Presuming your engine is in good shape internally and it has a good
hot spark there are three things that can keep it from revving up
better. One is restricted breathing. Another is not enough fuel
getting in for higher revs. Another is that it may not have enough
spark advance to rev on up.
The spark advance question is something you can find out about easily.
Let's concentrate on the advance in the dizzy first.
Don't worry about where exactly the timing is set. Just scribe a
pair of matching lines on the distributor body and the clamp (or on the
clamp and the block if you want to move the whole thing) so that you can
put it back where it was after you're done experimenting. Twist the
dizzy a few degrees against the normal direction of rotation (advance
the spark a bit) and go drive it. If it revs a bit more than before,
twist it a bit more and try it again. If it keeps improving, keep
twisting. You're sure to reach a point where it either doesn't improve
or it starts kicking back on the starter. So you twist it back the
other way (retard it a bit) until it doesn't kick back. That's as much
as you can advance it manually. Scribe another line for future
If advancing of the spark didn't make a difference to the engine's
revving ability then the problem lies elsewhere. If it did, then
there's not enough mechanical advance in the dizzy, especially if it's
pinking after you advanced it. The vac unit is supposed to retard the
spark when the manifold vacuum rises towards atmospheric pressure, such
as when the throttle is suddenly opened wide at low engine speeds. So
if it's pinking, there needs to be enough more mechanical advance in the
dizzy that the intial timing can be set back to, say, 10 degrees and the
engine can still rev up freely. This of course assumes that you have
the vac unit hooked to the correct vacuum source for the diaphragm on
the dizzy and it's working right. If there's any question, you can
disconnect the vacuum line, plug it and try this exercise again to see
how the vac unit effects performance.
Presuming you have the dizzy that came with the engine you could try
to find an earlier one that was intended for the twin SU carburetion and
I didn't cover all aspects of this but you should get the idea.
There are other considerations that we're gonna hear about, I bet'cha. (BG)
> Thanks for the responses thus far, it would appear that I really should look
> at the distributor setup before I delve into cam shaft swaps. Which suits me
> It was pointed out to me that the distributor dashpot for a 1980 MGB should
> be connected to MANIFOLD vacuum, as opposed to PORTED (carburetor?) vacuum.
> I originally had it set up that way, but after some problems last year
> wherein I could not eliminate the pinking problem I was having, switched it
> to PORTED vacuum. This made a huge improvement in the pinking problem, but
> now I wonder if perhaps I've just managed to mask the problem or make it
> worse? I was also asked what the timing was set at, but frankly, I'm not
> exactly sure since I think the timing mark is off by more than a little
> Anyway, I'd rather muck around with the distributor before I tear apart my
> engine. I have the stock ignition, although I've had to replace the module
> in the ignition amplifier. I guess it's time to do some more reading...