This is my second time writing in about my Oldsmobile. I solved the cooling problem with a mechanical fan, however now I am having another problem. As you may recall I swapped in a ZZ4 GM Performance 350 CI motor, and now it will “diesel” for awhile after I shut it off. It only does this after it has had a chance to warm up. Do you have any ideas for fixing this?
Dieseling is a common problem with carburetor equipped vehicles from yesteryear. If you’ve owned a vehicle with one of these glorified toilet bowls for an extended period of time, odds are you’ve experienced this. I did before, and I have again: our Ford Sierra project car and it’s 2BBL carb just dieseled last week!
Honestly, the five well-written causes for dieseling in the Wikipedia article (first sentence, paragraph above) does a pretty fantastic job addressing the issues. I assume your Olds, like most not-totally-complete project cars, isn’t driven on a daily basis: meaning that carbon build up isn’t a concern. Perhaps the idle speed is too high. Since the ZZ4 has a fairly mild cam profile, keep it around 800rpm. Wikipedia also mentioned timing: make sure that ZZ4 is set to the correct specs (10 degree BTDC @ 800 rpm 32 degree total), but I doubt that’s the problem here.
The remaining problems are my concern, and they all point to the condition/tune of the carb. How is the accelerator pump doing? Are its seals in tip-top shape? Is the carb tuned too lean and still running a bit too hot? Fatten up the mixture a little and address any more cooling issues. I hope you still don’t have cooling issues!
If the carb is some old pile you had lying around (or got for cheap) perhaps this is a good time to consider a stand-alone EFI swap. Man, they are dirt cheap these days, and would really add the element of modern luxury to one of the nicer luxury rides of all time. Of all time?
Don’t believe me? Just go sit in a 9th generation Olds 98 Regency (or Buick Electra/Park Avenue cousin) and get back to me. Plenty of old world Detroit luxury with a bit of modern production values stemming from the 1977 downsizing of these monsters. And introduction of gee-whiz tech goodies in the 1980s, natch. These are just as nice as a Caddy without being ostentatious, and leagues ahead of any Panther. Oh yeah, I just said that: 1980s C-body for the win.
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