Twin carb problem --- FIXED
Posted: Sat Apr 20, 2024 8:20 pm
Heya Knuckleheads!
I have been on the 'chasing my tail' roundabout for while now in regards to the grey motor not running right.
The problems were apparent on 91 fuel, when I changed 98 the engine has given me nothing but major problems.
SYMPTOMS...
-engine was misfiring on early acceleration ie first 10% of pedal travel then would act normally for the remaining 90%
-revs not returning to base idle without a few taps of the pedal, on return the base rpm was inconsistent- linkages checked out OK
-major misfiring, popping, flat spots, farting and generally the engine was sounding a pop corn making machine
-spark plugs were totally fouled on 1-3 cylinders, 4 was an average foul and cylinders 5-6 totally lean
-spark (on clean plugs) was strong and adjustment of timing had NIL effect on symptoms
-changing out to new plugs seen them have same symptoms within minutes of running the car
-both carbs base idle revs set via vacuum bubble sync tool, front idle rev screw hardly on, rear was 1.5 turns in
-setting base idle revs both at 1.5 turns in on front cab had vacuum to outer space, rear carb wouldn't even register
-carby idle air mix needles not working as they should, front carb air mix needle not really doing anything, rear seemed to be working correctly
Diagnosis at this point was as follows
Engine health - Excellent. No oil usage, no knock, no blow by and compression 150psi perfectly even across the board
Ignition health - OK. My auto electrician mate checked everything over and dismissed ignition as the issue.
Carby health - ABSOLUTE RAT SHIT
Then focussing on carbs I ensured my base rev idle and air mix settings were correct - I had always followed correct procedure so I eliminated operator error in carb tuning as the fault.
Pic below of the spark plug readings at this point......
I have been on the 'chasing my tail' roundabout for while now in regards to the grey motor not running right.
The problems were apparent on 91 fuel, when I changed 98 the engine has given me nothing but major problems.
SYMPTOMS...
-engine was misfiring on early acceleration ie first 10% of pedal travel then would act normally for the remaining 90%
-revs not returning to base idle without a few taps of the pedal, on return the base rpm was inconsistent- linkages checked out OK
-major misfiring, popping, flat spots, farting and generally the engine was sounding a pop corn making machine
-spark plugs were totally fouled on 1-3 cylinders, 4 was an average foul and cylinders 5-6 totally lean
-spark (on clean plugs) was strong and adjustment of timing had NIL effect on symptoms
-changing out to new plugs seen them have same symptoms within minutes of running the car
-both carbs base idle revs set via vacuum bubble sync tool, front idle rev screw hardly on, rear was 1.5 turns in
-setting base idle revs both at 1.5 turns in on front cab had vacuum to outer space, rear carb wouldn't even register
-carby idle air mix needles not working as they should, front carb air mix needle not really doing anything, rear seemed to be working correctly
Diagnosis at this point was as follows
Engine health - Excellent. No oil usage, no knock, no blow by and compression 150psi perfectly even across the board
Ignition health - OK. My auto electrician mate checked everything over and dismissed ignition as the issue.
Carby health - ABSOLUTE RAT SHIT
Then focussing on carbs I ensured my base rev idle and air mix settings were correct - I had always followed correct procedure so I eliminated operator error in carb tuning as the fault.
Pic below of the spark plug readings at this point......