6-packers:
I am soliciting hints on my rough idle/back fire problem. Here is some
background.
Setup:
1974 TR6, all emissions systems in place.
Original ZS carbs, manifold, etc.
New plugs, plug wires, freshly set valve lash to factory spec.
Compression 120+ in all cylinders, except #6, which is 80.
Timing set 12 BTDC with retard disconnected.
Fresh air filters (K&N)
Anti-runon valve in place.
Idle trim screws open 1-1/2 turns
Temperature compensators freshly overhauled.
5W-30 oil in dashpots.
Fresh thermostat, coolant, temperature sender.
Symptoms:
Long cranking times, although car does start reliably.
Will not idle without some choke applied, even when fully warm. Always
has rough idle.
When warm, will idle down to about 1000 RPM, any lower and it stalls.
Will backfire when pulling away from a stop, usually accompanied by a
puff of back smoke.
Lifting the carb slides 1/8" when warm will cause engine to stumble and
stall.
Forcing carb slides home when idling will cause idle speed to increase
and smooth out.
Unable to adjust needles per Bentley or Buckeye Triumph notes to obtain
correct mixture. Always acts 'lean'.
Disconnecting small vent hose from carbon canister to carb gives no
change.
Disconnecting large hose from carbon canister/Valve cover to carbs
gives slight increase in idle speed.
When warm, temp gauge reads < 1/2
No fuel leaks, drips of any sort.
Work so far:
Verified that vacuum retard is working (no retard when cold, +500 RPMs
if disconnected when hot)
Verified that carb diaphragms are free from rips, holes, etc.
Overhauled temp compensators.
Verified cold start cam setup (adjustment screw does not touch cam when
choke is home, rides on
cam when choke is pulled out).
Verified anti-runon valve is off when engine is warm, wiring to oil
switch is correct.
Have not touched bypass valves. Don't know what the DPO did with them.
According to Bentley, if
they were misadjusted, idle speed should increase 1000-1500 RPMs
with vacuum retard disconnected.
This does not happen, so I am assuming they are at least close to
correct.
Endlessly adjusted needle height, to no avail.
Things I have not done:
Checked float levels
Adjusted bypass valves
Other?
If anyone can give me a "been there, done that" kind of hint, I would
appreciate it. Thanks for your help!
Befuddled,
Vance
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