Folks:
As you may recall, I asked for and received many helpful hints last
week as to the cause of my rough idle, and inability to adjust the mixture per
the Bentley manual. To recap:
Setup:
1974 TR6, all emissions systems in place, OE Stromberg carbs
120+ compression in all cylinders, except #6 which is 80
Stock ignition, dynamically set 10 BTDC
New plugs, wires.
Valve lash freshly set at 0.010"
Engine idles with temp slightly below midpoint on the temp
gauge.
Symptoms:
Rough, lopey idle.
Engine will not idle without at least some choke.
Cannot set mixture or idle speed per Bentley. Engine will
stumble and die.
Raising carb slides 1/8" cause a stumble.
Pushing carb slides home causes idle to smooth out and increase.
Adjusting idle speed or needle settings seemingly has little
effect.
What I have done:
Inspected carb diaphragms for holes.
Rebuilt bypass valves, and set for minimum sensitivity.
Cleaned, calibrated temp compensators.
Checked jet height (-0.080" from bridge)
Adjust carb floats, checked for sticky float valves, leaking
floats.
Adjusted carb bowl vent valve per Buckeye Triumph.
Tried retarding the timing by 4 degrees.
Checked each cylinder with timing light, looking for weak spark
or
spark scatter.
Set idle mixture trim screw 1.5 turns open.
Used my propane torch (unlit - =:-o) and checked extensively
for
vacuum leaks, none found.
Checked anti-run-on valve operation.
Decoked the EGR, verified correct operation.
Drained oil from dashpots to perform tuning (recommended on
Buckeye
web site).
Current status:
Suicidally depressed. Car still won't idle, carbs won't adjust.
Am beginning to spend lots of time polishing my assault rifle, and have named
it "Benny". Chronic nightmares, and have begun to pull the wings off of flies.
Have developed a tic.
Latest incoherent ramblings:
OK, here goes my latest desperate theory. Keying off the observation
that pressing the carb slides home smoothes the idle and increases the RPM, I
have been inclined to believe that this is the single most important
observation. Mainly because absolutely nothing else seems to modulate the
symptoms - doh!
My slides are approximately 1/16-1/8" from home when the car is warm
and idling at 1000 RPM (Choke on, but barely). Pushing the slide home on either
carb dramatically smoothes the idle. I also observed that if I hold the slide
home, and test the mixture by raising the slide from the home position, the
carb seems to respond to mixture changes per the Bentley manual. If I raise the
slide starting from it's natural position (elevated 1/16-1/8"), the mixture
adjustments make no difference, and the engine will stumble and die. Assuming
that this points to a root cause:
Is it possible that the slides are raised too far when the carb is
idling?
Could my slide springs be weak, or perhaps are the wrong spring for
this carb?
How elevated should my slides be at idle for a correctly functioning
carb?
Has anyone measured their slide height when their engine is at idle?
Has anyone measured the length of their slide springs when removed from
the carb?
I appreciate the many helpful, friendly replies I have received so far.
I have eliminated many more possible causes thanks to your help.
Any additional hints would be appreciated.
Cheers,
Vance
P.S. 'Benny' says hello.
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