Kevin,
Is this something that just happened, or have you done something to the
engine lately?
Is the Mallory dist. a vacuum unit? Has the vacuum hose come off,
developed a leak? If it's straight mechanical, it's possible the springs
and weights may have become stuck in the advance position. Throw a light
on the timing marks to see how much advance you have a idle.
Have you checked the mixture at idle? Have you tried the piston-lifting
technique to check for mixture? Are you sure the pistons are moving
freely--back out the dampers to reduce oil resistance, lift and let
the pistons drop. They should fall freely and land with a click. Next
time you pull away from a stop, pull the choke out a little to richen
the mixture--does the condition get better? Worse? If there's no change
start looking for ignition problems.
Hope that helps.
Charlie B.
ps. Did you get the springs swapped out? New one's work OK?
>
> My '77 Spit (with '69 dual SU 1300 engine) has developed a bit of a low rpm
> misfire. It is only from idle to around 2200 rpm when it is fully warmed
> up. I only really notice it when moving off from rest, as all further
> shifts never drop the revs that low. I have noticed that giving the
> throttle a "blip" before moving off greatly reduces the occurance of the
> stumble. Other possibly useful information - the car has Crane electronic
> ignition, a Mallory coil, and the distributor cap looks nearly new (PO
> claimed recent tuneup). I am using 10w30 engine oil in the carb dampers.
> Any and all pointers greatly appreciated.
>
> Kevin Rhodes
> 77ish Spitfire
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