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Old 03-11-2011, 02:08 PM
SteveH SteveH is offline
Hard Core 4+
Join Date: Aug 2006
Location: Colo Springs
Posts: 1,838

I rebuilt my all-stock Federal spec. '78 carb in (gulp) 1990 and haven't rebuilt it since. It runs well and better than any other carbureted vehicle I have ever owned.

The secondary diaphragm was ruptured, and I replaced that, but I did not rejet. It runs great at 7000' and I've had it at sea level and 13K feet. It definitely runs rich at 13K and occasionally blows out a black cloud. Some of that would be from the unadjusted idle mixture, however. High speed jetting is only part of the whole occasion.

I once tried rejetting a '78 carb, and it was tragic - whatever I did, the vehicle wouldn't run, so I gave up on that carb. In general, if your truck runs well, I would leave the jets alone. The biggest wear items I have seen in LC carbs are the accelerator pump and the secondary diaphragm. My '78 ran so much better after I just 'put a kit in it' and re-set the float and mixtures, etc. that I have driven it since then with no changes.

If this were an Edelbrock or Holley, rejetting might be far more important. Fortunately, Toyota's carbs are so robust that they basically work well with factory jetting under most circumstances. YMMV - just what I have experienced. If you find a miracle jetting situation that really results in better power, lower emissions, etc., then I'm all ears.
Steve H. - KE0KNH
Colo Springs, CO
'78 FJ40, '89 FJ62, '98 4Runner
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