPM'S indicate shafts are leaking air.

...and that is a good test. Now allow me to offer yet another tip.
   Should one determine that air is being sucked in between the shafts and
the bodies, here is a temporary BandAid fix while the owner saves up for a
proper repair. Saturate snug fitting felt washers with vacuum grease and
place them on the throttle shafts adjacent to the carb bodies. Use the
linkage to hold them snugly against the bodies, or add a washer or two, as
required.
   Vacuum grease is the stuff used in chemistry labs to seal glassware
fittings. It is designed specifically to not migrate into the experiment,
even under moderate heat. The same characteristic will keep it in place
while sealing air from leaking into the gap between the worn throttle
shafts and bores. Yes, it's a BandAid fix, not a proper repair, but it does
do two valid things: It validates the problem identification, and it buys
the owner time to save up for a proper repair.

   Thank you again Joel for reminding me to check my TR6's timing stability
and throttle shafts for vacuum leaks!

Rick
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