<VV> Followup on lifter noise and driveability diagnosis

[Doug Mackintosh]

This is a followup to let everyone know the final diagnosis of some problems I reported on the car I was working on. 

Some time back I posted about a clacking lifter on the car I was working on. I had driven extensively on the highway, replaced a suspect pushrod, experimented with adjustment, both static and running, had removed and cleaned the lifter, eliminated the valve tip contact surface as a possibility, and did compression and cylinder balance tests, all without finding the cause of the recalcitrant #4 E lifter clack. I finally gave up and replaced the lifter with a new one. That, along with some fine-tuning of the adjustment, eliminated the problem.

Once the lifter was fixed, I began working on a driveability problem. This is on an engine just overhauled with rebuilt carbs and distributor disassembled and carefully inspected and refurbished. I had no information on how the car ran before the overhaul (it was not running when I started). This car is somewhat of a mongrel but should be close to a 1965 110 4-speed setup, including carbs with the power enrichment circuits. I had used .049 jets (up from the .048s I found in them) and set dwell to 33 degrees and initial timing to 12 BTDC. The Symptoms were as follows:  

- Starts and idles fine
- OK on initial acceleration, any speed / RPM.
- Cruises OK at high RPM (part-throttle)
- Misses during hard acceleration (2nd or 3rd gear) at high (above 3500) RPM.
- Seems to help to pump gas when accelerating hard 

The signal from the tach was smooth. For diagnostics, I tried first varying initial timing settings with these results:

- Retarded 4 deg (8 BTDC) --> worse. Misses ~ 3000 RPM. Still pulls fine at lower RPM.
- Advanced 4 deg (16 BTDC) --> better, begins missing ~ 4000 RPM. No ping, even when lugged.
- Advanced 8 deg (20 BTDC) --> better, begins missing ~ 4500 RPM, but still some roughness above 4000. Still helps to pump gas.

Next I changed the jets from .049 to .050. After this change, the car drives much better and pulls smoothly to 5000 RPM. 

So in summary:

14 BTDC and .049 jets - misses above 3500 RPM on hard acceleration
20 BTDC and .050 jets - runs like a top

 -- Doug Mackintosh
Corsa member since 1996
Corsa/NC member since 1996, Virtual Vairs member
Corvair owner 1969-1971 and 1996-on