1973 1.7L bucking skipping backfiring thru engine, 1973 1.7L bucking skipping backfiring thru engine Options

[johnoscar]

Hi all...my first post. ***** (07-10-2022)Updated at bottom

Original owner 1973 1.7 914 now having engine issues. Engine rebuilt top end at Tangerine Racing 2008-2009. The only real new added different part was pop-up pistons 91mm.

Slight bucking since then, but never before. Now gotten significantly worse with skipping and backfiring back thru engine. Car will do 80mph on the highway. Probably still skipping, but too fast to feel.

Car is bucking. Most felt when feathering throttle under even small load, Also skipping and backfiring while static and under load

So......what have I done............


Replaced throttle switch with new from AA
Removed electric connection to throttle switch and drove without change
Checked Head temp sensor ohms
cold 3600-3700
hot 80-90
Replaced Head Temperature Sensor new from AA without change
Trigger points cleaned/lubed replaced without change
Swapped trigger points with used without change
Replaced distributor cap, points, rotor and reset dwell to 48.5 degrees all new from AA
Replaced distributor with 123 ignition without change
Timing adjusted to 27 Degrees BTDC
Replaced all air hoses new from AA without change
Replaced ignition wires new from AA without change
Checked all ground wires and connections
Ignition harness is original but very flexible without brittle wires
Replaced push rod tube seals new from AA
Reset valve adjustment to .006 in
Swapped ECU with used and drove without change.
Swapped MPS with used and drove without change
Rebuilt MPS with new beryllium copper diaphragm and drove without change
Swapped coil with used and drove without change
Fuel pump and hose visually checked with nothing compromised.
Stainless steel fuel lines installed with rebuild.
Disconnected tach from coil and ran without change
Disconnected alternator from relay board and ran without change
Fuel filter changed within last 2000 miles
New Bosch Ignition condenser wire too short on replacement part (not replaced)

All above is done and results are totally without change in the issues

I'd be interested in anyone's thoughts.

I feel the list is extensive and I have had help with this project from a 50 year experience 914 guy.

What have I not done? Where else could the issues be generated?

Please feel free to comment on anything within the post!!!

***** Clarification within post

Cylinder compression 1=158 2=155 3=165 4=154 (all cold)
Don't know what the compression ratio is.
Fuel injectors cleaned and measured by Dr Injector and are not the problem according to him.
The backfiring is thru the intake. Intermittent. On increase in rpm's even in static position