Hi,
This question is for a 1974 144 all stock with a B20F and CIS fuel injection. We have been chasing a problem where, if you rev the engine slowly w/o load, it runs fine. If you rev it fast it stumbles. This happens both with and w/o load. My brother is helping me and he thinks it it is not firing on one cylinder when loaded due to possible fuel starvation. Here's the info so far:
1. It idles nicely, cold or warm.
2. Gas is old, 4-5 years, but we just added some new gas with fuel injection cleaner. Didn't make any difference.
3. Checked timing, valve clearance, tested compression. Compression (done on cold engine) was in the 115-150 psi range.
4. Looked at spark plugs. 1-3 from front have a light brown deposit on insulation, #4 is grey-ish.
5. Tried removing spark plug wires with engine idling and it does fire on all four when idling.

That's all I can think of so far. Any ideas?

Kåre