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Old 09-25-2021, 06:04 PM
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racerboy racerboy is offline
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Join Date: May 2003
Location: Great State of NJ
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Default Rebuilt 400 HO suddenly runs rough

I posted this over in the ‘67 GTO forum’ but I think this is probably the better place. My 67 400 HO has only 250 miles on it since a full rebuild. It is .040 over with a roller cam and ported 670 (Gessler) heads. Everything on car (tank, lines, pump, filter) is brand new.

I drove it today and about an hour into the drive I noticed it suddenly stumbled. It had been running perfectly before this. I thought maybe my fuel gauge might be inaccurate (but doubted that since this entire car just went through a 7-year frame-off resto). I stopped in gas station but it only took about 8 gallons, so that wasn’t the problem. After that, the stumble got markedly worse. Car would kick, stutter, jerk and backfire. I nursed it back hone and the first thing I checked was timing. The distributor was not loose and the initial timing looked like it was at about 8 degrees. But the timing was very erratic as I could never get engine to smooth out using the throttle. I checked the rotor and it wasn’t cracked or loose. I also put the timing light lead on each wire as the car idled (roughly) just to make sure that there wasn’t a miss. Each wire would trigger the light. I thought I might try swapping on a different carb, just to rule that out as a possible issue. When I went to pull the fuel inlet line, no fuel leaked out of the carb. I seem to remember every time I pulled a carb in the past, some fuel would always dribble out. Any suggestions would be appreciated.



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