Hi, I just bought an 84 Z28 and it ran fine for the first couple days. I just put in a full tank of 93 octane gas and a carb cleaner and everything was fine, then about 10 miles after I filled the tank my car suddenly started losing power and missing like crazy. Trying to get it home it stalled out and wouldn't start, backfiring all the while the car did manage to start up again and it ran home fine. So I figured hm dirty gas I'll wait til the morning and see if everything is fine, nope, it was doing it worse, I tried driving down the street to see if the car would even out but it backfired, started up spewing huge amounts of thick grey smoke, and BARELY ran down the road missing so bad it was shaking the car back and forth. When I got it home I ran the engine in park for a bit and after about 5 minutes the car stopped missing and was fine, so I took it for a ride and after a while it developed a slight miss again. I was wondering if anyone else had this problem? Does it sound like I melted the urethane floater in my carb which basically means huge repair bills or does it sound like simply dirty gas/fuel treatment? I'm worried that I got screwed when I bought the car but I guess the fuel treatment contains alchohol so it boils off around 180 and it was about 95 yesterday when I went for my ill fated ride, but that wouldn't explain the continued troubles today I don't think?
I don't know, I hope someone else does...
Thanks in advance,
Paul

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84 stock Z-28 V8 305 H.O.

 

A good thing to do with a recently purchased used car into which you've added a fuel system cleaner is to replace the fuel filter. It may have been nearly plugged, you pushed it over the cliff.

Or, it could have been a vapor lock condition. A weak fuel pump will become evident in warm weather.

I did have one experience in the late '70's with STP fuel system treatment: After filling up using a bottle of that stuff, hot summer noon, the car quit a mile down the road. Wouldn't start, left it there and went back a couple of hours later. Started right up, never gave any more trouble. To this day, I don't know exactly what happened, and I've never had it happen to me again (although I haven't used STP since, either).

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

 

Sounds to me like either the choke is defective in some way that causes it to stick closed, or there is something washed into the needle valve and hanging it open. Those don't usually go away and come back though.

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