Hi Bob,
This may sound perplexing, but the solution is probably less
complicated than it appears. First off, are you certain that TDC is at
the top of the compression stroke? There is a TDC on the top of the
exhaust stroke too, so if the spark fires then you get a backfire when
the exhausted but unburned mix lights off in the manifold.
Once you are sure that TDC is on compression, then note the position of
the distributor rotor. It could be that the original position of the
wires was correct, but that they were shifted because of confusion with
the TDC. Many distributors have a small notch against which the rotor
can align for cylinder #1 at TDC. Many don't, but it's handy if you are
starting from zero.
A timing light will help you to check your work, since it will flash
when the spark occurs. With the light connected to wire for cylinder #1,
crank the engine and see if the flash occurs about the time the pulley
notch aligns with the pointer. Once the engine is running, set the timing
again with the light. Most owners opine that the factory setting is too
retarded and that you can advance 10 degrees or more to advantage.
Good luck with this.
On Mon, 23 Jun 97 23:32:21 EDT RDWILLI@VM.SC.EDU writes:
>Replaced the points, (gapped @ .015), condensor, cap, rotor, etc.
>upon
>trying to crank, all i got was a hellacious backfire. set the front
>piston to TDC with the crank pulley, pulled the distributor to check
>for
>any strange damage, and upon finding none, put it back in. problem:
>had to re-route the wires to the cap in order for rotor placement to
>be
>at the first cylinder. one is now where four was, three where two,
>four
>where one, and two where three. does the drive dog only go in one
>way,
>or should i be able to turn the rotor 180deg. to put "one" back where
>it
>originally was?
>
>the car runs now, with no backfire, but it seems quite odd to me that
>a
>tune-up would cause a 180deg. shift in the firing order as it was
>prior to the tune-up. any help would be greatly appreciated. i have
>yet to try to set the timing, as i'm not sure of what i should do
>concerning the rest. please pardon if this is a stupid question, but
>this 73 B is my first experience with anything other than electronic
>ignition. BTW, the car sat for 2-3 years prior to my purchase of it,
>and ran surprisingly well before my attempted tune up. its running
>again
>after my attempted tune-up, just in a slightly different order...
>suggestions?...i'd really like to set the timing in the next couple of
>days, but would like any opinions/suggestions/etc. prior to doing so.
>
>thanks in advance,
>robert williford
>'73 mgb
>
|