I am back on the TR6 after some home remodeling and other family issues
and am continuing to be plagued by this infernal backfiring. Here's what
I have done (and redone) to date, not necessarily in this order:
* removed the carbs and cleaned the bowls and set the float height.
* installed new bypass diaphragms
* adjusted the throttle linkage per Bentley's (had to scrounge
around to find a 3/32" drill bit, don't know why it wasn't lying
right at hand)
* balanced the carbs by listening with a hose (I don't have a UniSync)
* Lifting the slide in the carbs results in an RPM decrease then
return to idle
* set the static timing at 12BTDC and with the vacuum retard
connected timing goes to 4ATDC.
* Disconnected the vacuum retard.
* Removed, disassembled, cleaned, reassembled, and reinstalled the
distributor.
* Checked the vacuum retard with a vacuum pump...it works.
* examined the valve activity while observing the distributor rotor
position. Valve and rotor position seem to be synchronized.
* Set/reset valve lash during this exercise. I also made sure that
pistons were at TDC by inserting a small screw driver into the
spark plug hole while rotating the crank.
* Another compression check (140/140/140/130/135/135)
Today I was so frustrated with this that I stripped and repainted the
valve cover! Actually, I simply wanted to clean it up a bit and sprayed
it with carburetor cleaner, being out of degreaser, and it took the
paint right off the valve cover. I'll have to remember that!
I was ready to ship the carbs to Wishbone Classics for rebuild but
decided to wait in case the carbs aren't the issue. The box is still
ready to be packed and shipped though.
I suspect there may be a vacuum leak since the idle settles in at 1100
to 1300RPM although I am at a loss as to where a leak might be. The carb
diaphragms are intact, supple, and correctly positioned and I installed
new bypass diaphragms. All the carb to manifold bolts are tight, the two
vacuum ports, 1 under the front carb and 1 on top of the rear carb are
capped with plastic nipples. The vacuum servo for the brakes was rebuilt
last year and seems to be fine and, most importantly, the car does stop
when commanded to do so.
Is 12 degrees too much initial advance? At the 1100-1300RPM idle the
timing appears to have advanced to about 24-26 degrees which I assume is
the effect of the centrifugal advance. Does that sound reasonable?
I can sit here and list all the things I have done but obviously there
is something I have not done! Any suggestions as to what I may have missed?
As always, the assistance of 6-pack members is greatly appreciated!
|