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Anyone have any idea what the primary jet size was? A bit of a strange issue for me where my plugs are all lean. I live in Albuquerque where the altitude is 5200, same as Denver. Every darn car Ive ever owned need jetted down for this altitude. Ill pull the top off tomorrow to get the jet size and then start moving larger probably 2 sizes at a time. Timing was pretty close, a bit off like 2 deg instead of 5 deg btdc. My points were a bit cooked too, all that is replaced now. Trying to get a new baseline now. The car came from Houston, so you would think it would be rich, but not so. The 4GC is a 7007000. The plug is a R43.
Last edited by madmax442.com; January 28th, 2024 at 05:04 AM.
Reason: added spark plug info
I can swear I saw those jet specs in the service manual last week. Let me check again later today. There are two sizes, one for the mains and another for the secondarys. I would suggest 1 size smaller for each 1500 feet in altitude, which is the "standard" formula. For ABQ, when I lived there, I was using jets in my cars that were 3 sizes smaller and they all ran great and the plugs looked fantastic with that setting (including my 1964 Dodge Dart with the typewriter transmission :-) .
I've started using AC Delco Rapidfire 7 (19360569) plugs in my 1954 and they seem to perform really well.
...and you can find the size jets you want at https://quadrajetparts.com/jets-c-104_116.html I like that you can even get just the accelerator pump cup from this site and other specific 4GC parts individually.
I've never changed the jets in my 55 and have been all over the Rockies, plus I have a summer home at 5200 feet and had no issues other than normal loss of power do to elevation, then again I haven't checked for plug color when on vacation either.
That plug doesn't look scary white to me, but it could just be my computer... Tedd
I've never changed the jets in my 55 and have been all over the Rockies, plus I have a summer home at 5200 feet and had no issues other than normal loss of power do to elevation, then again I haven't checked for plug color when on vacation either.
That plug doesn't look scary white to me, but it could just be my computer... Tedd
Honestly, that plug looks pretty good to me too. Much better than the gooey rich crud.
I thought it looked a little lean, but I love the opinions. The reality is that if still has the .049 jets (I did rebuild it but forgot to document the jet size), then going 3 more steps below that seems a little aggressive. It doesn't smoke or smell, maybe you all are correct. I agree, no carbon or oil on the 2 I checked, so yeah! Leave it alone!
BTW, got a 3rd opinion that slight knock and we couldn't hear it this time. Thanks all, I appreciate everyone on the Vintage Forum!
I thought it looked a little lean, but I love the opinions. The reality is that if still has the .049 jets (I did rebuild it but forgot to document the jet size), then going 3 more steps below that seems a little aggressive. It doesn't smoke or smell, maybe you all are correct. I agree, no carbon or oil on the 2 I checked, so yeah! Leave it alone!
BTW, got a 3rd opinion that slight knock and we couldn't hear it this time. Thanks all, I appreciate everyone on the Vintage Forum!
Of course not having hear the knock, that's pretty common on these engines. Diagnosing on the internet is not very easy.
Probably the most common cause is a sticky lifter. These engines seem pretty picky on what kind of modern oil to use. Many people have been using Shell Rotella 15w-40 with good results. It has the extra zinc in it. The knock comes and goes when it's a lifter.
January 27th, 2024, 07:00 PM
